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Re: Compare JJ's to Tung-Sol ?
To answer Mr. B's question: it all depends on the amp and your ears! However, I have tried various 12AX7s in multiple amps. JJs are dark and less defined to my ears. Tung Sols are one of my favorite preamp tubes. Tend toward slightly higher gain and clear upper-end. The other is Shuguang. Not quite as hot and sweeter (if that makes any sense).
[reference to non-existent Tung Sol EL-84 tubes deleted]
While Ei 12AX7s are horrible (microphonics), I loved the EL-84s the best out of 3 or 4 pairs. Smoother breakup and warm without being muddy (like JJ).
Whoever suggested getting one each of several brands of 12AX7 is on the right track. I guarantee that you will think tubes make a difference after you swap back and forth between JJ, EH, Sovtek, Tung Sol, Shuguang and NOS preamp tubes in a single amp. V1 - the first tube in the signal change - has the biggest impact by far. (Phase inverter tube really doesn't matter so long as it's not microphonic.) Even tubes from the same maker vary and it's worth finding "the one" for that first position.
Re-reading the first post, it doesn't sound like tubes are the problem here. Curly may be onto something regarding the bias of the power tubes. The Classic 20 is cathode biased, meaning the power tubes find their own happy operating point (oversimplified version). The Classic 30 is fixed-bias, but the bias is not adjustable. Peavey just guesses how your power tubes will behave and sets the bias voltage based on that guess. A qualified amp tech would need to measure the bias and then either find the right bias range resistor or add a bias adjustment pot (not easy on a PCB amp).
Bottom line, the Classic 30 is NOT just a Classic 20 with two more power tubes. Other than being fixed-bias instead of cathode-bias, the 30 has a choice of 2 or 4 gain stages before the tone stack. The 20 has 3 gain stages before the tone stack. The extra 12AX7 in the 30 should be a clue (reverb is all solid state). Check out Post '70s amps for the schematics: http://www.schematicheaven.com/post70s.htm Even the negative feedback loops are different (and ****ed weird in the Classic 20, but you like that amp).
HTH
Chip
To answer Mr. B's question: it all depends on the amp and your ears! However, I have tried various 12AX7s in multiple amps. JJs are dark and less defined to my ears. Tung Sols are one of my favorite preamp tubes. Tend toward slightly higher gain and clear upper-end. The other is Shuguang. Not quite as hot and sweeter (if that makes any sense).
[reference to non-existent Tung Sol EL-84 tubes deleted]
While Ei 12AX7s are horrible (microphonics), I loved the EL-84s the best out of 3 or 4 pairs. Smoother breakup and warm without being muddy (like JJ).
Whoever suggested getting one each of several brands of 12AX7 is on the right track. I guarantee that you will think tubes make a difference after you swap back and forth between JJ, EH, Sovtek, Tung Sol, Shuguang and NOS preamp tubes in a single amp. V1 - the first tube in the signal change - has the biggest impact by far. (Phase inverter tube really doesn't matter so long as it's not microphonic.) Even tubes from the same maker vary and it's worth finding "the one" for that first position.
Re-reading the first post, it doesn't sound like tubes are the problem here. Curly may be onto something regarding the bias of the power tubes. The Classic 20 is cathode biased, meaning the power tubes find their own happy operating point (oversimplified version). The Classic 30 is fixed-bias, but the bias is not adjustable. Peavey just guesses how your power tubes will behave and sets the bias voltage based on that guess. A qualified amp tech would need to measure the bias and then either find the right bias range resistor or add a bias adjustment pot (not easy on a PCB amp).
Bottom line, the Classic 30 is NOT just a Classic 20 with two more power tubes. Other than being fixed-bias instead of cathode-bias, the 30 has a choice of 2 or 4 gain stages before the tone stack. The 20 has 3 gain stages before the tone stack. The extra 12AX7 in the 30 should be a clue (reverb is all solid state). Check out Post '70s amps for the schematics: http://www.schematicheaven.com/post70s.htm Even the negative feedback loops are different (and ****ed weird in the Classic 20, but you like that amp).
HTH
Chip
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