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On your tetrode, you are matching 50 ohms to? 1000 ohms (now 500 ohms), so the PI net values are all different........ vs? the 50 ohms to 50 ohms on the 3x6 (and 3x3).?

When matching to 500 ohms, the C1 and C2 values are a lot less, but the coil is a lot bigger.? The 4x10 ( and 4x5) tube has 100 pf of tube C? (control grid to cathode)? that has to be absorbed into the? C2 cap on the PI tuned input.? That alone creates another big problem, since then the loaded Q of the tuned input has to be increased by a bunch.....esp on upper HF bands.? ? On 15m, with a Q of 20, the C1 =? 530 pf. Coil is just .55 uh.? C2 =? 123 pf ( and the tube is 100 pf, so the required C on the C2 cap is now just 23 pf).?

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On lower bands, you can use as low as an overall network Q of 4.5 on? ?160m + 80m.? On 80m C1 = 94 pf? L = 9.31 uh? ?C2 = 183 pf ( - 100 pf of tube C,? C2 is actually just 83 pf).??

On 160m,? C1 = 195 pf? L = 19.22 uh? ?C2 = 380 pf ( - 100 pf of tube C and C2 is actually 280 pf).? ? Required L on the 10-15 kw output tank is huge.? ?Now I can see why Asamoto? made it a 80-15m amp.? The required kintronics roller coil for 160m won't even fit.? The tuned input would be a mess on? 12+10m.?

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And if a 1:9 un-un used...along with a 450 ohm globar resistor,? you still have to cancel out the? 100 pf of tube C.? ?That 100 pf of tube C is directly in parallel with the 450 ohm resistor.? You would need a different value of coil, directly in parallel with the 450 ohm resistor, to cancel out the 100 pf of tube C.? ?And the XC of the fixed 100 pf of tube C will? change on each band, being highest XC value on the lowest bands....and lowest XC? value on upper HF.? ?Lower HF gets the bigger coil values.? ?You got lucky with no neutralization required.? That's a major pita on a 4x5/10/15.? The small neutralization cap interacts with the tuned input. ( they throw each other off).? To tweak it up right, Scott had to use a Boonton RF voltmeter, + sig generator.? ?Regulated screen and bias supplies? + protection is no mean feat.? ?Lose the B+, and with screen voltage still present, you better have super fast protection installed.? ( Both screen and anode over current...and also grid over current).?


Dunno what the chinese 3x3 and 3x6 cost these days.? ?The tuned input is dead simple. On the 3x6, it needs an IPA.? With the mini turns counter + 6:1 vernier on both the tune and load caps on any SB-220 / L4B, it makes for dialing up pre-sets a snap, mere seconds.? Any SS IPA is even faster.??

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So, yes, there is tradeoffs with a tetrode / triode.? In it's simplest format, the triode + IPA wins out.? ?Watch how the build progress's.?

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Hi Bob,

You asked that I let the group know how things went. Lou sent the meter, and a soft key module, and both are installed and working perfectly. And the new meter looks just like the original. The one glitch I did encounter is the terminal posts on the new meter are longer than those on the original. As a result, the positive terminal contacted the metal tray that the meter circuit board resides in, preventing the meters from being mounted back in place. I removed the meter and ground both terminals down about as short as they could be and still clamp the ring terminals under the top nut and washer. That fixed the problem. I'd recommend anyone mounting a replacement meter to do? the same before attempting to install the meter.
--
Jim McPhee
Placitas, NM
W5ABA

Hi,

New to RTTY. Looking to see what I need to know regarding the use of the Alpha 86 and FSK on RTTY at recommended power settings if any.

73

Ron
KK7GO

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Type 90 switch is? just under $500.00? ? It's rated at 40 amps @ 20 kv.? ?Scott doubled up on the contacts, and made it into 80 amp switch.?

I used a triple wafer model 88, and paralleled all 3 x wafers.? Modified into a progressively shorting switch by installing? 5 pole? sequential rotors on each wafer.? The 88 is rated at 30 amps @ 13 kv. With 3 x wafers in parallel it's now 90 amps @ 13 kv. Triple wafer model 85 switches will also work. 30 amps @ 12 kv.? ?90 amps @ 12 kv? with 3 x wafers in parallel.? ?Beware, those current ratings are for 60 hz AC...not RF freqs.? The triple wafer model 85 / 88 are reasonably priced.

Tubing in the plumbing section of Home depot (aisle 16) is dirt cheap.? I silver plate em with the cool-amp glop from Ore.?

The correct? KINTRONICS 40 amp (1/2" tubing)? ?roller coil, new is $1821.00? ? Called a LV19-40.? ( 19 uh).? ? Damned thing is massive,? ? 17.625" long x? 11.625" wide? x? 11.5" tall.? ?Not including shaft out the end. Plus must be mounted on 4 x 6" tall standoffs.? ?Total height is then 17.5" tall. That just kills it for any amp...period.? You need a chassis the size of a dump truck.? I would take the Kintronics roller coil ratings with a grain of salt too.? The actual rolling contact is the weak point on em.? The fixed tubing Kintronics coils are rated the same as their roller counterparts...which nobody else does.? Everybody else always de-rates the roller versions.? Since the roller is variable, required uh is easy to obtain. BUT the tubing used has to be sized for upper HF, which means 1/2" tubing.?

