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 Post subject: RCA AP-937 Duo-rectron questions
PostPosted: Nov Mon 15, 2004 3:52 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1911
Location: Mesa, AZ, USA
1) How do you get it open? Seems to be two metal tabs underneath preventing me from opening up the cabinet. Do I need to drill these out?<P>2) Is a UX-213 tube some kind of rectifier? Can't find one in the AES catalog.<P>3) I got the Riders schematics for this unit from Nostalgia air, but it does not show the values for any of the capacitors. Any suggestions?<P>Thanks,<P>-Mike<P>------------------<BR>-Mike


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 Post subject: RCA AP-937 Duo-rectron questions
PostPosted: Nov Mon 15, 2004 5:12 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3667
Location: Circleville, OH, USA
The UX213 is the predecessor of the 80. Replace with an 80. UX213s have not been made since about 1926.<BR>The caps are paper and mine were still good. Yours may be also. Bring it up on a Variac and see if you get the right voltages.<P>------------------<BR>


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 Post subject: RCA AP-937 Duo-rectron questions
PostPosted: Nov Mon 15, 2004 7:44 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3667
Location: Circleville, OH, USA
I had to get mine off the shelf and look at it to see how it comes open. If you have to go into it, here's how.<BR>Call the front the side with the binding posts. Remove tubes, turn unit upside down with front facing you. Remove 4 screws and baseplate.<BR>Remove 3 screws at rear edge and 2 at front edge. Do not remove any of the many nuts you will see.<BR>Carefully turn unit upright and work cabinet off of unit. I don't see any tabs that would require bending. There are 2 tabs protruding through base, but these are for locating, not fastening.<P>------------------<BR>


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 Post subject: RCA AP-937 Duo-rectron questions
PostPosted: Nov Mon 15, 2004 9:23 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1911
Location: Mesa, AZ, USA
I did exactly as you suggested to try andopen mine. However the two tabs prevent me from sliding the chassis out of the cabinet. On mine they have a solid metal rivet or post through them that prevents the tabs from sliding through the slots in the metal base plate. Looking carefully at the end of these metal rivets they have the RCA logo stamped on them. Must be some sort of anti tamper warranty voiding device. Should I drill out the rivets, or is there some other way to get it apart?<P><P>------------------<BR>-Mike


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 Post subject:
PostPosted: Apr Wed 14, 2010 8:42 pm 
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Joined: Oct Tue 13, 2009 1:52 am
Posts: 353
Location: Milwaukee, Wisconsin
I just purchased an AP 937 and was interested to read this older thread. I did not have any difficulty openning the unit as the tabs that protrude through slots in the bottom do not have the rivets described here.
I have two questions. There is the suggestion in this thread that the filter capacitors are "paper" and might be ok to keep. Is this possible? The filter caps are in this huge rectangular package.

This AP 937 is said to be a B+ eliminator, what did people do for filament power? I would like to use this to power a Pathe battery set, but I will have to also provide filament power. So far I have not been able to find a schematic for the Pathe to figure out what that might be, but once I do, I was thinking about adding a filament transformer to the AP 937. If I replace the filter capacitors with modern caps, there will be plenty of room under the hood for a filament transformer. This will, of course, hurt the authenticity of the AP 937, but it will improve its usefullness as a battery eliminator.

What do the experts think about this plan? The antique value of the AP 937 doesn't appear to be that great ($100?), so the addition of a filament transformer doesn't seem like a blasphemous thing to do.

Thanks,

Barry


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 Post subject:
PostPosted: Apr Wed 14, 2010 8:51 pm 
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Location: Livermore, CA
Barry

A 6 volt car battery was often used for the "A" battery. You can start with a filament transformer but need to rectify and filter the voltage.

Best to use a LM317 to regulate the A supply. Start with a transformer able to supply 8 or more volts. Some voltage is lost in regulation.

Check your caps for leakage. Could just bring up power slowly and see what happens. If there is any heating of caps they need to be replaced.

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 Post subject:
PostPosted: Apr Thu 15, 2010 2:18 pm 
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Joined: Oct Tue 13, 2009 1:52 am
Posts: 353
Location: Milwaukee, Wisconsin
Thanks Norm,
What do you think about building the A supply into the AP-937? It becomes somewhat of a home brew rather than authentic and that is a pity. Maybe the choice depends on whether the original capacitor block is still good. If it is not good, then I will replace the old block and use the space for the filament supply. Otherwise, keep it authentic.

Barry


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 Post subject:
PostPosted: Apr Thu 15, 2010 2:38 pm 
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Posts: 36892
Location: Livermore, CA
Barry

Since you will be using the AP-937 good idea to build an A supply inside. The A supply won't take up a lot of room and there is plenty of space in AP-937.

http://www.nostalgiaair.org/PagesByMode ... 040283.pdf

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 Post subject:
PostPosted: Apr Fri 16, 2010 9:47 pm 
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Joined: Oct Tue 13, 2009 1:52 am
Posts: 353
Location: Milwaukee, Wisconsin
Thanks Norm,

I see there are plenty of battery eliminator circuits described in old posts, so I think I will build one in. I now have 2 battery sets and having a complete battery eliminator will encourage me to acquire others.

Barry


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 Post subject:
PostPosted: Apr Wed 21, 2010 2:57 am 
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Joined: Oct Tue 13, 2009 1:52 am
Posts: 353
Location: Milwaukee, Wisconsin
I replaced the filter capacitors, added a fuse and did some rewiring. I tested the rectifier tube, but my tester will not test the UX-874 voltage regulator tube. When I turned it on it appears to work fine except the voltages (22.5, 45, 90, and 135) are high. The voltage regulator is connected to the 90 volt terminal and that voltage is 98. The other voltages are proportionately higher so I suspect the UX-874 regulator is not working properly. It appears to be working, it glows a nice blue color.

Before I run off and buy a replacement tube, I wanted to bounce this off the experts. The voltages are established across a huge wire wound bleeder resistor, but I would not expect its resistance to change with time and use. That doesn't leave much other than the regulator tube.

Any suggestions would be appreciated.

Barry


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 Post subject:
PostPosted: Apr Wed 21, 2010 4:08 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7308
Location: Bossier City, Louisiana
Barry,

If your voltage readings are with the eliminator unloaded I would expect them to be higher. Connect it to a set and you will probably find they drop to where they should. If my memory serves me right I did recap mine. It worked great when operated last. It has been a few years ago however.

FWIW I have found several of these eliminators that utilize the large paper caps to operate well without recap. However I never leave one operating unatended. :!:

Dave

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 Post subject:
PostPosted: Apr Thu 22, 2010 1:49 pm 
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Joined: Oct Tue 13, 2009 1:52 am
Posts: 353
Location: Milwaukee, Wisconsin
Thanks Dave.
I assumed the ballast tube would conduct enough current to draw the 90 volt terminal down to the correct level regardless of the load. In other words, with no load the ballast tube would draw the needed current and when a load is connected, the ballast tube would draw less current. I found one source for these tubes which listed the voltage level across the tube. One tube was 90 volts (exactly what I need) and the other was 95 volts. My tube is 98 volts, so it may be working, but is just high.
I replaced the capacitors because the original capacitors had already been replaced and who ever did the work did a lousy job. I now have the space to add an "A" eliminator in place of the old bulky capacitors.

Barry


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