I am attempting to restore a 37-84. The chassis has been stripped and painted, the sockets and cap blocks have been replaced, the power supply has been repaired, etc. I am starting to rewire the chassis with new caps and resistors and The coils have been checked.
Current issues:
The filter caps have been supplied with 10 MFD. One was damaged. would I be able to replaces them with 22 MFD caps instead without a problem?
The power supply schematic shows a center tap (5) that does not exist on the power supply (32-7180). Another center tap (8) exists that are connected together. Is it necessary?
The volume control schematic shows the 20,000 ohm grounded. It was not in the chassis when disassembled. Should it be? The volume control is isolated from the chassis.
Is there an easy way to check the tubes (80, 42, 77) for condition?
Is there a place to obtain an inexpensive signal generator for alignment?
Tha nk you to anyone who is willing to advise on the issues. This is my first journey into radio restoration. I'm sure i'll have more questions.
Forgot to enter photos of where I am in the restoration. I understand that the radio value may not warrant the restoration, but i'm doing this me myself, as a learning experience and because I like restoring old things.
so ...
I combined your two 37-84 threads to keep the topic together.
If it were me, I would replace the filter caps with something closer to 10mF but I have seen larger sizes used as replacements. Some of the folks with more electrical knowledge willhave a more precise answer.
The Code 122 version of the 37-84 (see: http://www.nostalgiaair.org/pagesbymodel...013225.pdf ) does not have that the center tap. Are you sure you have the right schematic. The model 84 is different from the 37-84. The first being an earlier model, the second a 1937.
You can check the tube for filament continuity and check if there any dead shorts across the pins that should be isolated but without a tube tester you can not check if they are working.
You can put a "Wanted Ad" for a signal generator and see if anyone has one. Another place is to get one is a radio swap meet and finally you can check ebay for one.
I am working on a 37-84, code 121. It uses an 80, a 42 and 2 - 77's. It's the same schematic as the 122, except that the tubes (which are essentially the same spec) are 4 and 6 pin tubes in the 121 and 8 pins in the 122. I tried to post the 121 schematic but can't seem to make it work. You're right, I see the center tap is not included in the 122 schematic. No shorts and good continuity on the tubes. I guess the only way for me is to fire it up and see if it works.
Tell you what will call it a model 84 it's got standard base tubes tube like yours. The tap on the filament is there to help cut down on the hum from getting into the detector stage. Don't ground any of the filament or pilot lamp connections. I would increase the value of the filters to 10 or 20 mf ea and add 20 or 25 mf to the bias filter too. Because of the det and the amp it needs p/s to be really clean from hum.
>The filter caps have been supplied with 10 MFD. One was damaged. would I be able to replaces them with 22 MFD caps instead without a problem?
Not a problem but would probably stick with 22mf as the highest. The spec on the 80 tube is 40mf max.
>The power supply schematic shows a center tap (5) that does not exist on the power supply (32-7180). Another center tap (8) exists that are connected together. Is it necessary?
It's just a different way to do the same thing. The tap may work a little better not sure. When I've built some regenerative sets I've added a diode and cap to apply dc voltage to filament of the detector stage. This works well but there is about a half volt drop across the diode 6.3 down to 5.8v.
>Is there an easy way to check the tubes (80, 42, 77) for condition?
Yeah tube test works good for me. Short of that no other than what Bob mentioned.
>Is there a place to obtain an inexpensive signal generator for alignment?
Bob comes to the rescue again!
Very common on these sets for the primary of the antenna and oscillator coils to be open. Pretty sure the info is over in the library to rewind. It's simple.
GL w/your project
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 11-04-2020, 11:48 AM by Radioroslyn.)
The schematic shows the tube filaments wired directly to the power supply. The chassis I am working with has the ground side of the filament power connected together and tied to a rivet to chassis ground. Does the filament power need to be above ground, or is it acceptable to mix the chassis grounds? Thank you for the help. See attached images.
It looks like you have all of the pin six's grounded so one end of the heater winding would be grounded. The other end would connect to one of the pin one's of the 6v tubes. The center tap is left unconnected. The lamp would be connected in parallel with one of the 6v tube's heaters.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 11-07-2020, 10:18 PM by Radioroslyn.)
If you are asking does it matter which way I connect it? As per the 84 diagram or the 37-84B code 122 I answered that before. I doesn't matter but it is important that if you ground one side of the heater don't ground the tap also.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
as far as generators go,a rca wr-50b will do if you can find a good one on ebay. i used two 10 mfd. caps in my 84 and it seems to be fine. depending on the stations power and distance and geography between you and them that radio can really surprise you.where i live i got it hooked up to a long wire with rg-58 coax as a lead in.
Question about the grounding. This chassis has the grounds connected to the chassis. The tube grounds are factory wired together and then to either a grounding lug or, for the tubes, connected to a socket rivet for grounding. This is the way I received it and it appears no mods were made to it since new.
So ... are you recommending I remove the grounds from the chassis and put them "above ground"? Or leave them the way the factory originally installed them.
I now know the difference between an 84 and a 37-84. I am working on an 84.
