52 Tweed Deluxe - Optional 5U4 Rectifier Tubes?

[Dan Lawrence]

Has anyone experimented with swapping the rectifiers in these bad boys for a 5U4? I tried it out of necessity and it sounds so good! Especially on the growl you get from the mic channel> Just wondering if I'm overtaxing other components. Thoughts?

d

[pdf64]

I think it's a bad idea to do what you've done, without keeping a close check on voltage levels / dissipation on the power tubes, and heat build up in the power transformer and power supply caps.
A 5U4 takes 3A heater current, compared to 2A of a 5Y3.
Also consider that your line voltage has probably risen above that which the power transformer was designed for.
Is this a real 1952 amp?
Pete

[Dan Lawrence]

Thanks for that info Pete. I have the most limited tube tester, and very few stats. They seemed to match up, but I did suspect there may have been more to the story than I could see. As for the amp, I do believe it is genuine. I bought it restored from a reputable dealer some years back. I've never really researched how to verify its authenticity, except for the cabinet and top plate style. It sure sounds amazing (if you like that style of sound ... and i do). I've had the honor to play through a fully restored '58 twin, and this is the only amp I've played that has a similar chiming quality to the harmonics. I'll definately swap out that rectifier tube.

d

[Gingertube]

If you want to try another tube rectifier in lieu of the 5Y3 then about the only commonly available option would be a 5AR4 (GZ34). It will certainly give you a little stiffer supply and a bit more voltage too (less drop in the rectifier tube).

If you want to explore some older tubes with pin compatible pinouts and heater voltage and current then:

5R4 will have similar drops (slightly less) than the 5Y3

5V4 will have a lot less drop (more like a 5AR4)

Cheers,
Ian

P.S. I would not necessarily be too fussed about runningvb the 5U4, YES you are drawing 3A from a 2A (probably) rated heater winding - that means you are adding an additional 5 Volt Amps (Watts) to the transformer loading. As the transformer is likely to be at least 200VA (when you add in 6.3V heaters, high voltagw windings etc) then that is less than a 2.5% overload. Unless the tranny is getting hot I would be reasonably happy with that.

[Bruce / Mission Amps]

Personally, I would be quite a bit anxious about running a 5U4 over the 5Y3, due to the extra 1 amp of current through the 60 year old rectifier filament winding in the tranny of a highly collectible amplifier, that will suffer GREATLY in value at resale when the potential buyers find out you blew up the PT and put in a modern something or other to unload the amp. ;0

The PT is a Hi-VAC, 90ma to 100ma PT... with a 2a-6.3v and a 2a-5v winding set. The OT if these amps was rated at around 18-20 watts.
The amp makes about 10-12 watts output into an 8 ohm load.

If you want more B+ and no extra strain on the 5v winding, use a Russian 5Y3GT, which is much closer to a GZ30 or 5V4GT.

[JoeM]

You could use a Weber Copper Cap, and not have to worry about the 5V winding.

[Dan Lawrence]

I appreciate all the added info on this matter. As for tolerances, etc., I like hearing the statistical margins, etc. But I suppose I am prone to err on the side of caution with this classic (at least, having been better informed now) as Bruce points out. I'm not inclined to look towards selling it, but having it intact as is IS the point. It's that just so sound, and I own 5 other tube amps. So thanks to all.

One general question to the knowledgable. I imagine the mic "harmonica" input (mic?) has different level and tolerance designs. Can I overtax the amp using it for guitar? I also wonder about overdriving the pre-amp stage with either an instrument-level over drive or even a line level overdrive. Are either of these not recommended for a classic like this? It may sound great, but I don't want to over tax internals.

Thanks again in advance,
Dan