I seem to have a signal issue with a RP-2 player. I have replaced all the caps, and all resistors out of speck. The 6A7 is good and I believe the 84 is good (no tube tester). It would seem the signal from the player is weak, I can hear it on a small radio I have on the bench, but no matter what I have tried the signal does not improve. I suspect the oscillator or possible the 84. What should the voltage be on each pin of the 84? How can I test the oscillator and can I hook a signal generator to the crystal leads instead of using a record for troubleshooting. From what I have read from searching the forums is, this is an easy restoration and the player should sound fine, I figure this is something simple I keep overlooking. I am fairly new to this but have enjoyed lurking on the forum and collecting "old stuff" as my wife and kids say. Look forward to get this done and start on other âold stuffâ I have waiting on the bench.
Skip
Hello and welcome!
Have you had the crystal cartridge rebuilt? This is the part on the tone arm which the needle fits into. These are notorious for going bad.
You can rebuild it yourself, and my friend Syl has posted a detailed how-to here on the Phorum:
http://philcoradio.com/phorum/showthread.php?tid=1019
But if you do not feel comfortable doing this yourself, there is a company which rebuilds these cartridges.
http://www.west-techservices.com/
I would suspect that before checking any further, if you have replaced all paper and electrolytic capacitors and any out-of-spec resistors. You should be able to rub your finger across the needle and clearly hear the resulting scratching sound in a nearby AM radio tuned to the 42-RP2's signal if the cartridge is OK and the unit is transmitting as it should.
Ron,
Thanks for the response. I do suspect the crystal cartridge and was planning on having west-techservices rebuild it. When I run my finger over the needle I do hear a scratching noise, but again it is real faint. I am not sure the cartridge is the original since it was glued into the tone arm with silicone and is designed to flip over. The number I see on the cartridge is Astatic 66-T5 or 56-T5, do you know what the original cartridge should be? I do have a couple of erly 40's 78rpm phonographs that do have good cartridges and work, can I use them to provide a signal to troubleshoot or just hook up my signal generator to the leads.
Yes, the original cartridge is held in place by two screws, and is very common in prewar phonographs as well as some early postwar units. I do not know the number of the original cartridge.
If one of your other phonographs has a known good cartridge, you could borrow it to install temporarily in your RP2 to see how it is doing.
Without a record playing, your RP2 should still broadcast a signal with no modulation when it is on. "Dead carrier" is the usual term used in this case.
Hi Skip,
I would guess you would see around 150-220vdc at the cathode of the 84 tube. You could try a different audio source than the cartridge. You would use something that has a high impedance output. Say like a portable CD player.It has a low impedance output but you can raise the impedance by adding an output transformer or small filament transformer.. Use the headphone jack output into a tube type output transformer. Speaker side or 6.3v side to the phone jack/ Plate side or 120v side to the cartridge leads. I noticed that the output signal is fed back into the ac line cord. You may try flipping the plug over for best signal.
Good luck
Terry
Ron, Terry thanks for the input. Turns out, one of the problems was the wire from the oscillator to the AC line was literally hanging on by a thread, and the record player I was using has weak cartridge. I tried using a MP3 player through output transformer and was able to pick up the signal from across my shop clearly. Once I get the original cartridge rebuild, it will be fun to show my kids about their grandparents "MP3" player.
Thanks
Skip
Great to hear she's workin' like she should. You may want to consider hiding a small 1/8 phone jack hooked you so you can switch between the cartridge and another input. I did it to the radio in my 1961 Ford. Now I can plug it in and listen to MP3's of old radio shows or unplug it and it reverts back to the AM BC band. The radio is kinda of an odd ball as it uses some 12v tubes with 12volts B+ and a transistorized (oophs I said a bad word) output stage. So I too used a 120v/24v transformer to drive the tube input stage. Without it the MP3 player couldn't make enough audio to drive the audio stage to full output and at max it was distorted.
One of the reasons I mention the phone jack is that it seems that Philco didn't have many sets (if any) that have a phono input. The RP-42-2 has a good design. Most phono oscillators back that where powered right off the ac line with a resistor line cord and without a power transformer (ac/dc style). Having a power transformer is good for a few reasons. Eliminates shock hazard from having the ac line tied to the metal chaiss. Makes it easy to hook up other inputs cause you don't have to figure out what's hot with 120vac. And having the transformer it helps stabilize the dc high voltage this in turn helps the oscillator from FMing (causing the output frequency to shift with the level of audio applied to grid of the osc tube, not amplitude that's what you want) FMing will make the audio sound distorted.
Terry
ps If you are cheap like me and like experimenting you could try building a small fet (another bad word) preamp. Could do it for a dollar or two in parts to up the output of your cartridge.