Thermionic Soundmirror

[TIMTAPE]

I watched the YT video.

I've never seen a Soundmirror to work on over here in the antipodes but I have transferred a number of paper and acetate tapes that came on Soundmirror reels, and were probably recorded on a Soundmirror in the early 50's. (local school musical concerts in the Dorking area)

Yes I'd make sure the capstan shaft and pinch roller are in excellent condition and the pinch roller is adjusted to specs. Pinch roller and capstan must be perpendicular to the deck plate and parallel to each other.

But even with that and everything else about the tape path ship shape, the tape can still wander wildly if the relative tape tensions of supply and take up are out of spec.

Specifically if the take up tension is too high relative to the supply tension, you can get that wandering effect. If possible, try reducing the take up tension. Perhaps there is a felt clutch on the take up reel drive which is binding due to the felt having deteriorated or the spring tension is incorrect. Ideally test the take up tension using a spring gauge. The tension should be smooth too. No variations such as tugs and jerks.

One of the problems with reel tension is that as the tape plays, the tension gradually decreases on the take up reel, and of course tension increases from the supply reel. This is especially a problem where the reel has a much smaller inner diameter compared outer diameter - as with those Soundmirror reels which are the worst I've seen for this. Problems tend to first appear at the very beginnings and ends of reels where the disparities in tape tensions are greatest. Of course this is not an issue with machines with constant tape tension from both reels.

Some of the Soundmirror paper tapes I worked with were damaged at the beginnings of sides, (many small folds/creases in rapid succession) probably due to excessive take up tension and/or not enough back tension, causing the tape to move down or up the capstan shaft. But equally, some of the recordings had recording speed problems towards the end of a tape side. One musical recording started to audibly lose speed regulation about half way through a tape side, and it only got worse as the tape progressed.
I don't think this was a paper tape problem as such. I suspected the machine they were recorded or played on was not set up correctly, but the Soundmirror reels with their very small hubs would have only made the situation worse.

Of course thinner base tapes will be more vulnerable to the twisting problem. Maybe when the machine came out there were only the stronger standard play tapes available.

Barry, I don't know if it's relevant to your historical accounts but the lady whose Soundmirror recordings I transferred, recently told me that the man who sold her husband their first tape machine back around the late 40's, probably a Soundmirror, was a Michael Gillam or Gilliam. He had his own mobile audio recording setup in a van with one or possibly two cutting lathes installed. His 78 RPM discs came complete with his name printed on the labels. I transferred some of these disc recordings as well. I think he later worked for the BBC so maybe he's the fellow Ted refers to.

[TIMTAPE]

Just to add: Maybe it does just need more back tension. Felt pressure pads for the head(s) provide some of this but there may be some sort of back tension clutch incorporated into the supply reel table which is not working properly.

[kalee20]

My Soundmirror came from my father, who used it a lot to help his violin playing (he became a professional musician, was in the Liverpool Philharmonic Orchestra and later a qualified teacher). It was not unreliable at all, though he did say when plastic-based tapes were developed they were a huge step forward from paper tapes.

The pressure pad for the head is important, it has an adjusting screw and needs to be set that the pull on the tape is 1 ounce, when pulled at 7.5ips. Obviously bypass the capstan for this!

Tension on the feed reel is quite small, as it is just a bit of drag from the leaf springs. Tension on the take up reel is larger, and although not completely constant, there is a self-compensating action as the reel fills. The tension is determined by the slipping of the reel turntable on the felt pads of the pulley underneath, and as the reel fills, on the one hand the radius increases (which reduces tape tension) but at the same time the reel gets heavier so increasing weight on the felt pads, increasing tape tension. The two would cancel out to at least some extent. In the Soundmirror it is of course non-adjustable, being determined by weight of the reel of tape, coefficient of friction between metal and felt, and gravity.

[brenellic2000]

Thanks Tim, the name Gillam doesn't ring any bells.

One famous name associated with TP (Soundmirror and Recordon c.1950-52) was Paul Spring (Paul Hans Springsguth) a German service Engineer (former PoW) who then joined Grundig(UK) and became Chief Engineer and Technical Director.

I wonder how much influence the Soundmirror had on Grundigs?!

[TIMTAPE]

Thanks for the hands on information Kalee.

Of course the pressure pad itself can deteriorate, requiring new felt to replace it.

Re felt clutches, over the years I noticed that often felt clutches actually increase in tension. It seems particles get trapped and form more of a dry paste-like matter, corrupting the original felt, and causing an increase in friction.

Sometimes cleaning the felt, and the metal or plastic disc it runs against, with a stiff bristle brush helps. If it's too far gone, new felt might be needed.

Service manuals state the reel tensions you should achieve in play, rewind and fast forward modes. The measuring device is a simple spring scale and a piece of string wound around the hub of an empty reel. If the figures aren't available for the Soundmirror, others from comparable types of machines would be a guide.