On this setup, the 2.3 uh coil is 1/2" tubing....and combines the .6 uh pre-coil / L coil and the 1.75 uh 20m coil, all in one coil. 20m Coil tapped for 17+15M. The required uh for 80m is? ?9.25 uh.? 80m coil is just 7.5 uh, since? the 1.75 uh 20m coil is already in series with it.? 160 required uh is 18-18.5 uh.? ?A simple 9.25 uh 160m coil is on the end of the mess.

Scott got lucky, and has a box full of silver plated 2.3 uh tubing coils, made from 1/2" tubing.? They all came from 13.56 mhz RF generators.?

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20-17-15m coil is made from 1/2" tubing.? 80-40m coil is made from 3/8" tubing.? ?160m coil is made from 1/4" tubing.?

Any roller...... (or tubing coils in series, and bandswitched)? that covers down to 160m is gonna create grief.? ?You will get the dreaded ....'suck out' on 20-10m every time.? That's why we use a progressive shorting style bandswitch if 160m is involved.? Multi-tech industries calls those switches.... 'multiple pole rotors'.? ?IE: instead of a single rotor, they use 5 x sequential rotor fingers...that all converge onto the central rotor hub.? ?1st rotor finger does the actual various taps, the remaining fingers just provide for additional shorts across un-used contacts.? ?You can test for? suck out very easily.? Temp wire a resistor ( = to the plate load Z) between anode to chassis.? Tweak tune and load and roller for 160m..with mfj-259B on output connector for 1:1 swr.? Then sweep the mfj and see what the upper /lower freq is for the 2:1? points.? ?Then repeat on 80m.? On 80m, the 2:1 points should be twice the BW.? And double again on 40m.? And double again on 20m. With suckout, the 2:1 BW is extremely narrow. Temp short out the last few turns at the 160m end of the roller...and the suckout effect? vanishes.?

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On a roller that covers 160m, the only option is to use a relay, and it's contacts, to provide for one extra short in the middle of the coil, like where 80m would reside.?

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Tetrodes are a? pita.? ?The 4x5 has a tiny under fin area? vs the 3x6.? It's dead simple to get 8 kw CCS anode diss from a 3x6. No screen supplies required, nor bias supplies, nor? screen grid protection.? (Lose the B+, with screen V still present, and you are in for a rude surprise).? ?3x6 is simple resistor cut off bias.? No neutralization required.? ?On my own YC-243, it's a socketless version of a 3x6.? ?Build in grid? flange just bolts to the chassis.? 50 ohm input. Simple tuned input. Fil choke is now dead simple....just slide on the fair rite oval beads over the pair of power cables.? Simple metering. Sorta like a SB-220 on steroids.

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Scott already has a 4x15 installed in his aerocom commercial amp.? Damned thing idles at 1000 ma ! (@ 8 kv).? ?Sucks 3 kw on RX....and 10 kw when keyed, on idle....and no drive applied.? And sucks 45+ kw when driven.? 3 x blowers used.?

It uses a 75 kva pole pig configured for 240 input and 5600 vac output.? You need 400 amp service to run it.? ?Totally impractical.? ?It's going up for sale at some point.

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Sure, a small IPA is required with the 3x6.? ?Everybody already has a 600 watt amp.? 80% of the drive power ends up in the output.

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Here is the 4x15 aerocom amp.?

Here is the 75 kva plate xfmr that runs it.? ?

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?The new cabinet is pretty small for this project.? ?It will all just barely fit.? Cab height, from chassis to top is only 9.25".

? Ok, that's the sob story for this week.?

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On Sun, Aug 27, 2023 at 02:14 AM, Alek Petkovic wrote:

That would be an interesting exercise. I use my nano vna all the time too but I don't think I'll bother in this case, as it seems to work fine with the cap in place. I'll let sleeping dogs lie. I'm just finishing off some mods for a local ham, which were started many years ago and the guy doing them got ill and sadly passed away.

I saw a reference where Rich Measures mentioned the addition of a small cap around this size from the normally closed I/O relay to ground, to improve the through SWR on 10m when the amp is bypassed. Why anyone would ever operate with the amp bypassed is beyond me.???

73, Alek, VK6APK

It's typ only 10-15 pf at most, for a cap...from either NC contact to chassis.... to flatten the bypass swr on 10m.? Typ used on a SB-220. Not required on my L4B's...and dunno abt the TL-922.?
In this config......Lou is correct. It will just increase the min C on every bands by 47 pf.?

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Yes. A silly activity.?

Alek. VK6APK

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