DSL Hum, C46 question

[JohnT]

Hi all,

First post.
Great place you got here

My 100W DSL went south after a power tube short.

On inspection R6 was fried. I replaced that and I've still got a hum.
C46 also looks discoloured, I believe it's likely to be the next candidate to check.

My questions are: The schem suggests C46 should be 500v 22p -
1. Do I need this cap or can I just take it out and bridge the board and
2. Does the replacement have to be 500v, only I'm having a hell of a time finding a replacement with that high a working voltage. Could I get away with something lower?

Thanks in advance guy's.

John.

[lowell]

can you post a schematic?

[Enzo]

Well you definitely don'r want to replace it with a wire, if that is what "bridge the board" means. That would be like the cap was shorted. The cap is between plate and scren on that end tube. Measure pins 3 to 4 for resistance - is it shorted?

You can take the cap out and the amp may or may not be stable - you may or may not experience parasitic oscillations. Take your chances.

Can't find a HV disc ceramic? Mouser:
Stock # 539-GP422 22pf 1000v disc ceramic 19 cents each.

Stock # 140-500N5-220J-RC 22pf 500v disc ceramic 8 cents each

I highly recommend using the 1000v cap. I am convinced that the reason these fail as often as they do is that they are not rated high enough voltage.

No 1000v disc ceramic dealers in the UK?

[JohnT]

Cheers Enzo. If there are I couldn't find any.
Mouser order in.

Edit: Pins 3 to 4 shows fluctuating resistance around 0.04 (started off at something like 19m and then fell away.
Either side of C46 shows none. The cap is also badly discoloured. (measured with tubes out).

Did you have something else in mind also?

John.

[Enzo]

SO remove the cap. If it is discolored, it is bad. Now does the amp work? You can certainly proceed with the repair without waiting for the cap-. You can always flip it back off if something funny starts to happen.

[JohnT]

Delay responding due to kids holidays, decorating, Blah Blah..........

Anyway, fitted new C46 and amp is back to normal i.e. sounds like a DSL without the hum

Thanks all.

John.