Ampeg v4/v22 filter caps substitution question

Started by iandy4, June 20, 2012, 05:57:24 PM

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liquids

I should say that I've only run two power tubes, rather than 4 in this amp for a while now.  I connected the feedback to the 4 ohm tap, which is now the 8 ohm tap, and I re-labeled the speaker switch accordingly with a p-touch - 2/4/8 ohm taps became to 4/8/16. 

I'm not going for breakup, but this amp is loud and huge in it's bass and low-mids response capabilities, even with 'only' two power tubes. 

For me, it's a matter of sense and economics not to heat 4 tubes at a time just to get an extra 3db of clean volume when it's more or less never needed, when I'm already running speakers that are 101db or 102db sensitivity, the circuit change is one aimed at maintaining the originally designed amount of feedback, and it's easily changed back if or when I decide I just have to run 4 tubes. 

I also re-wired and re-paired the power tubes, so that the push-pull pairs are L/R pairs instead of inner/outer pairs, so to speak.  That makes it physically reasonably to run 2 KT88s without one of the tube envelopes bumping up against or near the transformer...two sockets have ampeg-size bear clamps for running two 6L6GC tubes in the spots right next to the transformer (and they don't come close to it), the other two sockets now have spring clamps for the KT88 tubes, and are far away from the transformer, as it is currently...

Breadboard it!

amptramp

The high voltages you have found will be, in part, due to the lessened loading on the power supply of only using two output tubes.  You are only pulling half the current through R55, so the screen voltages will rise.  The power transformer secondary normally can be counted on to have a certain resistance that drops the voltages, but if only half the current is being drawn in the output, the voltages may remain higher than expected.