Philco 84 code 121 no sound - Printable Version
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RE: Philco 84 code 121 no sound - Radioroslyn - 11-15-2016
(11-14-2016, 10:25 PM)Mike L Wrote: Ok I'll give it a try. The few stations received are very very weak, So I feel there is something else going on too. I ordered a set of tubes to see if I might not have an issue there as well.
As far as using the signal generator is concerned, am I measuring output to the speaker with my VTVM? I have the alignment procedure, but It just states adjust for peak signal, but where? I'm also not 100% sure my SG is working properly either. With it connected to the grid cap of the det-osc tube, SG set at 460kc all I get is a low pitched squeal around the 460kc and 1000kc spots on the tuning dial. Nothing anywhere else.
Set radio dial at 550kc. Set sg dial at 460kc. Adjust #11 and 15 for max sound from spkr. Keep sg signal to a minimum as you adjust 11 and 15 for peak.
RE: Philco 84 code 121 no sound - Mike L - 11-19-2016
I'm stuck. Adjusting 11 and 15 has minimal effect. I literally have to put my ear next to the speaker to tune or hear a station. Here is what I have done lately:
Replaced all tubes, one at a time with no change.
Re-checked all voltages, all fall in line except that now the 2nd detector plate and screen voltages are "bouncing" around. They are not stable. The plate is around 60 and the screen is around 34. I tried another tube with the same result, slightly different readings but still bouncing. Checked and rechecked all grounds, all were good.
If by chance I re-wound the feedback of the oscillator coil backwards would it receive stations at all?
Before rewinding the coils I had nothing, just low level hum. After rewind I'm receiving a few stations on the low side of the dial, nothing on the high side, but all very very low, barely can hear them. The volume control is always at max.
RE: Philco 84 code 121 no sound - Radioroslyn - 11-19-2016
Replace 1M resistor and check #20 to make sure that the two caps are wired correctly. When the det 77 and output stage 42 tube are working properly should get a loud buzz when the grid cap of the 77 is touched. Wouldn't sweat the osc coil till we get this sorted.
RE: Philco 84 code 121 no sound - Mike L - 11-20-2016
Terry, I replaced the 1M resistor again, but I also checked cap block 9 to make sure I had the correct values in it. Then I was checking cap block 20. The values are correct and they are wired per the cap block information I have. 20 is a Philco 7762-B which is now a 7762-OEU. That diagram is what I used to stuff it. After looking again at the schematic, it looks to me that the control grid if the 42 output tube passes through both sections of cap 20 to get to ground. The way this is wired I don't see that is possible. The .015 section is from pins 1 and 2. The .001 section is 1 and 3. Seems to me that the .015 section should be pins 2 and 3. Am I reading this wrong? Below is a photo of this block. I know the resistors are not the exact value for 22 and 23, but the ones I used were within 10% of value called for. Everything is de-soldered at this point.
Also last night when I was working on this I did touch the grid cap of the 2nd detector and I do get a "buzz" sound, but not very loud. Touching the grid cap of the det-osc the radio goes silent.
RE: Philco 84 code 121 no sound - KCMike - 11-20-2016
I'm sure Terry will get back to you. It looks to me like what you said about the 0.015 should go to pin 2. The way it is now, it is grounded.
RE: Philco 84 code 121 no sound - Radioroslyn - 11-20-2016
The caps inside 20 are wired incorrectly, only the .001 is grounded. You have two connections from the caps grounded. Please wire as per the schematic and not the Philco p# cause it's the wrong one.
RE: Philco 84 code 121 no sound - morzh - 11-20-2016
The cap is wired NOT as per sch. The 15nF section is the DC blocking and CANNOT go to GND.
Your problem is, you need to look into
http://www.philcorepairbench.com/bblokcap.htm
here to the original 7762-B. If you have other cap, adjust the pinouts accordingly, the OEU pinout is not gonna work.
RE: Philco 84 code 121 no sound - Radioroslyn - 11-20-2016
I don't see any 15nf caps anywhere!!!!!![Image: http://philcoradio.com/phorum/images/smilies/icon_eek.gif] Yes his signal from the detector stage is not connected the the output stage wired in this configuration hence very low volume.
RE: Philco 84 code 121 no sound - morzh - 11-20-2016
(11-20-2016, 11:57 AM)Radioroslyn Wrote: I don't see any 15nf caps anywhere!!!!!![Image: http://philcoradio.com/phorum/images/smilies/icon_eek.gif]
Oh come on Terry.
Tell me that you don't know what a Megahertz is. And I am not referring to the verb meaning "it hurts a lot
RE: Philco 84 code 121 no sound - Radioroslyn - 11-20-2016
> Tell me that you don't know what a Megahertz is.
Sure I know!!! Whatda think I'm stoopid er sumptin!!
It's very large rental car![Image: http://philcoradio.com/phorum/images/smilies/icon_crazy.gif][Image: http://philcoradio.com/phorum/images/smilies/icon_lol.gif]
https://www.youtube.com/watch?v=GLpNmuPQE94
RE: Philco 84 code 121 no sound - Mike L - 11-20-2016
That was it!! Lots of volume, finally had to turn it down. Also receiving stations all across the range with just a 3' wire antenna in my basement.
I cant remember where I downloaded that cap block information but it was obviously wrong. I rechecked the others as well against the schematic and those were correct. Now I'm going to have to go back to my 80jr. to make sure that is correct since I used the same information on that one.
Pretty sure my signal generator is not working correctly so I went by ear to adjust 15, 17 and 11. After that project is done I'll come back and do a correct alignment.
THANK YOU Terry and everyone that contributed.
RE: Philco 84 code 121 no sound - Radioroslyn - 11-20-2016
Your welcome! Glad you got it sorted and working now your model 80 should be a piece of cake. Pretty much the same set except that it uses tetrodes instead of pentodes for the mixer and detector. I just noticed something the model 81 is the same vintage but it uses pentodes. I've got an 81 in the back room that need servicing. 81 is a two band version of the 80.