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Old 17th December 2007, 03:49 AM   #1
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Default Duosonic 40's era record player

I need either this schematic, or a simular one so that I can recreate this one. I can tell that there is no Power Transformer and the OT is built into the speaker. Any help to direct me to a schematic that will work or even this one would be great.
Patrick
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Old 17th December 2007, 06:44 AM   #2
gootee is offline gootee  United States
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You might want to try searching and then asking in the rec.antiques.radio+phono group, at http://groups.google.com .

Good luck.
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Old 17th December 2007, 06:47 AM   #3
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If that is a pic of the whole amp, it won't take long to figure the schema... what tube is it?

dave
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Old 17th December 2007, 09:30 AM   #4
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That single (78 RPM) player is somewhat similar to the mult-speed unit I used as a youngster. The circuitry appears to be incomplete. Where's the rectifier?

3 tubes is right, if my childhood recollection is valid. A high O/P (Volts) crystal cart. feeds a voltage amplifier, which (in turn) feeds a power O/P tube. The 3rd tube is the rectifier. Naturally, these things are very low fidelity.

Mounting a 2nd Octal socket is simple enough. Use a CL90 NTC inrush current limiter in series with a UF4007 for rectification. A 12SJ7 and a 50L6 are a reasonable signal tube combo. A 220 Ohm resistor and a 200 Ohm resistor, both rated for 10 W., complete the 150 mA. series heater string.

Crystal carts. go bad over time by absorbing atmospheric moisture. Unless the seals on that old cart. are unusually good, replacement will be necessary. The folks at Garage 'A Records may be able to provide something suitable.

BTW, what type of tube is currently present?
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Old 17th December 2007, 10:26 AM   #5
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Quote:
Originally posted by Eli Duttman
Use a CL90 NTC inrush current limiter in series with a UF4007 for rectification.
And an isolation transformer is highly recommended for safety.

dave
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Old 17th December 2007, 10:48 AM   #6
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Sam's 19-15 and 19-16 show Duosonic models K-1,2,3, and 4. This is all that is available. Not in Riders or Beitman's.

The rectifier may have been selenium. Year of Sam's pub is 1947. Use a 1N4007 and a resistor. I will post a value if I find a schematic, probably about 200 ohms.

The motor is probably in series with a 25L6GT, so 90V motor. People often replace them with 120V. the motors often run slow and must be disassembled to wash the old smelly green oil out of the bearing felts. All the old dried grease needs to be removed. clean everything with lacquer thinner, varsol won't cut it. be sure and vent the garage well.

The cart is probably a 3V crystal that feeds the grid of the 25L6.

There is no PT, off-line string heater setup.

Replace all the caps for sure, but don't start unless you plan to deal with the dried lubricants.

Don't get one of the original large metal carts with steel needle. Get an Astatic 146 flipunder needle with a real 78 sapphire and a diamond LP. The small tip usually sounds better on a worn 78. Be sure and get one with a red element. They are the later generation sealed in plastic. The others will go bad. ceramics don't go over 1V.

Canadian Astatic may have one, but be sure and get a red element otherwise they are only wrapped in paper.

They are a lot of trouble to rebuild, but they do have a nice sound. Good Luck Mark
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Old 17th December 2007, 03:41 PM   #7
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Hailteflon

Thank you for the feedback. What I actually want to do is turn this into an old school micro tube amp. I will be removing the motor, I will replace the stylus arm with a Phono jack for a guitar. I want really low volume tube distortion. I will have to take another look a the tube when i get home and i will post that. This thing definently did not ever have another tube in that empty hole though.
You mention Sam's 19-15 and 19-16 as a source for a schematic. Is this a book? I dont have a clue what values of these old caps were.

Patrick
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Old 17th December 2007, 05:23 PM   #8
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by whodatpat
Hailteflon

Thank you for the feedback. What I actually want to do is turn this into an old school micro tube amp. I will be removing the motor, I will replace the stylus arm with a Phono jack for a guitar. I want really low volume tube distortion. I will have to take another look a the tube when i get home and i will post that. This thing definently did not ever have another tube in that empty hole though.
You mention Sam's 19-15 and 19-16 as a source for a schematic. Is this a book? I dont have a clue what values of these old caps were.

Patrick

Seems like a lot of trouble for a low power guitar amplifier. I'll wager you could build a spud guitar amplifier on an inexpensive hammond chassis with modern tubes, possibly using this speaker and a small surplus power transformer or a couple of 6.3V transformers with one connected in reverse for B+. It will be safer and more easily tweaked.

The current amplifier design probably does not have enough gain for use with a fully passive electric guitar.
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Old 17th December 2007, 06:37 PM   #9
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Quote:
Originally posted by kevinkr



Seems like a lot of trouble for a low power guitar amplifier. I'll wager you could build a spud guitar amplifier on an inexpensive hammond chassis with modern tubes, possibly using this speaker and a small surplus power transformer or a couple of 6.3V transformers with one connected in reverse for B+. It will be safer and more easily tweaked.

The current amplifier design probably does not have enough gain for use with a fully passive electric guitar.
Alright I am intrigued, what is this spud guitar amp you speak of? Isnt the nedle on a record player just as passive? I want really low volume tube breakup. I am looking for fractional wattage here. Any sugestions are appreciated, but links to schematics are even better. :-)

Patrick
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Old 17th December 2007, 07:05 PM   #10
dnsey is offline dnsey  United Kingdom
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Don't even think of using that amp for guitar without fitting an isolating transformer

It's dangerous enough in its intended application, but there's much more chance of your coming into contact with potentially live connections if used as an instrument amp. You'd also run into severe hum problems if it's interfaced with other gear.

Crystal cartridges need a very high impedence to work into, so your lowish-impedence guitar pickup won't work well with this amp anyway.

Edit: The phono amp may possibly be run from an ancillary winding on the turntable motor, which is a bit safer, but you'd then have to fit a substitute transformer if you ditch the t/t.

Further edit: The input coupling cap (which is all that's between you and the live supply) looks as though it's about to expire - note that nearly all the wax has melted off due to overheating, probably because of leakage
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