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walterbeers 06-15-2016 08:37 PM

Illustravox record player/projector
3 Attachment(s)
I am restoring a Illustrvox record player/projector and need some suggestions. It's sort of a 1950s "power point" in which you play a record and advance slides in order to make a presentation. Well I am having the cartridge rebuilt, which is a crystal type, and I'm going to do a recap. I am wanting to ad an audio output jack in order to directly connect the audio into the input of a computer or stereo/mono receiver. This is an Illustravox JR, which was mfg in 1949. I am only concerned with the record player part. Where could I make connections to safely provide an audio output jack? Attached is the schematic of the amp and some pictures. It looks as if the 6SC7 is used an an inverter tube, driving the 2 25L6 output tubes. Cartridge connects to socket 220 on the schematic. Can I just take the signal off the secondary of the audio output transformer? The pin that is connector to C201-1 is the ground for the tonearm. Any suggestions would be appreciated.

Electronic M 06-16-2016 12:08 AM

The speaker winding is a good place (start with low volume). Hum is possible, but it is possible anywhere....Make sure you do not have any AC leakage between the line and your jack...If you connect a hot chassis (even if it is a transformer set with primary to secondary leakage) to a computer the results may not be pretty and could get expensive.

walterbeers 06-16-2016 06:07 PM

The AC leakage is one of definite concern. There seems to be a hot common circuit ground,, however the chassis, metal parts, and record player seems to be isolated by (2) .02 capacitors marked by my X on the schematic. Although I will be replacing the capacitors, I wonder how much current, hum, or leakage will be sneaking through those 2 capacitors. The .02 caps are only 600 volt, and I would want a lot higher voltage caps in there, as surges on the AC line could be much greater. I may be answering my own question, but I"m thinking maybe a ground loop isolater could get rid of the hum problem, if it proves that there is hum present. Of course a AC line isolation transformer is probably the best choice, but it would have to be an extra piece of equipment. Actually the audio output transformer should isolate the AC line, but I also notice 2 windings on the voice coil of the speaker. One cancels out hum (from the electromagnet on the speaker), and other is the main voice coil. I just got the rebuilt cartridge in the mail today, so it's onward and upward with this project.

Electronic M 06-17-2016 02:11 PM

What I'd (and have done) is break out the lines from the computer audio input, and the tube device output, and check AC and DC volts between (all) out and (all) in lines with a DMM with both devices on and off.

An external isolation transformer and or an audio line isolation transformer should be enough to fix any AC leakage....Another option is to connect to a laptop running off batteries with the power adapter unplugged.

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