Sony TC-377 playback hum

[ricard]

While working on a TC-377, I've noticed some low level hum in the left playback channel. It seems to be coming from the head, as it disappears if I short the head. Furthermore, it's only prevalent when the motor is running - disconnecting the motor removes the hum. Oddly enough it's hardly noticable in the rh channel. Any ideas? There's no movable hum shield on the head, in fact no adjustable shields or anything like that, so it seems to be part of the design. A bit bewildered why it is the lh channel only (or at least, mostly).

[TIMTAPE]

I noticed the playback hum in the 366/377 models is higher than I would have like. I guess the large overhang of the hum shield was an attempt to avoid adding a separate hum flap on these models, but maybe it was not totally successful. Will check left and right hum levels next time I have one of these on the bench.

[ricard]

Thanks Tim. It's a nice design detail that there is no 'tape slot' on these machines, so they're threaded by simply lifting the tape up towards the heads. This seems to be a Sony thing as a lot of older models have the same feature too. It does preclude anything in the tape path being south of the tape, unless special mechanical consideration is taken, like with the pinch roller. A movable head shield would have had to had a similar mechanical arrangement.

I might mention that I also tried reversing the connections to the motor to see if it would make a difference, but it didn't. (Incidentally, the motor connector is actually the only internal connector on this machine, and it's not polarized, so it seems that it is intended to be swapped over).

[TIMTAPE]

Originally Posted by ricard

Thanks Tim. It's a nice design detail that there is no 'tape slot' on these machines, so they're threaded by simply lifting the tape up towards the heads. This seems to be a Sony thing as a lot of older models have the same feature too. It does preclude anything in the tape path being south of the tape, unless special mechanical consideration is taken, like with the pinch roller. A movable head shield would have had to had a similar mechanical arrangement...

Yes by coincidence I have on the bench a Sanyo reel to reel deck (MR-805) which has both features used by Sony, the pop up pinch roller and the swing up pressure pad /hum flaps. Photos attached showing the similarity with the Sony design. I think I read that at some stage Sony and Sanyo cooperated on some design features. Maybe these are two examples.

[theredhouseinn]

That pinch roller could do with a clean Tim.
John.

[ricard]

Interesting design by Sanyo. It clearly shows that a movable hum flap would not have been as much as an issue as I initially assumed. I assume this is a 1960s machine, considering all the pressure pads?

Once one starts comparing designs it gets complex. Certain things, like the pop-up pinch roller and the V-shaped for acting as a tape guide before the erase head are similar to the Sony, but the Sanyo seems to have its heads mounted on a plate above the same, which is contrary to Sony's design. I wonder if one could chalk it up as being a typically Japanese design, rather than a specific similarity between these two companies? Ah, well, we can speculate ad infinitum ... (not that it might not be rewarding along the way...)

[TIMTAPE]

Originally Posted by ricard

Interesting design by Sanyo. It clearly shows that a movable hum flap would not have been as much as an issue as I initially assumed. I assume this is a 1960s machine, considering all the pressure pads?...

I havent been able to source any decent documentation on this Sanyo model, or interestingly any other Sanyo reel to reel machines, from the usual source. Still looking.

[TIMTAPE]

Originally Posted by ricard

Interesting design by Sanyo. It clearly shows that a movable hum flap would not have been as much as an issue as I initially assumed. I assume this is a 1960s machine, considering all the pressure pads?

I dont know the year unfortunately.

Originally Posted by ricard

Once one starts comparing designs it gets complex. Certain things, like the pop-up pinch roller and the V-shaped for acting as a tape guide before the erase head are similar to the Sony, but the Sanyo seems to have its heads mounted on a plate above the same, which is contrary to Sony's design. ...

I was thinking of the TC377, the subject of this thread, Yes the Sanyo is probably an earlier design than the Sony 377 but regardless of who did it first, both shared the pop up pinch roller and the top plate with heads suspended from it.