• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Bell Sound Systems Old Gem

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I've had this Bell Sound Systems 3710A for a few years. It resided in a Masonic Temple - probably used as a PA - until it was given to me by the building owner. He didn't even know what it was! I've searched far and wide, but here's all I know about Bell:

Columbus, OH
-Made radar etc. gear for WWII
-Made consumer amps, PAs, rell-to-reel, radios etc. until late '50's or '60's
-Usually made a quality product
-Yadda

Regardless, here's the skinny on the amp. (See huge picture - almost all of this is visible.)
-serial# 80524
-2 amp-3AG fuse
-117 volt - 50-6- Cycle
-80 Watts
-Coax microphone and phono inputs
-1/4" instrument input
-2 old school 4-prong variable impedance speaker outs
-2 - COM - 8 - 4 on one
-500 - COM - 16 - 4 on the other
-phono and micro volume control
-tone control doubles as AC on/off switch
-All GE Tubes - 6V6GT - 6SJ7 - 5Y3GT - 6V6GT - 6SL7GT
-big Sangamo B-20048P-28 dry electrolytic
-Larger of the transformers is stamped B-20076
-Smaller transformer has DD 107 32 in orange ink on paper around the coil & is stamped B-20231
-big Mallory Metal Tubular Electrolytic TC-75 under chasis
-also several marroon sangamo rounded cylinders - likely caps?
-and about 10 color-coded beehive striped caps/resistors

I just located a guy who will make photocopies of documentation he has for this model, though I'm not sure what he has. Could be interesting.

The unit powers on. Pilot light works fine. I quickly turned it off b/c it had no load and god knows how long it'd been since it was last used. Got a decent variac on eBay for respanking the caps. But haven't done that yet. What I need is advice.

This amp is beautiful. I don't want to hurt it.

Questions:
Which components, if any, should I replace outright - i.e. just assume they're bad, or getting that way?
Are the beehive things strictly caps?
What about the maroon things?
Where can I find a good online primer for recharging caps?
Is that what I should do?
What do you call the speaker jacks?
Who sells connectors for them?
Or should I just rig my own?
Would I just connect one wire to the com and another to whatever resistance I want?
Where can I find more Bell Sound Systems info?
Should I just rig a speaker, plug in a guitar and see if this thing works? ;)

Please discuss. I can point you to higher res pics if that helps.

Thanks.
 
frugal-phile™
Joined 2001
Paid Member
Bill Fitzpatrick said:
He's a new member. For some reason pics by a new member don't get posted right away. I think the forum must be afraid of something - porno?

Pictures attached to posts in moderation get put into a separate queue, and sometimes posts get cleared and the mod forgets to also clear the attachments.

In this case there is no picture.

dave
 
the pic

As this was my first post, I had to wait several hours b4 it went live. Guess DIY doesn't trust the newbies ;)

Here it is. (in two parts)
 

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Bell Sound

Hi uncoolcentral

Bell Sound was located on Marion Rd. in Columbus, OH. (My old stomping ground!) They went out of business sometime in the mid to late 60's, IIRC. Thompson Ramo Woolridge (something like that) I believe was their parent company. I've owned a Bell 6060 intergrated amp and an AM-FM stereo tuner but alas they're no longer in existance. :( That tuner was one of the best tuners I've ever owned.

I would definitly replace ALL the electroylitic capacitors, AES has a good selection of caps. www.tubesandmore.com
Check all those carbon comp. resistors, they can drift way off value just from age. Also check output tube bias/current.
Are the beehive things strictly caps?
What about the maroon things?
Yup most likely caps. Discharge the caps through a 10k 2W resistor. Don't use a screwdriver! And since you ask this question it looks like you don't know your way around a tube amp, so I highly advise caution.
HIGH voltage in a tube amp/circuit can cause severe burns, even death or fire! Or in the very least a sore arm!
As for the spkr jacks AES has a 4 pin plug that should be just what you need.
Very important: Make sure the CORRECT fuse is in place before powering up. Also use an Isolated power transformer/supply.
I post these cautions because you're a new member and I don't know your qualification or experience.
So be careful, learn first and have fun.

Wayne

BTW Nice find! :)
 
Just bought 3 22uf/450v caps and one 47uf/50v for the 6v6 cathode bypass from Kevin at www.houseofscience.com - Also grabbed a couple of 4-pin speaker connectors - might make a bud box w/ 1/4" for several different impedances too.

I've got plenty of hobby experience working on electronics - from electric toys, FX pedals, friends' Xboxes, minor amp repair, etc. - but sure enough, other than some work on a Chandler tube pedal, this is my first foray into old/tube (read - could kill me) electronics.

I'll take every precaution - and will leave a letter addressed to my lawyer absolving all BBS posters of responsibility should I get crispy.

Thanks for your help.

BTW - as far as I can tell, this is about a rare a piece as they come. The only google references are re: schematics, and there are only a couple. (search for ["bell sound systems" 3710a] and this thread is all that comes up!) Should I consider selling this once it's restored? Or should I give it to a museum? ;)
 
I was half kidding about the museum jab ;) I pick and sing plenty, so I'm sure I can find use - even if it's just studio fodder. (some of my bands/songs etc. on my portal http://www.uncoolcentral.com )

I've been tossing around the idea of making a cab - incorporating the amp either right on top - or even buiding it INTO the cab somehow. (If you *really* bug me - I'll even show off my ultra-ghetto concept drawings.)

Any speaker recommendations? This puppy can take all sorts of loads with zero modification... so use your imagination
 
here's the feng shui concept draft of a cab incorporating the two functional faces of the amp. Not too sure of the placement (controls are towards the rear of the right side of the amp) But it's a start.

I always liked the ampeg flip amps (b-15 etc)
http://the-operators.com/images/instruments/amp2.gif

- and might want to do something like that - i.e. flip the head upside-down into the top of the cab when it's traveling etc.

More drawings soon.
 

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I'm sorry I did not previously indicate what I think the tubes are doing. The 6SJ7 (pentode) is probably the "mike" preamp. The 6SL7 (twin triode) is a driver/phase splitter. The 6V6s are the O/P devices and the 5Y3 is the B+ rectifier.

My "read" is that the phono I/P is unequalized high impedance line level and was intended to be used with piezoelectric phono cartridges.

I will not hazard a guess about how the instrument I/P is set up without looking at a schematic.
 
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