Hi everyone, I just picked up a Kris power pump. It is currently providing about 100 AM carrier and 200 PEP. The driver tube is a single 6JG6A driving 2 X 6LQ6. I would like to purchase a backup set of tubes for this rig before they become totally unavailable. But before I replace them I have a couple questions, as I know about as much about vacuum tubes as I do brain surgery, so please pardon my ignorance

My goal is to find other tubes that I can put in it without modifying the circuit and to keep the amp original.

I am not trying to get more output power (but that would be ok) But I am hoping to find a driver tube that will allow slightly more input (high drive if you will) without putting a swamping resistor/capacitor on the input.

Also, I would like to buy tubes that are durable, I read somewhere that the 6KV6A might be a good choice.

The amp is designed to be driven with between 1-3 watts input, that I can do. But, this is going to be used on 10 meters only (seriously) and I would like to be able to drive it harder.

But I am open to any and all comments/info/mods on this amp. Its's a playtoy and its expendable.


Thank you!

I don't know what the ratings are for this thing, but the limiting factor isn't what kind of tubes you use, it's all about what the power supply can furnish. If it's not up to the task ...

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73 de K7KBN

I have one of those also and rigged it for 6/10m's.
The 6JG6A are getting expensive...I have seen them sell for more than the 6LQ6's.
I removed it for the same reason...I had radios for both bands that had bigger drive output...
I was using the FT-817 for 6m and HTX-100 for 10m.
I rewired the drive circuit from the input of the JG directly to the 6LQ6's...basicaly just removed the tube socket and all.
I added a bias Zenor diode as they show for the GLA-1000B mods (you can find this on-line)...then removed the RF keying circuit and triggered the amp directly with the FT-817 relay...the HTX-100 I used a home-brew QSK circuit I found also on-line with the RF sensor added on...I've got that circuit on paper some where here...Not to bad I built it up on 2 small perf boards from RS.

Well to shorten this up with the FT-817's 5 watts drive I get about 70-80 watts on 6m/ SSB...on 10m with the HTX-100 and about 20 watts drive output is around 120 watts....The tubes run very cool with a small muffin fan I installed inside the case and the amp is surprisingly clean looking at the output with these drive levels.
I did try driving the LQ's with 30 watts and got about 200 watts but she got dirty BADLY on the scope and the tubes got a little cherry red to suit me...so I left the drive where it ran cool and cleaner.

Info I used to do this:
Schematic from Knight-kit T-175(I think) 6/10m amp
Bias circuit(actually Cathode cutoff circuit) from GLA-1000B mods updates. Very easy change...and tube life much better than original set-up...

I changed all the caps and diodes on the Power supply to new...3 amp diodes and slightly bigger caps...B+ voltage is about 980 volts vs the 800 volts originally...

I see a smidgen more output with Sylvania tubes than RCA's but the 5 or 10 watts means nothing on the air!
I've had the same set of Sylvania's in there for at least a couple hundred hours and they are still running strong.

I was going to change the 6LQ6's out for Russian EL509's like I did for and old D&A Maverick(40m to 10m version) I have but it did not seem worth the effort with the results and tube life I have gotten the way she is...

One more thing Remember the voltage in this amp can be DEADLY...A 1000v DC supply will knock you on your backside and can burn you badly...So go slow Be careful inside that case...never work on it plugged in and turned on!!! Do a little reading on how to safely work on the amp before you dive inside...They can hurt you even when they have been unplugged and turned off FOR DAYS!!!
So just my thoughts...Good Luck
All The Best
BJ

Wow thanks for all of the excellent info. I replaced the rectifiers and capacitors. found some tubes on ebay. I can now produce a 200W carrier nice and clean without it heating up. Now I have a new problem!

I picked up a second one, however it is a KRIS 3plus3.

This one I need help on. This one does not quite match the schematic as the schematic shows a 6BQ5 for the keying circuit, and this one must be a later version as it has a NPN and PNP in its place. I replace the NPN and got it to key, however was only getting about 100 watts out of it. Took off the covers to repaint them, and then after replacement, NO OUTPUT.

I have 3 complete sets of tubes that all test good and I know that this is not the problem. If I measure the voltage on the tube caps B+? I get about 900 Volts. RF will pass through it in standby mode, but when I put it in line the RF output drops to less than the input.

I replaced the rectifiers and capacitors but still no output. Nothing looks burned, nothing is disconnected.

However it seems like it is producing output, the lights in the garage dim a bit when I key it, my field strengh meter pegs out. It just stopped. My best guess is that maybe the transformer was weak, and that it still works but cannot provide enough current.

Any ideas would be very helpful!

Schematic here.
Kris Inc. Mach III Plus-3