Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: isaac_teller on April 22, 2022, 01:46:18 pm

Title: 15 watt PA amp
Post by: isaac_teller on April 22, 2022, 01:46:18 pm

12a6parts.pdf (https://el34world.com/Forum/file:///C:/Users/zafim/Documents/12a6parts.pdf)
12a6schematic.pdf (https://el34world.com/Forum/file:///C:/Users/zafim/Documents/12a6schematic.pdf)



Hello. I came across an interesting schematic using inexpensive tubes(which I have, along with the OT) and thought that this would be a good junkbox build.
Changes to be made:
  1)diode rectification(FWB). Don't need the doubler, just a 220:220 isolation transformer(I live in a 220-volt country).
  2)parallel filament wiring, not series.
  3)Single channel-apparently there is an error, V1 should be 12SF5 not 6SF5. I'll probably use a 12AV6.
Anything else I need to switch to make it more guitar friendly? Once I get it up and running I'll fine tune the sound.
Thank you.

Title: Re: 15 watt PA amp
Post by: sluckey on April 22, 2022, 01:53:56 pm

Your links do not work. Looks like the links are pointing to YOUR computer.

Title: Re: 15 watt PA amp
Post by: isaac_teller on April 22, 2022, 02:10:39 pm

Having trouble with the computer. I'll try again later.

Title: Re: 15 watt PA amp
Post by: isaac_teller on April 23, 2022, 05:45:06 am

Fixed it!

Title: Re: 15 watt PA amp
Post by: PRR on April 23, 2022, 12:29:31 pm

Major changes needed. As drawn it is HOT CHASSIS which for guitar is deadly. You can't do that anyway at 220V wall outlet. But you have to compelely re-figure the heater power (or just go 12V). Without tube rectification the B+ will be far higher (~~320VDC) than the 250V rating of the power tubes.

Think this through.

Title: Re: 15 watt PA amp
Post by: isaac_teller on April 23, 2022, 12:36:47 pm

OK. As I mentioned in the original post I will be using an isolation transformer and parallel filament wiring. I suppose I'll also put a 250 ohm 10-watt resistor after the bridge.