Magnecord PT6-BN (Binaural) Schematic Needed

[mjrippe]

Greetings Folks,

I have the pleasure of servicing one of the first stereo tape recorder preamps, a Magnecord PT6-BN.  However, it has been a futile effort trying to find schematics for the beast.  As it sits, it passes audio from mic in to speaker but one channel is badly distorted and I haven't checked the tape functions yet.  The belly of this beast is quite full of components and I dread tracing it by hand.  Tubes are all 7 and 9 pin miniature, unlike all of the PT6 schematics I have found so far.  Any docs would be most appreciated!

Thanks,
Mike

 

[CJ]

different P/N suffix, probably the same one you found already?

http://www.qx13.net/Magnecorder/PT6JA.pdf

looks like a cool product, look at all that iron, how much you want? 

 

[mjrippe]

Hi CJ,

The .JPG and the schematic you posted are of two different models.  The .JPG is close to what I have on my bench - all miniature tubes.  The schematic with 6SN7, 6V6, etc. is not applicable.  Note that the two grey cans in the photo are record equalization, not xfmrs.  My unit has Triad inputs.  The search continues!

Mike

 

[CJ]

it is gonna be a leaky coupling cap, measure the voltages on the good channel and then the bad, tube stuff is great in that you really do not need a schemo, just an RCA Receiving Tube manual and pencil and paper.

be careful with the HV! 

asked Doc for a schematic but no joy,

":Of Course I have heard of MAGNACORD. That recorder was kind of DESIGNED on a train while two guys were putting this thing together. They decided on 7 inch 8 millimeter film reels for that unit. It was was called the PT-6. In 1956 I bought the Home HIFI version of that machine which had a power amplifier and speaker built in and was a half-rtrack unit. I remember paying $341.00 for it."

 

[Mike Cleaver]

Relatively simple machines.
The tape deck part was a nightmare though, the entire thing held together with a few screws that when removed, allowed the entire thing to fall into pieces.
What CJ says, suspect the caps.
The first ones were full track single channel and were radio station workhorses back in the day when Ampex machines were horribly expensive.
The first versions had the full sized tubes and later versions had miniature tubes.
I used to work on these back in the '60s, both using and maintaining them.
I did have a schematic for the mono amp but I can't find it.

 

[CJ]

the bias voltage on the tubes will tell the story, so only a few pins to check, not 9,

there is a tube data link in my sig at the bottom, forget the RCA manual, call frank.

 

[mjrippe]

Hi Guys,

Thanks for the advice, I'm good with tubes and have RDH4 and RC-30.  There are some components that are un-readable in their current state so I figured a schemo would help save some time.  Of course caps are the first suspects and as you mentioned I can compare the two sides so I think I'll be on my way ;-)

Mike

 

[CJ]

if you see a high bias voltage, that means the coupling cap from the previous stage is your man. voltage leakage makes the grid positive which saturates tube, which causes high current across the cathode resistor,

if you see low bias, the screen bypass cap, if used, could be lowering the screen voltage,