[Volatile]

Thanks for the input everyone, Well tonight i conclude another loss, i have been working on this thing since i came home trying to find the problem, here are my findings so far,

Pinch roller seems nice and even, tried another pinch roller of similar dimentions i had laying around and it did the same thing, tape path is nice and level, tentions on feed and take up are fine,

when the whole pressure pad, pinch roller assembley is shoved firmly against the head the problem stops, However there is allot of play in this mechanism, Rewind and FF barely engage anything, i think this thing has had allot of use over the years, and the mechanism has worn out ?

I am going to try the Pressure pad adjustment as Kalee said, i will report back

[Volatile]

OH WHY THANK YOU Kalee20!!!!!! I HAVE IT FIXED! Your comment about the pressure pad adjustment !

The set screw had miss threaded itself in the bolt and would not go in further, me being stressed last night never though to touch it, i can finally continue with the restoration !! Thank you all ever so much, you people are too kind !

[TIMTAPE]

That's great but increasing the felt pad's pressure decreases head life. There's a trade off. If excessive take up tension and/or or inadequate back tension from supply reel is causing the tape to wander those things should be attended to. Otherwise you might find the rare tape head irretrievably worn out in a short time.

[Volatile]

The tensions seemed alright to me, adjusting them made no difference at all apart , this is such a strange thing to work con compared to what I'm used too, il have another play tomorrow and see what else I can do

[Volatile]

After having a play this morning, loosening the pressure pad and staring at it for 15 mins I have discovered this,

The tape is not running evenly through the capstan / pinch roller. Adjusting reel tensions and heights has no effect and either makes it worse or just the same.

I have posted a photo of the problem point in the tape path

[Radio Wrangler]

It's difficult to judge, considering distortions from close-up lenses, but the pinch wheel axis looks to not be parallel to the capstan. The metalwork looks bent so that the top is further from the capstan.

David

[Kentode]

In the photo , post 30 , there's so much oxide on the rubber that I wonder if the tape is inside out?

Even if it isn't, cleaning the tape path again and using a known good tape with no sticky shed syndrome is the best way to proceed.

Don't give up on this!

[vidjoman]

Originally Posted by Radio Wrangler

It's difficult to judge, considering distortions from close-up lenses, but the pinch wheel axis looks to not be parallel to the capstan. The metalwork looks bent so that the top is further from the capstan.

David

My experience with tape mechanics is that the tape will squeeze up/down to where the pinch roller has least pressure on the capstan. In the photo it looks to me that the top is pressing harder than the bottom hence the tape trying to go downwards. A poor roller and too much pressure can also cause this to happen.

With all that oxide on the surface it’s surprising the tape will move correctly. The height of the roller looks to be too high relative to the tape path.

[Volatile]

You all are so helpful, thank you all

I am currently at work at the moment so i dont have the machine in front of me,
I will replace the tape when i get home, im having to use a BSR machine to wind tape on these thermionic reels as standard reels wont fit so it does take time.

I am leading towards something in the capstan and pinchroller contact department, The shedding tape did help me see wich part of the roller is making contact and wich part isnt, I shall examine the metal bracket closely to see if there is a bend in it, My downfall is i get stressed too easily, So having regular breaks from this machine is a godsend.

I shall try take some more detailed photos and video of tonights findings,

[TIMTAPE]

Looking at your latest photo the top of the pinch roller axle caught my eye. It appears to run in a slot. This is similar to a common Tandberg pinch roller arrangement as pictured. There is a spring at both top and bottom of the roller, pushing the roller onto the capstan shaft. You can just see glimpses of the single wire spring at the top. To the left and down is a rectangular bracket with a central screw locking it in place. Loosening this screw allows the bracket to be rotated to adjust the relative tensions of top and bottom springs and so to equalize the pressure of the pinch roller at top and bottom.

Maybe the Soundmirror has a similar adjustment arrangement. If it doesn't, there must be another way to adjust pinch roller pressure.

[Volatile]

There is no set screw sadly, The only way i can think of to adjust pinch roller pressure is to bend the spring, It seems like we have all narrowed it down to a pinch roller and capstan mating issue, Im hoping i can resolve this problem without having my rare tape head worn out, Kind regards,

[Kentode]

You haven't mentioned the service manual, which gives details of tape tension, tape guide and pressure adjustments.

It's available from up top for instant download.

Hope this helps.

[kalee20]

Originally Posted by vidjoman

In the photo it looks to me that the top is pressing harder than the bottom hence the tape trying to go downwards. A poor roller and too much pressure can also cause this to happen.

You two are actually contradicting each other!

Unless something is bent, in the Soundmirror there should be no reason for either to happen.

Maybe the pressure wheel is slightly conical? If you take it out and put it in upside-down, does the tape move to the other end?

The pressure on the pinch wheel is set, top and bottom, by a piano-wire spring. Hopefully the two arms of this are parallel (it is easy to take out, to check).

[Kentode]

Agreed. Check the spring.

[Volatile]

I have tried turning it upside down and it still does the exact same thing, and the spring that holds it is evenly tensioner