Bypassing cathode bypass caps - World-Designs-Forum

RobHolt · #1 5th January 2009, 08:14 PM

I'm currently rebuilding my Kit6550 and have some 100uf/100v Silmics for cathode bypass duties.

I also have some 0.56uf AN PIO caps sitting in my spares box doing nothing and wondered if it's worth using these to bypass the Silmics.

Anyone tried anything similar and what did you find?

Cheers,

Rob

RobHolt · #2 17th January 2009, 12:47 AM

Well, as the response has been so overwhelming

I've gone and done it anyway.

Very nice it sounds too.

Greg. · #3 17th January 2009, 01:02 AM

Hi Rob,

Bad response, I agree. The general rule is bypass where appropriate with caps that are 100th in value to the original cap and if like me you are pedantic to bypass yet again at 100th the value of that bypass.

Best wishes,

Greg

RobHolt · #4 17th January 2009, 01:28 AM

Hi Greg,

It was really the 100uf 100v electrolytics used as cathode bypass that concerned me. All a bit tight on the tag boards but just about do-able.
Thought I'd try some Mundorfs in the PSU while I was in there:

Richard · #5 17th January 2009, 09:48 AM

Hi Rob and Greg,

Not a lot of response here I agree but that's better than a load of bull surely

I guess no-ones tried this Rob so it will be interesting to hear what you think!

Are you back with valves full time now Rob or just revisiting?

Rich

RobHolt · #6 17th January 2009, 08:33 PM

Quote:

Originally Posted by Richard

Hi Rob and Greg,

Not a lot of response here I agree but that's better than a load of bull surely

I guess no-ones tried this Rob so it will be interesting to hear what you think!

Are you back with valves full time now Rob or just revisiting?

Rich

Hi Rich,

Never been away really as I've been using my Phono II ever since building it. I love it and it has seen off everything commercially built that I've heard.
I moved away from using the Pre/6550 a couple of years back but am now using it again as I'm back with sensitive speakers - Tannoy LGMs which have 12" DC paper drivers and are about 93dbw sens.
They can sound a little dry and bleached with a tight SS amp and seem to prefer being driven by the WAD.
I'll post some more on the bypassing once I've had more time to listen.
What I will say is that the effect of the cap changes is mild, ie it doesn't transform the amp but then it was fine to start with.

Oh, BTW you were right about C1/2 being shot and causing the choke to hum.
Got a pair of Mundorf M-Lytic in there now (bloomin huge) and the noise dropped by several orders of magnitude. I'd like to replace C3/4 with the same caps but space is very tight so for now I've just popped in some 100uf Panasonics.

Rob.

acorn · #7 18th January 2009, 05:00 PM

Hi Rob

I have just seen your post, yes I have by passed my caps on the input valve and the output caps with a 1uF solid state type, I also changed my 100uF to 50uF, what the addition of the solid caps do is that they charge up more quickly and the solid caps are of better quality which gives you cleaner response to the music from the bass right up to the highs, have you tried by - passing the power electrolytics and increasing your power cap after the choke to 200uf or 300uF.

Acorn

Richard · #8 19th January 2009, 11:36 AM

Hi Rob, Acorn,

Interesting to hear of Acorn's findings. I've tried bypassing twice in other locations (xovers and psu) but have taken them off in subsequent rebuilds and not tried since.

Glad your 6550 is well again. Be careful with a choice for first caps C1/2. That amp draws a lot of current, 350mA, and it will be the ripple that will have killed them. You need caps with a ripple capability of 700mA at 100Hz. Some modern compact caps won't do this, many are rated for higher frequency use (the first Panasonics I clicked on at RS can only manage half this).

RS 519-3696 Nichicon 100uF 400v would be fine http://docs-europe.electrocomponents...6b80634fdb.pdf

then use the boutique caps on the load side at C3/4.

Rich

RobHolt · #9 20th January 2009, 12:59 AM

Rich and Acorn, many thanks for the info and advice.

These are the specs for the Mundorf HV caps.
I have the 47=47 version with both halves wired in parallel - measures out at 105uf total on my meter.

They give the ripple rating as a percentage - 0.4% in this case.
But 0.4% of what?

Richard · #10 21st January 2009, 10:08 AM

Hi Rob,

I don't know what that rating means I'm afraid. They are a good size though and do seem to be sold as smoothing caps so they may well be fine. It's just worth remembering that this is a larger supply than most valve amps (hence those 2 large rects) as it's supplying both channels of a near class A 6550 amp so the first caps will get thrashed.

Rich