Checking B+ voltage. . . .newbie - Printable Version
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+--- Thread: Checking B+ voltage. . . .newbie (/showthread.php?tid=16277)
Checking B+ voltage. . . .newbie - conceptchris - 02-21-2017
I am relatively new to the electronic restoration and understanding of these old sets, so bear with me here. I can solder, replace parts, caps, controls, use a multimeter, but as far as understanding, processing, and diagnosing electronic issues, I am a novice. I have been reading up on things to check and do when it comes to the electronic restoration of these sets and understand most of it except that I have not found a good description of how to actually check B+ voltage or what this even tells us. I have a vague idea, but no hypothetical light bulb has gone on for me with this. I have 2 very similar sets doing different things and I was going to try and attach these sets as real world applications involving the testing of B+ voltage and what this can tell me in these 2 cases, if anyone has the time to explain.
Case#1. Philco 37-610 - recently cleaned, replaced bad volume pot and all caps including electrolytic, filter bakelite, and paper with correct values, above recommended voltage ratings, and good clean solder connections. The electrolytics used were older unused multisection can types that tested good before installation. After all this and checking tubes as well, the set played with no hum or distortion, however volume level was not as high as it should be, not many stations picked up on the am band (more came in with the short wave band), and after 1/2 hour of playing the volume dropped dramatically, a burning smell started, and after shutting off I noticed that one of my multisection electrolytic caps was physically leaking out the bottom of the chassis.
Case#2. Philco 37-630 with shadow meter - recently acquired from someone who just replaced all the electrolytic, filter, and paper caps, and power cord. Tubes were supposedly checked and tested good. Previous owner said that the set still slightly hums, no stations come in and no static or volume at all, just silence, and that the (metal) 6f6 power tube "overheats". He had mentioned that this made him concerned about the power transformer. Can someone help me to understand how he came to this diagnosis and how an overheating power tube can point to the transformer, or if this guy really has no idea what he is talking about. . .
I want to learn to be exact and knowledgeable about this, not just throw parts at it until it works.
Thanks in advance
RE: Checking B+ voltage. . . .newbie - morzh - 02-21-2017
For leaking lytics - check the polarity, voltage rating AND ripple current rating especially if it is the #56.
Also check the rectifier tube for shorts.
Now as for the B+: in 37-610 simply put your DMM between the Chassis GND (clip onto the chassis itself) and the "+" of the lytic cap #53.
What it tells you....well, simply stated it tells you that the radio has been powered and the plate voltages have their power source working. After that, whether or not any given plate receives the power is still unknown and has to be checked with the DMM.
RE: Checking B+ voltage. . . .newbie - Radioroslyn - 02-21-2017
Case 1 pull the 5Y4 tube and measure the ac voltage from pin 4 to pin 6. Remember to count the pins backwards as you are looking at TOP of the socket not the bottom. Should see about 500 to 600v there. If not your power transformer is bad and you will to replace it. The lowering volume is a sign that the p/s was slowly dying from the filter cap shorting. If voltage is ok then replace the 5Y4 w/a good one and the filter caps.
Case 2 > if this guy really has no idea what he is talking about. . .
Methinks ur correct. First off measure the dc voltage from chassis gnd to pin4 of one of the 6F6 tubes. Should see a few hundred volts. Next measure the voltage from gnd to each of the 6F6 tubes on pin 3. Again should see a few hundred volts. Do likewise with pin5. Should see -10v or so there.
RE: Checking B+ voltage. . . .newbie - Old Tube - 02-21-2017
Thanks Conceptchris for asking this question. I too am a newbie to this hobby. I think you got a good explanation to B+ voltage and how to check it. Hope you find the problem with your radios.
Don
RE: Checking B+ voltage. . . .newbie - conceptchris - 02-21-2017
Great responses, thank you so much, I will get to checking these things asap. BUT, one really basic and dumb question. . . Should these checks be done with the set plugged in but off? or should all voltage checks be done with the set ON? I'm guessing that it will need to be on for voltage to be present in most of these locations, I just want to be 100% sure before I roast something. . . . dont judge. . .
RE: Checking B+ voltage. . . .newbie - Radioroslyn - 02-21-2017
On!!! Gotta let the juices flow!!!!
RE: Checking B+ voltage. . . .newbie - morzh - 02-21-2017
Well, let's put it like this: if it is not plugged in, there is no B+....or any other voltages or currents.
Now that you said you are new to this, when you measure resistances or capacitances, or continuity etc - the power is OFF.
RE: Checking B+ voltage. . . .newbie - conceptchris - 02-21-2017
Ok, thanks for clarifying. This seemed glaringly obvious to me, but I have been known to be wrong at times, just checking.
RE: Checking B+ voltage. . . .newbie - Kenneth F. Besso Jr. - 02-21-2017
don't worry ,,we all have stuck our tongues on something that was live ,,,one time or another,,lololol