PT voltages for 5E3---300 VDC enough?

[PremiumPlus]

Hi all,
I've got a PT from a Wurlitzer that looks nice, but I'm concerned that the voltage available for the output tube plates is going to be low.
Is 300 to 310 volts (filtered dc, after the caps) enough? I know that an amp sounds terrible when the voltages are too high; what will too low (if it's too low) sound like?
Thanks!

[MWJB]

It's a bit lower than typical, but as you've got the PT why not give it a go. The amp will have a little less headroom than a regular 5E3, but if it's just for home/practice/recording it might be fine.

You could try fixed bias (or have it switchable) to claw back a few volts?

[PremiumPlus]

I don't want to lose the charm of cathode bias, so I'm going stock, except for maybe .022 coupling caps.

[MWJB]

Fair enough. It's worth bearing in mind that what we call the "5E3 circuit" was pretty universal in the late 50's/early 60's. It's about the simplest way to hook up a push-pull amp, with a low parts count. Other manufacturers built amps with the same basic topology, maybe different plate & cathode resistor values/coupling caps & usually lower plate voltages than the Fender...so if you're not fussed about building a "clone", there's room to manouvre.

[tubeswell]

If the output stage plate voltages turn out between 300-310, you can still get a decent sound out of it by biasing the tubes hotter (e.g.; by using (say maybe) a 220R cathode resistor, but check your idle dissipation). For the pre-amp you can always fiddle around with the dropping/supply resistor(s) to get the plate voltages somewhere near typical 5E3 voltages.

Or else you can use different output tubes (e.g.; 6K6s if you can find them, or build it with EL84s - 300V is good for EL84s)

[PremiumPlus]

I know...if any of you good guys have a variac and feel so inclined, dial the voltages down on your 5E3 so as to see 300 volts on the plates of the 6V6s and see how it sounds! That would be a cool experiment and it would tell me exactly how mine would sound. A power scaled Deluxe...hmmm...and thanks!
PP

[cminor9]

or try a recto that drops less voltage, like a gz34?

[Steve Conner]

Well, why not silicon diodes? Voltage drops don't come much lower than that. You never mentioned if your PT had a 5V winding for a tube rectifier, anyway.

If you used silicon rectifiers and fixed bias, you'd probably get back almost all the missing volts.

[PremiumPlus]

It does have 5 volt and 6.3 volt taps for heaters. I want to build the amp with a tube rectifier...and last night I began construction by drilling the fiberglass board and installing the turrets. It's about half way populated now and I'm looking at it thinking that maybe I'll invest in a proper voltage transformer...the thing is looking so nice that I'm really torn between wiring the old organ transformer and trying it first, or just saying 'damn the torpedoes' and going for correct, top of the line iron.
But then again, I can always change the trannie later. And it's only what, 10% low? What is the voltage range at the filters that you guys see?
Thanks for all your help. I'll try to post pictures as this develops. I told my son last night that I'm going to build this one as a work of art and love to leave him a legacy for his kids to use if they ever play guitar...So I want it to be special.

[MWJB]

"or just saying 'damn the torpedoes' and going for correct, top of the line iron." Not sure what 'correct,top of the line iron' means, the PT that gives you the voltage you specifically want is the right one...if you have no preference then why fret, build it as is, if you decide you want more headroom fit a higher voltage PT. PT shouldn't take more than an hour to fit.

As a guide, many folks like 350-370vdc, some "5E3" PT's might give as much as 385vdc, late 50's/60 amps might have as much as 410vdc. Lower the voltage the aerlier the breakup. If you had 380vdc plus at the plates you might want to try a 300-330ohm cathode resistor to bring plate current back into line, conversely with 300-ish volts 200ohms would be fine.

[PremiumPlus]

Aye. Point well taken. What I mean by period correct tol iron is a quality transformer that will output the voltage and current as needed to sound like a great Deluxe should. I'm definitely going to use the output transformer from the organ. Thanks for all the replies, guys! I've been restoring amps for many years, guitar and old high fidelity amps/preamps (My home stereo components are all from the mid 70's and sound great) BUT, this is my first scratch-build. I started a build thread with pictures if you're interested. Right now I've got the turret board drilled, mounted, and soldered. I'm deciding on which chassis and cab to buy right now. Have a great week!