Express-Liverpool experiment?

[dobbhill]

I was thinking again (dangerous, I know) of experimenting with my Express clone. I could use the 260 volt taps on the PT, make the minor changes to the preamp needed for a Liverpool preamp, run the output section with low voltage, cathode biased EL34's. I already like the Liverpool PI values in my Express better (did that change earlier). Should I change the Power supply dropping resistors to keep the preamp tubes at Express voltages, or just keep the power supply like the Liverpool? Does anyone have plate voltage measurements for the Liverpool (or Express)?
Maybe we should post some voltage charts for our clones, or has it been done?
I'm mainly curious as I don't have time to build a 'Pool from scratch right now. Do you guys think I'd be wasting my time, or should I try it?
Thanks for sharing.
D

[Zippy]

What's the object of your game? Do you just want to try a cathode-biased EL34 output? If so, start there. You could even make the biasing switchable to better compare the effects of the bias method.

[UR12]

Unfortunatly I don't think you can capture the sound of a Liverpool using EL34s. They just don't sound the same as a EL84. IMHO the EL84s are a big part of the Liverpool sound and there isn't much difference between the preamps, just a few component values are changed. So basically if you go with the EL34s you would still have a tweeked Express.

[Jackie Treehorn]

Don't do it, it's a waste of time. I did the same thing, dropped the voltage, adjusted the 12ax7's for the same voltage as the 300 volt tap and it sounded far worse. It didn't get much quiter either. There's a thread about it somewhere, too. Maybe it would work better with cathode bias, though...

The phase inverter is an enormous difference between the two. I think the Liverpool phase inverter in the Express sounds a lot better than the Express phase inverter; more bass and chime.

The Siemens EL34's may get you a bit closer to an EL84 sound, since they've got a good upper midrange.

[dobbhill]

Dana and Jackie: thanks for the replies.
Jackie-I did read your post, but was curious about the cathode biased EL34. Has any else tried it? Like you, I prefer the 'Pool values in the PI.
Are the preamp and PI plate voltages in the Liverpool a lot lower than in the Express?
Does the sound of an EL34 change much when reducing the plate voltages?
D

[Jackie Treehorn]

I'm not sure of the Liverpool voltages. I can tell you that I bought an actual Trainwreck power transformer from ebay awhile back and it does not have a 260 volt tap. It's 300, 275, and 250 at 250 ma. I figured it's express, rocket, liverpool respectively.

I've also suspected that the use of 2 9k2 resistors in the power supply was so that power transformer taps could be switched while maintaining the same preamp voltages. Essentially you could switch the tap down and remove one 9k2.

Yes, lowering the voltage had a negative impact...sounded more grey and 2 dimensional. My output transformer is a 5.2k, so maybe it would work better at 6.6k. I think you can still cathode bias a pair of EL34's at 400 volts, though. I had planned on having a cathode bias switch and even bought the parts, but ditched the plan to finish the amp.

[Allynmey]

The constellation uses a 250-0-250 sec. PT and a 4.8K OT

[dobbhill]

I tried the cathode bias on the Express last nite. Different. For some, it may be better. I rather like the stock output arrangement. The volume was virtually the same, with a bit more compressed feel and a good bit more grit, or less smoothness to the notes. I'm going to try the low voltage taps this weekend with cathode bias, just to experiment if I have time.
Allyn and others-have you ever measured the plate voltages (preamp, PI and power amp) in your 'Pool clones?
Thanks, D