The Phase Inverter tube. How to choose?

[crusty philtrum]

Re: The Phase Inverter tube. How to choose?

One time i was tracing the signal through my Matchless DC30 clone. What i discovered was that the signal stayed clean all the way up to the input of the PI. The first point where i was able to detect any form of signal distortion was at the PI output once the channel volume controls reached a certain point.

Even with the channel volume controls set to maximum, the signal was clean all the way to the PI input. This is probably true of many or most old-style, non-mv amps.

BTW, matched PI tubes (and power tubes) may well be somewhat of a waste of time unless you have a perfectly balanced output transformer. And if you did have everything balanced, you probably wouldn't like the sound. Most famous guitar amp tones come from the imperfections and imbalances.

[crusty philtrum]

Re: The Phase Inverter tube. How to choose?

..... at7s can take 10x the amount of voltage that an ax7 or 5751 can.

Not sure that's correct .... the AT7 can deliver 10 times the current (10 mA) than an AX7 (1 mA). I think you may have your wires crossed, so to speak.

[Quencho092]

Re: The Phase Inverter tube. How to choose?

If AT7's deliver 10 times the current, that means that they deliver 1/10 of the voltage if power output is assumed equal?

AT7's are lower gain, so their power value is lower as well, right? The ratio of current to voltage in an AT7 must have a functional impact on the amp.

When I was a tube amp user, I liked a 'balanced triode' AT7 for phase inverter, no V1, and an RCA in V2 for DRRI. Didn't like the duller 5751, absolutely loved the 12AX7M mullard copy in V2 tonally but didn't like the breakup.

12AX7's made the amp sound flabby and mushy. Maybe I would like a 12AX7 in a higher power amp like a Plexi more to make it more breakup responsive, but in <40 watt amps it lowers the distortion ceiling too much.

[jeremy]

Re: The Phase Inverter tube. How to choose?

you are prolly right. My marshall uses an ax7. I just found i cook them a lot in my fender twin, so i just use at7s now

your fender was designed to have a 12at7 in the pi, not a 12ax7. marshalls are typically just the opposite

[Rick330man]

Re: The Phase Inverter tube. How to choose?

A decent P.I. tube makes a big difference to my ears. Amazingly, those cheap, crappy Sovtek 12AX7As and 12AX7Bs make pretty good ones. As Myles Rose noted, JJ ECC83S tubes do something in the P.I. slot that is not pleasing. I dont' think they do good service there. I think of the GE 5751 as the gold standard P.I. tube. In an amp calling for a 12AX7 P.I., the GE 5751 will bring out the best presence and detail in your amp. That's just my experience.

Lots of folks push the 12AT7 as an ideal P.I. tube. It depends. In some amps, it sounds great in that role. In amps that want a 12AX7 there, the 12AT7 just sounds like it is lacking punch. Let your ears be the judge.

[Chickenwings]

Re: The Phase Inverter tube. How to choose?

Not sure that's correct .... the AT7 can deliver 10 times the current (10 mA) than an AX7 (1 mA). I think you may have your wires crossed, so to speak.

yeh. something like that...

[erksin]

Re: The Phase Inverter tube. How to choose?

Some would say the opposite, as it is one of the deciding factors on how the power amp will behave. I think it depends a lot on how the amp is designed overall that determines the amount of difference a certain tube will make. V1 in any amp pretty much is guaranteed to be the most noticeable change.

Absolutely this.

If v1 is the gain/EQing slot, the PI slot is the 'feel' slot.

[Rick330man]

Re: The Phase Inverter tube. How to choose?

It has now been over seven years since I (and others) originally posted on this thread. I am curious as to how peoples' opinions have changed or been reinforced.

I have two Crate Vintage Club 50 heads that I love. I've had them over 15 years and they keep going strong. The manual calls for 12AX7s in all 4 pre-amp slots. Sticking a 12AT7 in the V4 P.I. slots brings out the best in these amps. By comparison, I have had a pair of Hot Rod Deluxes - though I am now down to one. Using 1980s production GE 5751s in the V3 P.I. consistently brings out the fullest, cleanest tones these amps produce. Other amps don't seem to be impacted much as long as you use the tube the factory specs call for.

[esandes]

Re: The Phase Inverter tube. How to choose?

I experimented with preamp tubes for my 1959RR mostly and I like the 12ax7 for more gain. Also be sure to buy a PI tube the best you can afford. Be sure it's not microphonic.