Philco 19B Open IF Trans?? - Printable Version
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Philco 19B Open IF Trans?? - hunter2115 - 12-27-2013
Ive been working on a nice, original 19B Code 123 and have run into troubles.
http://www.philcoradio.com/tech/images/19v5.jpg
I have a thread going on ARF and hope to get some input from "the Philco Experts".
From what I have seen, the radio was never previously worked on. All components, including the two electrolytic cans, are original. I re-stuffed the electrolytics, checked the tubes, and tried the set. I got nothing but a low steady hum that is controllable with the volume control. I went ahead and replaced all the caps in the blocks and checked the resistors. Still no reception at all-nothing. I have not yet replaced the caps in the tone control as it looks like it will require some disassembly. I also have not checked the shadow meter coil.
I checked tube socket voltages and Im only seeing 100v on the 36 oscillator plate. Other voltages seem reasonable. Im not the greatest at checking coils, but im finding "sets" of pins on the Antenna, detector, and oscillator coils that add up to close to what the schematic says. 2nd IF looks good as well. Antenna post to chassis ground = 27 ohms.
However, I cannot find the secondary winding on the 1st IF transformer. There are two compensating capacitor trimmers on the back wall of the chassis.
Measuring between the top and the bottom terminals of the IF primary yields 55 ohms- good. Measuring between top and bottom terminal of the IF secondary shows open/high resistance.
My questions are:
Is this a reasonably accurate way of checking the two 1st IF trans windings, and if so, does it in fact indicate an open 1st IF secondary?
Would this account for the low 36 plate voltage?
Could the old tone control caps or shadow meter coil shut down all reception if defective?
RE: Philco 19B Open IF Trans?? - morzh - 12-27-2013
1. If you are sure of the pins and the coil shows openm then, well, tis open.
2. If the coil is the primary and so it is the load, that is it is between the plate and the plus voltage then yes, it will make the plate volrtage near zero.
RE: Philco 19B Open IF Trans?? - Mondial - 12-27-2013
If you are measuring across the 1st IF transformer compensating capacitors then you will get an open indication on the primary because this cap is not directly across the winding. The primary is also part of the autodyne oscillator circuit. The secondary compensating cap is directly across the secondary so you should get an indication there.
The voltage on the 44 RF stage plate and the 36 converter plate should be about the same as they are both fed from the same B+ supply decoupling resistor. If the 36 plate is significantly lower, then something is wrong with the IF primary or the oscillator winding as they are both in series with the plate B+ supply.
You can try checking for oscillator output by placing a transistor radio near the osc coil, tuned to a freq 260 KHz higher than the Philco's dial freq. You should hear the carrier as the dial is tuned if the oscillator is working.
RE: Philco 19B Open IF Trans?? - hunter2115 - 12-28-2013
Heres what Im seeing on the oscillator coil. Reading clockwise from the top:
pins 1 & 2 = 5.4ohms and cont
pins 3 & 5 = 5.4ohms and cont
K of 36 tube connects at pin 1
P of 36 tube connects inside coil and shows up at pin 4 of coil with 5.2ohms and cont to 36 socket plate pin
This says to me that the osc coil is probably not the problem. The 1st IF trans probably is.
RE: Philco 19B Open IF Trans?? - Mondial - 12-28-2013
Yes, I would agree that the osc coil looks ok as the resistance readings are exactly what they should be.
Can you measure the resistance from the 44 RF amp plate to the 36 plate? This should read about 67 ohms if the 1st IF primary is good (2 ohms RF plate coil + 5 ohms osc coil + 55 ohms IF primary)
RE: Philco 19B Open IF Trans?? - hunter2115 - 12-28-2013
44 RF plate to 36 plate = Full blown open.
I guess that settles that. Also guess I need to start looking for a 260KC transformer.
I will pull it tomorrow and see what it looks like. Maybe it can be fixed.
Thanks for the help ID'ing the culprit.
RE: Philco 19B Open IF Trans?? - hunter2115 - 12-28-2013
Confirmed- open winding on the 1st IF transformer. I think its the primary, but the wiring attaches to the secondary trimmer?? Anyway, its the winding that connects to B+ . Cant see any breaks when looking over the coil so it must be deeper. Very simple looking coil. Guess Im looking for a replacement or somewhere to have it rewound.
How critical is the accuracy of the winding?
Im thinking that any 1st IF trans from a Model 19 or 89 would work. 260KC with 56 ohms on the primary and 56 ohms on the secondary.