12 KW CCS ON 160-15M....USING THE 3CX-6000A7..... Part 13
Here the complex chain drive is finalized. Spur gears used on the inside of the inner front panel.
The idea of the 3 x chains is to get the tune + load turns counters, and the bandswitch knob located in the correct positions on the outer panel. After some preliminary attempts, this latest version works good...and the front panel simply sides off....leaving all 3 x chains intact.
On a side note, I shipped the new 397 uh plate choke today, along with a pair of .01uf @ 30 kv disc caps, used for bypassing at the cold end of the plate choke....used for the lower bands. A pair of 500 pf doorknobs will also be used at cold end of same plate choke...for bypassing at the upper bands. A pair of 100 amp supercon panel jacks also shipped. It's slowly coming together. This chain drive setup complicates things quite a bit, and required a lot of head scratching. But it's finally done...and works. The mapping has yet to be done (turns counter markings vs actual pf) for the tune + load caps. Once done, the mapping....aka .....'cheat sheets' can be made up.
https://www.youtube.com/watch?v=Q3zf2PrzJs0
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
As already mentioned, the physical size of L and C is meant with smaller of course.
And a Q of 5-6 with Pi-L is sufficient where 9 with a simple Pi might not be sufficient for harmonic supression.
?
With Pi-L you don?t need 1/2" coil tubing and multiple band switch sections in parallel with a 3CX6K
?
73
Peter
?
?
?
?
-----Original-Nachricht-----
Betreff: Re: [ham-amplifiers] High Temperature in Toroid of the PI-L network (Alpha 78)
Datum: 2024-03-08T18:56:21+0100
Von: "Jim VE7RF" <jim.thom@...>
An: "[email protected]" <[email protected]>
?
?
?
On Thu, Mar 7, 2024 at 11:02 PM, Peter Voelpel wrote:
<Pi-L is great.
<Not only the capacitors become smaller in size also the coils and band switch can be made much smaller with that far lower current through them.
?
<73
<Peter
## Not quite.? In software, or in Orr's books, on any PI-L,? BOTH the C1 and C2 caps are a lot lower value, BUT the main Coil ('L1')? is one helluva lot bigger in value. Coil has to be a lot bigger in value, since the C1 tune cap is a LOT smaller in value.? ? ?In the GM3SEK? PI / PI-L software, he uses a specific common? formulae to?arrive at the ...'image Z'.... that the PI-L initially transforms the plate load Z? down to....and is typ in the 200-400 ohm range.? Then the 200-400 ohms is transformed down to 50 ohms.? On the software? spreadsheet, the actual image Z can be manually changed to anything you want... like 100-1000 ohms.?
?
?
?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
On Thu, Mar 7, 2024 at 11:02 PM, Peter Voelpel wrote:
<Pi-L is great.
<Not only the capacitors become smaller in size also the coils and band switch can be made much smaller with that far lower current through them.
?
<73
<Peter
## Not quite.? In software, or in Orr's books, on any PI-L,? BOTH the C1 and C2 caps are a lot lower value, BUT the main Coil ('L1')? is one helluva lot bigger in value. Coil has to be a lot bigger in value, since the C1 tune cap is a LOT smaller in value.? ? ?In the GM3SEK? PI / PI-L software, he uses a specific common? formulae to?arrive at the ...'image Z'.... that the PI-L initially transforms the plate load Z? down to....and is typ in the 200-400 ohm range.? Then the 200-400 ohms is transformed down to 50 ohms.? On the software? spreadsheet, the actual image Z can be manually changed to anything you want... like 100-1000 ohms.?
?
###? In both the ORR book? and GM3SEK software, the Q remains the same for both the PI and also PI-L.? Done that way, the harmonic suppression is substantially increased by using the PI-L config.? BUT the C1 + C2 values are much reduced? vs the PI ( using the same loaded tank Q)..and the main Coil (L1) is increased substantially.?
## here's the rub.? Use the PI-L config, then reduce the Q by a bunch, the C1 + C2 values? become even smaller still, BUT the main coil..L1, become even bigger in value...too big.? So you end up with a huge main coil value, but less current through it, and degraded harmonic suppression ( but still adequate), and you still have the 2nd coil (L2) to install, and tap the 2nd coil...pita.?
?
##? after running all of this several times through software, and actually testing it on the bench, I came to the conclusion, the PI-L was a wasted effort.? It's easy to test on the bench. PI or PI-L built on a spare sheet of aluminum, with a resistor on input side ( to simulate the tube's plate load Z)...and an analyzer plugged into output side.? Both caps are individually mapped out beforehand? for fractional turns on turns counter vs pf.? Calculated coil values are done via lcr meter, and taps done in the correct spots.? ?If a roller used, the fractional turns are 1st mapped out? vs turns counter.?
?
##? with tune + load caps tweaked for 1:1 swr, then compared to the mapping cheat sheet...they always come out dead on, or within? a few pf.?
?
Below is what the software spits out for PI, and also a PI-L? using 2 x different loaded Q values.??
?
##? ?3x6 tube. 7 kv loaded @ 2.5 amps.? 1.8 mhz.? ?68% eff.? PO = 11.9 kw? ?Plate load Z = 1556 ohms.? ?400 uh plate choke used.
For the PI network only, the overall network Q = 12? ?( Input Q= 10.4 )? ( output Q = 1.6)? Note Overall network Q =? input Q + output Q.? In the older arrl books, and also EIMAC, they only used the INPUT Q...and a value of 10 was common.? These days, they use total network Q...and use a value of? 12.? ?In software, only the overall network Q can be changed (but the input + output Q values are also spat out lower down in the results.?
