Huge improvement in sound from change in V4

[Mark 63]

I've been swapping tubes around since I got my Express 5:50 last month; was basically happy with what I got from Doug's Tubes:
V1 Tung Sol 12AX7
V2 NOS JAN GE 5751
V3 Penta 12AX7
V4 Sovtek balanced 12AX7
V5 Penta 12AX7

I had also tried a few other NOS tubes in V1 and V2 (Ge 5751s and a balanced GE 12AX7/ECC83) as well as a Mesa SPAX7. But none of these were an improvement on the Doug mix above.

Then in the spirit of the holidays, I tried the GE 12AX7/ECC83 in the PI slot (V4), and it made a gigantic difference. The amp is just bursting with musical energy, and I don't feel like a tool for spending stupid money for old tubes. A Festivus Miracle!

Others have mentioned it on this board, the PI is integral to the overall sound. It's probably as important as V2.

So now, the set up is:
V1 Tung Sol 12AX7
V2 NOS JAN GE 5751
V3 Penta 12AX7
V4 NOS GE 12AX7/ECC83
V5 Mesa SPAX7 (because in all the switching around, I shook something loose in the Penta)

 

[J.J]

V2 and V4 are the two that make the most difference. I changed my V4 just to see if it would do anything thinking that it would be a waste of time. No waste of time V4 really is a secret of great tone.

 

[FXR]

It's amazing how much affect V4 has IMO. FWIW, the Chinese Penta tubes ruin the sound of the amp for me. I tried the Penta in V3 and V4 and thought the tube was a waste of money. So far, for me, I know Tung-Sol in V2 and Sovtek LPS in V4 are the basis of the sound platform to build on. Then there's V1 and V3 for a slight tone tweak. V5 seems to be about the same no matter what I put there.

 

[EtherealWidow]

Anyone care to share their thoughts on a Tung Sol 12AX7 Reissue for the P.I.? I'm going for it because it has a ton of gain (from what I hear) since I'm using two 12AU7's in the preamp.

 

[Mark 63]

For the PI to work optimally, balanced triodes are desirable. But I should think higher gain would also be a good thing.

 

[J.J]

I have used the Tungsol RI in V4. I liked it in that position and it added clarity and some brightness.

I didn't really test for overall gain with that tube in V4. I know everyone says the Tungsol RI is high gain, but they seem to have less gain than the stock tubes at least when in V1 and V2.

I ended up taking the Tungsol out of V4 for two reasons, first I was trying to get a warmer sound at stage volume. The other reason was the heater to cathode insulation issue that was causing tubes to burn out in other amps when used in the PI slot.

It would seem the Express 5:25 does not run at high enough voltages to have cause the Tungsol to fail in V4 or the production has been improved. As far as I know if the tube fails (heater to cathode) no damge is cuased to the amp, but it is still something to be weary of.

As for adding gain to the PI stage, I am not sure that get you anywhere. If the master volume control is after the PI then yes, you could make the PI clip which may or may not help your tone. Other wise adding gain to the PI will make your master volume more touchy and harder to set right.

Also, once you get to a given level out of the PI stage, adding more gain will turn things bad. The limit is really that when the voltage swing gets past 0 volts on the power tubes grid, the grid starts drawing current like mad. That is not really a bad thing, but it affects tube bias and starts to choke the power tubes off which results in volume loss. That is called blocking distorsion and I am pretty sure you can make that happen even with stock tubes if you crank the master enough.

 

[EtherealWidow]

Ah. Well I just tried the Tung Sol in V4. Didn't sound too bad. Things sounded a bit scratchy, but I'm not going to blame the Tung Sol's for that just yet. I gotta replace the power tubes. One of them has a small burn mark on the plate. :lol: I'm running 2 12AU7's so I do need a little bit more gain to push the power tubes just a bit. When I put a 12AX7 back into V3 I noticed a HUGE volume increase and yes, the master was very, very touchy. Also, when I cranked it, I noticed that the tone was HORRIBLE sounding and just way overly compressed. Not sure if it was blocking distortion, but it sounded bad, bad, bad. The 12AU7's are a much better fit and the power tube distortion is much better, along with the tone of the amp in general.

 

[edward]

I've always like the TungSol ax7 RIs. I've found it to be a smooth-sounding and consistent tube in the various positions in the three Mesas (and a Fender SF) I've tried it in. Great all-around tube, IMHO.

FWIW, try a set of lower-gain EL84s. Depending on your music style, of course, but I've found Boogies in general tend to have far more OD than I ever need (though never tried an ElecDyne, a different animal altogether). And so far, "gaining down" has always yielded me sweeter, smoother clean and semi-clean tone, and smoother, richer OD that's more creamy and less in-yer-face (unless you like that kind of thing, of course). In some Boogs, I find gaining down the preamp (over the power amp) works better. But in my 525, I found leaving the preamp with a set of ax7s (yes, some of them TS-RIs) and going to NOS EL84s got me that sweetness I wanted (trimmed a bit of the "aggression" or "modern voice" off the express). I tried a few ELs and ended up liking a pair of NOS RCAs, FWIW.

Bottom line is ya gotta experiment. "NOS this" or "brand name that" guarantees one nothing ...it's all about what one hears and being honest about the results, regardless of what's printed on the glass.

Edward