My current project uses an '01A as the audio output tube. I thought it was going to be OK at 90V, but I get more adequate volume if I run its plate at 135V. Here's the tube data: http://www.nj7p.org/Tube1.php?tube=01A

The specified nominal plate voltage is 90V, but 135V is listed as the maximum (design center value). Am I inviting any big problems at 135V?

The way this battery-powered TRF set is designed, there's a separate B+ connection for the audio output tube and the other tubes. Thus, only the output tube would be running at 135V.

Hi Doug

Using 135 volts on the plate of an 01A is ok but grid bias should be increased to - 9 volts. If you don't increase grid bias your tube will draw too much plate current and can distort. Excessive current will also shorten the life of your tube.

Norm

:My current project uses an '01A as the audio output tube. I thought it was going to be OK at 90V, but I get more adequate volume if I run its plate at 135V. Here's the tube data: http://www.nj7p.org/Tube1.php?tube=01A
:
:The specified nominal plate voltage is 90V, but 135V is listed as the maximum (design center value). Am I inviting any big problems at 135V?
:
:The way this battery-powered TRF set is designed, there's a separate B+ connection for the audio output tube and the other tubes. Thus, only the output tube would be running at 135V.

OK, thanks Norm.

This set has two C- connections: one for the 1st AF and one for the 2nd AF. I'll run C- @9V for the 2nd AF (running @ 135V B+), and -4.5V for the 1st AF (which is still running at 90V B+). OK?

It sounds pretty good.

Doug, you can also use a 12A for the output, which may yield even less distortion.. At 135 volts, you can run the same bias voltage as the ‘01A. This tube can also be operated with 180 volts on the plate, and requires about 13 or 14 volts for the bias. Better yet, use a 71A. It too will work with 180 max voltage, but requires about 40 volts for the bias.

Most of the time I just run an ‘01A at 90 volts or less, but at a reduced volume. Even when operated at higher voltages, a good bit of distortion is still there, and the listening fatigue will get to me after an hour or two. However, when the volume is reduced far enough, I can listen to one all day

Thanks, Billy. I've got the Crosley "Bandbox" all back together now, and it's working fine. The '01A output tube is running at 135V with a grid bias of -9V. I don't particularly hear any significant distortion.

The volume with the 2nd audio tube at 90V is plenty good, except for WLS, the station that I listen to the most. For that station, the volume at 135V is better. But, I'm playing it in the basement with a 15' antenna wire hanging from the joists. Probably, with a better antenna, WLS' volume would be OK at 90V.

That thing will come on like gangbusters with 100' of wire....br

:Thanks, Billy. I've got the Crosley "Bandbox" all back together now, and it's working fine. The '01A output tube is running at 135V with a grid bias of -9V. I don't particularly hear any significant distortion.
:
:The volume with the 2nd audio tube at 90V is plenty good, except for WLS, the station that I listen to the most. For that station, the volume at 135V is better. But, I'm playing it in the basement with a 15' antenna wire hanging from the joists. Probably, with a better antenna, WLS' volume would be OK at 90V.