##? FOR the PI-L config only, the overall Input Q is?also 12. (? PI network portion input Q = 9.9).? Input Q1 = 7.0? Output Q2 = 2.8? L network QL = 2.1?
.............................................................................................................................................................................................................................................................................................................................................................................................
PI config.? Overall network Q of 12? 1.8 mhz.?
C1 = 563.4? pf
L1 = 15.1 uh?
C2 = 2815.7 pf?
?
PI-L config? Same overall network Q of 12? 1.8 mhz.?
C1 =? 370 pf
L1 = 26.78 uh
C2 = 1581.8 pf
L2 =? 9.44 uh?
.................................................................................................................................................................................................................................................................................................................................................................................................
OK, now let's reduce the overall network Q down to 9.?
PI config. Overall network Q of 9.
C1= 423.4 pf
L1 =? 19.12 uh
C2 = 1839.0 pf
?
PI-L config. Overall? network Q of 9
C1 =? 252.0? pf
L1 =? 36.6 uh?
C2 =? 1283.5 uh
L2 =? 9.44 uh?
?
Ok, notice a few things here.
On the PI-L config, the L2 value remains the SAME, at 9.44 uh, whether the higher OR lower overall network Q is used.?
On the PI-L config, with the higher Q, the L1 coil value is insanely high. (26.78 uh)
On the PI-L config, with the LOWER Q, the L1 coil is now into the stratosphere. (36.6 uh).
OK, now you know why (failure prone) TORRIDS are typ used on the main coil? ( and also on the L2 coil on an alpha 77)
You folks have any idea how big the 1/4" tubing coil for the 160m portion of the tank circuit has to be? when? sky high values of L1 are used ???? ?Hint, it's just not happening.?
?
On Scotts latest 160-15m amp, I used a simple PI, and used an overall network Q of just 9.....on all bands.? ( see the PI config with the lower Q).
PI config. Overall network Q of 9.
C1= 423.4 pf
L1 =? 19.12 uh
C2 = 1839.0 pf
Done that way, his ceramic? 12-500 pf (@ 15 kv rated) vac tune cap will easily suffice for the C1 tune cap. Actual vac cap measures 12-540 pf...and they are small things.? Calculated value required at 1.8 mhz = 423.4 pf. ( vs 563.4 pf if the higher Q is used).
L1 coil only has to be increased a bit.? ( from 15.1 uh to 19.2 uh)
His ceramic 50-3000 pf @ 5 kv vac load cap is ample? for the C2 cap with the lower Q config.? ( but marginal with the higher Q config....2815.7 pf required).?
Ok, then it's dead simple, and NO padders used for either the tune or load caps..... or? having to use even? bigger tune + load caps, like a 12- 750 pf tune...and a 50-4000 pf load.? ( note I have several 50-4000 pf vac caps, and they are small things.? But my 10-1000 pf @ 15 kv motorized vac caps are big....and ditto with my plane jane 17-1000 pf @ 15 kv Jennings ceramic vac cap).?
?
His tank circuit? consists of a total of 3 x tubing coils used.?
1/2" tubing used for the 20+15M coil (and also the small value uh used between the plate block cap assy and the C1 tune cap)
3/8" tubing used for the 80+40M coil.?
1/4"? tubing used for the 160M? coil.?
Of course, in normal operation the? required 19.12 uh for 160m consist of the total of all 3 x coils in series being used.? So the actual 1/4" tubing coil for 160m is a lot lower value than 19.12 uh? ( it's 10 uh)?
On 75m, the required 9.02 uh consist of the 1/2" tubing coil? plus the? 3/8" tubing coil in series.? ?Actual 3/8" tubing coil is just? 7.3 uh
On 20m, the required? coil is just 1.72 uh .? Since we incorporated the 'pre-coil' (.6 uh between block cap and C1 tune cap)? the actual value of the 1/2" tubing coil is now 1.72 + .6 = 2.32 uh. ( Scott just happened to have a mess of 2.32 uh 1/2" silver plated tubing coils in the junk box, used in henry RF generators, so we lucked out.? Only 2 x copper tubing coils had to be fabricated...( 10 uh, made from 1/4" tubing...and 7.3 uh, made from 3/8" tubing).??
?
NOTE, when a PI-L used, on the upper bands, like 20m-10m, you can't use the lower Q value,? even with the .6 uh pre-coil installed.? The C1 values end up negative pf.? The only fix is to increase the loaded Q a lot higher than 12.? This is the problem when using large metal tubes on upper HF..( with the 24.5 pf anode to grid C on a 3x6...which rises to 42 pf, when tube plugged into the grid ring. The extra 18 pf? comes from the proximity of the lower anode fins, to the chassis below em.? ? The PI-L values? ?don't work on upper HF...unless the Q is increased by a bunch.?
?
On the simple PI network? I designed in software, a loaded Q of 9 can be used...... including 15m. It's a 160-80-40-20-15m amp.? ?The .6uh pre-coil is used so the lower Q can be used on 15m.? ?The tube's 42 pf of anode to grid C plus the .6 uh coil, form a step down L network.? That steps down the 1556 ohms plate load Z....down to just 487 ohms on 21.225 mhz.? Ok, now a practical? PI network can be used, with reasonable values.?
Harmonic suppression is ample. On upper HF, with the extra pre-coil installed it's sometimes called a L-PI? (or a L-PI-L, if a PI-L used) .? Harmonic suppression on the lower bands is more than ample.
Per the VK expert, (Owen Duffy)? any tube already has 7 db of 2nd harmonic suppression in class A.... and close to that in class AB or B. (6db).? ?Then toss in the harmonic suppression of the PI network.? Then toss in the additional suppression from the PI tuned input circuit...and it's more than ample.??
