Record players with low volume
 

This is now the third time I've run into this.....

Your average 1950's three tube stereo suitcase record player, tubes test good, replace the electrolytics, and the volume is still just about barely listenable. Are the audio transformers in these things junk? I'm puzzled, because this is now record player #3 that has me scratching my head with the same issue....

I'm guessing that the cartridge has degraded, low output.
jr

I would second the cart as an issue.

Dont the old cartridges have some kind of crystals that absorb moisture and fail?

yep, thats the way I understand it. I have had NOS carts that had zero output, keep that in mind when buying one.

Has anybody here used this service?
http://www.west-techservices.com/p1.htm
not affiliated,
jr

The potting compound inside crystal and ceramic cartridges can get hard and brittle and prevent reed vibration. This kills the output. I've used west-tech before and they're ok. I've had about a 90% success rate.

You might think about substituting a newer ceramic cartridge. Not only are they better on records with lighter tracking, but sound better. The only thing you run into is output.

A crystal cartridge and some older ceramic carts put out anywhere from 2-5v p-p - whereas you're lucky to get 600mv out of a modern ceramic cartridge. This could be remedied by the use of a single stage FET amplifier. The gain wouldn't have to be tremendous (about 4-5) which would mean about 5-8 parts on a postage stamp size piece of perfboard. This would yield adequate volume and decent sound quality. a late 60s, early 70s electrovoice cart or good ol TN4 cart would be good contenders for this project.

Many cheaper players, even into the solid state era, used a 3 volt crystal cartridge. It is very easy to tell on a tube unit. If there is no preamp tube (12AX7, 12AT6, etc) ahead of the output tube(s), you have a 3 volt cartridge that is designed to drive the output stage directly. More than likely, the old cartridge is weak or dead. Unfortunately, I know of no current production 3 volt cartridges. I have used a current production 1.3 volt mono Astatic 89T cartridge in place of an older 3 volt unit; but, the volume will not be very loud. If space permits on the chassis, you could mount an additional tube socket for a 12AX7 or 12AV6 and add a preamp stage. I've heard of people doing this and I don't think it would be too difficult.

In the cheap kiddie players, there was usually a 25L6 output tube, with it's filament wired in series with the 90 volt turntable motor. This tube was driven directly by the high output crystal cartridge. For the rectifier, they usually used a selenium or, in later years, a silicon diode. However, some models had a tube rectifier. When stereo came along, there was an output tube for each channel (50EH5, 60FX5, etc), with either some form of solid state rectifier or a tube rectifier.

If your amp has a preamp tube ahead of the output stage, you should be able to get away with using a current production 1 volt cartridge (Pfanstiehl P228, etc). If using in a mono player, simply wire the two channels of the stereo cartridge in parallel.

I have used West-Tech services to rebuild two of the old style '40's era 78 rpm crystal cartridges. The rebuild + new stylus cost $55; but, it saves me from having to modify the tonearm for a modern cartridge and it keeps the record player more original. Given that a new cartridge will run $25-$30 and will often require modifications, I usually opt for a rebuild. Especially on 78 rpm only models.

Tube complement is a pair of 50C5's and a 7025. Cart is an Astatic 80TS.

I found this on fleabay, shows 0.7 volts, does that seem correct?

http://cgi.ebay.com/PHONOGRAPH-CARTR...item43a81e52de

If you are going to add a preamplifier, why stop there? Replace the whole cheapie amplifier with something decent. Even a modern headphone amplifier might do it.

If you want to preserve the antiquity, to restore it, you will have to find a proper cartridge. Rochelle salt is the material that was used for the most part; there is a web site that shows you how to make your own.

http://blog.makezine.com/archive/201...rew-piezo.html
http://www.seawhy.com/xlone.html
http://www.seawhy.com/xlroch.html

I think I'd throw it out if I had to go that far to play records on it ;)

The 7025 is a high grade 12AX7 so it's obviously not original. But that circuit should have enough gain to use a low output cartridge. A pair of 50C5s oughta put out a couple of Watts easily. The three heater voltages add to 112.6, close enough to 120 I guess. To do the 50C5s justice a voltage doubler would be the best idea but that thing probably doesn't have one. In any case adding a stage of gain should be an easy change, just add one tube.

It would be cool to be able to rebuild cartridges on ones own using cheaply avaliable materials.

Tom C.

PS: I found those sites about growing piezo electric crystals fasinating.

Actually, it is. It's right on the tube diagram......

Think I'm gonna pick up an eBay cart and see what happens......I'm a decent repairman and an excellent part replacer, but not proficient in DIY modification.....

7025 may have been specified just because the manufacturer happened to
have a bunch of those tubes on hand while designing the circuit. A 12AX7 should
work find in such a high level circuit, of course.