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 Post subject: just picked up an old Bell Systems Portable PA Model 630
PostPosted: Aug Sun 22, 2021 10:00 pm 
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Joined: Aug Sun 22, 2021 7:40 pm
Posts: 3
Hi. Looking for guidance and next steps. I bought at an auction a Bell Model 630 and a pair of Bell Jensen speakers. Everything seems to be complete, although there was no microphone with the system. I have not tried to power it up yet and I know that I should check things before doing that. But what?

From looking at pictures available on another site I can tell this is pre 1937 from the speaker design. The serial number on teh 630 is 6510. The jensen speakers have these numbers on the edge ST476y (Stock number?) PM12H C1126 2.

Any help is appreciated.
Thanks.
Keith


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 Post subject: Re: just picked up an old Bell Systems Portable PA Model 630
PostPosted: Aug Mon 23, 2021 1:09 pm 
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Joined: Nov Wed 07, 2007 12:44 am
Posts: 1470
Location: Kingman, Arizona
If your amp has not been powered up in recent history, then I would recommend at least testing the tubes for shorts and gas along with at least replacing the filter capacitors before powering up the unit. Leaking filter caps can kill the power transformer and a shorted or even gassy output tube can destroy the output transformer. If the amp was mine, I would also replace the coupling caps to the output tubes as leaking coupling caps can take out the output tubes. Harry


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 Post subject: Re: just picked up an old Bell Systems Portable PA Model 630
PostPosted: Aug Mon 23, 2021 2:18 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11087
Location: Sunbury, Ohio 43074
Advice on what you should do would heavily depend on your level of skill and/or experience in working on vintage electronics. Can you give us some idea of where you are on this? That would determine what steps we can recommend that might be successful, and what NOT to recommend that could do further damage.

One thing for sure... DO NOT power it up to "see what happens". If you awaken the smoke diety, it gets expensive fast. Do you have a local radio or ham club? Perhaps someone near you can help you get this thing going safely.

If you are, as Clint Eastwood said, feeling lucky ..... power it up slowly with a variac and roll the dice. But even in this case you have to know what you are doing, what the warning signs are (such as electrolytics getting warm). My bet is you will lose ;-)

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Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


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 Post subject: Re: just picked up an old Bell Systems Portable PA Model 630
PostPosted: Aug Mon 23, 2021 9:55 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4783
Location: Boston, MA USA
I think Harry's advice is correct -- test the tubes, replace the filter and output stage coupling capacitors, and I'll add one more: carefully inspect all wiring including the power cord for cracked or crumbling insulation. Many amplifiers at this time were built with rubber-insulated wiring which dries-up and cracks off. Then power up and see what you have. If the amplifier sort of works, start replace all the paper capacitors a few at time, checking to see if the amplifier still works after each set of replacements.

-David


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 Post subject: Re: just picked up an old Bell Systems Portable PA Model 630
PostPosted: Aug Tue 24, 2021 12:37 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3775
Location: Seattle WA US
Your Jensen PM12-H speaker was listed in Bell's 1945 catalog sheets (in Radio's master) for $23.50 (big money back then). Described as suitable for use in a bass-reflex enclosure. Voice coil rated 8 ohms, 15 watts. Permanent magnet field.

Model 630 amplifier listed in same catalog, for $93.50, plus $14.30 for set of tubes.

-Chuck K7MCG


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 Post subject: Re: just picked up an old Bell Systems Portable PA Model 630
PostPosted: Aug Sat 28, 2021 5:45 pm 
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Joined: Aug Sun 22, 2021 7:40 pm
Posts: 3
Thank you for the great advice. I called our local ham radio club and spoke with the president. He said bring it over. Tested the amp and the speakers and everything worked, just some unwanted humm. He did some magic with some alligator clips, a filter and some chanting and the humm disappeared. He is in the process of recapping and replacing the mic and phono connections with standard 1/4 inch jacks.

So thanks for the advice, and thanks to John DeMajo for the huge help.


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 Post subject: Re: just picked up an old Bell Systems Portable PA Model 630
PostPosted: Aug Sat 28, 2021 5:52 pm 
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Joined: Aug Sun 22, 2021 7:40 pm
Posts: 3
Chuck. Thanks for the info. Would love to know the specs for this thing. 1945 seems later for 2 reasons. First, the Jensen code of 220 is not on these speakers. And second, the shape of the speaker grill and the handles on either side of the top of the amp look different then the ones that I found on the web. Are there any pictures in the catalog that you can compare mine against?


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