The PHILCO Phorum
Growing up quick...with a 38-690xx Pics added. - Printable Version

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RE: Growing up quick...with a 38-690xx Pics added. - Gene Pederson - 01-07-2013

Well I'm late to the party, but that is impressive work on that chassis!!!

Gene

RE: Growing up quick...with a 38-690xx Pics added. - badwaxcaps - 01-22-2013

I'm still here guys. Been really busy at work. I should have the '690 back on the test bench this week. I have been kicking around the idea of proceeding with a full resistor replacement before testing further. If I cannot work it out I will most likely be taking it to the "Philco Kid" as he is only 45 minutes away.

RE: Growing up quick...with a 38-690xx Pics added. - badwaxcaps - 02-23-2013

Did more testing on the power/amp chassis and found the choke #167 is open. The other choke #175 is fine. I have chokes in my junk box but nothing like this. I would prefer a direct replacement as original appearance is high on my list for this radio. Opinions? Thoughts? Thanks guys!

RE: Growing up quick...with a 38-690xx Pics added. - Ron Ramirez - 02-23-2013

32-7115

5.25 H, 125 DC mA, 170 ohms DC resistance.

Hammond's 159P is probably as close as you can get without having one custom wound - 10 H, 125 DC mA, 155 ohms DC resistance. Open frame, not enclosed. Maybe the 159P might fit inside the 32-7115 shell? You can take the measurements from here and compare with yours:
http://www.hammondmfg.com/153.htm

RE: Growing up quick...with a 38-690xx Pics added. - badwaxcaps - 02-26-2013

OK.. I subbed in a resistor for the choke so I could do some more testing. Theres no reception on any band. I injected a signal directly at the grid of the 6A8 tube and it plays through the set but VERY weak and garbled. I did the "touch" test with the other grid caps and listened for a scratch or pop noise from the speakers but no dice. I then went for the throat and injected signal at the grid of the 6F6 and voila, it plays through beautifully. So I have some work to do. I will work my way backwards through the stages and see where the signal shows up. The volume control does not have any noticeable affect on the volume level until its turned all the way up and then its only marginal. Something else I noticed is the field coil on one of the tweeters gets a bit warm after about 10 minutes of testing. Its not hot, just warm. The other field coils are nice and cool. Another thing that comes to mind is that the characteristic noise of switching between bands is not present. I swing the switch and shes silent aside from the hum of the resistor substituted for the choke. I did voltage checks and they all seem to fall in line with recommended levels in the RCA manual. There was no voltage present on any pin of the 6J5 AVC/Bass Amp tube in the amp chassis. It looks to be wired as a diode on the schematic I believe. Sorry, I know I bounced around a bit but thats how the info came to me as I type this at work. Any help is greatly appreciated.
On a side note: This radio sounds GREAT! I know I was kinda cheating by putting signal to the driver tube but she sure does sing none the less!

RE: Growing up quick...with a 38-690xx Pics added. - badwaxcaps - 03-05-2013

I'm an idiot. When I re-capped the RF chassis I left out a .01 cap in the signal path!Icon_redface I am so embarassed. Anyways, I put the cap in and now have full signal (from the generator) playing through the set. I am pretty sure theres an issue with the volume pots, which now work somewhat, as they are very scratchy and intermittent despite a good blast of cleaner. Still no radio signal though. Only plays with the signal generator hooked directly to the antenna connection.

RE: Growing up quick...with a 38-690xx Pics added. - BrendaAnnD - 03-05-2013

Try to check your input coils (antenna section) on the rear of the bandswitch. My 690 had open primaries on all 5 coils (of course, it had some help from an external voltage source..)

One quick way to check for potential problems there is to touch the cap of the RF amp tube. If you touch the antenna connection with your finger and get no static, then touch the cap of the RF amp with your finger and DO get static, this is a good indication of coil or bandswitch problems.

RE: Growing up quick...with a 38-690xx Pics added. - badwaxcaps - 03-05-2013

Thanks for the advice! I will get back to testing this one soon. I'm leary of working with it too much with the resistor subbed for the choke. Further updates as events warrant Icon_biggrin..

RE: Growing up quick...with a 38-690xx Pics added. - jerryhawthorne - 05-22-2013

Hum not increased with the volume is typically in audio circuit after the volume control. Try pulling one tube at a time and see when it disappears. This will give you an idea as to where to look. If 60 cycle, probably filament associated (filament to cathode leakage). If 120 cycle probably B+ related.
Good luck, nice job so far!
Jerry

RE: Growing up quick...with a 38-690xx Pics added. - morzh - 05-22-2013

Very nice results, I'm impressed.

RE: Growing up quick...with a 38-690xx Pics added. - badwaxcaps - 05-23-2013

    SUCCESS! After obtaining a replacement choke (the Hammond, thanks Ron!) and installing it along with some tube socket cleaning this wonderful old guy came to life! Icon_biggrin Reception on all 5 bands. Voltages within specs. Transformers run nice and warm but not hot after an hour of playing. All three speakers work. One tweeter field coil runs rather warm but I've read this is a normal occurance. It definitely needs an alignment and it has a hum I can't seem to track down. Its not affected by the volume control which now works perfectly by the way. Bass response is a little lax but I suspect when the speaker is back in the cabinet that may change. This guy is LOUD too. I was lucky enough to come by a set of Philco 6L6G's that test over 90% and they are now happily living in the amp chassis.

Next up.. Alignment, track down that hum and then look at the tweeter wiring as I have read that the factory wired them wrong. Also gonna address the tweeter capacitor issue I have read about. Something to do with changing the value to increase frequency response? Any advice on these issues is greatly appreciated. I will get some pics up tonight or tomorrow.