W8JI sez he measured? 50 db of? 2nd harmonic suppression on an AL-1200? on 40m...(and even more on 3rd and 4th harmonics).? ?That amp uses a simple PI network on 40-10m.? JI sez the only reason they used a PI-L on 160+80m on that amp is so smaller tune and load caps could be used.? Trade off is, he still had to pad both the tune + load caps, and use a toroid on low bands.? Exact same, identical network used on the AL-1500 + AL-1200.?
A 26.78 uh / 36.6 uh total uh for 160m if either a higher Q / lower Q,? ?PI-L network on 160m, gimme a break, not happening.? Just look at how big that 10.0 uh (1/4")? tubing coil is in the u tube video (plus the other 2 x coils).? The RF deck would have to be double the size to even fit? the oversized coils in.?
?
?
?
?
?
?
??
?
?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
Pi-L is great.
Not only the capacitors become smaller in size also the coils and band switch can be made much smaller with that far lower current through them.
?
73
Peter
?
?
?
-----Original-Nachricht-----
Betreff: Re: [ham-amplifiers] High Temperature in Toroid of the PI-L network (Alpha 78)
Datum: 2024-03-07T20:03:28+0100
Von: "W7WRX" <clark@...>
An: "[email protected]" <[email protected]>
?
?
?
Great Info Jim, I thought the main purpose of a Pi-L is to use a smaller C2?? ? If you have that L then C2 goes way down in value.?
On the Henry you need to make absolutely sure that L is tuned correctly.? If not power and IMD suffer greatly.? Its a real compromise.? If you tune that L for one Band you gain huge power and EFF.? But then, All other bands are screwed up.? Its a balancing act to cover all the bands.?
I also enjoy moving the roller inductor around to experiment. You are absolutely correct that the lower Q does make more power and runs cooler.? Standard procedure for me is to step that roller a small amount at time and retune the caps.? There is a point where you hit pay dirt and anything more or less makes less power.? IMD does suffer slightly but I have never seen a major effect.?
Also one thing to note This same thing happens with the C2 loading.? If you step that up or down by a fixed amount and retune C1, you can again find the exact spot where the amp is at max power and EFF.? ?Its a mountain and you fall off on each side of that magic spot.
Some amps, this has little to no effect, like an SB220. But other amps, this method has a HUGE effect, Example would be a Henry 2k4.? ?If you attempt to just peak the tune and load you will never ever get the PI net in the right spot.? Stepping the load and going back to tune is the only way.? The effect is dramatic.? I always wondered why this was and assumed it was due to the Q.??
C
?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
Great Info Jim, I thought the main purpose of a Pi-L is to use a smaller C2?? ? If you have that L then C2 goes way down in value.?
On the Henry you need to make absolutely sure that L is tuned correctly.? If not power and IMD suffer greatly.? Its a real compromise.? If you tune that L for one Band you gain huge power and EFF.? But then, All other bands are screwed up.? Its a balancing act to cover all the bands.?
I also enjoy moving the roller inductor around to experiment. You are absolutely correct that the lower Q does make more power and runs cooler.? Standard procedure for me is to step that roller a small amount at time and retune the caps.? There is a point where you hit pay dirt and anything more or less makes less power.? IMD does suffer slightly but I have never seen a major effect.?
Also one thing to note This same thing happens with the C2 loading.? If you step that up or down by a fixed amount and retune C1, you can again find the exact spot where the amp is at max power and EFF.? ?Its a mountain and you fall off on each side of that magic spot.
Some amps, this has little to no effect, like an SB220. But other amps, this method has a HUGE effect, Example would be a Henry 2k4.? ?If you attempt to just peak the tune and load you will never ever get the PI net in the right spot.? Stepping the load and going back to tune is the only way.? The effect is dramatic.? I always wondered why this was and assumed it was due to the Q.??
C
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
Jeez, I love your sob stories, Jim !!! What a read. You should write a small book ¨C a little like the ¡°Care and Feeding¡± thing from Eimac. All of us amp geeks would love it. ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Jim VE7RF
Sent: Thursday, March 7, 2024 12:53 AM
To: [email protected]
Subject: Re: [ham-amplifiers] High Temperature in Toroid of the PI-L network (Alpha 78)? On a side note, on these hb amps,? I design the PI net in software...but I also use a LOT lower loaded Q.? (I gave up on the PI-L...major pita.? The PI-L config uses a LOT more L1 coil between the caps...and a LOT smaller C1 + C2 caps.? That results in L1 coil values that are absurdly too big on lower bands.? It also results in impractical extremely low values of C1 on upper HF.? ?It also means the extra L2 coil, plus tapping the L2 coil...pita.? ?It also means much higher voltage across the C2 load cap, since it's then at a 200-400 ohm point.? It also means when using a lower loaded tank Q, the C1 + C2 values decrease even more...and the L1 coil increases even more).?? I have done a lot of experimenting over the years....(PI net) esp on hb amps that used a roller coil.? Like trying both the calculated L1 value for a 'normal' tank Q of 12.? (input Q of 10..and an output Q of 2)..... then progressively using MORE L1...