Technik > Tech-Talk Amps

Bias Drift bei aufgedrehtem Gain

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raffau:
Racing,

I did measure the negative Bias Volatage. It stays like it should -51V...Whatever the GainVolume Pot is crancked or not!

raffa

Racing:
@ Raffa.
Ok.
In that case start by pulling the phaseinverter tube out of there and set bias for the powertubes. With the PI tube out there´s no real chance of signal being presented to g1 and hence you will have a stable condition at that point rendering it possible to set powertube bias regardless of what the front end/PI is up to.

Albeit crude  this actually works to a degree when trying to figure out where the oscillation stems from. Just yank a tube at a time until it goes away.

raffau:
Will report! :-)

cca88:

--- Zitat von: raffau am 19.10.2015 11:51 ---Racing,

I did measure the negative Bias Volatage. It stays like it should -51V...Whatever the GainVolume Pot is crancked or not!

raffa

--- Ende Zitat ---

Hallo raffa,

was mir noch auffällt... die G1-Gridstopper sollten GANZ nahe an den Fassungspin ran... Du bist zwar "relativ nahe dran, aber ich würde die Orientierung der Widerstände umdrehen...

Wäre aber vom Symptom her eher ein "Knarzen"

Grüße

Jochen

Racing:
@ Raffa.
All good.
If i understand you correctly what we have at hand here is an oscillation that stems from the preamp or phaseinverter.?

In that case,not to come down on your build but ment as constructive critisism,you need to look into the lead dress of the amp. Simply pinpointing the actual oscillation will in that case only be half the answer.

There are "do´s and don´ts" when building an amp and attention to lead dress is certainly one of them.

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