Sony TC-K71 Debauchery

[George S.]

I see the brass drive stub contacting the tire.
Is there not a felt disc clutch with a spring somewhere in the mechanism that would permit proper tension and slippage?
The Phase Linear deck I'm working on has two felt clutches.
One clutch for fast F+R, and another clutch for play.
I can already see that I'll have potential issues with tape tension if the felt or springs are out of spec.

 

[ButchJames]

I see the brass drive stub contacting the tire.
Is there not a felt disc clutch with a spring somewhere in the mechanism that would permit proper tension and slippage?

No, not that I can see, and it's the same (from memory) on the TC-K61. The slippage between brass driver pulley and idler tyre determines how much torque. If anyone knows otherwise for definite, then please chip in.

(a) Take Up Reel Table
(b) Idler gear and slippage rubber (to driver contact)

(a) and (b) are geared together as can be seen in above (earlier) photo.

 

[ButchJames]

The Phase Linear deck I'm working on has two felt clutches.
One clutch for fast F+R, and another clutch for play.
I can already see that I'll have potential issues with tape tension if the felt or springs are out of spec.

I've been working on an AKAI GXC-710D, which works off a pressured felt clutch system (PLAY/RW/FF), and indeed I've had to make some changes there too.

 

[George S.]

James, page 10 in the manual I posted, there is a spring loaded adjustable back tension lever.
Don't know, but perhaps this needs adjusted for less tape tension.
Gotta love these electro-mechanical devices!

 

[ButchJames]

Previously, I've been through all the back tension settings to combat the original tape creasing problem. I even added some extra back tension above the max setting - that did the trick, but it is not the answer. The problem is very probably that either one or both pinch rollers are not exerting enough traction; the problem is only with thin tapes. Concurrently, the rightmost reel tension ('take up') was also too high IMO, and this afternoon I reduced take up tension with the silicon grease on the rubber idler. It works great, but I do sense that this isn't going to last for more than a day or two as the silicon grease will begin to dry out under the continual pressure between brass drive and that rubber idler. The friction creates heat of course, accelerating the decline in the effectiveness of the grease.

I need a new idler and new rollers. ITMT, this 'fix' works for now.

 

[ButchJames]

Of interest to mr_rye89, the pinch roller sizes if you need new ones:

Supply = 11mm x 8mm x 2mm,
Take-up = 13mm x 8mm x 2mm.

I went looking for any pinch rollers I had in stock and found that I have two that would fit the Take-up side; a 13x8x2, and a 'chancy' 13.5x8x2. So the little devil in me has put in the 13.5x8x2, with about 0.5mm clearance with the roller frame. Fingers crossed it'll be okay, I don't see why not? if it does create problems, I have a 13mm roller.

I chanced the 13.5mm diameter roller as it should exert slightly higher pressure between capstan and roller.

Naturally the motor loading affect has changed slightly and I get 3155Hhz for a 3150Hz tape, and wow/flutter is as above in an earlier post, no change there; average of around 0.04x% wrms.

I took a photo of the new roller, note the hair on the roller! ... ha ha, sods law or what???

All working well, no tape creasing.

Also, observe the supply side, all nice and calm there now.

PS: I hope I haven't hogged this thread too much, but I just thought points here are relevant also to any TC-K71/75.

Apologies, having trouble uploading images!? ....

 

[ButchJames]

Images .... hopefully.

 

[laatsch55]

Ohh...we hog threads all the time...it's an art held In high regard here...

 

[mr_rye89]

This looks like a supply reel tensioner to me.... little felt pad on that white lever touches a hub on the back of the supply reel, has adjustable spring tension

 

[mr_rye89]

I also gobbed some JB Weld on there good and it's holding that spring plate, and I put a little ball bearing under said spring plate. I'd have buttoned it up tonight but getting the capstan flywheel belt on is a pain in the dick

 

[ButchJames]

Back Tension: Make sure the pad is clean; 'sticky' or inconsistent back tension can worsen wow/flutter especially at the end of the tape. Although I am speaking from experience with a single capstan machine - the Sony TC-206SD.

