'62 Truetone consolette record player

[radiotvnut]

Last week, someone I know called to say that they were about to tear down his old family home that he grew up in and inside the house was an old hi-fi that his parents bought when he was a small child. He wanted to know if I wanted it and I accepted his offer. Last night, when I went out with the dog for her to do her business, I found the record player in the driveway (I talked to him today and he said he simply left it when he couldn't get me to the door).

It's a Truetone (Western Auto) 3-tube (50C5 x 2, 12AX7) stereo unit with a VM 1223 series record changer. This one is going to need some help and I thought about parting it out; but, I think I'm going to attempt to restore it. Cosmetically, a piece of trim is busted on the front and the grille cloth could stand to be replaced. The piece of broken trim is simply screwed in place and I'll probably try to replace it with a piece of molding. The lid support is broken; but, I just ordered one off ebay ($5 and some change, including shipping).

Electronically, someone has been inside and the back was laying inside the cabinet. One tube is missing and one of the 4" speaker cones is gone. The changer will need the usual service and the tonearm needs to be rewired.

This is a little bit of an oddball setup in that they send the low frequencies to a center speaker, with the higher frequencies going to L and R 4" speakers. There are also external speaker jacks on the rear panel. With 50C5 output tubes, it won't rattle the windows; but, it should sound decent. Years ago, I had a similar Truetone unit with the same amp and I remember it sounding OK.

Had I not taken this unit, it would have wound up getting crushed by the tearing down of the house and been thrown in a construction dumpster; so, I think I should at least try to bring it back to life.

It's amazing that the low end stuff back then often is better than the low end (and, sometimes, the not so low end stuff of today).

[mstaton]

Looks like the paper on the left speaker is gone

[dieseljeep]

Originally Posted by mstaton

Looks like the paper on the left speaker is gone

It looks like it could've been mouse damage. It's funny that only one speaker is damaged.
When the OP said one tube was missing, I thought for sure it was the 12AX7.
A lot of those smaller amplifiers used Mullard or Amperex, 12AX7's. Back then, they weren't that more expensive and they didn't have to be selected for lower noise or microphonics.

[radiotvnut]

I tore into the amp tonight and what I found is not good. One of the output transformers is open and this set uses oddball transformers with 3 seperate windings. We have the secondary winding going to the speaker, we have one primary winding that reads 220 ohms and is in the plate circuit of the output tube, and we have a second primary winding that measures 10 ohms and I haven't traced where it connects (it's nice when the amp is stereo - I can use the other transformer for reference). I suspect the only luck I'll have is finding a good used transformer; but, the chances of this thing living again went down a great deal when I found the open transformer.

[Electronic M]

Your 'two primaries' comment about the output transformers makes me think what you may have are 'ultra-linear' (screen tapped) output transformers.

I had a conceptually similar Decca brand unit that sounded and looked quite decent. I got it for a song and parted it out as it had the same changer (only in much better shape) that was in my first console (a Philco AM FM(MPX) stereo phono).

[Olorin67]

The extra winding might be for the 3 channel set up.

[radiotvnut]

Here's the schematic and the extra winding is actually on the secondary side of the output transformer, for negative feedback. Finding a transformer with this extra winding will probably be hard to do; so, I may have to figure out a way to eliminate this winding.

[maxhifi]

Weird - the tweeters are connected out of phase! I think thwy used a separate feedback winding because of the phase reversal on the secondary. You could redesign it to take feedback from the plate to the grid of the 50C5 instead, if the speakers really require a lower output impedance and to tame the gain a bit.

[Electronic M]

Most feedback I've seen comes off the speaker windings. Given the resistances I suspect a higher impedance feedback winding to supply a higher feedback voltage. If you can determine the correct ratio it might be feasible to use a normal output xfmr and another small one to step the speaker winding back up to feedback level.

[maxhifi]

Originally Posted by Electronic M

Most feedback I've seen comes off the speaker windings. Given the resistances I suspect a higher impedance feedback winding to supply a higher feedback voltage. If you can determine the correct ratio it might be feasible to use a normal output xfmr and another small one to step the speaker winding back up to feedback level.

I think they used a separate winding not for a different voltage, but because the way the bass driver is connected it would prevent feedback from being connected normally. (look at the reversed green and black wires)

The higher resistance doesn't necessarily mean a different voltage ratio either, it could just mean finer wire (the feedback winding will pass very little current, so can be a much finer wire than the voice coil winding). Easiest way to find out is to apply some voltage to the primary of the good transformer, and measure what appears at the secondary and feedback windings.

There are a few ways to fix this amplifier, what it looks like to me is a somewhat semi ignorant copy of a clever design. I say so because the two tweeters are out of phase, and it seems like they went to a lot of work to order custom transformers which in such a cheap console probably weren't justified.