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 Post subject: Help Needed - Philco Model 46-1209 with D10-A Phonograph
PostPosted: Jul Thu 13, 2017 7:55 pm 
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Joined: Mar Mon 06, 2017 8:30 pm
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I am restoring a Philco 46-1209 Radio with a D10A phonograph. The radio work is done (replaced all caps and resistors) and it sounds great over the full range of the volume control. My issue is getting the D10A phonograph to electronically function. Mechanically it works fine. The Philco custom/specific design needle/stylus is no longer available. I have tried magnetic and ceramic replacement cartridges with the correct needle for 78 records, and have gotten the tone arm into a reasonable balance. It actually plays, but can only be heard decently at full volume. The phonograph needle feeds a pre-amp which is one half of a 7AF7 tube. The tube plate is connected to one end of the volume control, which adjusts the grid bias (?) on a first audio amp (7X7), which then feeds the other half of the 7AF7, then on to the output amp tubes. The needle is coupled through a transformer (impedance matching?). I can't find anything on the original output of the Philco cartridge. The magnetic cartridge output is 5 mV, and the ceramic is .5V. They both require full volume control to be heard. The connecting cables and transformer appear to be OK per resistance and continuity checks. Tube voltages also appear to be nominal. I don't know whether the issue is an impedance match problem, tube bias problem, or if it is supposed to work this way. If anyone has any insight or recommendations to help me sort this out, I would love to hear them.
Thanks


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 Post subject: Re: Help Needed - Philco Model 46-1209 with D10-A Phonograph
PostPosted: Jul Thu 13, 2017 9:54 pm 
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Joined: Jan Wed 16, 2013 12:04 am
Posts: 975
Location: 77001
Here's a thread that discusses your record changer.
Appears it had a 3 volt output crystal cart. That could be the
problem.
Do you have the original phono cart to post a photo ?
Hotwax

http://www.antiqueradios.com/forums/vie ... hp?t=40857

http://www.radiomuseum.org/r/philco_d10a.html


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 Post subject: Re: Help Needed - Philco Model 46-1209 with D10-A Phonograph
PostPosted: Jul Fri 14, 2017 3:24 am 
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Joined: Mar Mon 06, 2017 8:30 pm
Posts: 5
Hotwax,
Thanks for the quick response. I was puzzled a bit by the post. It sounded like there was some confusion about what phonograph model was being discussed between a D10 and a D10A. All of my research shows that the D10 used a ceramic pick up while the D10A used a dynamic pick up. I believe the ceramic with a 3 v output was for the D10. I definitely have the D10A model with the removable head shell on the tone arm. My D10A pick up is destroyed and cannot be rebuilt or repaired (so no good pic is available). I have a Philco replacement parts list for the D10/D10A and I could match some, but not all, of the part numbers listed in the post. I believe I had the 76-1622 (it was listed as "76-1622-1 Unit, Pickup (D10-A) on my parts list). I have not been able to find the output specs for the dynamic pick up but suspect it is in the range of a few volts. I think you are correct in that the higher voltage cartridge output might be the the issue. I just need to find one with the higher output that can play play 78's. This site has some recommendations (http://www.esotericsound.com/cartridgeGuide.htm) but list very few of the output voltages, such as 4mv or "high". I'll keep digging and will definitely post the results here if I get this resolved.
I probably won't play this phonograph very much, but now it's a challenge to get is working well.
Thanks,
domperna52


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 Post subject: Re: Help Needed - Philco Model 46-1209 with D10-A Phonograph
PostPosted: Jul Fri 14, 2017 3:40 pm 
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Joined: Mar Mon 24, 2014 5:19 pm
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Location: Eugene, OR
Gary at voice of music lists the voltages for the cartridges he sells on his website. I'd ask him if can recommend a good replacement for your dynamic pickup.

_________________
Handyman of the apocalypse


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 Post subject: Re: Help Needed - Philco Model 46-1209 with D10-A Phonograph
PostPosted: Jul Fri 14, 2017 3:54 pm 
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Joined: Nov Wed 27, 2013 5:59 am
Posts: 326
Location: Hillsboro Oregon
I guess I'm a little confused, maybe just by all the information that others have gathered. If it were me, I would not be that worried about magnetic vs. ceramic from a fidelity standpoint, and just use whatever is easiest to adapt, which in this case would be the ceramic. I have no idea why a ceramic with a 3v output would be used in a console, as those are typically only needed in a cheap changer that has no first audio stage. Because you have a radio, you're going to have a first audio stage anyway (the 7X7). I would suggest installing the ceramic with it's .5V output, and connect the output directly to the end of the volume control (presumably though a switch that selects radio/phono?). The 1/2 of the 7AF7 is presumably to boost the signal from the magnetic pickup and would not be needed, at least from what I gather from your description. Try that and if it doesn't work, I will download the schematic and dig a little deeper.


