V4 PCB component repair/updating

[beedoola]

Ya, it was C1 - teal cap in the center of the main PCB. I snipped one of the legs to lift it up to see the PCB mark as I was gonna replace the cap and then saw that it said C1 on the PCB.

EDIT*** The PCB says "C1" on the top, but "C11" on the trace side of the PCB! The schematic value for it is .33, but there was a .1 in it's place.

[Hangman]

the teal cap in the center of the main pcb in your picture is c12. it is supposed to be .1uf.

c11 and c13 are the big rectangular yellow caps on either side of that teal cap.
frankly, those could be brought to .1uf with no difference in sound. such large coupling caps going to the power stage are really unnecessary.

Ya, it was C1 - teal cap in the center of the main PCB. I snipped one of the legs to lift it up to see the PCB mark as I was gonna replace the cap and then saw that it said C1 on the PCB.

EDIT*** The PCB says "C1" on the top, but "C11" on the trace side of the PCB! The schematic value for it is .33, but there was a .1 in it's place.

[beedoola]

Thanks, hangman, you're correct!

Question: Should I worry about replacing the power tube and filter cap wiring? The wire gauge for this V4 is thin, and solid core, compared to the last V4 I owned. I think, given the layout of the rear panel, that this current V4 is older than my previous one, and I'm not sure if Ampeg started using thicker gauge wire or a previous tech replaced all the wire.

The first pic below is the current amp I'm working on, the second picture is from the previous V4 I owned - which I suspect is newer than the current one.

[Hangman]

yeah, some of the later v4s had a thicker gauge wire. Its certainly a good idea to use thicker gauge stranded wire rather than the thin solid core. if you have the wire on hand... go for it. if not, its not going to make or break the amp.

[beedoola]

Ok, I don't have the wire on hand, though I need to go buy some caps at a local store. If it's not totally necessary then I won't replace all the wire.

Another question: In the first picture above. The two brown wires coming off the top filter cap - with the 100k resistor. One of the wires goes to the series diodes that go to R40/45, and R39/46. The brown wire that goes to one end of the stand-by switch and the D1-4.

Do I keep those wires together when I redo that caps? - like in the picture below with the redone caps. Only in the picture below, there is only one brown wire going to the new cap. I don't have any clear pictures that show where the diodes went in the V4 I no longer have.

[Hangman]

good question. the answer depends on what you wanna do.

I always pull the flyback diodes out, because I see them blowing up more often than I see a output transformer from a v4 without flyback diodes blowing up. (in fact I've only seen the latter once, and it was from an amp that had the flyback diodes installed)

so if you remove the flyback diodes. it makes the question moot. there would only be one wire left.

if you leave the flyback diodes, then i would put the brown wires all to the capacitor.

[beedoola]

Cook, I'll just remove them.

For the can caps, its 100uf towards the rear of the chassis and a 50/50 above it, correct?

Its been awhile since I did a recap. I already installed the 50/50 cap and 47uf on the right side.

I was going to do the same thing as in the second picture above (the pic with the thicker gauge wire).

[admin]

the 50/50 is the one that you strap together (the one towards the rear of the chassis) and the 100/100 is the one closer to the circuit board that is used for both the screen supply and the main reservoir cap.

[beedoola]

Here are some pictures of the V4 after the updates:

The bumped up 5W (from 2W) screen resistors were all too big to fit together so I had to put one on the trace side.

[Hangman]

was there a reason you opted to keep R53 on the main board rather than moving it near the 40x40x40?

I the build up of heat right there can become an issue. all of those large value resistors will get pretty hot.

other than that everything looks good. you do clean work, good job!