[Milsurplus] BC604 capacitor question

[WA5CAB at cs.com]

George (and Dean),

The rated output of the DM-35/37 is 625 volts.  Under normal operation all of 
the low power circuits are fed from this through two big 667 ohm resistors, 
with C45 at the low end.  However, if someone were to for example pull all of 
the tubes or actually since its a series/parallel arrangement, only certain 
tubes, and fire up the dynamotor, the only fixed bleeder amounts to about 70 K 
ohms to ground if the radio has had all the MWO's (more if it hasn't), which 
won't drop much through 1334 ohms.  A 630 volt 2.2 ufd unit would probably 
survive but I'd consider it marginal, especially as with no load to speak of the 625 
VDC will probably go higher (until the capacitor fails!).

Personally, if I didn't have a parts radio with a good C145, I'd open up the 
can and install something like two 4.7ufd/630V in series if I couldn't find a 
new 2.2ufd/1000V or higher unit.  I'm not sure what the next higher standard 
voltage above 630 is these days.

In a message dated 9/5/2006 10:14:35 AM Central Daylight Time, 
gl4d21a at juno.com writes: 
> I am restoring a BC604 that had a tremendous "hum" in the audio 
> and 
> have found a leaking capacitor that seems to be the cause.  The 
> capacitor has a metal case and appears to be grounded through that 
> case.  The capacitor is listed in the TM as:
> 
> C145     3DB2.21  Type TLA10020, 2microfarad, 1000VDC   Plate supply 
> filter
> 
> 
> If anyone has an idea where to find one or a reasonable alternative, 
> I would appreciate a suggestion.
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Dean:
> 
> My 603/604 manuals are out in the archive at the moment, but I cannot 
> recall why that capacitor needs a 1000 volt rating.  Disconnect the + 
> lead of the existing capacitor and connect a 2 or 5 Mfd. 250V or 
> higher electrolytic in its place and see if that cleans up the hum.  
> If it does, then all you need to decide is how to accomplish an 
> acceptable restoration.  Most likely, your only option will be to 
> open the case of the old cap and restuff it with a modern 
> replacement.  Check wit some of the antique radio archives for 
> details of restuffing capacitors.
> 
> 73,
> George
> W5VPQ
> 

Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
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