( and progressively using LESS? C1 + C2) and the results always astound me.? With the lower Q? (amp re-tuned each time for max PO), the PO kept increasing.? Anode diss kept decreasing.? The amp is far more broad banded ( doesn't require constant re-tuning, esp on the lower bands), and way less heat in the tank coil.....and? way less current though both caps...and the tank coil (roller or bandswitched)..and roller contacts ( weak point in any roller)...and less current in bandswitch contacts.? The tradeoff being... slightly less harmonic reduction.? IMO, that's a good trade off.? As noted before, monoband ants are not resonant on their even harmonics..... and even with a? lower tank? Q, harmonic suppression is still, greater? on the 3rd-4th-5th harmonics...vs 2nd harmonic.? And on loaded 40m yagis, mine does not resonate on 21 mhz ( it resonates on 24 mhz...and will screw up a nearby 12m ant).?? ? I recently experimented with the adjustable hb manually tuned input, and VARYING the tuned input Q.? ? ? Without any tuned input (or the un-un gong show they used in the henry 3/8 k ultra) harmonic? suppression is degraded.? ?Eff is reduced, and IMD increases a bunch...(and that's with a tube that already has a 50 ohm input Z).? ? ? With the PI? tuned input (and the typ low Q), amplifier harmonic suppression increases a bunch ( as Clark noted when he installed the new relay switched PI tuned inputs on his 8K).? ?Typ a low Q is used, so the tuned input is tweaked for the middle of each band...then left alone.? With the new 0 - 4.4 uh roller coil (8 ga solid wire) and the pair of broadcast caps, I can vary the tuned input Q between extremes...on any band.? What I found was, it's a trade off.? With a? slightly higher tuned input Q, (more C1+C2..and less L)? everything improves, BUT on the lower bands, it's not broad enough to cover the entire band.... but almost.? ?Being manually tuned, it's a non issue.? ?IE: run into the shop to tweak the vac? tune+ load caps? from 3900 khz...down to 3504 khz ( using the handy dandy cheat sheets), it only takes a few more seconds to tweak the C1 + C2 broadcast caps on the manually tuned, tuned input. ( same cheat sheet. Cheat sheet divided up for each band, with 2 x columns... Vac C1+C2 caps...and tuned input? broadcast C1 +C2 caps.? ?Then everything done at 3 x freqs per band.? Bottom-middle-top.? ? On the bandswitched, manually tuned, tuned inputs... they are configured for a slightly? higher tuned input Q.? Same deal, just tweak the C1/C2 broadcast caps? via cheat sheet.? ? Get the tuned input Q too high, and the resulting? current through the tapped? coil? /? roller contacts? /? bandswitch contacts becomes too great.....esp on upper HF....and esp when? more drive is used...like 500-700 watts on the bigger tubes.? ? On these 50 ohm input 3CX-3000A7's....and also the 3CX-6000A7's,? I designed the tuned inputs with an overall network Q of ...'4'.? ?( input Q =2.? Output Q = 2).? This results in the best compromise.? ?The C1 + C2 values are tabulated below.?
160m -? 3600 pf
80m - 1800 pf
40m - 900 pf
20m - 450 pf
15m - 300 pf
10m - 225 pf.? ? As you can see from above, the C1 + C2 values are a lot higher vs what you normally find in typ amplifiers.....with their fixed fixed values, tweaked for the middle of each band.? ? I also put watt meters on both sides of the manually tuned, tuned inputs, and measured PI vs PO. (that came from John, K5PRO).? ?On my 3x3 amp, with it's manually tuned, tuned input, complete with bandswitched? 4 uh coil ( made from 17 turns of? 6 ga solid cu, with a 1.5" ID).? ?Pin = PO.... except on 15m.? On 15m, the Pin was 200 watts, but the PO was only 160 watts !? ?I had the Q too high on 15m..... and that 40 watts lost was dumped into the remaining 2 turns used on the 4 uh coil.? I could easily feel the heat on those last 2 x turns.? ?40 watts is a lotta watts for 2 turns of 6 ga wire.? ?My fix was to increase the inductance on 15m by re-tapping the coil? by just 1/4 turn. ..which then required slightly less C1 + C2.? ?PO increased to 195 watts on 21.225 mhz..... good enough.? ? It's not always easy to do exact coil taps.? IE: the? 1/4" wide interconnecting copper strap may have to go over the top of the coil (or beneath it) to get to the opposite side....( 9 o'clock)? ?A longer strap also has more XL...and also has to be factored into the equation, along with the total path through the bandswitch used. IE: from C1 to coil, then through the various taps, back to the bandswitch, then to C2 cap.? ? IE: bandswitch contacts face the coil at the .....3 o'clock? position. On upper HF, each turn is a lot of XL, so fractional turns are used, like top of coil...and bottom of coil? ?(12 o'clock and 6 o'clock). So I use a lower Q on the multi? KW? output PI network, but a? slightly high Q on the tuned input.? Then u get ur cake ...and eat it too.? Good imd, flat input swr across each band, excellent harmonic reduction,? easily handles up to 1 kw CCS CXR of drive.? I wasn't about to attempt to construct 6-9 fixed? fixed tuned inputs, and either bandswitched or relay switched, that would handle 500-800 watts? CCS of drive.? ?Ok, that's my sob story for this week.?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
On a side note, on these hb amps,? I design the PI net in software...but I also use a LOT lower loaded Q.? (I gave up on the PI-L...major pita.? The PI-L config uses a LOT more L1 coil between the caps...and a LOT smaller C1 + C2 caps.? That results in L1 coil values that are absurdly too big on lower bands.? It also results in impractical extremely low values of C1 on upper HF.? ?It also means the extra L2 coil, plus tapping the L2 coil...pita.? ?It also means much higher voltage across the C2 load cap, since it's then at a 200-400 ohm point.? It also means when using a lower loaded tank Q, the C1 + C2 values decrease even more...and the L1 coil increases even more).??
I have done a lot of experimenting over the years....(PI net) esp on hb amps that used a roller coil.? Like trying both the calculated L1 value for a 'normal' tank Q of 12.? (input Q of 10..and an output Q of 2)..... then progressively using MORE L1...( and progressively using LESS? C1 + C2) and the results always astound me.? With the lower Q? (amp re-tuned each time for max PO), the PO kept increasing.? Anode diss kept decreasing.? The amp is far more broad banded ( doesn't require constant re-tuning, esp on the lower bands), and way less heat in the tank coil.....and? way less current though both caps...and the tank coil (roller or bandswitched)..and roller contacts ( weak point in any roller)...and less current in bandswitch contacts.?
