----- Original Message -----
From: "Vic Rosenthal" <rakefet@rakefet.com>
To: "Amps reflector" <amps@contesting.com>
Sent: Sunday, September 22, 2002 7:08 PM
Subject: [Amps] Henry solid-state amp problem
> I have a Henry SS750 solid state amp. It has 8 2sc2879's (four push-pull
> circuits on individual boards). It operates at 14v.
>
> There's a decoupling circuit on the 14v lines going to each board: the
cold end
> of the output transformer windings is bypassed by a 0.33 uf cap, followed
by
> some ferrite beads, and finally a 100 uf 25v electrolytic.
>
> My problem is the 100 uf electrolytics: I keep blowing them. I have
replaced
> them with 50v parts, I have tried 105 c rated parts, and I have bypassed
them
> with 0.1 uf discs (on the theory that RF is heating them up). They keep
> blowing. There's a bang like a firecracker, a little smoke, and part of
the
> innards get blown out of the vent hole (on caps without vents, the whole
end
> gets blown out).
>
> This happens when ragchewing (CW) on 15 or 10 meters. It has never
happened on
> 20 or below. The amp is not especially hot when it happens. I am running
about
> 550w output with about 70w of drive. Interestingly, it doesn't appear to
affect
> the functioning of the amp (although I always shut it down).
>
> My questions are:
>
> 1) What's blowing the capacitors?
My guess is that its the 'af' ripple on the supply line that's causing the
ripple current rating of the capacitors to be exeeded.
To prove this does it happen when the amp is driven with continuous
carrirer?
If Ok check the PSU for regulation also ensure that the dc cables are up to
the job.
>
> 2) What is their function? 100 uf is a lot of capacity if you are
bypassing
> RF!
Also not much use for, what, 70Amps of ripple.
>
> Vic K2VCO
Roger
London UK
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