Ampeg V4 (1976 with distortion model) Filter Cap replacement

[mikeydee77]

I am working through the above amp and need to replace several of the filter caps (C301, C302, C303). Appreciate any advice from the Ampeg experts out there.

• C303 cap has been replaced by a tag board with 2007 caps - they have ruptured perhaps because they are in a very hot corner of the amp.
• C301 is a 100/40uF and is open circuit.
• C302 is ok, but I thought might be wise to replace at the same time
• All the other oldies seem ok.

My approach is to use F&T 100/100uF caps which are readily available here in the UK. I was planning on using two of these (stacked to give my C301 + C302A (50uF@1000v) and then use one of the remaining 100uF section as the screen supply replacing C302B.

My concern is that the original value of C302B is 40uF and doubling it would place some extra strain on the PSU components but I am not sure if this is a significant concern. Of course I suppose that I could always add another cap in series on a tag board to reduce it.

I was looking at the thread http://music-electronics-forum.com/t1941/ which provided some good ideas but keen to here from other ideas

Thanks for reading

[g1]

Don't think you need to worry about the extra strain on the PSU for the screen supply, but maybe worry about the extra current capability to the screens, you might want to think about a common (or 4 individual) screen resistor. But with the low screen voltage (relative to plate), it may not really be a concern. Hopefully others here will comment on this.
Be sure to check/replace the bias filter caps C207 & C208 (replace if originals).

Also, you mentioned C303 being replaced with a board and ruptured, did you mean C303 and C304? Did their voltages meet the rating on the schem (600V for C303 and 500V for each section of C304)?

[mikeydee77]

Thanks G-one.

Yes I planned to change the bias caps although actually just checked and they look fairly new anyway.

C303 was replaced by a tag board and two 68uF/400v in series with 220k equalisation resistors so whether they blew because strain, heat or bad luck I am not sure.

In terms of the screen resistors actually there are none on this model but I know what you mean; probably should have mentioned that this amp is running with KT77 tubes.