Ruby 5AR4 low voltage output?

[Luthierwnc]

Hi guys, been a while,

I got the iron out to work on some long neglected projects. One of them was a 6L6 Princeton Reverb (sorta). I'm using a 6L6 power transformer at 670VCT. I originally had a NOS Sylvania 5U4-GT in there. The B+ was 407VDC with the power tubes biased at 33ma each. I was hoping for more like 425 to help with the cleans so I ordered a Ruby 5AR4 which has been sitting on the shelf since for a couple months.

Finally tried it and at the same power tube bias it came in @ 408VDC. I haven't pulled any 5AR4/GZ34's out of my other amps to test but that seems a bit low -- especially since a known-good 5U4 delivered on spec. Other than some thump in the trem it is up and running fine so we're talking about an amp that works.

Any thoughts or experiences with that tube?

Thanks, Skip

[Structo]

Several articles I have read about guitar amps seem to agree that plate voltage is not a huge issue.
Unless of course you are way out of spec, either high or low.

But as far as tuning an amp to voltage specs, it doesn't seem that important as far as tone goes.

I would just play it with the rectifier that it was designed to use and play it for a while.

Double check you bias in relation to the power tube plate voltages measured.

[rdjones]

Hi guys, been a while,

I got the iron out to work on some long neglected projects. One of them was a 6L6 Princeton Reverb (sorta). I'm using a 6L6 power transformer at 670VCT. I originally had a NOS Sylvania 5U4-GT in there. The B+ was 407VDC with the power tubes biased at 33ma each. I was hoping for more like 425 to help with the cleans so I ordered a Ruby 5AR4 which has been sitting on the shelf since for a couple months.

Finally tried it and at the same power tube bias it came in @ 408VDC. I haven't pulled any 5AR4/GZ34's out of my other amps to test but that seems a bit low -- especially since a known-good 5U4 delivered on spec. Other than some thump in the trem it is up and running fine so we're talking about an amp that works.

Any thoughts or experiences with that tube?

Thanks, Skip

Is the Ruby 5AR4 an indirectly heated cathode ?
I would have expected a larger voltage increase than 1V !

Do you have an SS diode plug-in that you can try (as a point of reference) ?
I'd be curious how much the voltage might rise if the bias was a bit cooler ...

rd

[Luthierwnc]

Yeah, a single volt doesn't get it.

My spare GZ34 croaked a while back so I'll have to fish one out of my 5F4 clone. I could also rig up a diode string to test but it is the tube itself I'd like to know about. At that draw and those volts it should have easily delivered 425 on the plates. sh