The 39-116 project: the beginning - Printable Version
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The 39-116 project: the beginning - BrendaAnnD - 03-20-2015
Now started on the recap and rewiring of my 39-116 (thanks, Murf, for helping me out with this!). I've done the caps in the remote receiver section, and most of the ones in the audio section. There is one coupling cap from the phase splitter to one of the output tubes that's buried pretty deep in wiring that I still have to get to.
As you may note in the pic above, there are still several paper caps in the middle section of the set that I need to be replaced, as well as the electrolytics. I have some nice capacitor housings that I will use to replace those. I only have to install the new caps into them.
Also need to see what all needs to be done under the various cans, but that shouldn't be much nor too difficult.
I have started on the crumbled rubber wires as well. Started with the ones going from the switch to the cord and transformer. Those were highest on the priority list since they carry the mains power. New cord, too.
RE: The 116 project: the beginning - Chuck Schwark - 03-20-2015
Ah. . . . you second career starts. . . .
Slow and steady wins the race.
Chassis looks in decent shape too.
Good luck with the Beast.
Chuck
RE: The 39-116 project: the beginning - Ron Ramirez - 03-20-2015
Hey Brenda, good luck with this one!
I edited the title of your thread so that no one would get this confused with a 1936 model 116.
RE: The 39-116 project: the beginning - BrendaAnnD - 03-20-2015
Chassis shouldn't be too bad. The motor for the vol control works (though it seems a bit slow, likely needs a new NP cap). I'm just hoping that the stepper works.
Now, the cabinet.. that will take some effort. I'm not good enough to make it look new, but I think I can make it look decent.
RE: The 39-116 project: the beginning - morzh - 03-20-2015
Brenda, when you say "stepper" do you mean a switch or a motor?
RE: The 39-116 project: the beginning - BrendaAnnD - 03-20-2015
Audio section, now pretty much complete. Just need to make a permanent connection where that clip lead is.
Remote receiver section. Recap complete, but still doesn't seem to get signal through the first amp tube.
RF section. Recap complete. This one was fun, with the shields in place.
Now for the rest: Audio section had several bad resistors, as in completely open. The cathode resistor from the phase splitter was open. The grid leak resistor on one of the outputs was also open. Add to this, the junction of the grid resistors was never reconnected to the B- supply. (how in the h-e-double-toothpicks did this beast sound as good as it did?!?!?). Once all of the caps were replaced, all this other stuff started showing up as severe distortion in the output. Yuck. Back to sounding pretty good now, with more power.
OK.. so there's yet another issue. Whomever let out the magic smoke from the original power transformer replaced it with one that does not put out the requisite B+ voltage. The output of the rectifier should be 345V, but is more like 260V. This not only gives inadequate B+ for the radio to perform to spec, it also fixes the B- at too low a voltage to properly bias the output tubes (they have only ~10.5V). Not at all sure what to do about this.. finding a proper transformer may be quite a challenge.
RE: The 39-116 project: the beginning - morzh - 03-20-2015
How'bout finding the specs or a proper iron with bad windings and involve a Heyboer or a like of it?
RE: The 39-116 project: the beginning - Mondial - 03-20-2015
In the meantime, you could replace the 80 rectifier with an 83V, which has lower internal voltage drop and will raise the B+. The 83V is pin for pin compatible as a plug in replacement and draws the same 2 Amp filament current. The main difference is the heater-cathode construction and closer electrode spacing.
The other possibilities are to wire a 4 pin tube base with silicon diodes and increase the first filter cap to give an additonal few volts over what the 83V would provide.
RE: The 39-116 project: the beginning - BrendaAnnD - 03-22-2015
I made up a SS 80 with a couple 2.5A 1KV diodes. That brought the B+ up to around 320, that helped.
I finally have the remote receiver working with good (I think) sensitivity. I can trigger the thyratron with a -34dB input to the terminals. It will stay triggered down to -41. It was tricky to get it right, as the impedances on the grids of the 87 and the 6J7 (I'm temporarily using a 6K7) seem to be quite high, and even my scope probe loads them to a point they won't properly tune. I ended up feeding a +10dB signal in and getting the thyratron to fire, then backing the level off till it extinguished. I then tuned the first stage until it fired again then backed the level off till it extinguished again. Lather/rinse/repeat until I found what appears to be the best gain.
Now the next fun part. The stepper does not work reliably. This could be because I'm not able to send it properly spaced pulses until I get the Mystery Control working. We shall see.
The final chassis issue I have not wanted to deal with because it's going to be a total PITA is the volume control. This one has issues. Toward the lower end, it acts like a typical old volume control with either dire need of cleaning or a completely worn out trace. The volume jumps around as well as the timbre and the amount of distortion. If I find a sweet spot where the thing makes proper contact, it sounds great, but in the meantime it crackles and just makes very unpleasant noise. Once it's past this bad spot on the way up, it works fine and sounds great (but loud!!) This one of course is far more problematic to clean because it moves so slowly as you run the motorized volume up and down. I shudder at the thought of having to replace that control...
RE: The 39-116 project: the beginning - BrendaAnnD - 03-28-2015
OUCHIES! (also posted to WTB)
I'm an unhappy camper. I nearly had my 39-116 chassis up to 100%, but tonight it ate it's output transformer.
Was playing beautifully then started crackling. I thought possibly SMD, but no. After a few seconds, it stopped playing, the input current almost tripled, and all the B+ voltages tanked.
First I checked to make sure none of my caps had died. They hadn't.
The output transformer had shorted one side of the primary to chassis (about 100 ohms).
I've verified with a single ended transformer that the radio still plays (odd duck, this one.. without the negative feedback circuit working, the thing will never lower the volume much past deafening).
At any rate, I really need this transformer. So, if anyone has one, you can pretty much name your price.
RE: The 39-116 project: the beginning - morzh - 03-28-2015
Brenda
If it is to chassis, this means it cut through the bobbin? I wonder how.
Maybe you could inspect it and it is something obvious?
RE: The 39-116 project: the beginning - morzh - 03-28-2015
Brenda,
Can you try this:
Get any suitable pushpull xfmr you have that would work.
Parallel a divider (1:1 for start) to the secondary, make it say 250:250 Ohm (can be 1k:1k).
Via a capacitor 5-10uF connect your divider center to where the feedback goes.
See if this works.
RE: The 39-116 project: the beginning - BrendaAnnD - 03-29-2015
Did some checking this evening. I found my one lonesome hi-fi P-P transformer with a 4/8 ohm output and wired it into the set so that it would work as closely as possible in place of the factory transformer. The audio sounds pretty good, overall.. but because the plate load and output impedences don't match well (the set uses a pair of 42's (6F6 equiv.), whereas the transformer is designed for four 6L6's in P-P/Parallel) and the output impedences is fairly critical to obtain the proper negative feedback and tone control range. So..... I will have to have something that more closely matches the original.
RE: The 39-116 project: the beginning - morzh - 03-29-2015
If a universal xfmr exists that fits the load matching reqs the output taps for different larger loads could be tried for the feedback tap.
RE: The 39-116 project: the beginning - Chuck Schwark - 03-29-2015
Brenda,
BINGO!
Philco Output Transformer p/n 32-7996 specs:
Pri. Imp. = 12,000 ohms
Sec. Imp. = 5 ohms (Sec tapped for feedback 7%)
Watts = 13 w.
Turns Ratio = 46:1
Height = 2-3/8"
Core Width = 2"
Coil Width = 2-1/8"
Mtg. Hole Centers = 2-3/8" Vert mtg config.
Chuck