Philco model 18 (code 121) - HELP!
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Pith, I agree with Ron on close help, it is really hard to do here. Again, if you bypassed the choke and still didn't get any voltage on the 42 plates, there is just not a problem with the choke. Again, assuming you hooked the resistors across the choke and not somewhere else. Simple DC measurements across the choke should let you know. Measure from ground to one side then the other you should get some whapping DC voltage on both sides.
Jerry
Edit: Mike I should add a note here, Pith did PM me and indicated he added 20 watts of 50 ohms (what he had) across the choke. Again an assumption he got it in the right spot. No offence Pith. Still got nada on the 42 plates. If indeed he put that resistor in the right location, it would indicate to me that either nasty connections on the speaker plug or field coil problem. One reason why Pms are not the best way to communicate problems.
A friend in need is a pest! Bill Slee ca 1970.
(This post was last modified: 08-02-2013, 05:51 PM by jerryhawthorne.)
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City: Sunny Michigan
I just noticed the culprit (I hope) the bond on the 10 mfd cap broke.
I'll have to re-solder that and take measurments again.
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I re-soldered the 10 ufd cap but then I found my multi-meter wasn’t working properly (it’s old anyhow) so I order a new one. It came in the other day.
I just checked the resistance (set OFF) across the two 8 ufd e-caps and got nothing.
Looking at the schematic and going on what you’ve all said, I think it’s safe to say that the filter choke is open. Additionally, after I got my new multi-meter, I re-checked the DC voltages on the P-K of the #42 tubes and go zilch.
I have no idea what size/type of transformer to buy. The schematics show 166 Ohms but I can’t find any information on what I’m looking for.
Ideas?
Thanks.
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Pith, please read my edit note on post 181. If indeed you placed a resistor across the the two e-caps and did not get any HV it does not sound like the choke is open or if open you have other problems. Your resistance measurement seems like it is. One other check please, DC on your meter set for HV reading and measure ground to one side of the choke and then to the other (radio on and be careful). That would be ground to one + on one e-cap and then ground to + on the other. Your PM information has me confused, as I usually am.
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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Jerry,
This time I put the resistance 'jumper' across the two positive points of the e-caps, re-measured the #42 and got nothing. Then I measured from positive e-cap to ground (DC) and got a few big sparks but no voltage measurement (?). Then I measured the #80 tube got a few big sparks again? But no DC voltage reading.
I checked the tubes, they all 'light up' but I know that doesn't mean they work properly and I don't have a tube tester.
I think I'm just going to start taking continuity readings for every connection and highlight on my schematics where I don't get any readings. At least that way I might be able to pinpoint the vacinity of the problem. Not gonna lie, that will take me a while especially since I'm going away this weekend.
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Pith, we both need a weekend off/
Once again I'm a little confused how you can get a spark measuring from the B+ to ground and no reading on your meter? Is your meter toasted? Got another?
Regards and confused Jerry
A friend in need is a pest! Bill Slee ca 1970.
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Story of my life Jerry, I jump into projects not knowing a thing about them (although I've learned a lot on this on in the past year) I have a college electronics book from 1964 that I got at a used book store which has all the components of the radio spelled out in it that I've been reading--though not recently. I just need to revisit that book and continue on.
I didn't realize I was this stubborn, but I am I guess. I don't remember 'Quitting' anything, but I tell ya what, this is definitely what's known as 'Doing things the hard way'. I'm not going to pay someone to fix this radio, that would sort of defeat the purpose in my opinion, although I will start looking more into yours and Ron's advice about finding someone local...although, would they be as willing to help me as much as I need it?
Follow ups to come, have a good weekend!
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Simple: you have you meter on Amps or Ohms maybe, but not on Volts.
Will pull sparks. Will also kill the meter.
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After doing more research on the circuit as a whole I found all tube P-K voltages (except for the #80) tube were very low, like anywhere from a few volts to .05 volts. The #80 tube which should be about 350 volts is at 480 volts.
It’s a complicated circuit, but I thought that maybe the power was coming through the transformer and stopping at the rectifier (#80 tube) as I don’t have a tube tester I just bought another #80 tube. Checked all the voltages again and got the same numbers.
This made me think that maybe the power transformer was the problem? Let’s assume that the power transformer is the problem. It looks like there are several wires coming out of the transformer, I might be able to remove and test the transformer however I have no idea how to do that.
How do I test the power transformer?
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Pith it doesn't sound like your power transformer or the 80. Your power supply sounds fine. I'm making the assumption that your 80 voltage reading was DC from the filament to ground. Let us know if it was something other than that. Some where the power is not getting to the radio so there is no load. No load means the 80 will read high. Speaker plugged in? Test field coil for open. Check large wirewound resistors for open. Follow the schematic from the cathode (filament) of the 80 and see where you loose it.
Regards, Jerry
A friend in need is a pest! Bill Slee ca 1970.
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Hi Jerry,
For the 480 volts I went from Plate to Filament, I checked across the #80 tube from one of the two ‘P’ pins to the opposite ‘F’ pin using DC.
Ok, I’ll start from the cathode (filament) of the 80 and see where I lose current.
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Silly question (sorta) but I wanna check the circuit using AC voltage on my meter, correct? And then check for a voltage drop using AC current from point to point, to point etc?
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Pith, go to DC on your meter and check from the filament (either of the two large pins on the 80) to chassis. This should give you somewhere around 280V DC. Set your voltage on the meter high. I'm guessing as have not looked at the schematic. If you have a nice high DC voltage, your 80 and power transformer (for the HV) is working.
Report back, with haste!
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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ok, I'm getting 467V DC from big pin (F) to chassis. So, the transformer must be ok then even though it's almost 200 volts above where it should be?
I'll check for a voltage drop from that point on.
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Yes Pith, I was guessing but based on a load on the circuit. I'm guessing it is unloaded due to an open field coil or choke if it has one. Chase the voltage on your schematic something is open. Seems your transformer and rectifier are in great shape.
Regards, Jerry
A friend in need is a pest! Bill Slee ca 1970.
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