About three months ago I sent an audio interstage transformer for a Philco 38-690 (Part 152 on attached schematic) off to Heyboer Transformers to be rebuilt; it had an open primary. Just got it back today and the resistance readings are WAY off:
Primary should read 475 ohms. It reads 186. There are two secondaries that are supposed to read 260 ohms. Each reads 64-73 ohms. The third secondary reads a few ohms; not sure what the spec is, as it is not listed on the schematic.
What should I do? How crucial are the exact resistances? These seem pretty far off; send it back to Heyboer? Give it a try?
PS: Ignore purple marks; they are not pertinent to this question.
Did you provide them with the resistances for each of the coils on the schematics, or a copy of the schematics, when you sent it off to be rebuilt ? If you did, you would have a better ground to stand on with a complaint. Otherwise, they may have just guessed.
As morzh said, "Well, if you give them a transformer they should gauge the gauge and count the turns. I mean, Heyboer are pros." and as the Romans said, "Erare humana est."
Thanks for the advice, all. I ended up corresponding with two gentlemen who'd had the exact part re-made for them by Heyboer. They noted diffferent ohm readings (likely due to thicker wire being used) but both said the part worked as it should, despite the difference from spec. That was good enough for me so I reinstalled the transformer yesterday, and finished up recapping the power supply. It will be a while before the set sees any power; for now though I'm finally making progress again. I have to say, Heyboer impressed me. They repainted the bell and even used the same color code transformer leads as called for in the schematic. Pretty great! And all this for $90+shipping. That can't be beat, far as I'm concerned.
Now to the hard part: The receiver chassis (GULP).
Quick question: Does anyone know where I can find a voltages chart for this radio? Trying to troubleshoot the set (currently DOA) and just realized that the packet I got from Chuck at the Philco Repair Bench doesn't include a voltage chart. I'm surprised Philco didn't produce one, as I know Chuck's packets are pretty comprehensive. Thank you.
No voltage chart was ever published as far as I know. It appears that Philco did not produce one of their usually fairly well-documented Service Bulletins for this model - just a schematic, under-chassis drawings, and parts list.
Once you have established the B+ power and your filament voltages are OK (easily detectable), start mapping voltages across the tubes.
It is normal for anodes of most tubes to be at high enough voltage (100V-250V, or a bit more in case of audio output ones), the screen grids should be also fairly high, almost equal or a bit less than anode voltages, control grid is at low DC potential, and Suppressor grid is at Cathode potential.
Absence of Anode voltage is a good indicator of the load open, like the primary of an interstage RF/IF transformer.
Voltage chart helps but I rarely actually look at voltages against the chart values, I just look at the absent/present and the value if it makes sense. Like, on a plate detector Anode voltage of 250V does not make sense. It should be much lower. On the other hand in the output pushpull stage Anode voltage of 80V does not make sense - should be almost as high as B+.
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.
Huh. That's too bad; thanks for that info though.
Replaced all the electrolytics, checked tubes etc and brought it up for the first time today .... Deadsville. Not a peep out of the speakers. I was hoping it would be something simple like a blown fuse in the AOT, but no such luck.
This radio came to me with two blown 6L6 tubes and that open interstage transformer, which was replaced by Heyboer (see posts above) and re-installed. The power supply chassis has been recapped, and the five-section lytic in the receiver section has also been replaced. All the tube heaters are lit; getting 300-sometthing volts in the 6L6's, but the other two tubes in the power supply (6F6 and 6J5) are giving odd readings, not much voltage going through them.
I'll continue checking the loads on the tubes for now, and double checking my work. We shall see
Any other suggestions?
(This post was last modified: 06-30-2015, 04:25 PM by Diverted.
Edit Reason: Clarity
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Start your check with pulling the rectifier and checking the AC outs.
Power down.
Then measure the load across the rectifier output, check if short is present.
If not, put rectifier in, put the loads (speakers) in, power up, briefly see if the DC develops and where it goes, once reached about 500V it should go down a bit and stabilize. Watch for smoke.
Power down AND watch the DC going down. If very slow, you have no load. If fast (second or few) - OK.
Once this is OK, start measuring voltages.
Check the transformers' continuities, check speakers.
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.
Started looking at voltages in the power supply chassis. I'm getting about 330V on pins 3 and 4 (plate, grid) of the 6L6 output tubes. I'm getting no measurable voltage on the other two tubes in this chassis, apart from -5 on pin 5 of the 6J5 and -16 on pin 5 of the 6F6. There is voltage elsewhere in the power chassis. For instance,
274 on one side of choke #167, 260 on the other. Other places where I would expect there to be voltage, such as the non-grounded side of the non-polarized cap feeding the tweeter, I'm getting nothing.
I wish I could give you a better description of what's happening; just having a tough time tracing out this voltage; pretty complicated schematic!
If anyone can point me in the direction of places to check for specific voltage w/in this power supply, I'd sure appreciate it.
Thank you.
EDIT/ADDITION:
Plates of the two transformers are giving good AC. Getting 280 off the plates of Transformer 178, and about 340 on the plates of Transformer 179.
Also: Speaker coils all check good; field coil, audio output transformer etc.
(This post was last modified: 06-30-2015, 09:55 PM by Diverted.
Edit Reason: additional info
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