Heathkit W5M - Rebuilding hints anyone?
gkau...@the-planet.org
many Heath amps with blown transformers. Any hints or ways to protect the
transformers?
Also, one of the amplifiers has a small bimetal contact with heater
resistor. Is this the "surgistor" mentioned in one of the service
bulletins?
Many thanks in advance,
- Gary
Mjzuccaro
Make sure you have good filter capacitors!That and the rare rectifier arcover
are what kills power transformers.Also,on all of my equipment I make sure that
I use the smallest possible fuse that will hold in normal use-often you can use
a fuse that is smaller by 25% or more.Most units were overfused to prevent
nusiance blowing at high line voltages or during bench testing when making full
sine wave power continuously.As for the bimetal contact you found,sounds like
someone installed a circuit breaker or protector of some kind-probably in the
AC line,right?
Best,
Mike Zuccaro
William Mollard
gkau...@the-planet.org says...
Hiya Gary,
The larger 16458 trannies were a replacement for the smaller OPTs that
blew often, I wouldn't worry about the 16458 (IMHO)
I replaced the PS with cerafines and the decoupling caps with solen
polyprops.... very worthwhile. I would also recommend changing the input /
driver to a 7119 or 5687. The phase splitter; well I would be interested in a
Lundhal 1638 interstage tranny for starters. Yes, the bimetal / nichrome wire
is the surgistor. All in all, the Heath W5M was pretty well the culmination of
prior heathkit efforts and is quite a nice amp... just lose the 12AU7A
distortion tubes!
My opinion only!
Oh yea, change output tubes to EL37!
FWIW
bill
Randolph Fay
it. Them W-5 power trannies are very very prone to failure, and the extra
current demanded by the 7119/5687's versus 12AU7's can only hurt. Why not
do an full outboard 6.3V DC supply for both amps? PT's will run cooler and
you can turn the heaters on 20 seconds before you turn the B+ on. Also you
can remove 6db feedback by doubling the feedback resistor and halving the
associated compensating cap.
Randy Fay
William Mollard wrote in message <36ce...@news.vphos.net>...
Randolph Fay
too. Lets see...total current for two amps: 2 series-connected pairs of
KT66's/7581/6L6GS and 4 5687 = around 4 amps @ 12v. Use a 10,000uf-22,000
cap 16v or 25v at the amps for extra filtration.
Randy Fay
Randolph Fay wrote in message ...
ronald.j...@exgate.tek.com
"Randolph Fay" <F...@netcom.ca> wrote:
> Unless you have a separate heater supply for them 7119/5687's I wouldn't do
> it. Them W-5 power trannies are very very prone to failure, and the extra
> current demanded by the 7119/5687's versus 12AU7's can only hurt. Why not
> do an full outboard 6.3V DC supply for both amps? PT's will run cooler and
> you can turn the heaters on 20 seconds before you turn the B+ on. Also you
> can remove 6db feedback by doubling the feedback resistor and halving the
> associated compensating cap.
>
I have a pair that use the small opt, have been modded to use EL34's, 5687's
6FQ7 and a GZ34 rectifier. The power transformers have hung in there just
fine. And these have been running for several years now. I have noticed that
Stancor made some of the power transformers on these. And this seems to be
the one of my two that doesn't get as hot. Everything I did stresses the
power transformer harder than the orig ckt, but still they live.
The extra 6.3V supply does make sense. I don't see a need for DC though.
The other pair I own use 6B4's in the output, DC was a necessity here.
Should one lose a power transformer, there are good substitutions out there.
And the sneaky guy might even be able to fit one inside the original can.
Have fun!
Ron S.
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