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 Post subject: Re: Help Needed - Philco Model 46-1209 with D10-A Phonograph
PostPosted: Jul Fri 14, 2017 5:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3898
Location: Boston, MA USA
I believe that changer used a specific low-impedance magnetic pickup which is not available. That's why the transformer is in the circuit. The transformer will kill the output of a ceramic or modern magnetic cartridge which are designed to work into higher impedance, so it must be bypassed and a modern ceramic cartridge be connected to the 7AF7 or even directly to the high side of the volume control (audio level, not grid bias).

Other Philco combination sets call for 3V crystal cartridges but connect them to an attenuating network to knock the output down to 0.5V. I have no idea why. Modern ceramic cartridges can be used by bypassing the attenuation network.

-David


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 Post subject: Re: Help Needed - Philco Model 46-1209 with D10-A Phonograph
PostPosted: Jul Mon 17, 2017 3:37 pm 
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Joined: Mar Mon 06, 2017 8:30 pm
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OK. Just getting back to this post. Thanks to everyone for all the responses. I will try the suggestions about changing the phono input connections and see what happens, and will post the results. I'll check the schematic to see where the best connection point is. There is a phono/radio selector switch so maybe just upstream of that would be the ideal place. I also have a few higher voltage cartridges coming fro the Voice of Music. Part number EV5549 is an Astatic 146 replacement at 3 volts, and part number EV5146 replaces a lot of different cartridges art 4 volts. I believe I had sent a recommendation request to VOM and the response hesitated to offer one since there was no tried and true solution that was know to work.
More to come.
Thanks again.


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 Post subject: Re: Help Needed - Philco Model 46-1209 with D10-A Phonograph
PostPosted: Jul Mon 17, 2017 5:02 pm 
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Joined: Mar Mon 06, 2017 8:30 pm
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OK. Problem solved. I have a .5 volt mono cartridge installed on the original D10A phonograph tone arm. It is a Ceramic with a 3 mil sapphire needle for 78 records. VOM Part number P51-3 (info from VOM is --
Part Number-P51-3; Description-Ceramic mono cartridge with 3 mil sapphire needle for 78 rpm records; Replacement Comment-Astatic 51-3J, 51-3M, AC-C78, GC-78; Replacement Needles(s)-700S3).
I used the suggestion provided by dberman51 and connected one lead of the cartridge output to the phono/radio switch contact from the 7AF7 plate (phono pre-amp) which directs it to the high end of the volume control, the other lead is grounded to the chassis. The volume control is now effective from just shy of half way to all the way to max volume, and max volume is loud. This is fairly comparable to the volume response when listening to the radio. The phono/switch will isolate the cartridge when it is the radio position. This effectively just bypassed the phono pre-amp circuitry. Simple and elegant solution. I am learning a LOT about this stuff talking to you guys and I appreciate it VERY much.
A few more items to consider:
Cartridge mounting - The VOM cartridge has the standard 1/2" mounting screw arrangement. I removed the entire original cartridge and fabricated a sheet metal adapter to hold the cartridge using the original mounting hardware holes. The adapter is made from .040" thick steel replacement door skin from a 1970 Chevy pick up. It's what I had laying around. The extra connections on the cartridge lead were from when I tried a stereo cartridge. I will get rid of them. Cartridge and adapter weigh about 12.5g. The adapter can't allow the cartridge to hang too low below the tone arm or it will hit the tone arm rest when it rejects.
Tone arm balance - The tone arm on the D10A is a heavy beast at 109g. It has about a 200g counter weight in the rear end. The original cartridge weighed about 43g. This originally set up worked fine. I don't know the original tracking force. Since the pivot point is offset (lower) from a direct line between the two arm weights, the center of gravity actually shifts rearward when the arm is raised by the mechanism and it just stands up and will not come back down onto the records without sufficient weight on the cartridge end, and just adding weight to the cartridge end doesn't solve this. The rear weight must be reduced to avoid this. I cut the large weight into four slices to experiment. I ended up with about 100g on the rear end and installed the ceramic cartridge and adapter with no additional weight on the cartridge end. The arm behaved correctly through the reject cycle. Tracking force is about 14g. Plays well, no skips. I'll balance this better as needed to get the 8g tracking force recommended for the cartridge. I think washers can be added to the rear counterweight mounting screw for fine balance adjustment.
Hopefully this write up will help others get around the issues with getting this old beauty to play well.
Thanks to all.


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