Model 60 fun - Printable Version
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Model 60 fun - Simon Wa3uay - 01-03-2021
The Library’s ‘Evolution of Philco Model 60’ explains a lot about this little monster.
I have two discrepancy’s from the one I’m working on; a ‘Run 6’ which is the latest one.
1, the coil resistances in (25), the Second IF, measure 33.7 ohms (primary) which is ok, but the Secondary is 45.3 and should be 85 ohms according to the print. I yanked it out of the chassis for inspection, but no obvious blemish.
2, on the IF tube (78) the Screen Grid volts (SG to K) is 75 volts DC. Table 1 wants 120. I swapped the tube for a 6D6, same result.
Will either of these prevent reception of stations?
When Philco changed the Second IF part number on ‘run 6’, is it possible that the 85 ohms was changed to the 45.3 that I’m getting?
I get plenty of noise, which originate Within my humble abode including 460 Kc so maybe the wave trap will work for me!
I have recapped and re-resistered almost everything, and the tubes are good. AF works good, but no RF being mixed or detected. I get lots of noise when touching the mixer grid. With antenna, noise only.
When I put 465 Kc modulated IF to the plate of 78 tube, I get nothing. But then also, there is that low voltage on the screen grid.
I rewound the Antenna coil primary (.7 ohms)
I checked the Osc coil, it’s ok.
Hoping everyone had a great New Years,
Simon
RE: Model 60 fun - Radioroslyn - 01-03-2021
Neither the lower sg voltage or the coil resistance would seem to be a fatal fault. Using a 6D6 for the 78 is a bad idea. Electrically they are similar in reality they don't work.
I would try applying a 460kc modulated signal to the grid of the 78 or the plate of the 6A7. This way there won't be any adverse effect from the generator loading the circuit and you can peak the IF trimmer(s) that are downstream. If you really think the 2nd if trans is bad you can use a 455kc can from the junk box to give it a try.
Happy New Year!
RE: Model 60 fun - radio1 - 01-03-2021
Strange you get 45.3 vs 85, did you measure it unconnected? Check the feeding resistors again.
RE: Model 60 fun - n1ps - 01-03-2021
Hi Simon...agree with Terry above. Put the original IF tube back in. Lower G2 volts only affects the gain of the stage and not a major thing. I would not be too concerned with coil ohms....nothing open?
Check all the voltages for the RF/IF/mixer stages. The grids should be a little negative. The best tool to check IF and RF stages is a scope. So you have one? You can also try the old trick of placing another radio near this radio ( a portable) to see if it hears the osc....455 + dial freq.
Peter
n1ps
RE: Model 60 fun - Radioroslyn - 01-03-2021
Just out of curiosity did you replace the two 110mmfd caps in the det/avc circuit? Some think there micas but some know better.
RE: Model 60 fun - Simon Wa3uay - 01-04-2021
Terry, I think I will put it back in- and try the things you suggest with the SG...and I did take the 6D6 back out. I don't have a 2nd IF in my junk box, but I do have another 60 I could rob....
Brobertson, yes I did check it out of circuit. it's the same. I will check the feeding resisters again.
n1ps, it's definitely not open, and no signs of trauma...I wish I had a scope that works! would be nice. You know, I forgot about "that old trick"; I have a 590s nearby that I bet I could use.... unscrew the coax and clip some wire to the center...
The grid volts on 6A7 det. osc. is -.18 (normal), and is a little higher than specified on I.F. and 2nd Det. (about -.3)
Radioroslyn, I did NOT replace them! maybe that's what's going on!
Thanks guys...will keep working on this, will let you know how it goes!
-Simon
RE: Model 60 fun - Simon Wa3uay - 01-14-2021
One of the .00011 caps tested good (in circuit) Terry, the other wouldn’t give a reading, and was so entwined with other parts I just cut the sucker out and replaced it. It tested good out of circuit (oh well!).
Replaced one resister that was marginal, Brobertson, and fired her up; lots of RFI!! But hear stations.
Tweeted IF trimmers, peaked the Osc at 600 Kc still a lot of crap noise; my house is full of RFI!!
Anyway, I’m cleaning off the chassis top now, then putting it in the cabinet, will see how it works then.
Thanks, one and all
73 Simon