Peavey Classic 30: Phase inverter distorts first?

[APO]

Lately I've been running the volume on my Classic 30's normal channel at 4 or higher. I've noticed around volume level 4 to 6+, that's when the normal channel starts overdriving and the low end gets kind of woofy/loose.

Up until recently, all the tubes were the stock Sovteks that came in the amp new in 90-something. I got some different output tubes, slightly used 6P14P-EVs. I did some swapping between the old Sovteks EL84s and the 6P14P-EVs; while there was a fair difference in tonality, there was no obvious difference in breakup. If it were the output tubes distorting, the 6P14P-EVs should distort much less since they're higher rated, similar to a 7189, but again there was no obvious difference in breakup.

Also, most of the time I use a separate preamp straight into the FX return, and at higher volumes the low end will still end up sort of loose. I swapped out the speaker for a Celestion G12K-100, a speaker known to have tight low end, so I doubt it's that. I also load the extension speaker output with a an attenuator, so the Celestion inside the C30 shouldn't be seeing a whole lot more that 15 watts.

So, I doubt it's the output tubes, the preamp, or the speaker distorting causing this looseness in the low end.

Does all this mean that the phase inverter is starting to breakdown first, causing some looseness? I've been thinking of changing the phase inverter since it's the stock Sovtek the amp came with; I've read it's not such a good tube in general, and even worse as a phase inverter.

[Enzo]

Yes, the C30 starts to clip in the phase inverter at about 4-5 on the clean. It isn't breaking down, it is just clipping. That means the signal level exceeds the tube bias.

[TedBPhx]

I replaced a Sovtek 12ax7LPS in V3 with a 5751 to try to reduce the phase inverter clipping. Killed the tone. Turned it into a lifeless amp.

[ScottMarlowe]

Agreed. I too tried a 5751 there and a few other 12AX7 types and none of them work as well as either the sovtek 12AX7LPS or the JJ ECC83 LPS one (I forget the exact model). Luckily when I bought my C50 4x10 it came with 3 sovtek 12AX7LPS in it so I have a few spares.

5751s btw, work really well in V1. I like Chinese 12AX7A or B or Sovtek 12AX7A or C in V2.

[dalrymple]

Reframe the issue. I think that woofy bottom is the poor EQ range of the bass control on a C-30. It does not control the frequency I wanted control of when I used one for a decade as my gigging amp.
But the solution was not tubular, it was a simple EQ in the loop, which allowed the flappy bottom to be brought to heel. Dont allow the amp to control you. Make it accentuate the positive and respond the way you need it to to play your best.
Fish & Chips in the loop will probably get you a lot closer to where you'd like to hear it than any tube swap mentioned. Control. YMMV.
Dalrymple

[APO]

TedBPhx, could you be more detailed about your experience trying a 5751 in the phase inverter? You say lifeless, but you didn't say if it reduced the clipping after all. I've read people say similar things about the 5751, while others really like them.

Dalrymple, I agree under some circumstance it may be the C30's EQ. It's worth noting again I usually use an external preamp into the FX return; this bypasses the C30's preamp as well as the tonestack completely. Another thing is I don't really want to lose any low end either, I like the voicing I am getting mostly. While I am considering it, an EQ just to cut the ultra low frequencies doesn't appeal much to me.

I should also mention, after looking at the tubes (V1-V3), I actually do not know what make they are. I know the original output tubes were Sovtek EL84s. The 12AX7 tubes have no label, appear to be short gray plates with a weird guard around the plates; they look similar to Shuguangs albeit with a different getter.

I'll try to describe what I'm hearing a little better. It seems I can get quite tight low end just until the phase inverter starts clipping; then it sounds like the trail of the note attack gets longer, making a squishy sound for lack of a more accurate term. It seems much more obvious if the back of the amp is facing me, rather than if the front is facing me.

[TedBPhx]

Don't know what else to say. The tone was so dull I didn't care if it had more headroom.

[stoneyvision]

Sounds to me like you need a choke installed. I had a problem like that with my 50watt 2x12 5150 converted to a head. It gets loose at 4. Had a choke installed & now it stays "together " much better at high volumes.

[APO]

Anyone else have experience with a choke? Can I use any choke besides the one Mercury Magnetics offers?

[stoneyvision]

Mine is from Hammond. Good quality. Only paid $15 on ebay if I remember correctly.

[APO]

Anyone know what spec choke to buy?