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pmillett 21st January 2017 10:17 PM

50W monoblock "Engineers Amp"

As some of you already know I designed a PCB for a 50 watt monoblock version of the "Engineer's Amp". It uses 6HJ5 tubes, B+ of about 410V, and does an easy 50 watts out into 8 ohms.

You can see the details on my web site: Engineer's amp 50W monoblock

I have one assembled into a chassis now. I will be doing more measurements soon. It works very well :)


Tubelab_com 22nd January 2017 02:13 AM


I used the 6HJ5 sweep tube for the outputs. I am using 6GU5 tubes for the input/driver. Thanks for the idea George!
And only 50 watts.........

smoking-amp 22nd January 2017 02:58 AM

I hope there's more of those tubes left. George and friends might have burned up a few working on those 100 Watt and up earth shakers.

21LG6, 17KV6 and 26DQ5 are fairly similar tubes except for pinout and socket. Might be useful to allow for some pinout re-assignments and optional plate caps. And then there's bigger TV tubes.... 1/2 KW dreams-obsessions

smoking-amp 22nd January 2017 03:55 AM

Maybe the -bias V should have a Zener regulator, if the screen V is regulated.

hooman 22nd January 2017 04:06 AM

work very well..... tv tubes in hifi sound .

aardvarkash10 22nd January 2017 04:21 AM

the incredible unfairness of living on the bum of the world.


ta240 22nd January 2017 06:05 AM


Originally Posted by aardvarkash10 (
the incredible unfairness of living on the bum of the world.


yeah, but you get the really cool accents and great words like bum.

smoking-amp 22nd January 2017 07:03 AM

There is a Hammond 291FX upgrade xfmr ($114) for the presently specified 290FX ($92). It's more expensive, but has 29M6 laminations for quieter running.

I assume the rather more expensive 300 series (373FX, $182)) has M6 laminations too. Weighs 1.5X as much. Must run at lower flux density.

The EDCOR XPWR247 looks like the only similar XFMR, but only rated 325 mA (versus 450 mA for 290FX) and it doesn't have enough current for the 6.3 VAC heaters.


"the incredible unfairness of living on the bum of the world."

As long as Atlas doesn't take a break, you should be fine.

TonyTecson 22nd January 2017 09:22 AM

for some reason i could not get his boards, still having fun with point to point wiring...


but has 29M6 laminations for quieter running
i use 0.35mm H18 and rm18 taiwan laminations for power traffos that
i use in my tube amp builds....

Schultz 22nd January 2017 10:30 AM

Excellent.... Maybe I am gonna try....

Can you post ebay link for pcb's.....?

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