More Thomas Vox repair boards

[R.G.]

Just got in the prototypes for two more repair boards.

One does the power amp on any of the "Big Head" models: Beatle, Royal Guardsman, Viscount, Buckingham, Westminister, Sovereign or Scorpion.

The other retrofits two modern snap in caps for the twist-lock caps on the original chassis.

Now soldering in parts...

[tedmich]

pictures of PCB would be great RG! Are they std green FR4?!

[R.G.]

Yeah, standard green FR4 with white silkscreen. None of the PCBs look like the originals. They just have the same circuits and fit in the same mounting.

I'll see if I can get some pictures up.

[tedmich]

I love duping circuits without axial caps, they take up sooo much space. I often etch my own but plated through holes and vias on a modern board are wonderful to work with.

[R.G.]

My wife has the camera off somewhere, so I had the PCB software dump imgages. Try these.

http://i.imgur.com/qfQuYwV.jpg
http://i.imgur.com/3W3wFe8.gif

And I notice that I forgot to tell the software to put the holes layer on the filter board. ACK. Oh, well. The board has holes in the right places. I'll get real pictures as soon as I can.

[52 Bill]

I see that you have moved the rectifiers off of the main board to the filter cap board.

[R.G.]

Actually, I didn't. I put the rectifiers both places.

Let me explain.

The boards were each intended as a standalone replacement for an otherwise stock amp. So the rectifiers had to go on the power amp board in case the stock filter caps were used. Bad choice for the amp owner, but someone will insist on it.

It's a bad idea because there is a hum penalty to be paid unless the wires to/from the filter caps are not just so and the CT from the transformer is not wired just so. I did the layout on the filter caps board for lowest hum from the rectifier pulses, and that requires putting the rectifiers there, and running wires from the filter caps out to the power amp PCB to be used, with all the rectifier pulse-hum left back on the filter cap board. So I designed the filter cap board with a position for the rectifiers so you can get lowest hum.

The rectifiers don't do anything either place unless there are transformer leads connected to them. Otherwise, they're just reverse biased diodes.

So if you replace the filter caps but not the power amp board, you can use it the way the old board worked by leaving the rectifier module off the filter board and just running the stock wires from the old power amp board to the filter cap board. Or for lower hum, you can put the rectifier module on the filter board and move the transformer leads to the filter board, and get lower hum. The old rectifiers on the power amp board can be left there or clipped out. Makes no difference unless they're faulty.

If you replace the power amp board but not the filter caps, you can put the rectifiers on the power amp board, and it operates just like the stock power amp board but doesn't get the hum advantages.

If you replace *both* the power amp board and the filter caps, you can put the rectifiers either (or both!) places. But only the rectifiers that have the transformer secondary leads connected do anything, so it makes sense to leave them off the power amp board and put them on the filter board for lower hum.

Can you give me good AAACKKKK!! ?