Hi I'm building a new guitar amp with a 5U4 rectifier. Wired as far as the power section only and thought I'd bring it up on the variac. 3 x 33uF with a 10K 5W and a 5K 5W seperating. The 5K first. Anyway as I was bringing it up on the variac I noticed the plates on the 5U4 starting to glow red in spots.. So I shut it down quick. Is it because the rest of the circuit is not on it ie a load,, or should I be able to fire it up to max on the primary with no load atached.. It's a Sovtek 5U4 maybee it's a cheap tube... THanx

Hi

Plates should not glow red. Something is overloading the 5U4. Not a tube problem. Do electrolytic filter caps have a high enough voltage rating? Is their polarity corrent?

Norm

:Hi I'm building a new guitar amp with a 5U4 rectifier. Wired as far as the power section only and thought I'd bring it up on the variac. 3 x 33uF with a 10K 5W and a 5K 5W seperating. The 5K first. Anyway as I was bringing it up on the variac I noticed the plates on the 5U4 starting to glow red in spots.. So I shut it down quick. Is it because the rest of the circuit is not on it ie a load,, or should I be able to fire it up to max on the primary with no load atached.. It's a Sovtek 5U4 maybee it's a cheap tube... THanx

Yeah, you know I don't know where I got these filter caps from but one or more are shorted. They are 450V 33uF.. I measure 0 ohms across the caps one must be shorted? The wiring is right I checked. Cheap bloody Chinese caps..Ugh.. Never again. I have to see which is shorted, now.

Thanx
Bubba

:Hi
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: Plates should not glow red. Something is overloading the 5U4. Not a tube problem. Do electrolytic filter caps have a high enough voltage rating? Is their polarity corrent?
:
:Norm
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::Hi I'm building a new guitar amp with a 5U4 rectifier. Wired as far as the power section only and thought I'd bring it up on the variac. 3 x 33uF with a 10K 5W and a 5K 5W seperating. The 5K first. Anyway as I was bringing it up on the variac I noticed the plates on the 5U4 starting to glow red in spots.. So I shut it down quick. Is it because the rest of the circuit is not on it ie a load,, or should I be able to fire it up to max on the primary with no load atached.. It's a Sovtek 5U4 maybee it's a cheap tube... THanx