Hello
I could use some help with this 37-650 floor model,I took on this repair for an older lady,the set belonged to her father,not working when I brought it home so first I checked all tubes changed the power cord,then I changed the large caps and all of the paper caps I could get at and changed about 6 resistors,I did not change the paper
caps under the tuner because I could not get at them.I replaced the bad tubes and the output transformer
with a old one I had, the one in the set was open on one side,then I powered it up ,worked fine and sounded great
with lots of volume.I refinished the cabinet and put it back together ,ran it many times for a few hours at a time
no problem so I took it back to the lady.She ran it off and on for about two weeks and it stopped ,had very low
if any sound at all.I went back with some spare tubes ,I lost track on what tubes I changed but the set
started to work again,it played great for about three weeks then quit again,same thing very little if any
sound,one thing I noticed that when it stopped playing the shadow meter did not move like it did befor.I have
the set back home again,powered it up and it plays great,not knowing what to check now I changed the
output transformer and put in a new one,I put my very small round file down every tube pin hole and with
a tooth pick put dioxit contact cleaner in every tube pin hole.The reason I changed the output transformer
again was I had a set after trying every thing found out it was the output transformer,I was told by a
fellow to try it because some times when the copper wire in them separates it leaves a carbon track
that will allow the set to work until it gets hot enough to separate again,then it will cool and work
again,that was 6 years ago and the set is still fine.I now have the set on the bench working and while
running I have tapped every joint and move every wire thinking there must be some thing loose,I
wish I could move some thing and have it stop but no luck,I did change one more resistor # 36,the
schematic calls for a 190 K but this thing test at 539 K,the colour on it is yellow body with a white
or cream strip around one end,is 190 K correct or am I reading it wrong,never seen one that far
off befor,I am going to let the set run for as long as I can every day to test it,I don,t want to take it
back only to have it stop again,that won,t be good.If anyone has any idea on what else I could check
please please help me out,I am going to try to post a link to Nostalgia air for the schematic but I don,t
have much luck with that,anyway thanks for your time and for any help you can give,I must say that
set sounds great when working and the cabinet turned out great ,all the very best Rick
PS -I will send the schematic on a new thread
Best thing to do is to replace ALL the old caps. Maybe because they are so old they change value on you, plus it is dangerous to leave those old caps in there.. sooner or later they will go out.. could go out with a fire. Good chance after those are replaced your problems will be solved if you have also checked all the resistors. There are a lot of people here more experienced in the electronics than me that might have more ideas but these are a couple basic things that need done before other things.
I guess it depends on how well your service bench is equipped, but in this case I would start at the speaker with a signal generator and a scope & ear, and I'd track backwards toward the antenna to see where the signal path is interrupted. That's where the problem will be.
If that dogbone resistor has a yellow body, white end and yellow dot (i.e. you see no dot because its the same color as the body) then its a 490k resistor. There is a 490k (resistor #53) in the set as well as a 190k (#36). A better set of schematics on the 37-650 can be found on the audiphool site and you can order a really good set from Chuck for just a few bucks.
paper caps: not only they change value (that would not be a problem as they are rarely used where the value is critical, especially in decoupling where only the lower limit is important) but they develop leakage which is why we need to change them. The leakage results in DC current and this affects biases in tubes where they serve as DC blockers, changing the tubes' working regimes, sometimes to the point of them not working at all.
And if such a cap is in decoupling it no longer decouples well plus might heat up and then smoke, possibly also taking the power supply along with it.
So, try your best to reach them, yank them and change them.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Hello and Thanks
I think I will try and change those two caps under the tuner and switch that resistor
take out the 190 K I put in and put in a 490 K.Those caps are very hard to get at,
when I look at them and try to follow the wires ,the bottom ones seem easy on
one it goes to the wafer switch and one goes to the chassis but on the top it is
very hard to follow,can anyone tell me do they both go to the bottom of the
tuner then off to the top caps on the 6K7 tube and the 6A8,if so I could attach
a wire at the tuner and feed it to the end of the cap,would be much better for me
to solder,there is no room at all down there,and will a bad cap work great then
stop and then work again ?,thanks again for any help this set is a great looker
and player,all the very best Rick
By the schematic that is posted,,,#36 is 490,000-----Not the PARTS list-----Parts list 190,000,,,,,put back what you take out,,,I always take a ohms reading on old,,just to cheek how far off,,,the old one would be,,,,Cheers
Hello Again
Has anyone changed those two caps on the 37-650 that are under the tuner without
pulling out the tuner unit,when I look and you can,t see much the wire that comes
off the cap the one end you can,t see ,looks like it goes thru the tuner section chassis
and hooks up to the bottom of the tuner and then to the 6A8 tube top cap and the other
one looks like it goes thru thee tuner section chassis as well and hooks to the bottom of
the tuner as well and then goes on to the 6K7 tube top cap,if this is true I could solder
a wire at the bottom of the tuner were it seems the cap wire goes to,the other wire from
the cap seems easy ,one goes to the wafer switch and one to the chassis,these ends are
a lot easier to solder to.I just don't want to tear the whole tuner unit out if I can get
away with it,but I am not sure if those wires really go to the bottom of the tuner,has
anyone pulled out the tuner and if so could you let me know if those two caps hook
up to the bottom of the tuner,I don,t want try and pull it out and end with a radio
that will never work,be thankful for any help here ,all the very best Rick
One other thing
Thanks so much for the replies,I would not have thought the schematic was
different from the parts list,keep learning as I go ,I will check both
from now on,thanks again-Rick
If,,,I remember right,,,there is something on you-tube,,,it might be this set,,or something close to it,,,,were he squeeze the capacitors and turns them in place ,,,with the end,, that is the tuffest still soldered,,,he leaves that part still attached,,and pulls the paper cap,,( in a twisting manner) off the lead that is still soldered---reconnects the NEW capacitor,,, to the lead left behind,,,He put a snake tail on new capacitor,,and slide onto old capacitor lead and solder,,,,HOPE this may work for you,,,and I hope ,,I was some Help,,,,CHEERS
Yes, there are errors on the schematics/parts lists that come to light from time to time. Some get corrected in later Service Bulletin notices, others don't.
I'm on my third 37-670 / -2670 and still feel the easiest way to handle the cleaning and replacement of capacitors and resistors in the RF subchassis is to just bite the bullet and disassemble the thing! Once the unit is removed from the radio (to me, that is the hard part), the remaining disassembly only takes about 30 minutes. Other threads mention how to remove the bandswitch shaft, and mention the warnings about not rotating the switch wafers after removing the band switch shaft (it is keyed in case you do). This also makes removal of the tuning capacitor for cleaning, and the filter capacitor 37 for restuffing easier. In my case, a few wires also had to be removed.
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