The Mighty 39-80 - Printable Version

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The Mighty 39-80 - Radioroslyn - 01-13-2018

After speaking with a new member abt his set he was a little hesitant to service it himself so I offered. Normally I don't take in service work but I was getting tired of beating my head against the wall on a couple '40s Philco sets (I hate loctal tubes and their worthless sockets!) so it was a nice reprieve to work on something nice and simple.

So the chassis was sent along w/a bevy of batteries. First order of business was to replace the battery cable and ant/gnd wiring. Next where the caps and checking the resistors. All where close to tolerance. Strung up some batteries and tried to wake her up. Heavy sleeper didn't want to wake up. Did some checking to find that the off/on switch on the filament side was open. A jumper fixed that temporarily and gave it another try. It sprang to life and was working w/a few gremlins.

Volume control was very noisy and only turned about 40% of it normal rotation. Out and apart came the control used a little bit of WD-40 on the pot and contact cleaner on the switch section. Bart (the Simpson 260) said it was ok. I believed him. Back it went and work fine. The rotation issue was caused by the actuator for the off/on flag it was hitting the bracket for the dial. With a little manipulation was able to clear up path for the actuator. Did the IF and RF alignment. Plays swell! I was curious about how much current was it using from the B batteries. Well the answer is about 6ma on a strong signal and about 6.25ma on weak signals do to the avc action. That works out to about .5 watt total power consumed. Sounds like just about all of it is used in the audio output stage as it plays pretty loud for a farm set. The more important question does it draw any current when it's turned off as this will run the batteries down. Nope no current when off.

Was listening to CHML out of Canada last night.
Next step is to figure out how to make up a friendly battery pack. Have to buy some 9v battery snap connectors and make some sort of connector to fit the old A/B battery plug. Have to see what I've got in my bag of tricks.

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RE: The Mighty 39-80 - NostalgiaRadioTime - 01-13-2018

These are nice looking sets. Looking at the schematic, I see it uses the same 1.5V A Supply / 90V B Supply set up as the 39-70 I just finished (actually the schematic looks very similar altogether). Since that power supply worked so well on mine, that could certainly be an option for this set as well (should the owner want to do away with batteries and make it an AC set). Your schematic for the power supply was a winner!

I had the same issue on mine with that off/on flag. It took some coaxing to get it to work properly. And I'm glad I'm not the only one who hates the troublesome loctal sockets.

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RE: The Mighty 39-80 - Arran - 01-14-2018

Terry;
  Most of those battery sets with the low current tubes perform pretty well given the limitations, about the same as a three way portable that uses all battery tubes. I've never worked on this Philco model but the on/off flag is a pretty common feature on many battery sets, I had one where it was worked with a short piece of dial cord attached to one end with the string wrapped around the volume control shaft , and a spring on the other end of the flag, it took a few tries to get that fixed. One common feature of just about all of these is a power switch with a very sharp "clack" sound when you turn it on or off, I guess to let the operator know that it was in fact turned off. Some of these sets had dual IF amplifier tubes, not an actual extra stage but an extra IF amp like some 1940s Philco models had, other models had dual output tubes connected in parallel, where if you wanted to save on batteries you could switch one tube off, a lot of thought went into designing some of these battery sets, I dare say more went into some of them then their AC powered brethren at times.
Regards
Arran

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