1932 GM Little General 250A Help - Videokarma.org TV - Video

fixmeplease · #1 01-01-2021, 11:44 AM

Hi folks. I took a quick look at this radio yesterday but have done zero testing yet. I will say it was very well built for the time. I like the cabinet design too. Too bad they only made radios a few years. Anyway the schematic (link included) does not give voltages on the capacitors, including the electros. In the pics you can see the 2 tall electros, one with a cardboard sleeve over it. The other is 2 parts clamped together. Wet ones im guessing. What would be the procedure for figuring out the voltage of these, especially the electro's? If I do restore it I may have more questions but thats it for now. Thanks!

http://www.nostalgiaair.org/Resources/103/M0043103.htm

init4fun · #2 01-01-2021, 01:24 PM

Just to get it out of the way , the aerovox cap and the blue one next to it , as well as the two red ones , are replacements and not native to the set . I figured you already know that but in case you didn't it's worth mentioning .

As to the power supply caps , anytime I see an 80 rectifier (or it's many revisions , the 5Y3 , 5U4 , etc) I always go with 450 volt caps as a matter of routine . My reasoning is that the 80 has directly heated cathodes and pretty much instantly begins passing voltage to the filter caps , while in many radios the indirectly heated cathodes of the rest of the tubes take a few seconds to heat up to where the tubes begin conducting , and begin loading the power supply down to it's normal running voltage . During that warm up time the B+ can shoot up quite high till the rest of the circuits begin drawing power , and that initial turn on spike is why I'd use 450V caps even though while running it looks like around 225 V is the highest B+ voltage listed on the schematic . In running tests you may not see all that big of a voltage difference with your radio since the output 47 tube is also a directly heated cathode , and will come on as instantly as the rectifier , the biggest warmup B+ drop will be noted with indirectly heated audio output types like the 6V6 , 6L6 , etc .

MadMan · #3 01-01-2021, 03:37 PM

Well modern film caps are mostly rated at 600 or 630 volts anyway, so just use those.

For the rest, can't you read the values off the old ones?

fixmeplease · #4 01-02-2021, 10:12 AM

I havent looked it over much yet. Im assuming 630v is enough on the regular caps because of their sizes. I do see a little work done on it, but not as much as I usually see on 1930's radios. Someone hacked a newer cord onto the cloth one to make it longer so it was likely working for a lot of years.

There are no markings on the electro cans other than the maker. 450 volts it is! I need to order them before I start on it, but I will test the transformer 1st cuz Im sure a replacement would be difficult to locate. Its the 1st cathedral style Ive done. Thanks guys! If I proceed with it I may have another question on the multi-section resistors, or not.

vortalexfan · #5 01-03-2021, 11:29 PM

Quote:

Originally Posted by fixmeplease

I havent looked it over much yet. Im assuming 630v is enough on the regular caps because of their sizes. I do see a little work done on it, but not as much as I usually see on 1930's radios. Someone hacked a newer cord onto the cloth one to make it longer so it was likely working for a lot of years.

There are no markings on the electro cans other than the maker. 450 volts it is! I need to order them before I start on it, but I will test the transformer 1st cuz Im sure a replacement would be difficult to locate. Its the 1st cathedral style Ive done. Thanks guys! If I proceed with it I may have another question on the multi-section resistors, or not.

It looks like your radio is very similar to my 1932 U. S. Gloritone Cathedral Radio which was made by the United States Television and Radio Company of Marion, Indiana and my radio is a 5 tube set with a 47 Output tube, and 80 Rectifier Tube, a 27 Tube, and 2 35 tubes and on mine someone had already replaced the orginal cloth cord with a reproduction cloth cord that they attached to its original Bakelite plug end, and recapped the radio, but unfortunately it was never realigned and I can see why, its because all of the IF Can alignment points are under the chassis which means the radio has to be out of the cabinet for the alignment process which could be dangerous because you're working around a live radio chassis and one slip could put you into contact with 600+ volts DC.

init4fun · #6 01-04-2021, 04:58 AM

Quote:

Originally Posted by vortalexfan

.... and one slip could put you into contact with 600+ volts DC.

Quote:

Originally Posted by init4fun

.... it looks like around 225 V is the highest B+ voltage listed on the schematic ......

vortalexfan · #7 01-04-2021, 01:35 PM

Quote:

Originally Posted by init4fun

I was using that as a means to make a point, that there is a lot of high voltages inside the radio that you could get into contact with if you were to slip while trying to do an alignment of a radio that has its alignment points on the bottom of the chassis...

init4fun · #8 01-04-2021, 04:56 PM

Quote:

Originally Posted by vortalexfan

I was using that as a means to make a point, that there is a lot of high voltages inside the radio that you could get into contact with if you were to slip while trying to do an alignment of a radio that has its alignment points on the bottom of the chassis...

"Making a point" while properly explaining the risk is the right thing to do . Making a point while grossly exaggerating the risk is needless sensationalism and has NO place in a technical discussion ! Give good and factual advice and I'll back you up 100% . Post up the kind of Malakas you posted about 600+ volts in a radio whose B+ goes no higher than about 250 and you can EXPECT to get called out on it . Every time !

fixmeplease · #9 01-04-2021, 09:02 AM

A lot of old radios were copy cats so i wouldnt be surprised of similar ones. I have an isolation transformer. Im allergic to B+ voltage, lol Ive only aligned a couple as most sound ok.

The capacitor pack will be the fun part as the new caps someone put in were bypassing that. They pretty much hacked them in but apparantly it worked. Im thankful I have a schematic as that pack would be difficult otherwise. I think when I counted there are 10 wires that attach to it. Ive never cleaned out one of those cans before so hopefully that goes well. it may just be easier to fab a new can to put the caps in than to remove all that hardened goo in the winter time.

Electronic M · #10 01-04-2021, 07:45 PM

B+ shocks are fairly easy to avoid if no part of your body is touching anything grounded. If no part of your body is touching anything grounded or electrical and you grab B+ you won't be harmed or even feel it....you are essentially (as linemen call it) a bird on a wire. Birds land on energized power lines carrying several KV and are not harmed by it because they are not touching anything else at a different voltage thus no current is flowing through them.
When doing live underchassis work like voltage measurements or alignment I try to keep one hand in my pocket and avoid touching grounds. That way if I touch B+ I'll do it in bird on a wire mode and not be harmed.

Another practical example of this is something that happened to me as a teenager. I was steaming off the wallpaper in the kitchen of my parents last house close to a switch plate an standing barefoot on the brick floor of the slab the house was built on (in short I was standing barefoot on earth ground) touching the wall anywhere within 1' of the plate I got a pretty good electrical tingle. I mentioned this to my dad who was wearing rubber shoes and he came over, touched the wall and couldn't feel it and was wondering if I had lost it.... After a moment of wondering WHY he couldn't feel it I told him to take off his shoes and touch the wall. THEN HE FELT THE IT!