Switchable Tube Rectifiers in 5E8-A Style Tweed Twin

[priesty]

Just wondering about how to have variable "Sag" on a 5E8-A style low powered tweed twin. Obviously this design has a fairly inefficient but stiff supply in the form of the two parallel 5U4GB rectifiers. As the 5F8 high power tweed twin showed, one 5AR4 would have been man enough for the job.

I wondered what sort of funky electrical happening would occur if a switchable 5AR4 was put in parallel with a single 5U4GB, hence switching between the "Stiff" 5AR4+5U4GB supply and "Saggy" 5U4GB supply. Is there a problem with running the two different types in parallel, or will most of the electrons naturally bypass the 5U4GB due to it's higher internal resistance??

[Gtr_tech]

Yer 5v winding won't take the I draw from both tubes. The only way to do it would be to switch *everything*. And if yer gonna do that, you may as well just swap tubes.

Plus, supply voltage will vary between the 2 tubes (they have different voltage drops), so there is more difference than just "sag". You'd need to make sure yer bias is adjusted to be within safe/tolerable limits with either recto tube.

[deci belle]

You can just pull one of the stock 5U4GB rectifier tubes for more sag and run the amp with a single tube that way if you like, is what I read in a Tone Quest article.

[priesty]

Thanks guys, I should have said I'm actually in the first stages of amp design on this one so issues such as 5V filament current draw will be dealt with by transformer specification. I just wanted to check running tue two different types together would be a bad/pointless idea. Thanks!

[Diablo]

Two 5U4GBs in parallel aren't going to sag much at all, just like a single GZ34. I would just build the amp stock and you can swap different rectifiers in and out. The range could be a single GZ34 to a single 5U4GB in terms of voltage drop. I've been running a single 5U4GB in my clone from the beginning, and I like the way it sounds.

[Gtr_tech]

Whoops....I just looked at the schemo for that model. I see it used 2 (!) 5u4s. My bad. Carry on....