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Philco 17 SW band not working - Printable Version

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Philco 17 SW band not working - boxjoint - 09-10-2022

I am restoring a Philco 17 and I have already recapped the whole radio.  The broadcast band is working fine however the SW band is not working.  I have cleaned the band switch thoroughly and I tried to inject a 1600 khz signal but did not get a tone.  I believe that I should be gettting low ohms from the antenna jack to ground and even lower when the band switch is in the SW position but I get 36 ohms with the switch in both positions.  Please see the schematic I have attached.  Any help would be greatly appreciated.

-Carlos

   

RE: Philco 17 SW band not working - Radioroslyn - 09-10-2022

I'd take a listen for the local oscillator on sw and measure the resistance of the rf coils that switch contacts connected to them. Check the total resistance of the winding then throw the switch to be sure the contacts are making connection. You should see a drop in resistance when switching to sw. GL

RE: Philco 17 SW band not working - Radioroslyn - 09-10-2022

I see that there are 2 sb for the model 17. Don't know if the coils are the same. Didn't read them closely.

https://philcoradio.com/library/download/service%20info/service%20bulletins/Philco%20Service%20Bulletin%20161.pdf
https://philcoradio.com/library/download/service%20info/service%20bulletins/Philco%20Service%20Bulletin%20161B.pdf

RE: Philco 17 SW band not working - boxjoint - 09-10-2022

I tried listening for the local oscillator on another radio while the band switch was in the SW position but I heard nothing.  I have a donor Philco 17 chassis so I swapped out the oscillator coil and now I am receiving one SW station however as I move the tuning up to the end of the dial I get a terribly loud squeal.  So I am not sure what that is ?

-Carlos

RE: Philco 17 SW band not working - mikethedruid - 09-10-2022

Looking at the schematic for the model 17 it appears that the two bands are actually:
520 - 1500 K.C. and 1500 - 4000 K.C. The modern Broadcast band extends from 550 - 1600 K.C. So, the modern AM broadcast band is split between the two bands on your radio. This means that you should hear regular broadcast band stations between 1500 and 1600 K.C. on the lower end of the higher frequency band. What was above that in the old days was the lower frequency Police band, 1600 - 1700 K.C. and a higher one from 2200 - 2300 K.C. This band also covered the 80 meter ham band and some lower frequency short wave stations. You are at a point where you need a signal generator to really hunt down the situation with your radio, and do a proper alignment.

RE: Philco 17 SW band not working - boxjoint - 09-10-2022

I have a signal generator. I am trying to get a tone while injecting the 1600 khz modulated signal but I don't hear it. I have already aligned everything else except the SW band which still does not seem to work.

-Carlos

RE: Philco 17 SW band not working - mikethedruid - 09-11-2022

Try injecting a modulated 16-- KC signal through a .01 MFD condenser into the grid cap of the 78 RF amplifier tube, which will bypass the RF coil for and let you see if the problem is before there. If not, then try injecting it the same way into the grid cap of the 6A7 and see if you get a signal when you tune across the dial. If you do, it tells you that the oscillator is actually working. If not, when you know that is where things are screwed up. If the radio is working OK in the lower frequency band, but not on the upper, I would try cleaning the band switch contacts well. Also, note, the radio uses one coil for the oscillator, using a tap to change the band. If it is working OK on the lower frequency band, it means the coil is most likely OK, since that band uses the WHOLE coil, whereas the higher frequency band uses only a part of it. Remember, in an LC parallel tuning circuit, as you decrease L you increase the resonant frequency of the circuit.
[Image: https://ecstudiosystems.com/discover/textbooks/basic-electronics/ac-circuits/images/lc-parallel-resonance.png]

RE: Philco 17 SW band not working - Radioroslyn - 09-11-2022

To parallel Mike's comments if just the osc is the fault on the sw band you can try this as a troubleshooting technique. Set your radio dial at 1700kc. Set your generator at 1875kc without modulation. Turn the output down fairly low and connect it to the grid cap of the 6A7.

If all is well but the osc you should be hearing WJCC. What we are doing is substituting the generator for the osc. If you keep the generator frequency 175kc above the 17's dial frequency you should be able to track all the way up to 4000kc with the generator at 4175kc.

RE: Philco 17 SW band not working - Ron Ramirez - 09-11-2022

> The modern Broadcast band extends from 550 - 1600 K.C.

Not to argue, but the modern AM broadcast band in the USA is 540 to 1700 kc (kHz). The FCC expanded the AM band above 1600 kc starting in 1990; the first stations were licensed to use the expanded portion of the band in 1995.

The 540 kc frequency was added to the USA broadcast band in the early 1950s.

RE: Philco 17 SW band not working - boxjoint - 09-11-2022

I took out the band switch and cleaned it in my ultrasonic cleaner and reinstalled it. I also replaced the 6A7 Oscillator tube. With the signal generator set at 1600 khz with modulation on and connected to the antenna jack I get a tone on the speaker when the dial is at 1600 khz, but when I turn the trimmer cap it has no affect.

-Carlos