@mr_rye89: I'm sure you've seen this, but thought I'd upload it anyway. ;o)

 

[ButchJames]

Luckily, I haven't had a problem similar to yours at that frontside, just different ones elsewhere.

I have pinch rollers in the post, so when I get that supply capstan-pinch side done, I'll let you know as these transports appear to be near identical.

 

[ButchJames]

The rollers arrived today, bought from FixYourAudio.

Sorry to hog the OP's post, but it's worth a ganda if you have a similar deck.

I took the old supply pinch roller out; the 2mm pin will tap out and was/is held by frictional fit. Maybe I ought to put a spot of glue on the pin-casing just to be 101% sure?, although I really don't think it'll come out.

Sound as a pound now, was 99.5% okay before, but two new rollers should make things 99.99% good. Also has been C120 tested.

I tried to get a shot of the tape into the supply capstan-pinch 'side on', but I couldn't be bothered setting up a macro lens and tripod etc. But it's all good at that end, or no or very little signs of the tape micro-buckling etc.

 

[ButchJames]

Oh, and the tape guide is dead centre with the tape.

This job was a little awkward when returning the guide assembly back, and that - you have to leave the cassette loading/holding tray off while the supply guide is centred. It's common sense, experience with trial and error etc.

 

[mr_rye89]

That's good stuff! I had to remove the supply reel pinch roller arm so I'm gonna have to line things back up.

 

[ButchJames]

That's good stuff! I had to remove the supply reel pinch roller arm so I'm gonna have to line things back up.

Take care when returning the pinch assembly nut, it's easy to incorrectly fit the supply pinch roller assembly and accidentally press down on the REC/PB head sliding mech. Clearance is a must.

BTW, I forgot to upload this pic, not that it makes any difference.

 

[ButchJames]

Although this is a nice machine, there's a degree of cost cutting involved. As I've said before - no provision for variable pinch roller pressure.

 

[ButchJames]

To get that supply guide 'spot on' you'll need a 'cut out cassette'. During PLAY, I could raise and lower the said guide with my finger nail. The objective is to make sure that the guide walls do not catch the edges of the tape. It's a game of trial and error, but you'll get there. A good mirror tape is probably ideal, but I don't think it's vital.

While during PLAY, I used a magnifying glass (or very strong glasses) to study the tape flow at that end, watching carefully for the edges to clear the guide.

 

[ButchJames]

TESTING TESTING:

With everything aligned, and fingers crossed I checked out these https://fixyouraudio.com rollers ...





The quoted SM specs for wow/flutter was 0.04% WRMS, so at a mean value of around 0.042% ... 0.043%, that's good enough for me!

The belts were 'DeckTech' labelled. I know of someone in Edinburgh who sells belts at more than twice the price, but his belts are always (so far) better than any others. Anyway, I won't be seeking an extra potential reduction in w/f - who can hear it anyway? ;o)

 

[vince666]

The rollers arrived today, bought from FixYourAudio.

Sorry to hog the OP's post, but it's worth a ganda if you have a similar deck.

I took the old supply pinch roller out; the 2mm pin will tap out and was/is held by frictional fit. Maybe I ought to put a spot of glue on the pin-casing just to be 101% sure?, although I really don't think it'll come out.

Sound as a pound now, was 99.5% okay before, but two new rollers should make things 99.99% good. Also has been C120 tested.

I tried to get a shot of the tape into the supply capstan-pinch 'side on', but I couldn't be bothered setting up a macro lens and tripod etc. But it's all good at that end, or no or very little signs of the tape micro-buckling etc.

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Those ferrite heads, even if they show a sticker with Sony written on, they are really Alps ferrite heads... and they are just wonderful heads!