5E8-A rectification

[Luthierwnc]

I'm putting together my winter project and was thinking about a low-power Twin. The general view is that one difference between the Twin and the other late cathodyne Fenders was the lower level of sag because of the dual 5U4's. A friend who had an original (many moons ago) only used one tube so he could get it to "give it up" in smaller rooms.

Has anyone analyzed the power section to see the load difference between two tubes and just using a diode string? I know I'd need beefier caps at the first stage and maybe a lower voltage PT but what do you think?

Thanks, Skip

[David Root]

Diode rectification should give you 30V or so more B+ OTBE, as I think you know, but it will change the tone some, even if you lower the B+ with a suitable Zener. Beefier caps will also change the tone even further away from tweed.

No tube rectifier sag and bigger caps will tighten up and "modernize" the sound a bit.

If you like tweed tone, why fight it? I've built two amps with dual tube rectifiers (5AR4s and 6X4s) and I think there is a lot to be said for them, including having the option of pulling one tube to cut the power down.

You could always put in tube and SS rectification and switch it. That might be interesting but I have found thru experience that there is not a lot of spare space in a tweed chassis. It's difficult to add a DC heater supply in most of them, for example.

[Luthierwnc]

Thanks David;

I have a 2xEL84 head with a switchable tube/SS rectifier. It is set-up so the selector switch also engages an extra 100uf cap on the first rail node on the SS side. I forget where I pinched that idea. I just leave it on the tube setting which should have told me something.

After having cloned just about every amp, I am coming to the slightly-past midlife conclusion that I am a tweed guy. My 5E5-A Pro is my go-to clubber. I'll probably use the 2 rectifier tubes and see what that gets me.

sh

[CaseyJones]

Too bad the chassis has more holes than you need. 'Cuz a big ol' 83 tube lit up back there would be cool!

Or... a 5U4G with an OA3 regulator. Use that extra hole to amaze yer friends wif a tube seldom seen in guitar amps.

My issue with 2x5U4Gs is the 6 amp filament required. I have big ol' junker transformers removed from this and that I could use. Some old organs have a power supply you can weld with, 2x5U4G, 0A3, etc.. It's a lot of iron to lug around.

[jaysg]

Has anyone analyzed the power section to see the load difference between two tubes and just using a diode string? I know I'd need beefier caps at the first stage and maybe a lower voltage PT but what do you think?

You're basically describing Eric Clapton's version as built by John Suhr. Don't bump up the first cap until you've lived with it a bit. fwiw, Clapton's run about 485V for B+. They're pretty durn stock otherwise.