• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Interesting GM70 scheme... Some questions on the PSU, who helps me please?

"I love the smell of burning Teflon in the morning"

I see you met our intern of a few years ago. That lad was a pro at making high voltage power supplies arc and he managed to blow an amazing amount of multimeters 😀

But those connectors are the defacto ones on most high voltage powersupplies we have in the labs. Safe for a few amps of current and very high potentials, beyond what is reasonable for an amplifier. One piece of warning though, they can be disconnected quite easily by design and I would not trust them unsupervised with children around as curious fingers could disconnect them and get a shock. One in a million freak accident but still worth to keep in mind
 
I used Amphenol MILspec locking connectors from Mouser for the 1100v B+ (I can't find the exact reference) and 5kV rated silicon isolated wire.

For the 350v and bias supply I used some locking militay-style Chinese connector off eBay. Good enough quality.
 
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Hole punches are great, if you only have a cordless drill to work with.


Try to get the one with the roller bearing on top, these have far less friction and are easier when you need to do mild steel.



They take longer than a step drill, but a step drill needs more de-burring, and a step drill with a cordless power tool is not ideal..
 

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Shunt idea.

I had some stupid idea to do a shunt regulator with some cheap run of the mill components. Nothing special in here:



The most expensive part is the TIP50 transistor at about 50 cents. If you want better performance the toshiba TTA006B may do the trick.


Those shunt blocks are just plain TL431 shunt regulators in shunt configuration. And they are dead quiet like this.. depending on the grade they produce about 10-25uV RMS noise.
 

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So friends, last question about output transformer:

I read that max output power for a gm70 is 43W @1200V plate.

Now on my shortlist there are these with high impedance:
Fc-40-10s SE Iso (former Tango) 10k primary impedance, 40W, around €900 each;

Fc-30-10s iso 10k, for 30W, around €520 each

Vincent's lundhal ll1168, different input impedances (5k2, 9k), 30W (or 60w according to primaryZ) power, around €350 each,

Monolith sa-15, amorphous core, Z=6.1k, 30W, €730 each.

Will 10k not be too much?
Will 30W suffice?
 
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