What 12AX7 make a good inverter tube?

[kiteman]

I was trying out tubes in V5 on my Alchemist 112 and was getting different results. First I tried a Mullard RI and it sounded pretty good. Next was a ruby 12AX7AC5 HG (Chinese) and that sounded awful. Next was an EH and it turned out the best of the lot so it's staying for now.

What I have left is the RCA 5751, EH 12AY7 and a Jan 12AT7. Those have lower gains and I don't know if I could try these so I didn't. What does lower gains in the inverter do?

 

[deeaa]

Seems to me it maybe reduces power amp drive, which IMO is a bad thing. In any case I don't think it's wise to use an AY or AT or such there. I wouldn't change from original specs in other than V1, where it's quite handy to use a lower gain tube if you want to lessen preamp drive.

I also have a plug-in SS thingy for the inverter. There's less sag and full chords retain clarity better with the solid state 'tube' though.

All in all I don't find there is very much difference with tubes used except for V1, or in a multichannel amp, each 1st tube the signal sees...I rather go for filling the other slots with sturdy mil-spec sovteks for instance.

Just my 2c.

 

[kiteman]

That's interesting, a solid state inverter? Where do you get something like that?

 

[deeaa]

That's interesting, a solid state inverter? Where do you get something like that?

http://www.webervst.com/ccap.html

 

[Bloozcat]

kiteman is asking about a phase inverter tube, not a voltage rectifier tube. The amp in question already has a solid state rectifier.

There is much debate about the validity of this subject, but you might want to try a 12AX7 with balanced triodes. It's about the only slot in the pre-amp section where this is ever suggested. It may help.

I'd suggest a balanced triode Tung Sol re-issue 12AX7.

 

[deeaa]

My bad...surfing with cell phone sometimes makes for careless reading

 

[kiteman]

kiteman is asking about a phase inverter tube, not a voltage rectifier tube. The amp in question already has a solid state rectifier.

There is much debate about the validity of this subject, but you might want to try a 12AX7 with balanced triodes. It's about the only slot in the pre-amp section where this is ever suggested. It may help.

I'd suggest a balanced triode Tung Sol re-issue 12AX7.

I have Tung-Sols but they're not balanced so they're in V1 and V2. I think the EH I have in there now is balanced if the marking 08 08 is it. The other EHs are 08 09.

 

[tunghaichuan]

There is much debate about the validity of this subject, but you might want to try a 12AX7 with balanced triodes. It's about the only slot in the pre-amp section where this is ever suggested. It may help.

Balanced triodes in a PI tube would only matter in an amp that uses the Schmidt/LTP phase inverter circuit. It wouldn't matter in a 5E3 Deluxe as it uses the cathodyne type PT, which only uses one of the triodes for phase inversion.

But in the case of Kiteman's amp, it most likely has the Schmidt/LTP phase inverter circuit, which uses both triodes for phase inversion.

 

[Bloozcat]

Balanced triodes in a PI tube would only matter in an amp that uses the Schmidt/LTP phase inverter circuit. It wouldn't matter in a 5E3 Deluxe as it uses the cathodyne type PT, which only uses one of the triodes for phase inversion.

But in the case of Kiteman's amp, it most likely has the Schmidt/LTP phase inverter circuit, which uses both triodes for phase inversion.

I was hoping you'd check in and clarify that tung...:AOK

I knew it was dependent upon the type of phase inverter circuit, I just didn't known which type it was that used both triodes.

 

[tunghaichuan]

I was hoping you'd check in and clarify that tung...:AOK

I knew it was dependent upon the type of phase inverter circuit, I just didn't known which type it was that used both triodes.

Just an educated guess on my part (I have not seen a schematic), but for the most part most tube amps that are push pull and over 30-40 watts use the Schmidt/LTP phase inverter because it can drive the output tubes to full power. The cathodyne can't.

For example the 5E5 tweed Pro and 5E3 tweed Deluxe are basically the same circuit, except that the 5E5 uses 6L6GB tubes and the 5E3 uses 6V6GT tubes:

http://www.schematicheaven.com/fenderamps/pro_5e5_schem.pdf

http://www.schematicheaven.com/fenderamps/deluxe_5e3_schem.pdf

The Pro puts out about 30 watts because the cathodyne PI can't drive the tubes to full output power. The 5E3 only puts out 15 watts from a pair of 6V6s for the same reason.

So modern amps using 6L6-type tubes usually have the Schmidt/LPT PI as most manufacturers want to get the most clean power out of their amp as possible.

Fender used this discrepancy for their mid 60s Blackface Princeton Reverb and Deluxe Reverb. The Princeton uses the cathodyne PI and puts out about 12-15 watts. The Deluxe Reverb uses the Schmidt/LPT PI and puts out about 20-22 watts. I believe that Fender did this to have two different models using basically the same tubes.