The tradeoff being... slightly less harmonic reduction.? IMO, that's a good trade off.? As noted before, monoband ants are not resonant on their even harmonics..... and even with a? lower tank? Q, harmonic suppression is still, greater? on the 3rd-4th-5th harmonics...vs 2nd harmonic.? And on loaded 40m yagis, mine does not resonate on 21 mhz ( it resonates on 24 mhz...and will screw up a nearby 12m ant).??
?
I recently experimented with the adjustable hb manually tuned input, and VARYING the tuned input Q.? ? ? Without any tuned input (or the un-un gong show they used in the henry 3/8 k ultra) harmonic? suppression is degraded.? ?Eff is reduced, and IMD increases a bunch...(and that's with a tube that already has a 50 ohm input Z).? ? ? With the PI? tuned input (and the typ low Q), amplifier harmonic suppression increases a bunch ( as Clark noted when he installed the new relay switched PI tuned inputs on his 8K).? ?Typ a low Q is used, so the tuned input is tweaked for the middle of each band...then left alone.?
With the new 0 - 4.4 uh roller coil (8 ga solid wire) and the pair of broadcast caps, I can vary the tuned input Q between extremes...on any band.? What I found was, it's a trade off.? With a? slightly higher tuned input Q, (more C1+C2..and less L)? everything improves, BUT on the lower bands, it's not broad enough to cover the entire band.... but almost.? ?Being manually tuned, it's a non issue.? ?IE: run into the shop to tweak the vac? tune+ load caps? from 3900 khz...down to 3504 khz ( using the handy dandy cheat sheets), it only takes a few more seconds to tweak the C1 + C2 broadcast caps on the manually tuned, tuned input. ( same cheat sheet. Cheat sheet divided up for each band, with 2 x columns... Vac C1+C2 caps...and tuned input? broadcast C1 +C2 caps.? ?Then everything done at 3 x freqs per band.? Bottom-middle-top.?
?
On the bandswitched, manually tuned, tuned inputs... they are configured for a slightly? higher tuned input Q.? Same deal, just tweak the C1/C2 broadcast caps? via cheat sheet.? ? Get the tuned input Q too high, and the resulting? current through the tapped? coil? /? roller contacts? /? bandswitch contacts becomes too great.....esp on upper HF....and esp when? more drive is used...like 500-700 watts on the bigger tubes.?
?
On these 50 ohm input 3CX-3000A7's....and also the 3CX-6000A7's,? I designed the tuned inputs with an overall network Q of ...'4'.? ?( input Q =2.? Output Q = 2).? This results in the best compromise.? ?The C1 + C2 values are tabulated below.?
160m -? 3600 pf
80m - 1800 pf
40m - 900 pf
20m - 450 pf
15m - 300 pf
10m - 225 pf.?
?
As you can see from above, the C1 + C2 values are a lot higher vs what you normally find in typ amplifiers.....with their fixed fixed values, tweaked for the middle of each band.?
?
I also put watt meters on both sides of the manually tuned, tuned inputs, and measured PI vs PO. (that came from John, K5PRO).? ?On my 3x3 amp, with it's manually tuned, tuned input, complete with bandswitched? 4 uh coil ( made from 17 turns of? 6 ga solid cu, with a 1.5" ID).? ?Pin = PO.... except on 15m.? On 15m, the Pin was 200 watts, but the PO was only 160 watts !? ?I had the Q too high on 15m..... and that 40 watts lost was dumped into the remaining 2 turns used on the 4 uh coil.? I could easily feel the heat on those last 2 x turns.? ?40 watts is a lotta watts for 2 turns of 6 ga wire.? ?My fix was to increase the inductance on 15m by re-tapping the coil? by just 1/4 turn. ..which then required slightly less C1 + C2.? ?PO increased to 195 watts on 21.225 mhz..... good enough.? ? It's not always easy to do exact coil taps.? IE: the? 1/4" wide interconnecting copper strap may have to go over the top of the coil (or beneath it) to get to the opposite side....( 9 o'clock)? ?A longer strap also has more XL...and also has to be factored into the equation, along with the total path through the bandswitch used. IE: from C1 to coil, then through the various taps, back to the bandswitch, then to C2 cap.? ? IE: bandswitch contacts face the coil at the .....3 o'clock? position. On upper HF, each turn is a lot of XL, so fractional turns are used, like top of coil...and bottom of coil? ?(12 o'clock and 6 o'clock).
So I use a lower Q on the multi? KW? output PI network, but a? slightly high Q on the tuned input.? Then u get ur cake ...and eat it too.? Good imd, flat input swr across each band, excellent harmonic reduction,? easily handles up to 1 kw CCS CXR of drive.?
I wasn't about to attempt to construct 6-9 fixed? fixed tuned inputs, and either bandswitched or relay switched, that would handle 500-800 watts? CCS of drive.? ?Ok, that's my sob story for this week.?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
Sounds about right.? I will measure the IMD just for fun.? ?
For 10 meters it has a fixed tune cap so you only need to set the load to about 80.? ?If you leave that alone, You can switch 10, 15,20,40 and 80 without tuning.? I have resonant Mosely beam.? I run the amp at 1kw pep on SSB this way.? Yesterday afternoon,
I worked Brazil, Jamaica, Uruguay, and Japan with it.? I was jumping from 10 to 15 to 20 meters.? It's a great amp for this type of DX.? ?I never get to do this as all of my other amps have to be tuned manually. Its a chore and just prevents me from even working
another band.
The amp does 1kw with the same drive through the phone portion of the bands. I don't notice a change in power output spinning the VFO.
