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24.20.10.236
In Reply to: RE: The Dynaco looked better with the dust posted by Byrd69 on May 26, 2022 at 07:15:28
A tube rectifier is not linear in the way it conducts. So at low voltages from your variac, it is not on at all, then, at some point, it comes on.
If you are trying to find out if the amp is bad, or reform the caps, buy one of the cheap, socketed, solid state rectifiers off of the internet, or break open a worn octal tube and solder in a couple of diodes, or even tack solder them to the back side of the 5AR4 socket. You can then bring up the amp in a linear fashion.
Follow Ups:
The slightly easier way is to just plug in something else. a 5Y3 for instance, and some 6V6's or perhaps cheap 6L6's. Goal is not to get full performance, but reach 75% of B+ and deliver some idle current load.
All in all, for a flipper amp, bring it to the point where you can guarantee the transformers is a useful thing.
And heating up an amp with a GZ34 is not too difficult with a variac and volt meter. Recognize the non-linear behaviour and account for it with the variac's knob.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Popped in a borrowed quad of shitty china EL34s and a low testing russian GZ34. That's how you do it. lol
Powers up!
It's sold....cheap.
Your interest may vary but the results will be same. (Byrd 2020)
I can't compete with the dead. (Buck W. 2010)
Cowards can't be heroes. (Byrd 2017)
Why don't catfish have kittens? (Moe Howard 1937)
Nt
I have a tube base with a couple 1KV rectifier diodes wired for 5AR4/5R4 testing. Don't risk that nice Mullard 5AR4 in an unknown circuit. As you raise the Variac, the 5AR4 will conduct suddenly and without much warning. If there's a bad cap or other component, the tube can be damaged before you have a chance to remove voltage.
I bought the amp only for the tubes. I have no interest in having it restored for my own use. I have had a couple 70s over the years and did not care for them. Sold them both. A friend wants this one to restore. I'll sell it assuming it doesn't work. I'm not going to risk killing a tube. Doing the diode thing is beyond me. It's not that important for me to know if the amp works.
I'm happy the preamp is running. I'm sure some updating might benefit it, but I don't need it so I'll pop in some USA 12ax7 and send it on it's way.
Thank you for the tips, inmates.
Your interest may vary but the results will be same. (Byrd 2020)
I can't compete with the dead. (Buck W. 2010)
Cowards can't be heroes. (Byrd 2017)
Why don't catfish have kittens? (Moe Howard 1937)
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