A friend has a line on a very nice looking DuMont 109 television in Boston, probably available for the taking.

But do not plug this into the wall - it is a weird DC variant. Apparently North Boston still had a bit of the old DC network in the 1950s, just as New York City still had DC in the 1990s. I have no idea how the power supply is different - probably a vibrator.

Anyway, if there is any interest, I can bother my friend a bit more.

--
Will

I can't imagine a vibrator being hefty enough to provide the power needed for a 40s TV set, but I can't figure out another way they would do it. Please get more information.

Dynamotor maybe? Would be really annoying to listen to it whine while trying to watch TV, though...

a supply like a sweep circuit to make B+ would be possible but the current would take quite a output tube to work. Possibly a push pull type supply with some HOT's would work and keep you warm in the winter!

I have a couple Raytheon sets that were also designed for AC/DC.
The rectifier assembly plugs into an Octal socket on the chassis and can be replaced by whatever it is that makes it work on DC, but these are also series strung with no transformer.

I can't imagine a DuMont without that massive Sola Transformer on the chassis?

I'd like to see a picture or two, my 109 sits awaiting a 19AP4 rebuild or the 21" rectangular conversion I saw on eBay once...

Eric, are you sure these sets were designed for DC? I can't imagine how they would work, since the B+ would only be 120v.

Eric, are you sure these sets were designed for DC? I can't imagine how they would work, since the B+ would only be 120v.

Steve, yes.
Take a look at Sams 75-1 http://www.earlytelevision.org/images/Raytheon-10DX21-22-24-10AXF43-Sams-75.pdf

It has the option for DC power with a "Polarizing Relay" (vibrator?) the diagram is on page two.
You're right about the B+ I don't see anything higher than 127 volts listed in the voltage chart.
It has no Flyback using an RF type supply so maybe that's why. I'm guessing they managed to duck most or all of RCA's Patents with that chassis!

Amazing. Yes, it is a vibrator. Must be a hefty one to power that set - 1.7 amps at 117 vac.

Sounds fascinating from a technical standpoint. Hope someone gets it and shares photos.

I hope we see a schematic also! That Raytheon is TWISTED! Three 50B5 audio outputs in parallel! And yes, a vibrator! Can you imagine having to replace the vibrator! The customer would be boiling oil to throw!

Correction: the 50B5s are horizontal outputs in parallel. It hardly gets more twisted than that.

I recall marveling at the oddity of the Raytheon design when I scanned that SAMs and submitted to ETF. Three 50B5s in parallel for the hz output, and a 35Z5 for damper!

Looking carefully at the circuit, I believe the "polarizing relay" is NOT a vibrator, but merely a relay which makes the set work regardless of which way you plug it into a DC outlet. Probably a relay with a permanent magnet that is sensitive to polarity of current in its solenoid.

Note how the voltage from the output of the polarizing relay bypasses the filter, which would not be done if it were a vibrator. Also note (as mentioned above) that the are no DC voltages over 120 VDC in the voltage chart (except where boosted by the hz output).

Tom, thanks for setting the record straight. Amazing that they could make a set with maximum B+ of 120. I guess there was a market for DC sets, since there were still pockets of DC power in the US in the late 40s.

Looking carefully at the circuit, I believe the "polarizing relay" is NOT a vibrator, but merely a relay which makes the set work regardless of which way you plug it into a DC outlet. Probably a relay with a permanent magnet that is sensitive to polarity of current in its solenoid.


Doing that would avoid the voltage drop you get with tube rectifiers, and hopefully gives enough protection to the electroytic caps against reverse polarity. If the relay is normally open with no power applied, then maybe only when it sees power it makes the correct connections without the caps ever seeing reverse polarity. Like a cross wired DPDT switch with center off.

Interesting.

I've used a full-wave bridge rectifier on the input side of DC-operated equipment in the past, where there was a possibility of incorrect polarity being applied. If you connect the positive and negative output terminals to the equipment, you can apply either polarity of DC to the AC input terminals, and the diodes will "steer" the output to the proper polarity, regardless of how the input is connected. Handy on small inverters, battery chargers, etc. subjected to use by people who may not understand simple conventions like Red=Positive, Black=Negative.

Still want to see how DuMont does it. Anyone know the Sams # for it?

Interesting chassis, I say. Unusual. Learned some history I didn't know.