model 18 no reception - Printable Version
+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: model 18 no reception (/showthread.php?tid=17878)
+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: model 18 no reception (/showthread.php?tid=17878)
model 18 no reception - madsowry - 02-02-2018
Hello all. New to this phorum but have read as a guest for quite a while. I've been working on a model 18 for about a month now. Replaced all caps and ecaps, all resistors that were out of spec, rewound the small coils on the outside of the oscillator and detector coils. I think you call them tickler coils. Found a broken wire on the inside of the antenna coil- tore it apart and spliced it. Good continuity afterwards. Checked all tubes - all ok. Ohmed out all transformers and coils- all good except the 2 coils I rewound are about 2X the ohms on the schematic( the detector primary is supposed to be 3.7-is now 6ohm and the osc. pri. is supposed to be 3.4- is now 6 ohms). Powered it up with variac and all seemed to go OK but got very little reception and nothing above 1100khz. So I used SG and got good tone in every stage. Thought I should do an alignment so following the instructions on the Philco schematics from Radio Museum I set the SG on ant. term. and grd. on grd. term. They said to put output meter on output trans. or the plates of the 2 output tubes. I tried the 2 42 tube plates and powered everything up and blew out the 80 tube. I have another 18 chassis that has not been tampered with except for the 2 ecap cans and the 10uf ecap can which was missing. I made sure when I installed that cap the pos. went to grd. I tried it again with the meter on the voice coil and could not get a sound out of it. Put the meter on the plates and blew another 80 tube and a ecap. Replaced both and turned on slow with variac and it stayed on. Hooked up an antenna and 1 very weak station for 30 sec. then fades out. Moved dial down- got another station then faded out. Now nothing. I'm lost now. I know this is a long narrative but I thought you guys would need as much info as possible. Any ideas or instruction would be greatly appreciated. Thank You madsowry
RE: model 18 no reception - morzh - 02-02-2018
What kind of meter is it that blows rectifier when placed across push-pull plates? What was it set to?
Personally, I almost always place my meter across the voice coil of the speaker set at VAC.
RE: model 18 no reception - Radioroslyn - 02-02-2018
Welcome,
Have a look at the 42 sockets @ pin 2 see if there are any carbon traces (burns).
RE: model 18 no reception - madsowry - 02-02-2018
Thanks morzh and Radioroslyn for replying. Morzh I used my Eico vtvm but I had the AC probe in it. Don't know if that was the problem or not. When I put my vtvm on the voice coil I couldn't get a signal through. I may have to look into my SG.
I don't see any traces around the 42 tube sockets.
Reohmed every coil all is good. I was taking voltages and when I touched pin 5 of 6A7 reception came back for a bit below 900khz. I will post voltages tomorrow. Have to go out of town tonight. Thank You
madsowry
RE: model 18 no reception - morzh - 02-02-2018
Is one of the two clips if the VTVM - GND? If yes, then you grounded a plate, hence the exposions.
RE: model 18 no reception - madsowry - 02-03-2018
morzh does that mean you use 2 clips on the pos. to go across the plates?
RE: model 18 no reception - madsowry - 02-03-2018
Hi all I have reception now but at the low end of the dial. None above 800khz. Any ideas would be appreciated. Thanks
Dick
RE: model 18 no reception - Radioroslyn - 02-03-2018
Hi Dick and welcome,
So are the stations that you hear below 800kc are they at the proper places on the dial??
Take a listen for the local oscillator by using another set tuned the 1060kc and the philco to 800kc. Can you hear the lo as you tune the dials up in frequency?
Have a look at the voltage at pin 4 of the 6A7 should see some hv there. Is the 6A7 tested and good?
RE: model 18 no reception - madsowry - 02-03-2018
Thanks Terry for the reply Yes the stations are right on the money with the dial. The 6A7 is tested and I've tried 3 different tubes tested good with same results. I will try the 2 radio test tomorrow and post results. Thanks again
Dick
RE: model 18 no reception - morzh - 02-03-2018
Dick
You never put the GND clip anywhere other than GND/Chassis. Unless it is a floating GND which is then ok. I don't know what VTVM you have and if one of the clips is Grounded.
You could use your DMM to put the clips across the plates without problems.
But this notwithstanding, I use voice coil.
RE: model 18 no reception - madsowry - 02-03-2018
Thanks morzh I know that was pretty stupid on my part. I've never really had a lot of practice in aligning radios. Still learning how to make the connections and where to make them. Just been doing this hobby for a couple yrs. but its addicting. Voice coil from now on but can you tell how you hook up your vtvm to the voice coil? Is the grd to chassis and does the pos. have 2 clips to the voice coil? Thanks
Dick
RE: model 18 no reception - morzh - 02-03-2018
I don't own a vtvm. Use a multmiter, whether the antique one I own or a DMM.
But in your case since you have an output transformer and the voice coil is isolated, you could just hook the VTVM leads any way you like.
RE: model 18 no reception - madsowry - 02-04-2018
morzh My question is if you were doing an alignment on this radio(Philco 18) where would you put the leads of a vtvm? And where would you put the leads of a DMM?
RE: model 18 no reception - morzh - 02-04-2018
Well....as I just said, across the voice coil of the speaker. Or, which is the same, across the secondary of the output transformer.
In this case it doesn't matter if it is a DMM or a VTVM.
Set at Volts AC.
RE: model 18 no reception - madsowry - 02-04-2018
Hi Terry Now today the radio is a little off the dial by 30 kHz. Yesterday it was right on. I did the 2 radio test for the oscillator. I could hear it up to 1030kc and the other radio was at 1250kc. That's where it drops out. Also checked voltage @pin 4 of 6A7 -- 106.2 to grnd. 102 to K. I hope this gives you an idea. Also when I first turned the radio on I had to touch pin 5 of 6A7 to get reception. Don't know if there is a bad connection in the socket or what. Thanks
Dick