KAT 6550 problems

[bob orbell]

In a word, yes Gerry, but pricy, see my other post. Bob

[gerrygwm]

Oh yes only just seen that sorry.
I will check out RS thanks.
Gerry

[gerrygwm]

Great, I will look at that.
Thanks, Richard

[John Caswell]

Hi all,
The usual reason for a elco to go s/c is if it is overvoltaged. I would guess that the valve went s/c g2>g1 up goes the bias and the elco goes s/c hopefully rather than blowing its guts all over the place (which is nice).
Replace with 10 Watt rated resistors as that keeps the heat down. The dissipation remains the same but because of a larger surface area the temperature is lower.
As bob says 100V rating capacitors are a good way to go.

John

[bob orbell]

If you are replacing the capacitors I would use RS part no 707-6552 quantity 5 min. at .58 p each and resistors I have used 187-1236 .986p each, also 5 min. plus VAT. Bob

[pre65]

If 10W ceramic 680R resistors are any good I have 4 left over from a job on another WAD amp.

Yours if you want them.

[gerrygwm]

Hi Philip,
Thanks for the offer. I ordered some resistors yesterday so I will see if they turn up first.
Thanks, Gerry

[pre65]

Originally Posted by pre65

If 10W ceramic 680R resistors are any good I have 4 left over from a job on another WAD amp.

Yours if you want them.

680R resistors reduce the 6550 power dissipation a tad.

[bob orbell]

Hi Philip, I hope all is well in Ashen, the original were 500 and the change was to 560, yours may be just a tad to far. Keep safe. Bob and Janet

[Greg.]

680R are fine, Bob. These are what I’ve fitted to my friend’s 6550. Some in the past still had plate glow with 560R. Remember, Andy Grove used to design driving the valves at maximum dissipation.