Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: J Rindt on April 02, 2012, 08:07:49 am
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In this schematic for the Haze.....
What are the diodes for, on the power tubes, from suppressor to ground.?
Thank You
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In this schematic for the Haze.....
What are the diodes for, on the power tubes, from suppressor to ground.?
Thank You
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These diodes are a "failsafe" feature to guard the power tubes against voltage surges. Note that a similar arrangement is added to G3. The plates need a more robust diode, or a string of 3X 1N4007's. See: "How to Service Your Own Tube Amp", by Tom Mitchel, Modifications, p 228. Some people claim to hear a downgraded tone. Bets used for an amp on road tour to keep it less prone to failure.
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Yeah.....I understand the diodes to ground on the plates.
I am talking about the diodes on the Suppressor Grids (as you say, G3).
Those grids are already at ground potential.....or at least cathode potential. So what do the diodes do.?
Thank You
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I can't think of a single reason to do that. :dontknow:
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> What are the diodes for, on the power tubes, from suppressor to ground.?
They are CATHODE to ground. (The G3 connection is incidental.)
> I can't think of a single reason to do that.
I agree.
The idea is they "protect" the 1r 0.25W cathode bias-test resistors.
The real-world reality is they do nothing when the amp is happy; and if it is not happy they ensure the $30 EL34 fails before the $1 resistor.
At least IMHO this is a sign of a designer who has not burned-up enough tube amps to know the consequences.
Ignore them or take them out.