5U4GB rectifiers?

[JJ Gross]

Hi,
I'm just getting into building & designing simple guitar amps these days after spending about a year and a half fixing old, broken or otherwise screwed-up ones. Not rushing into anything, I'm taking forever to make sure I'm well prepared before just soldering a bunch of parts together and powering it up to see if it starts a fire.

I've come into some nice old 5U4GB rectifiers but am having a hard time coming up with schematics or designs that use these in guitar amps. I did find them used with EL84s and 12AX7s in late 50s Motorola Hi-Fi sets.

Any suggestions for guitar amp applications? I'm trying to stick with single ended rigs for now along the lines of early Champs/Princetons. Not that it means I wouldn't get outside that box.

Cheers

[NTBluesGuitar]

The 5U4GB is used in the Tweed Super/Pro/Bandmaster circuit (5F4, 5E5A, 5E7).

[Kap'n]

It's also used in a number of SF amps.

5U4G's and 5U4GB's are relatively common to find in period high-current consumer equipment. IIRC, both tubes have the same electrical specs, they "G" version just has the big "ST" coke bottle glass.

One of the reasons they're not popular in Fenders is that they're a directly heated rectifier. This means that they have fairly large internal resistance, and sag more than the indirectly-heated 5AR4/GZ34.

You'll see that people will mention that they're used in SF Fenders because the voltages are higher. That's sort of the cart before the horse. 5U4's were/are cheaper than 5AR4's. Once the bean counters got ahold of Fender, they went with the cheaper tube, and adjusted their transformers to try to compensate. Unfortunately, the increased sag was still there.

I've got a 5U4G in my 5E7 Bandmaster. The big coke bottle tube just looks cool in there.