I think if you had poorly tuned antennas (as most hams do) this could be a real problem and you would have to open it and tune each band or maybe arc out those components as they are small.? A neat piece of ham radio history for sure.
C
toggle quoted message
Show quoted text
Clark, u are correct. The 374A has 160m...the 374 does not have 160m.? And on all of em, 160+10m is strictly manual tune.?
Glen, AE0Q ( who used to work for alpha....(and still answers their tech email) tells me the... 'bandpass tuning' was dumped since it did not meet the new FCC? -44 db harmonic specs. ( even though the 87A / 374 et all manuals all say they have-50 db down
for harmonics).? They also don't use a progressively shorting bandswitch either.? They all used a 10 position, single pole? switch, with positions 1 + 10 used for 160+10m.? ? Positions 2-9 ( remaining 8 x positions) are used for 'manual / bandpass? for 80-40-20-15m.?
( 2 positions per band, manual + bandpass).? ? ?That's when the 87A? etc, came out, with their motorized bandswitch, and motorized tune + load caps...and microprocessor.? Later..'alpha max' software was installed on the 87A...., which fine tweaked the caps
for optimized output .? IE: say ur on 3502 khz....and ur swr is 2:1.? ??
?
All those pre-sets on the 87A / 9500 are into a DL.... not an ant, that may or may not look like 50 ohms and no reactance.?
?
For the OP,? USE the low B+ setting...(1400 vdc).... AND also use the 'bandpass' tuning option.? And no more than 500-600 watts out on FT-8 / data modes.? ?By using the 'bandpass'? setting (80-15m), the tank Q is WAY down, which will result in way LESS RF?
current through the coils, toroid's and bandswitch...and both? C1 + C2 caps + loading padder caps.? To really optimize it on bandpass mode, he may well have to get in there, and tweak the C1+C2 caps for the FT-8 freqs on 80-40-20-15m .?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
Clark, u are correct. The 374A has 160m...the 374 does not have 160m.? And on all of em, 160+10m is strictly manual tune.?
Glen, AE0Q ( who used to work for alpha....(and still answers their tech email) tells me the... 'bandpass tuning' was dumped since it did not meet the new FCC? -44 db harmonic specs. ( even though the 87A / 374 et all manuals all say they have-50 db down for harmonics).? They also don't use a progressively shorting bandswitch either.? They all used a 10 position, single pole? switch, with positions 1 + 10 used for 160+10m.? ? Positions 2-9 ( remaining 8 x positions) are used for 'manual / bandpass? for 80-40-20-15m.? ( 2 positions per band, manual + bandpass).? ? ?That's when the 87A? etc, came out, with their motorized bandswitch, and motorized tune + load caps...and microprocessor.? Later..'alpha max' software was installed on the 87A...., which fine tweaked the caps for optimized output .? IE: say ur on 3502 khz....and ur swr is 2:1.? ??
?
All those pre-sets on the 87A / 9500 are into a DL.... not an ant, that may or may not look like 50 ohms and no reactance.?
?
For the OP,? USE the low B+ setting...(1400 vdc).... AND also use the 'bandpass' tuning option.? And no more than 500-600 watts out on FT-8 / data modes.? ?By using the 'bandpass'? setting (80-15m), the tank Q is WAY down, which will result in way LESS RF? current through the coils, toroid's and bandswitch...and both? C1 + C2 caps + loading padder caps.? To really optimize it on bandpass mode, he may well have to get in there, and tweak the C1+C2 caps for the FT-8 freqs on 80-40-20-15m .?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
As per the manual, your amp has a limit of 1kw INPUT for constant carrier or data modes.? This translates to about 500 to 600W MAX.? ?Running this amp on FT8 At 1k output is way way way above its design limits.? You are also supposed to run it in the LOW or
CW position.? ?
On the ETO group I find most people run these around 500W on RTTY and data modes with no issue, The man I got my 76CA from ran strictly CW and RTTY. He participated in RTTY contests for many years. He ran it at 500W.
C
toggle quoted message
Show quoted text
Dead right, Alek. Hence the need for a YC156 amp !!
?
?
Well, that's no surprise.
Don't run any more than 30% of maximum power in FT8 mode. That goes for radios and amplifiers.
Stick to that and you'll never have a problem.
73, Alek VK6APK.
?
On 3/03/2024 12:55 pm, Arturo LU6ETB wrote:
Hi,
Last week my Alpha 78 stopped working.
I found the windings of the L5 was burned.
I rewinded the toroid with new wires.
Now, it is working.
I checked the temperature after transmitting on 80 meters FT8 with approximately 1 KW output.
Plate current 0.85 Amper, HV 2000 V and Grid current 25 mA.
After 30 minutes the temperature readings with a digital multimeter were.
L5 119 C (246 F)
L4, 64 C ( 147 F)
L6, 49 C (120 F)
Are those temperatures right?
What maybe the cause of the high temperature?? ?
Should I have to replace also el toroid???
Thanks in advance for the comments.
73 de Arturo, LU6ETB
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
Dead right, Alek. Hence the need for a YC156 amp !! ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Alek Petkovic via groups.io
Sent: Monday, March 4, 2024 5:54 PM
To: [email protected]
Subject: Re: [ham-amplifiers] High Temperature in Toroid of the PI-L network (Alpha 78)? Well, that's no surprise. Don't run any more than 30% of maximum power in FT8 mode. That goes for radios and amplifiers. Stick to that and you'll never have a problem. 73, Alek VK6APK. ? On 3/03/2024 12:55 pm, Arturo LU6ETB wrote: Hi,
Last week my Alpha 78 stopped working.
I found the windings of the L5 was burned.
I rewinded the toroid with new wires.
