Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on February 12, 2015, 04:40:44 pm
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What are some opinions on having plate voltage diodes on the power tubes?
A. I don't see the need for them in guitar amps.
B. They are trouble waiting to happen. (rare but the possibility is there))
C. If these diodes go bad in SS PI couldn't the bias transistors get zapped as well?
D. That's not what had happened with the amp i am working on. The diodes read good but could be leaking.
E. I have not lifted the diode ends to test for voltage leakage.
I just replaced a pair of 6465 cathode driver transistors Cross reference NTE 280 in a Peavey MX VTX Series amp.
I would feel better knowing these plate diodes were removed. If a tubes going to blow i would rather see it blow
on it's own due to any other issue (Caps,Bad Tube,Etc) than because a diode shorts the plate voltage to ground.
Am i wrong?
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Those diodes are not there to protect the amp from some tube failure. They are there to protect the amp from not having a speaker plugged in, whether due to some head banger that just forgot to plug it in and just kept turning up the volume 'til the fire starts, or if the cable just accidentally comes undone. Those diodes can prevent some costly repairs, especially in big amps. They are a good thing.
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Thanks for the explanation Steve. I had the wrong idea of what they are used for. I am slow but i am learning. Thanks
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They protect the transformer (not the tubes).
I too am dubious. However if the amp originally had them, I would leave them.