Revox reproduce amp troubleshooting problem

[Riley Casey]

I'm restoring my 40 year old tape machine and have run into a problem - well lots of problems but this one I haven't found a solution for. The issue is getting signal into the repro amp to signal trace. Its not practical to signal trace from a running roll of tape so I thought to disconnect the PB head and connect the oscillator to the leads and thus to the PB amp inputs. I can see signal at the input terminals of the repro board but I don't see any signal in the gain stage or at the level trimmer that feeds the output stage. After replacing a shorted tantalum coupling cap I have what looks like good DC voltages on the BC109s in the gain stage so presumably have the dead channel fixed but I'm stumped as to why I can't see signal anywhere but the H-REPR-R terminal (pin 6 ). Grounding or ungrounding pin 5 makes no change. The other channel behaves the same way. Do I need to couple the oscillator to the repro amp with a transformer to simulate the head loading? Feeding the signal in with the head connected loads the oscillator down too much. Its an old Leader unbalanced out sig gen.

Thanks for any suggestions

 

[ruffrecords]

Two problems with that. First the head is floating so connecting your sig gen will connect one side to 0V which will mess up the bias point of the second transistor. Secondly, you need a capacitor in series with the line that goes to the base of the first transistor. If you want to connect direct to the reproduce amp inputs I suggest you go in via a 1:1 transformer (10K:10K will probably be OK).

Cheers

Ian

 

[Philbo King]

You might go through it and measure the DC voltage on B, C & E on the transistors.

 

[guy_4]

Hello Riley,

I would suggest you to use a Flux Loop to test the PB section of your Revox ( or any TR )

https://www.tapeheads.net/threads/example-of-a-flux-loop.102957/

Best,
Guy