1935 Philco 144 - Printable Version
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1935 Philco 144 - PhilcoPhan1936 - 05-23-2020
I'm working on a Model 144B for friend and fellow member Scott D.
Have run into some issues after doing a re-cap and replacing some out of spec resistors.
1. Wave trap was missing. (Spare 44 chassis has been purchased for parts)
2. Radio is deaf as a post, not even static on all bands except very end of upper SW band.
(I have clipped into circuit a wave trap from a 645 chassis, but part numbers are not the same)
I'm going through and checking EVERYTHING.
I found the B'cast band antenna coil had an open.
(Internal spool looks toasted).
I pulled it and reconnected the end that was broken off, and it now measures 40 ohms.
There are no specs on the diagram. Is this anywhere near what it is supposed to ohm out at?
The other coil (outer winding) checks in at 4.7 ohms. (This is coil 8 on the diagram).
I'm still in process of checking all other coils and making sure all connections are as they should be.
Diagram for reference:
RE: 1935 Philco 144 - RodB - 05-23-2020
Hi Jeff - I would try feeding a modulated 460 KHZ IF into the control grid of the 6A7. If that works then you have a large part of the circuit that works. Then you can work backwards through the switch with different frequencies. Or maybe the oscillator isn't running.
If the IF doesn't work then move forward to the next control grid until you get a signal.
Rod
RE: 1935 Philco 144 - morzh - 05-23-2020
Jeff
1. Ditch the trap, it is not needed.
2. You need to make sure at least that your audio section is alive.
Everything from the speaker, output xfmr and back to the 1st AF (touch grid, hear hum).
Then go about other things.
RE: 1935 Philco 144 - PhilcoPhan1936 - 05-23-2020
The audio section is working. I do get an audible hum, and a buzz when touching the cap of one of the tubes, and like I mentioned, I did get static from the very top of the upper SW band.
Will continue running tests and checking circuits today.
Thanks for the tip RodB.
I’ll poke around and see what happens.
I have a spare chassis on the way that I can hopefully borrow good parts from.
RE: 1935 Philco 144 - Scott D - 05-23-2020
I am curious why morzh thinks the wave trap is not needed? Was it just a gimmik? I always thought is was put there for a reason - to help tune the signal from the antenna. What am I missing? Thanks for taking time to help me understand.
RE: 1935 Philco 144 - morzh - 05-23-2020
Scott
There were some military/govt coastal /maritime stations that worked at frequencies close to the IF, so the wavetraps attenuated the signal from those stations.
These stations no longer are in service so there is nothing to protect from. So a bad wavetrap can be simply removed with no ill effects today.
RE: 1935 Philco 144 - Scott D - 05-23-2020
Thanks! It's always good to know why.
RE: 1935 Philco 144 - PhilcoPhan1936 - 07-20-2020
I'm still in a quandary with this chassis. We ordered and received a 44 chassis, in hopes of doing some organ transplanting.
The antenna transformer coil has been replaced. The replacement from the 44 was an exact replacement (Part #2 in the Schematic) and checks out.
It turns out the 1st IF coil has been replaced with a non-Philco part.
I jumpered in the 1st IF from the 44 chassis. The part numbers are not the same.
Radio is still deaf as a post.
A schematic with coil values would be helpful, so I know what to look for.
I'm guessing this chassis was a victim of a lightning strike, since there's a char mark on the chassis near the wave trap, the toasted Antenna Transformer, and now the discovery of the replacement 1st IF.
Any further suggestions? Or Ideas where to look?
RE: 1935 Philco 144 - Radioroslyn - 07-20-2020
Hi Jeff,
You could use the the 2nd IF transformer for the 1st. They are pretty close in an impedance match , the the third is different a it matches the for diode detector. Is everting good up to the 2nd IF IF amp??
RE: 1935 Philco 144 - PhilcoPhan1936 - 07-20-2020
Terry,
Thanks for the suggestion.
Would the fact of different catalogue part numbers
(144: 32-1369, 44: 32-1274) make a difference?
One problem I had was switching over or jumping in the replacement first IF, The adjustable capacitors are external to the coil, and there is no place to mount them in the 144 chassis. On the 44, they are mounted on the back of the chassis with holes drilled for mounting and a hole for adjusting. There is no such place on 144.
RE: 1935 Philco 144 - PhilcoPhan1936 - 07-20-2020
I took the time to sit down and compare coils and part numbers. With the exception of the first IF and the wave trap, all coils parts numbers are the same, and the coil values are listed on the 44 schematic. So now I need to go through and measure every coil and make sure no other coils are fried From the lightning strike.
