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  #31  
Old 01-12-2018, 07:49 PM
old_coot88 old_coot88 is offline
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Please don't mess with video alignment without first checking for plate and screen voltage on the IF tubes, and that their heaters are lit.

The set uses intercarrier sound. So you'd think that with a dead video IF stage, it'd kill the sound too. But since the sound carrier is FM, it could be going through by capacitive coupling.
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  #32  
Old 01-12-2018, 08:19 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by old_coot88 View Post
Please don't mess with video alignment without first checking for plate and screen voltage on the IF tubes, and that their heaters are lit.

The set uses intercarrier sound. So you'd think that with a dead video IF stage, it'd kill the sound too. But since the sound carrier is FM, it could be going through by capacitive coupling.
Fair enough. I'll check those voltages.
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  #33  
Old 01-12-2018, 09:07 PM
Crist Rigott Crist Rigott is offline
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OK, here's what I measured. There was no signal to the antenna terminals.

Also the "mains" was only at 114VAC. Hence the low voltage on the heaters and B+ was only 237V. When the mains was brought up to house voltage of 124VAC, the heaters went up to 6vac and B+ went to 257V.

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  #34  
Old 01-12-2018, 09:46 PM
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jr_tech jr_tech is offline
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Got to get some plate voltage to pin 2 of the 6J6 for openers...perhaps the 15 k resistor in A4 is open?

jr
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  #35  
Old 01-13-2018, 12:25 PM
Crist Rigott Crist Rigott is offline
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Originally Posted by jr_tech View Post
Got to get some plate voltage to pin 2 of the 6J6 for openers...perhaps the 15 k resistor in A4 is open?

jr
Yeah, I agree. I checked that resistor. It ohmed out to 21K. I'll pull A4 and replace that resistor too.

I went through the tuner last night in great detail. No problems found except that resistor.
I have another tuner and I'll clip lead the tuner in and try it then swap tuners and try it again.
Then go on to an alignment.
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  #36  
Old 01-13-2018, 01:53 PM
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jr_tech jr_tech is offline
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If it has only increased to 21K, I doubt that the voltage would drop that much (75 to 8.2 volts)... is the 6J6 ok?

jr
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  #37  
Old 01-13-2018, 02:02 PM
Crist Rigott Crist Rigott is offline
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Originally Posted by jr_tech View Post
If it has only increased to 21K, I doubt that the voltage would drop that much (75 to 8.2 volts)... is the 6J6 ok?

jr
Yeah, I agree. I'll swap out the 6J6 next time.
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  #38  
Old 01-13-2018, 02:06 PM
Crist Rigott Crist Rigott is offline
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I pulled A4 1st IF transformer off the tuner to replaced the 15K resistor. It consists of the 15K resistor, a coil, and 2 mica caps at 10pf and 130pf.

Here is what it looks like:



I was expecting some "real" mica caps. Now I'm concerned that those caps could develop silver mica disease. I'm having some real trouble getting a cap reading on each of those with my cap checker. I could cut them in half and install real mica caps.

What do you think?

Last edited by Crist Rigott; 01-13-2018 at 02:10 PM.
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  #39  
Old 01-13-2018, 04:36 PM
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jr_tech jr_tech is offline
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Is the 10 pf leaky to ground? that could pull down the plate supply to the 6J6. Otherwise, I think that I would leave them alone, and try to figure out the reason the 6J6 plate voltage is so low first.

jr
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  #40  
Old 01-13-2018, 04:55 PM
old_coot88 old_coot88 is offline
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With the 6J6 removed, check the voltage at pin 2 (plate), and see if it still lugs down.

Dittos to jr_tech on leaving the caps alone unless one is leaky/shorted. Their values are for bandpass-shaping so are fairly critical.

Last edited by old_coot88; 01-13-2018 at 05:04 PM.
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  #41  
Old 01-13-2018, 08:58 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by old_coot88 View Post
With the 6J6 removed, check the voltage at pin 2 (plate), and see if it still lugs down.

Dittos to jr_tech on leaving the caps alone unless one is leaky/shorted. Their values are for bandpass-shaping so are fairly critical.
I checked the voltages on V1 and V2 with the tubes removed.
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  #42  
Old 01-13-2018, 09:04 PM
Crist Rigott Crist Rigott is offline
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Well Late this afternoon I decided to replace the mica caps in A4. I thought that while I had it out, why take the chance. I replaced them with 500V 5% micas. I had the 10pf but didn't have the 130pf so I put 2 in parallel. When I checked them with my cap checker I got 129pf. Good enough. And I also changed out the 15K resistor which read 23K once removed. BTW, all the caps in the tuner were replaced using carbon film caps.



I re-installed the tuner and I now have a much better picture.



On to the alignment.
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  #43  
Old 01-13-2018, 09:26 PM
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jr_tech jr_tech is offline
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Excellent! did the plate voltage on the 2 6J6 plates change?

jr
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  #44  
Old 01-13-2018, 09:30 PM
Crist Rigott Crist Rigott is offline
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Excellent! did the plate voltage on the 2 6J6 plates change?

jr
I haven't checked it. I'll do that and report back.
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  #45  
Old 01-13-2018, 09:52 PM
Crist Rigott Crist Rigott is offline
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Yeah, I have 137V at pins 1 and 2 of V2 the 6J6.
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