[Milsurplus] B+ Problem in 1MC system

[Mark]

Rob Flory wrote:

> Rather annoying problem with a second PA unit that we were trying to get running again.  After isolating a leaky filter cap and everything downstream from the rectifier, we were still blowing fuses when we put the B+ on.  We could run the HV transformer alone, disconnected from the 866A rectifiers or even with either side of the transformer connected, but with both sides of the transformer connected to the rectifiers we got a lot of current as indicated by bright purple flash in the rectifiers before the HV primary fuse blew.
>
> We suspect an arc in the rectifier filament transformer, which shows no sign of leakage from the rectifier winding to the case or any of the other windings under test with an ohmmmeter. 
>
> The next step is to try replacing the filament transformer, which also runs the 838s, with a seperate winding for each 838 filament.  Weighing in at something like 50lb and located just above the deck, this is what we call fun.
>
> Anyone have any other suggestions?
>
> RF

I may have missed some posts in this sequence, and this might be obvious, but have you tried replacing the 866s?  When those those puppies get gassy, they will tend to develop arcing problems -- that "bright purple flash".  :)  That might account for high instantaneous current and blown fuses.

Replacing the tubes would be a heckuva lot easier (and cheaper!) than goofing with the transformer(s).

--Mark Francis
  KI0PF

Author of "Mil Spec Radio Gear Volume 2"
available direct from the author,
$29 cash/check/MO including postage, 
$30.17 via Paypal, both within U.S. 
(foreign buyers please contact me).
Signed by request.

Excerpt here:
http://www.mmfrancis.com/MSRG2/MSRG2.pdf

Also available from:
Universal Radio
http://www.universal-radio.com/catalog/books/3495.html
Fair Radio Sales
https://www.fairradio.com/catalog.php?mode=viewitem&item=6569
Electric Radio
http://www.ermag.com/index.cfm?v_link=product_detail&v_key=415

Volume 1 is still available direct from
CQ Magazine,
http://store.cq-amateur-radio.com/Detail.bok?no=113
Universal Radio,
http://www.universal-radio.com/catalog/books/0415.html
and Amazon


There are people who make things happen,
there are people who watch things happen,
and there are people who wonder what happened.
To be successful you need to be a person 
who makes things happen.
                           --Jim Lovell
                             Astronaut