New Amplifier

[sorenj07]

Worked on a new amp over break. It's not 100% done (missing some resistors) but here's a shot of the wiring to last you until then

[sorenj07]

schematic:

shot of the top:



the huge transformer in the back is the 10H 300mA input choke.

[Rob11966]

Hi,

Really nice job. Neat wiring for sure. That is one hell of choke!!

Hope it sounds good for you.

Rob

[planet10]

Looks nice, i'm interested in comments on how it sounds when you get it done.

dave

[kevinkr]

Nice job, you'll need to protect the cathode/filament insulation of the 6922 during warm up though - it won't like a 200V+ differential across it. (Even worse if you need to elevate the filaments and depending on whether your B+ is SS rectified or not.)

You can use a simple NE-2 neon lamp between cathode and ground to do this. It will glow until the voltage at the cathodes drops to about -40V or so and then will extinguish, leaving effectively a very small capacitance to ground at that node. (pFs worth, and less than a few inches of wiring.)

[sorenj07]

All right. Where can I grab a lamp like that? Someone on AudioKarma also suggested using a small switching diode, with its cathode to the 6922 cathodes. I didn't quite understand why before, but does it also protect the tube during warmup?

[kevinkr]

Hi Soren,
You can buy neon lamps at most Radio Shack stores last time I checked. They are also available from Mouser and Digikey, either NE-2 or NE-2H will work fine.

The diode will work too, but I prefer the neon in this application. In the past I have used generally similar designs to what you came up with. In a case where the operating voltage on the cathode is positive enough in normal operation to light the neon I used a normally reverse biased diode in series with the neon. This covers just about all possible scenarios..

[sorenj07]

Thanks! I think my 6922's (actually 6N23P's) are biased at around 5V, which probably won't light the lamp, right? In any case, I bet those diodes are dirt cheap so I'll just grab a couple in case.

[kevinkr]

Hi Soren,
Yes the neons will work just fine by themselves, no diodes needed in this case. (Just the nude bulb with no resistor, i.e. not a panel lamp or anything.)

[nhuwar]

Wow there is 3 of us.









Nick