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Old 6th Dec 2017, 4:17 pm   #15
gramofiend
Pentode
 
Join Date: Aug 2010
Location: Cowbridge, Vale of Glamorgan, UK.
Posts: 110
Default Re: Revox A700 flutter only at 7.5ips?

Hi, if I may put my two pence in, you say you have checked the tape path completely. Do remember that this machines tape tensioners are part ofthe electronic control. Are the tape guides on each side of the headblock free and do the guide rollers run free? Several times whilst using the A80 in the BBC I had instances of flutter introduced by chattering damping guide rollers more on the take up side of the headblock, I know the A 80 is a much more advanced unit than the A700 but the machine, built in 1967/8 was the first with all electronic control and incorporating 19 integrated circuits, specifically made for that machine, very few of which were subsequently used in any other studer product! The audio ic's , TBA931 for which there is a work around replacement of a A signetics 231, direct plug in, or a signetics NE5532 which requires a bit of a rewire involving a piggy back board. Unfortunately the motor control chips including the three TCA561 devices, as rare as rocking horse do do's, are available from certain dealers but at prices that make eyes water! If you have noticed or seen a Studer B67 you will have seen that the control switch bears an uncanny resemblance to that of the A700 also the capstan control board. I found this out when I took a chance and bought the capstan board at the NVCF a few years ago and when a friend and I experimented with biasing arrangements managed to convert the board to run the A700 at all speeds with 'lock' achieved. Whatever you do, be vary careful around the pins of the TCA561's. I have a non functioning 2nd A700 awaiting total rebuild of the back tension/motor control system. I will base this on I hope simpler but as effective circuitry and if successful will make it available.
Mike
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