I bet it worked ok ... the two 80s were in series with equalizer resistors across each one to keep the voltage on both caps approx equal. The two 80s in series would add up to one 40 with twice the voltage rating. Substituting a 10 for the 40 would result in increased "hum", but perhaps not terrible.

jr

I wondered why they used two caps in series in the first place, when a single 40 would do. Over-engineering for longevity? Parts cost/availability?

Phil

I suspect that that point might hit over 500V before the other tubes in the set warm up and start drawing current, so two 350V caps in series would provide a 700V rating. I don't think that 600 or 700V electrolytics were available. I think that to a certain extent, Dumont over engineered the design, to promote longevity. Since the set was likely quite well filtered, replacing the "40" with a 10 probably worked ok, perhaps introducing only a slight amount of hum. The ESR of the 10 was likely less than the two 80s in series, as well.

jr

Speaking of over-engineering, the TV has a time delay circuit to reduce surge. See the 6AL5 tube, V224, and K201 in the schematic.

From the service manual:

The relay circuit has been designed so that the relay is energized approximately ten seconds after the power is applied to the television receiver. In this way all capacitors and other components are protected from the high surge voltage which otherwise would occur before the tubes heated up and started to draw plate current.

Some of my later sets use a thermistor, instead. Maybe they didn't exist when this was designed (?).

Phil

Phil, that relay will have an open coil as often as not.
There's a modern relay that can be cannibalized for the 5000 ohm coil if needed.

WOW! I did not spot that... a 10 second delay should take care of *most* of the surge. These folks were serious ! :yes:

jr

I guess the relay's OK. Replaced four caps in the p-s and brought it up on the variac. Makes a dandy FM radio, with nice bright magic eye. TV audio is fine, too. Picture has some issues, but hey -- it's only 5% restored :)

Phil

Well you know it's the last 5% that's hard to get right. :D

Tell me about it. I think I have earned a gold membership card in the Ninety-Five Percenters club.

Phil

39 caps later, percentages are looking up.

Phil

:banana::yes::banana::thmbsp::banana:

Good job!

jr

Nice job Phil!

You've given me hope for my Crosely with the very similar chassis.

Sure is looking great Phil! I'm kind of jealous! I am really looking foward to seeing the finished product, back in the cabinet.

Long live the Dumont's!
have fun!
Matt Davala

I wish I liked refinishing as much as making pictures show up. Now I have two console cabinets stacked up to refinish. They'll get done this Fall, I promise.

This set was a treat to work on. Even I can see the quality difference between this and some others.

Phil

DuMont RULES!