Now, it is working.
I checked the temperature after transmitting on 80 meters FT8 with approximately 1 KW output.
Plate current 0.85 Amper, HV 2000 V and Grid current 25 mA.
After 30 minutes the temperature readings with a digital multimeter were.
L5 119 C (246 F)
L4, 64 C ( 147 F)
L6, 49 C (120 F)
Are those temperatures right?
What maybe the cause of the high temperature?? ? Should I have to replace also el toroid??? Thanks in advance for the comments.
73 de Arturo, LU6ETB
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
The 374A model does have 160.? ?I have one here.? I think the NON A model did not?
?However, They don't allow bandpass on 160. Just manual tune.
I just repaired a 76CA and a 374A. I got them from a friend, both not working.
The 374A is really nice and makes over a kw easy on the Bandpass modes. I can be on 10m,? flip to 20, run a kw, Flip to 15, Run a kw.?
I did have to adjust the bandpass caps slightly on some bands.? It does cover the entire band and the loss from manual tuning is really not that much.? Maybe 100W at band edges.
Its a super IPA amp.??
I had low hopes that this scheme would work very well,. I have been told it does not.? I can't see a fault with it.? Maybe if the antenna match was way off the results could be poor.? I am sure you could tune each band slightly to dial it in for that station.??
Its super nice to work DX without tuning the damn amplifier.? I jump around constantly with this thing.? I am keeping it
C
toggle quoted message
Show quoted text
That Alpha? 78 is interesting.? It appears to be an updated version of the older Alpha 374A.? ? Both had the option of either...'manual tune' ..... or? 'bandpass? mode'.? The...'bandpass mode' only works on the? Alpha? 78 on 80-40-20-15m. On 160m, and also
10m, it's manual tune only.? ?They used a 10 position bandswitch, which is NOT a progressive shorting type.?
Looking at the schematic, in 'bandpass mode', they used small variable TUNE? caps for 15-20-40-80m (padded on 80+40m)? that were pre-set for the middle of each band....(and internally adjustable).? ?Ditto with the LOAD cap setup.? On the load setup, there
is relays in there to switch in (grnd the cold end) of small caps to add more load C? for lower end of each band.??
?
Here's the interesting part.? In 'bandpass mode', they use MORE inductance on the main tubing coil (L4)....and also the? toroid coil (L5).? ?It's a PI-L network....and on the L coil, they use the same coil taps,? regardless of manual tune or 'bandpass mode'.?
I always suspected this scheme, but never saw the schematic.? KM1H told me they used a series of L networks to broadband it....they don't.? It's just a mess of pre-tuned PI-L networks, one for 80-40-20-15m.?
The way they broadband it is.... by using MORE coil ( between the tune and load caps), they have lowered the tank Q by a huge amount.? That alone will broadband it by a huge amount, albeit, the harmonic suppression will suffer.? ?BUT being a PI-L to begin
with, no big deal, since the typ PI-L already has way more harmonic suppression? ?vs a plane PI network.? ?End result is it's broad banded, and still has reasonable harmonic suppression.? The scheme was later? dumped by Alpha, since it did not meet the newer
FCC 2nd + higher harmonic specs.? (which are now -44 dbc for 1.5 kw PO)...even though the Alpha 78 manual sez it has 50 db of harmonic suppression...go figure.?
The alpha 374A is similar, albeit it has no 160M.?
?
On these hb amps,? I use a plane jane PI net.....but with a lot lower loaded Q than normal.? More broad banded, more eff, less current in the tank coils and bandswitch...and harmonic suppression is not high on my list anyway, since the mono band ants are
not resonant on their harmonics.? The 40m yagi, due to it's coil loading scheme, does not resonate on 21 mhz... ( it resonates on 24 mhz) .?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
That Alpha? 78 is interesting.? It appears to be an updated version of the older Alpha 374A.? ? Both had the option of either...'manual tune' ..... or? 'bandpass? mode'.? The...'bandpass mode' only works on the? Alpha? 78 on 80-40-20-15m. On 160m, and also 10m, it's manual tune only.? ?They used a 10 position bandswitch, which is NOT a progressive shorting type.?
Looking at the schematic, in 'bandpass mode', they used small variable TUNE? caps for 15-20-40-80m (padded on 80+40m)? that were pre-set for the middle of each band....(and internally adjustable).? ?Ditto with the LOAD cap setup.? On the load setup, there is relays in there to switch in (grnd the cold end) of small caps to add more load C? for lower end of each band.??
?
Here's the interesting part.? In 'bandpass mode', they use MORE inductance on the main tubing coil (L4)....and also the? toroid coil (L5).? ?It's a PI-L network....and on the L coil, they use the same coil taps,? regardless of manual tune or 'bandpass mode'.?
I always suspected this scheme, but never saw the schematic.? KM1H told me they used a series of L networks to broadband it....they don't.? It's just a mess of pre-tuned PI-L networks, one for 80-40-20-15m.?
The way they broadband it is.... by using MORE coil ( between the tune and load caps), they have lowered the tank Q by a huge amount.? That alone will broadband it by a huge amount, albeit, the harmonic suppression will suffer.? ?BUT being a PI-L to begin with, no big deal, since the typ PI-L already has way more harmonic suppression? ?vs a plane PI network.? ?End result is it's broad banded, and still has reasonable harmonic suppression.? The scheme was later? dumped by Alpha, since it did not meet the newer FCC 2nd + higher harmonic specs.? (which are now -44 dbc for 1.5 kw PO)...even though the Alpha 78 manual sez it has 50 db of harmonic suppression...go figure.?
The alpha 374A is similar, albeit it has no 160M.?
?
