Subminiature 5902 based amp

[toskrlec]

Hi,
I would like to build some SE amp, based on 6112 and 5902 tube. I have found one schematic on the net, it is exactly what I need, but voltages seems a way to high, according to tubes reference data. (for 5902 Max. plate voltage is 165Vdc, 110VDc recommended). Have anyone experiences and advice ? (shematic is attached)
Thanx.

[Stevem]

It’s that 1.5K ohm cathode resistor as opposed to one of about 300 ohms that keeps the higher voltage its getting from burning up the tube.

The question I have is which taps of that multiple tap 125E transformer is needed to be used?

[toskrlec]

It’s that 1.5K ohm cathode resistor as opposed to one of about 300 ohms that keeps the higher voltage its getting from burning up the tube.

The question I have is which taps of that multiple tap 125E transformer is needed to be used?

Something between 3.5-4 kOhms on primary side will be OK, or I am wrong ?

[katopan]

The push-pull 6112 & 5902 based amp I made years ago, I had a B+ of 170V to stay within the published valve limits. Sorry I don't have any experience running them any higher to share.

[toskrlec]

It’s that 1.5K ohm cathode resistor as opposed to one of about 300 ohms that keeps the higher voltage its getting from burning up the tube.

The question I have is which taps of that multiple tap 125E transformer is needed to be used?

Something between 3.5-4 kOhms on primary side will be OK, or I am wrong ?

Update. I am wrong. According to the Valve Wizard SE Output calculation rule of thumb with Va = 250V, and Pa=3W

Z = Va^2 / Pa
Where:
Va = Anode voltage.
Pa = Maximum anode dissipation
Z = aprox. 20 kOhm

[didit]

Hello -

Correct both in arithmetic and your initial assumption 250V is too high. Suggest focussing your search on DIYaudio board, as there are a few informative threads there on this. In the past TAG had some people playing with these sub-miniatures, but apparently they've moved on. Based on reports, 5902 appears to be more rugged than the spec sheets indicate but 200V at the top of your output transformer would be a recommended max.

Best .. Ian

[toskrlec]

I have decided to give a try to https://www.ebay.com/itm/DC-12V-to-150V ... SwL9pauPNv PSU, for more flexibility in
experimentation with voltages. I am a little bit concerned about EMI noise with using booster PSU... but ZVEX nano is also based on booster PSU, so I guess it will be OK.
Goal is to set working points on output 5902 tube for 5Kohm primary OT, what is actually Hammond 125 ASE. I hope that given calculator is correct.

[didit]

Hello --

Interesting PSU. Given the target application one would hope they have designed for minimizing EMI noise.

You might also experiment with 200V "plate" and 800-900 Ohm cathode resistor, with that ASE set up for 10K primary.

Best .. Ian