Can Tung-sol 5881s take blackface voltages?

[skeezbo]

I got a set from ebay, and they sound great in my tweedish combo, but I used bassman transformers and have 450 volts on the power tubes. Tweed bassmans used 5881 tubes, didn't they? One of the Tung-sols has a faint cherry glow, not on the wide plates, but on one of the side structures. I would hate to fry these; the original JAN boxes say packed 2/56!
They are biased at 23 mA using the 1 ohm cathode resistor method, which seems plenty low. I know 5881s are rated for lower voltage than the 6l6GC, but I thought the general consensus was that the lower rating was very conservative for military purposes, and that 5881s, especially the Tung-sol and the Phillips 6l6wgb were fair game in place of 6l6GC. So what should I do: ignore the glow and enjoy the tubes, save them for a different amp, try to set the bias lower, or find a 5u4 or other rectifier tube to replace the 5ar4 and see if I can get the voltage to come down enough to reduce the glow?

Thanks,
Skeezbo

[Structo]

My data says VaMax 360v.

I know that the military under rates stuff for reliability purposes.

I have seen guys use the 5881's in places where 6V6 tubes were used.

Have you swapped sockets with the tubes to see if the glow follows the tube or stays at the socket?

450v seems like a lot for a tube rated at 360v.

Depending on the amp, some power transformers can't handle the extra demands of different rectifier tubes.
My data shows the 5U4 drops 44v and the 5U4GB drops 50v.
But they also draw 3 amps of current.

I see the Bassman 5F6 uses 5881's with a #83 rectifier which also draws 3 amps.
The schematic shows 430v on the plates.

Dunno, if they didn't cost too much, I'd just play them.

[skeezbo]

Thanks Structo,

The glow stays with the tube. I got them for $65, less than half of what they go for NOS from dealers; they look unused and are matched close enough (less than 5mA difference when I biased them). I have other great sounding tubes I can use if I am likely to roach these.

Skeez

[dynaman]

I say smoke 'em. I've ran plenty of 6V6s at 450DC and never had any probs. Prolly gonna need good regulation on the screens.

[billyz]

You can decrease the plate voltage by increasing the plate current. Run them with less bias voltage not more. Assuming the plate current is not excessive.

[David Root]

My understanding is that 5881s can handle high voltage, way higher than 450 Vp, but if you do that don't push the screen voltage too hard above 400V and don't of course exceed the plate or screen dissipation.

+1 on good screen regulation.

[skeezbo]

Thanks everyone!

I have 470 ohm screen resistors installed. I'll check the screen voltage and proceed from there. If it is too high I'll put 6l6GCs or KT66s back in and save the Tung-sols for another build.

Skeezbo

[dynaman]

1K or higher certainly wouldn't hurt!

[solderstain]

I have a pair of Tung Sol 5881s that I throw into my '66 Bassman and my Bassman/Reverb project amp once in a while. They like it just fine. They squish earlier than the 6L6GTs do, so that's fun when I'm in the mood.

But they live in Blackface-voltage-land just fine (436vdc and 443vdc respectively).

[Buschman]

Its the tube of choice in Bassmans as far as I am concerned.

[rfgordon]

I seriously doubt there's really a true 5881 in production today. The guts are most likely 6L6 anyway.