Hi Everyone, This could go on the main Poddwatt thread, but it might get lost there. Sometimes I just build something because I have the parts. Such is the case with this amp. It is a variation of the basic Poddwatt. I had some tubes I wanted to try (12A6 pentodes). They are low power “metal” tubes designed originally for automotive amps. In many ways it is similar to 6AQ5. Anyhow the amp uses the boosted grid voltage of later model Poddwatts and the DC heater supply (AC ought to be OK though). Otherwise it is rather similar. Idle current is 31 ma per tube to stay within dissipation ratings. The driver is my favorite 12SL7. Total heater power is just under one amp at 12 volts. I used inexpensive parts where possible. All coupling and most bypass caps are general purpose Solens. The build is not critical but care must be taken to insure pin one on each of the power tubes is either connected to the chassis (I did this) or the signal ground (probably work OK, but I don’t recommend it). This is to prevent the possibility of accidental shock if there is an internal tube failure. Actual performance was a lot better than I expected. Response was down 0.1db at 40HZ and 32KHZ at 1 watt (yes that is 0.1db). It was only down about 10 db at 80KHZ. The bottom end was -3db at 14HZ. At that frequency distortion was clearly evident though. Response was clean at 20HZ. S/N was a bit lower than many of my projects at -77dbv, still quite acceptable. Power output was just over 2.5 watts RMS into 4 ohms. I didn’t measure distortion, but the sound was quite nice. I estimate less than 1% at 1 watt going to around 4% at 2 watts. For a cheap amp it is not to bad IMO. Tubes, caps and trannies are lower cost than what I generally use. I would expect you could duplicate it for under $200 easily.
Edit: use 200uf /350 volt caps for the first two in the power supply.
Good Listening
Bruce
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