5F2a Princeton bench amp

[M Fowler]

A while ago I built a 1 watt bench amp 12ax7 and 12BH7 and while I like it, my ears needed more watts.
1w: Stand-a-lone reverb PT and Reverb Driver OT

So I built this 5 watt amp today. 12ax7 and 6v6

Had to swap the OT secondary due to oscillation, easier to reach the speaker jack then the primary wires to octal tube socket and b+ wires.

The PT is from rjguitars, something he gave me a few years back and it finally found a home and new purpose.

PT-31 is from CEDistribution. 5K 8 ohm.

Mark

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[xtian]

Cute city!

[martin manning]

Cute indeed, and portable too!

[M Fowler]

Some builders charge a lot of cash to put this in a pretty cabinet.

I need to stock up on 8uf/450v e-caps because I'm out and swore I had some.

I ended up using 30uf/450v B+1 filter cap, 22uf/450v B+2 and 16uf/450v for preamp.

[M Fowler]

If anyone has a line on some of those Stancor PC8407 PT's I sure would like them. Ebay is too expensive.

[martin manning]

...

[martin manning]

I think the standard cap value is going to be 10uF now. Close enough.

What voltage are you running on the 6V6? I see the PT secondary is 325-0-325, Si rectifier... Must be around 460V? 5K OT impedance seems low. I think what you have may be clipping asymmetrically, and maybe that distortion sounds good? If you have voltages (plate, screen, cathode, and Rk) I'd be interested. There's too for a 5Y3 there, I think, and a 5V winding available...

[M Fowler]

I'm going to go with a larger cast enclosure next time too, so a rectifier would indeed be able to be incorporated.

I will record voltages, I checked them but didn't write them down.

Mark

[M Fowler]

Also, going to put the transformer near the front and tubes near the back next time.

Will add 5y3, 6V6 and 6SL7 or 6SN7 preamp tubes. Love those octal preamp tubes.

Mark

[Guy77]

They look great and they look affordable to build too . I like the green knobs on the left one.

Cheers
Guy

[M Fowler]

That 5 watter is great and plenty loud through a 1-12" Eminence hemp cone.

[M Fowler]

I think the standard cap value is going to be 10uF now. Close enough.

What voltage are you running on the 6V6? I see the PT secondary is 325-0-325, Si rectifier... Must be around 460V? 5K OT impedance seems low. I think what you have may be clipping asymmetrically, and maybe that distortion sounds good? If you have voltages (plate, screen, cathode, and Rk) I'd be interested. There's too for a 5Y3 there, I think, and a 5V winding available...

Martin, yeah the plate voltage is high but not more then a stock 5F2 I don't think. The info I was looking at had both 5k primary OT and the higher 8K OT.
I went with this 5k because they must be selling them out, cheap maybe because people use 7k or 8k OT's.

I really like how this little amp sounds and I use it so often on my bench or just to noodle some times.

Next one I will go lower HT on the PT and higher K on the OT and tube rectifier.

Mark