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Phono preamp question - Printable Version

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Phono preamp question - radiotvnut - 01-06-2013

This is my first post here; but, I've been collecting/repairing vintage electronics for almost 25 years.

One of my collecting interest includes portable record players from the '30's to the early '70's. Many of these record players, both manual and automatic models, use a high output crystal cartridge that drives the audio output tube directly. This practice also continued into the solid state era.

The problem is that, after all these years, the original crystal cartridges have often gone bad and NOS ones are often on their way out. AFAIK, no one currently makes a ceramic/crystal cartridge that's over one volt in output. Of course, a one volt cartridge can be installed in place of a three volt cartridge; but, the volume will be very low. Frankly, I've been burned so much with buying NOS cartridges that had problems that I try to use current production models, whenever possible.

I realize that the older flat crystal 78 rpm cartridges can usually be rebuilt and I've read the excellent threads on this forum on how to do it; but, it's not always possible to rebuild the cartridges found in multi-speed models from the '50's and newer.

In some models with a single output tube, I have successfully added an extra preamp tube that will allow a .5V-1V cartridge to work in a record player that was originally designed for a 3V cartridge. Most of those models used a 25L6 tube with it's heater wired in series with the 90V turntable motor and the additional added 6AV6-based preamp stage seems to work well in these models.

However, there are some models where the chassis may be too small to add another tube or it may be a model that I'd rather not drill extra holes in the chassis in order to add the extra tube. For situations such as these, it would be nice to be able to come up with a solid state preamp design.

I've looked around on this site and have read about other members using such a design; but, I can't find a schematic. I've thought about going thru some old Sam's Photofact folders to find a suitable solid state preamp stage; but, if someone here already has such a design that they have used with good results, I'd love to hear from you.

I have a '66 Arvin consolette solid state stereo record player that uses a total of 4 transistors (2 for each channel) and it used a 3-volt stereo crystal cartridge. A modern 1V cartridge will work; but, I have to crank the volume all the way up on many records. This is another example where a solid state preamp stage would come in handy.

I'm sure others are in the same boat as me and I'd like to hear your thoughts on this subject. In the meantime, I'll do some experimenting to see if I can come up with something that will work.

RE: Phono preamp question - vaguy22 - 01-06-2013

Ebay is your friend. key in the search phono preamp u will see some new (China) preamps. you can dissamble them to fit in a confined aera. they are stereo so you can use in any project you are doing Hope this helps.