Fisher 500B Iron?

[Tom Bavis]

I wouldn't worry about 60 mA idle current - the DCR of the transformer is only 200 Ohms, so it will dissipate 0.8W - no big deal. But 50 mA may be just fine...

[Blair]

Will this driver circuit amply drive a pair of 6L6 tubes?

All this talk of potential output transformer damage in class A has me scared into not doing it:(

http://tmamps.com/pics/832sch.jpg

Thanks!

Blair

[Blair]

Can I parallel the two filament windings of this fisher power transformer to get more current?

One has a current rating of 2A and the other 3.8A gathered from the tubes and bulbs they powered.

I'd like to use KT77 tubes vs. 6L6 tubes if I can get away with it, but the extra 400mA would push the 3.8A winding past my comfort zone.

Thanks!

Blair

[battradio]

Yes as long as you get them in phase

[Blair]

Thanks Mark,

I was worried about the two windings sharing and trying to "share" equally. One winding is 3.8A and the other is 2A.

I will likely stick with 6L6 tubes to be safe.

I have a 10K pot installed for bias. I did not have room for the independent bias I usually use. So, what value and where to I install a balance pot? I see anywhere between 25-100 ohm pots for balance.

Thanks!

Blair

[Blair]

I elected to use this iron and implement a 7427 front end similar to the old Dyna models.

http://www.angelfire.com/electronic/fun ... son-4-back

I used the circuit in this circuit because it mated well with my B+ of 390-400V. I did have to tap the phase inverter section at a 290V point in my PS because it was picking up noise from my plate currents I assume. Anyway, all is quiet now with the various levels of feedback I've tried.

Looking at the driver on my scope, the signal is good from about 250Hz up, but my sines fall apart below that. This is probing at the anode of the VA stage between pin 6 and 2 where it feeds the second triode. It starts to clip/fall apart very non-linear.

I can get about 22W out from 500hz-20K, but I've never had issues with a driver being the source of the wave falling apart. Any ideas? I used all the same values as in the schematic, but an 18K and 330pf in the "ringing" circuit described in the top of the article. Removing it does nothing though.

Thanks!

Blair