Power supply for phonograph amplifier

[hearforever]

I picked up a Bogen amplifier that has a phonograph player on top of the metal case. I'm planning to convert it for guitar use but I have a question about the power transformer which is designed to also run the motor for the phonograph. I've attached the relevant part of the schematic for the amp.

I'm planning to disconnect all of the phonograph related parts. I'm assuming that leaves (on the schematic) the top 2 primary leads for the PT. What should I do regarding the bottom 3 leads that are for the motor? Also, what's going on with the heaters in this circuit?

[Rob Mercure]

Any chance this set up is for a "juke box" or where the record player is remotely controled by a coin mech? Enzo is out juke box expert and I expert he'll have this one figured out in a jiffy - for myself I'l like to see the rest of the schemo. As far as your heaters go they probably come from the same source as the 7Z4 heaters and I suspect that your AC feeds in at the top center where the two caps are in series with the center grounded and the light bulb across them. There's part of the control mech missing so you're gonna need our remote expert.

Rob

[Enzo]

I've seen those. Pretty standard Bogen "PA" amp except there is a turntable on the roof. 50 years ago it would have been very handy in like a grade school classroom. Tape was almost unheard of, and a lot of things were on phonograph record - aside from music.

I would also like to see the whole schematic - that 15 pin Cinch connector is the key to eveything.

[Rob Mercure]

Enzo,

Guess I've not seen too many Bogen classroom phonos - but the Newcomb design with the SE UL 6BQ5 output is one of my favorite conversion chassis. Anyhoo what's throws me is that the "power transformer" winding on the right has too many taps on the lower left winding while other transformer serves as, what, an isolation tranny for the turntable? Yer right, I'd like to see the wiring for that 15 pin plug (don't see much Cinch stuff - but you know that I like locking plugs) - definitely not the commonest classroom turn table setup. Hmmm, any chance the record triggered a slide projector?

Rob

[hearforever]

Yeah it's basically a Bogen PA with a turntable. Here's the whole schematic

[Enzo]

There should be another page in the Photofact with the rest of the wiring. We still don't know where the Cinch plug goes.

The TT already has its own transformer, so no isolation function needed. That extra secondary seems elevated by the output tube cathode voltage, but the associated 15 amp fuse is a mystery. Process of elimination plus the elevation makes that winding for the heaters, but why the second center tap? I guess that old thing might need a 15 amp heater fuse if there were other things potentially running off the CInch plug.

[hearforever]

The "cinch" plug is a female plug in the back of the amplifier. I'm uploading the first page of the Photofact which refers to a "6V storage battery". Does that seem relevant? There are no other pages in the photofact unfortunately.

[Enzo]

Oh very cool. I imagine there was a battery power pack - basically an inverter - that connected there. APparently it was considered a separate product it seems.

Does the amp work as is? If so, I think I would just unplug the motor itself and be done with it.

We always called them Cinch plugs, but I guess they should be called Jones plugs. CInch is the main company who made them.

[hearforever]

Ahh very cool. Can you still get those? I need to add a 3-wire power cord. It might be cool to leave the cinch plug in there and wire a 3-wire power cord with ground to the male end of the cinch. On the schematic, that'll be the hot line going into the fuse, neutral above it.

I want to turn it into a bass amp. I was reading that the 6SF5 is similar to 1/2 of a 6SL7 or 12AX7... I was thinking of pushing it in the Ampeg B-15 direction.

I just had a confusing thought though. I see where the heaters are now coming off of the lamp. Might the 6V battery have powered the heaters? Not sure how I can wire that...

[Enzo]

120v mains on the male connector? AH, the old death cord.

They still make them, that photo was from the Allied catalog. DOn't know if the 15 is still common stock item. They come in like three sizes of prongs, so watch the sizes when shopping.

No, it shouldn't have needed a battery to operate off the mains, the battery would have been an option so it could be used for example on the field for the marching band practice.

We can probably figure it out, but maybe there needed to be a jumper plug in there when not using the battery pack. From the schematic I'd be surprised if not.

The extra winding wires to M1, with C24 across it. Do you get 6VAC there? Oh wait, I think I see something. The extra winding has two taps. I am thinking now that the upper one is the 6VAC center tap, and the lower one the other end of the 6VAC, and the bottom end of the winding is a higher voltage used for something at M1. Quite possible a chopper and that winding becomes the primary for the PT when under battery use.

What kind of sockets are M1 and M2? Is M1 large like for an old 4-pin rectifier tube? I wonder if M1 was for a chopper?

Looking at the 15 pin connector, and numbering the pins like reading a book, it looks like the mains would go to pins 2 and 8.

And a jumper from either 2-3 or 2-1 would have enables the TT motor either on always or through the motor switch. You wouldn't need that.

The heaters appear to run off pins 5 and 13, so if the winding is indeed 6VAC, then we'd need jumpers at 7-13 and 9-5.

Of course if you can find 6VAC on the transformer somewhere, I'd have to assume it was for the heaters, and why not just run wires.

[hearforever]

I opened this thing up for a second yesterday but I'll have to take another look this weekend. Thanks for all of your patient replies to my questions...

[hearforever]

Well I think I figured it out. M1 and M2 are marked as Vibrator on the parts list and have 6V marked for input volts...looks like there must have been a jumper

[Enzo]

I was right. CHopper = vibrator.

SO explore that extra winding. Are there reasonable 6VAC between two of the wires or taps?