Moondog battery filament supply

[Erik Mandaville]

For those with Moondogs -- or other amps, as well:

I was listening to the latest Iraq news on my restored 1920s Atwater Kent radio, and the idea of a battery filament supply for my Moondogs suddenly popped into my head.

So..............I've wired the 6SN7 filaments in series, and have finished one channel. I'm using two 6 volt lantern batteries (just for a try -- if all goes well, a rechargeable gel cell will take their place)wired in series for 12 volts.

I'll let you know how it goes.

Erik

[Erik Mandaville]

Thanks for your concern! I appreciate that. However, we are talking about DC batteries. Both AC and DC can be used for filament supply, just as the 2.5 volts on the 2A3 tube heaters are AC, as well as the 5 volts on the rectifier tube. DC is preferred on signal tubes because it's obviously more free of AC hum.

Take care, thanks for responding/

Erik

[Tom Mobley]

Erik,

OK, I'm not afraid to ask a dumb question. Those 6SN7 are 6 volt tubes, why would you run 12 volts to them? And like Mark said, those 12 DC volts are equivilent to about 17 AC volts (12 x 1.414 = 16.97). Did I read you wrong?

Tom

But, I do agree about the "....talking about DC batteries....". Haven't run across any AC batteries lately. Might be some rare ones up on ebay though.

[Erik Mandaville]

Tom:

Know, you didn't really read me wrong. The reason I'm using 12 VDC, has to do with a future plan of using large, 12 volt rechargeable gel cell batteries. 6SN7s are 6 volt tubes, you are both correct. The significant thing in this case has to do with HOW they are wired. Parallel connection of the heater supply maintains a 6 volt supply across the tubes from a 6 volt source -- in the Moondogs, this was by way of 6VDC from a full-wave bridge rectifier and filter circuit. The Moondog uses two 6SN7s -- heaters are pins 7 and 8. To connect in PARALLEL, pins 7 and 8 are connected to the respective pins on the second tube -- pin 7 to pin 7; pin 8 to pin 8. Wired in SERIES, there is the input voltage to pin 7, which is then connected internally to pin 8 by the filament. A lead is then soldered to pin 8 on the SAME tube, which is then connected to pin 7 on the second tube. pin 8 on the second tube is referenced to ground and A- voltage. In this way, it's possible to still impose 6 volts on the filaments with a 12 volt supply. It all depends on whether the tubes are wired in series or parallel.

The AES AE-1 Preamp is wired in exactly the same way. It uses rectified AC into a 12 volt regulator, but the 4 6SN7s are wired in SERIES, not PARALLEL. See?

Where in the world are you all getting the idea that I'm heating these tubes with alternating current???

Erik

[Tom Mobley]

Erik,

I haven't had a moondog upside down, I didn't realize the heaters were already DC. I guess I triggered off Mark's post.

question: If the heaters are already DC and I imagine DC is pretty clean since these are a top quality amp, what's to gain from going to battery? DC is DC, right?

Tom

[Erik Mandaville]

Batteries are inherently quieter than most rectifiers. One can use greater capacitance across the rectifier, but I just wanted to try it out -- for curiosity, and since I have antique radios that use battery supplies for all voltages.

What I gained was slightly reduced hum and simple entertainment -- I think battery supplies are interesting!

It's how I 'play' in my free time, Tom.

Erik

[WMcD]

If I may disagree with md.

A.C. rms voltage is the equivalent of the same D.C. voltage in terms of power, particularly when you use it to drive a resistive heater. That is why the value is so handy.

If you have an sine wave of 1 volt rms, the voltage swings between plus 1.414 volts and minus 1.414 volts. Therefore the peak to peak voltage is 2.824. They should have called it peak to valley voltage, but there you go.

Gil