Philco 16b-Measuring voltages
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I have a 16b cathedral that has all the caps replaced, and it is playing fine. I am trying to do voltage measurements to see where things are at. My experience is mostly on Zenith radios where all voltages are measured to the chassis.
I see on the voltage chart that I measure P to K, SG to K, CG to K, and K to F. P to K voltages are pretty close. The others are nowhere close.
What is the way to measure Philco voltages?? I am using a Micronta with a 250K resistor in parallel to simulate the load.
I'm sure that this is a question that will become obvious to me once someone sheds some light on it.
Any help is appreciated!
Thanks
Chris
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Are the readings too low or too high?
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Some are too high, and others are too low. That's what is so confusing.
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Does it list any particular conditions to the measurement (tuned or not, volume, tubes in socket or not and such)?
Also you did not indicate if the resistors have been checked and/or changed.
To be truthful, I did not have all the voltages correct either on my 20. All works fine. But the detector (I think) lists some 30 something volts and it is over 100.
I rtried to ask here, got no clear answer. All is fully recapped, resistors are all cjanged. After all, 20 is a very simple radio, not much to it.
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The resistors will be getting changed over the next 2 weeks. I found enough out of spec that I ordered a complete set of what I need and will simply replace all of them. One problem is that the schematics show the 5YZ as rectifier and my model runs the 80. Voltages are a bit lower on the plates. The directions didn't have much detail to them. I have my 1st AF showing 45 on the plate and it is spec'd at 130, and I have my AVC showing 45 on the plate and it is spec'd at 1.8. The other plates are all on target, so I'm guessing I'm doing something wrong here-that's why I asked. Even with the original resistors in it, it is really a great performer.
I just don't understand why Philco radios had voltage charts set up like this. It doesn't make any sense to me.
I'll replace the resistors and record my voltages. That way if there is a problem in the future I'll have a baseline reading.
Chris
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I would go with the measurement points suggested in the service data. Many of these 1930s sets don't really have a common negative to everything because of the bias networks they have set up so they use voltage measurements with respect to cathode or "K" as a reference point which is as close as one can get to common negative. The plate will always be positive with respect to the cathode, same with a screen grid, the control grid will usually be negative with respect to cathode. It's hard to say how much the original voltmeter would have loaded the measurements down, if it was a standard analog voltmeter it would have, if it was measured using a VTVM then it would not have. I would just measure the values of the carbon resistors and forget the voltage chart, if any are more then 25% out change them, if any voltages are way out then those would be the cause anyhow.
Regards
Arran
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The schematic that shows a 5Z3 rectifier would be for a 16X (console version). The 16B uses a type 80 rectifier.
As far as the voltage reference point, it would only mater for the RF and IF tubes. From the second detector on, K and chassis ground are one and the same.
Steve
M R Radios C M Tubes
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Also, remember that you are using vic 10 more volts from your wall socket. This will affect all of your radio's voltages.
The values listed are not exact, especially as a set ages. Replacing out of spec components will help, but the resistance of coils and transformers has probably also drifted.
These old sets are not precision pieces of equipment. The more you work on them, the more of a "sixth sense" you will develop about what is OK and what is not.
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Thanks to all of you for replying! This will help me better understand the radio. I wasn't aware the 16x was the console and 16b was the cathedral!!
Chris
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Most Philco voltage tables were measured with only a 1000 ohms per volt volt meter, which loads circuits down (your resistor). Also AC
line voltage was usually specified at 110-115 VAC.
That's why I use a variac on the AC line and a 100 ohms-per-volt DC voltmeter and not a VTVM or a newer hi-Z multimeter.
Many times this is written out and specified right on the Philco Service Bulletins in the aligment section.
Chuck
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