On these hb amps,? I use a plane jane PI net.....but with a lot lower loaded Q than normal.? More broad banded, more eff, less current in the tank coils and bandswitch...and harmonic suppression is not high on my list anyway, since the mono band ants are not resonant on their harmonics.? The 40m yagi, due to it's coil loading scheme, does not resonate on 21 mhz... ( it resonates on 24 mhz) .?
|
Re: Kudos to Digi Key and Hammond Mfg.
Mine went from Hammond to DigiKey and then was shipped to me.?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
Well, that's no surprise.
Don't run any more than 30% of maximum power in FT8 mode. That
goes for radios and amplifiers.
Stick to that and you'll never have a problem.
73, Alek VK6APK.
On 3/03/2024 12:55 pm, Arturo LU6ETB
wrote:
toggle quoted message
Show quoted text
Hi,
Last week my Alpha 78 stopped working.
I found the windings of the L5 was burned.
I rewinded the toroid with new wires.
Now, it is working.
I checked the temperature after transmitting on 80 meters FT8 with
approximately 1 KW output.
Plate current 0.85 Amper, HV 2000 V and Grid current 25 mA.
After 30 minutes the temperature readings with a digital
multimeter were.
L5 119 C (246 F)
L4, 64 C ( 147 F)
L6, 49 C (120 F)
Are those temperatures right?
What maybe the cause of the high temperature?? ?
Should I have to replace also
el toroid???
?
Thanks in advance for the comments.
73 de Arturo, LU6ETB
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
I just read through the entire manual.??
On data modes, like FT-8, that amplifier HAS to be operated in the LOWER 1400 vdc? B+ position. And no? more than 1 kw dc input (aprx 500-650 watts PO).?
IE:? 1400 vdc @ .710 amps? (= 1 kw DC? INPUT).? ?I would suggest no more than 600-700 ma on FT-8.?
DO NOT run it in the SSB / 2100 vdc position.? ?You will just overheat the L5 toroid again.? ?L5 is used on 160-80-40m.?
I would use the manual tune (instead of the broadband tune).?
|
Re: High Temperature in Toroid of the PI-L network (Alpha 78)
FT8 is a 100% duty cycle mode and at some point depending on wire size and physical size of the toroid it will at some point overheat. ?It it overheats too much the permeability of the core itself will change and rewiring it will change the actual inductance. ?I had the toroid in a Commsnder 2500 catch on fire and totally destroyed for running 1500 watts RTTY. ?I a customers amp that is. ?It¡¯s the nature of the beast that it will eventually burn up at some point .
On Saturday, March 2, 2024, 11:55 PM, Arturo LU6ETB <lu6etb@...> wrote: Hi, Last week my Alpha 78 stopped working. I found the windings of the L5 was burned. I rewinded the toroid with new wires. Now, it is working. I checked the temperature after transmitting on 80 meters FT8 with approximately 1 KW output. Plate current 0.85 Amper, HV 2000 V and Grid current 25 mA. After 30 minutes the temperature readings with a digital multimeter were. L5 119 C (246 F) L4, 64 C ( 147 F) L6, 49 C (120 F) Are those temperatures right? What maybe the cause of the high temperature?? ?
Should I have to replace also el toroid???
?
Thanks in advance for the comments. 73 de Arturo, LU6ETB 
|
High Temperature in Toroid of the PI-L network (Alpha 78)
Hi, Last week my Alpha 78 stopped working. I found the windings of the L5 was burned. I rewinded the toroid with new wires. Now, it is working. I checked the temperature after transmitting on 80 meters FT8 with approximately 1 KW output. Plate current 0.85 Amper, HV 2000 V and Grid current 25 mA. After 30 minutes the temperature readings with a digital multimeter were. L5 119 C (246 F) L4, 64 C ( 147 F) L6, 49 C (120 F) Are those temperatures right? What maybe the cause of the high temperature?? ?
Should I have to replace also el toroid???
?
Thanks in advance for the comments. 73 de Arturo, LU6ETB 
|
Re: Kudos to Digi Key and Hammond Mfg.
On Fri, Mar 1, 2024 at 01:57 PM, Dave w6de wrote:
How do you find the Peter Dahl transformer listings on Digi Key?? Or any US seller?
Trying to find the price to decide on a tube switch for an Alpha 76PA 3-tube amp.
73,
Dave, w6de
DigiKey sells the Hammond transformers, but does not stock them. They are ordered through DigiKey, and then shipped direct from Hammond.
First, you look up the listing of Peter Dahl transformers: HERE:
Find the transformer you want, and click on the part number you want, then copy (or write down) the "Hammond Part No." from that site...
  Then go to the DigiKey website (HERE:) and enter that "Hammond Part Number" for the transformer you want into the "Enter keyword or part #" box at the top of the page, and click the search button. The detailed info for that specific part will come up, at which time you can enter a quantity and hit "Add to Cart".? Then check out!
 
I think you need an account & Login info with DigiKey, but you can do that at checkout.
? -- 73,
~Alan
|
Re: Yaesu FL-2100B Key Line Polarity
On Fri, Mar 1, 2024 at 09:29 AM, Jim VE7RF wrote:
I would toss the 1/2 wave rectifier......and replace it with a FWB.? ? Then bond the negative to the chassis.? ?A 1/2 wave rectifier is abt the stupidest thing I have ever seen.? You end up with DC current flowing through the xfmr secondary winding on 1/2 cycles.
About the only thing a 1/2 wave rectifier is good for is...... it's the basis for a FWD.? ?A FWD? (full wave doubler) is just 2 x 1/2 wave rectifiers in series.?
? Agree 100% Jim. I've got some nice little 3-amp FWB rectifiers. I'll toss the single diode and stick an FWB in, along with a fresh cap.
-- 73,
~Alan
|
Alan - W5ARM