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 .?
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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
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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 !! ?
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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
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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) .?
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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) .?
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Re: Kudos to Digi Key and Hammond Mfg.
Mine went from Hammond to DigiKey and then was shipped to me.?
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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).?
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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
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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
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Re: Original GM3SEK/G3SEK Tetrode Boards
It's two?boards. One for control & the other for bias voltages.
On Fri, Mar 1, 2024, 20:15 Steve < k0xp@...> wrote:
Are there more than one set of boards: i.e., are you selling
multiple sets of boards for multiple amplifiers??
Or is this just one amplifier-set of boards?
TNX,
Steve K0XP
On 3/1/2024 6:48 PM, Mark Schoonover
via wrote:
Boards are 95% assembled and configured for 4-250A
tubes. If you plan on using different tetrode tubes, you'll need
to do the math outlined in the printed manual I'm including.
Includes R14 wire-wound adjustable resistor, heatsinks &
mounting hardware for TO220 transistors, off-board connectors,
500-ohm wire-wound pot, 5k 50W chassis mount resistor, remaining
discrete components, and Stancor P-8671 117V 50-60hz/36v/1A
transformer. I can provide photos of the boards. I am asking
$550 + Shipping. Send your zip code, and I'll calculate the
final cost. I prefer Zelle/Venmo and USPS money orders, too. No
PayPal. All items are sold as-is with no returns.
73! Mark KA6WKE - DM34st
Website:
Youtube:
--
See my QRZ.com page at
|
Re: Original GM3SEK/G3SEK Tetrode Boards
Are there more than one set of boards: i.e., are you selling
multiple sets of boards for multiple amplifiers??
Or is this just one amplifier-set of boards?
TNX,
Steve K0XP
On 3/1/2024 6:48 PM, Mark Schoonover
via groups.io wrote:
Boards are 95% assembled and configured for 4-250A
tubes. If you plan on using different tetrode tubes, you'll need
to do the math outlined in the printed manual I'm including.
Includes R14 wire-wound adjustable resistor, heatsinks &
mounting hardware for TO220 transistors, off-board connectors,
500-ohm wire-wound pot, 5k 50W chassis mount resistor, remaining
discrete components, and Stancor P-8671 117V 50-60hz/36v/1A
transformer. I can provide photos of the boards. I am asking
$550 + Shipping. Send your zip code, and I'll calculate the
final cost. I prefer Zelle/Venmo and USPS money orders, too. No
PayPal. All items are sold as-is with no returns.
73! Mark KA6WKE - DM34st
Website:
Youtube:
--
See my QRZ.com page at
|
Original GM3SEK/G3SEK Tetrode Boards
Boards are 95% assembled and configured for 4-250A tubes. If you plan on using different tetrode tubes, you'll need to do the math outlined in the printed manual I'm including. Includes R14 wire-wound adjustable resistor, heatsinks & mounting hardware for TO220 transistors, off-board connectors, 500-ohm wire-wound pot, 5k 50W chassis mount resistor, remaining discrete components, and Stancor P-8671 117V 50-60hz/36v/1A transformer. I can provide photos of the boards. I am asking $550 + Shipping. Send your zip code, and I'll calculate the final cost. I prefer Zelle/Venmo and USPS money orders, too. No PayPal. All items are sold as-is with no returns.
73! Mark KA6WKE - DM34st
Website:
Youtube:
|
Re: Kudos to Digi Key and Hammond Mfg.
I bought one last year from? them,10 week wait and total cost was about 1K.?
?? 73s Bob W5RG
On Friday, March 1, 2024 at 01:57:47 PM CST, Dave w6de <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
?
From: [email protected]
<[email protected]> On Behalf Of Alan - W5ARM via groups.io
Sent: 1 March, 2024 01:19
To: [email protected]
Subject: Re: [ham-amplifiers] Kudos to Digi Key and Hammond Mfg.
?
Yessir!? Hammond Mfg. and DigiKey are great resources.
I've ordered a couple of their Peter Dahl transformers, and they make a first-rate product! Pricing was fair enough, and they shipped quickly.
The listing of transformers is extensive, and the documentation is great. Find the one you need, copy & paste the P/N into DigiKey's main site to order, and you're done (well... after you pay).
Hammond/PWDahl Transformers are HERE:
--
73,
|
Re: Kudos to Digi Key and Hammond Mfg.
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
?
toggle quoted message
Show quoted text
From: [email protected]
<[email protected]> On Behalf Of Alan - W5ARM via groups.io
Sent: 1 March, 2024 01:19
To: [email protected]
Subject: Re: [ham-amplifiers] Kudos to Digi Key and Hammond Mfg.
?
Yessir!? Hammond Mfg. and DigiKey are great resources.
I've ordered a couple of their Peter Dahl transformers, and they make a first-rate product! Pricing was fair enough, and they shipped quickly.
The listing of transformers is extensive, and the documentation is great. Find the one you need, copy & paste the P/N into DigiKey's main site to order, and you're done (well... after you pay).
Hammond/PWDahl Transformers are HERE:
--
73,
|
Re: Yaesu FL-2100B Key Line Polarity
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.?
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Re: Yaesu FL-2100B Key Line Polarity
That’s true, once you bias the cathode instead of the grid you no longer need a negative voltage. Lou
On Thursday, February 29, 2024, 9:52 PM, Alan - W5ARM <W5ARM.mail@...> wrote: Hi Louis,
Thanks for the reply.? As I said, I can't see where the polarity change would create any problem, and sounds like you've had the same experience.
Appreciate the info!
-- 73,
~Alan
|
Re: Yaesu FL-2100B Key Line Polarity
Hi Louis,
Thanks for the reply.? As I said, I can't see where the polarity change would create any problem, and sounds like you've had the same experience.
Appreciate the info!
-- 73,
~Alan
|
Alan - W5ARM