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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 7th Nov 2018, 11:53 am   #61
NorfolkDaveUK
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Default Re: Revox A77 calibration.

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Originally Posted by ms660 View Post

If the OP isn't too sure about what's what with tape deck setups in general I would recommend downloading a Sony tape deck manual to study, the TC-366 is a good place to start, the instructions and functions are easy to follow and most Sony manuals include level diagrams for both record and playback, with those diagrams you can practice your db to voltage or voltage to db calculations just to get the hang of it and compare the results with those given in the diagrams, the instructions are very clear and include pictures of what's connected to were and the signals journey via the tape where applicable, the level diagrams even give the levels in and out of the record volume controls when set for 0db line out at the prescribed input level and frequency.
I will be in a much better position once the above meter gets here. I only got the scope recently so I'm very green with it and I'm still very much learning how to use it. The meter will be much simpler as Maurice said. As for the fault that's bound to be something I was doing wrong, as you know my health is not great and I get a bit confused sometimes, but I get there in the end usually. I appreciate everyone's patience with me. I suffer from bipolar disorder if you weren't aware so confusion sets in sometimes. Anyway, I'm learning as I go and winning for the most part.
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Old 7th Nov 2018, 12:14 pm   #62
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Default Re: Revox A77 calibration.

A known good test set is good for tape deck setups etc if you do a lot of them, back then the Ferrograph RTS2 was a popular choice, I see you are aiming for one of those, that's the type I used, you can just see the left hand end of one set into the bench panel in the photo, that was my old bench at Sony, the 'scope was nothing special (single trace B&K) shortly after the photo was taken I upgraded to a better spec dual trace job in preparation for Sony Betamax servicing as the Betamax had just been launched, needless to say there were scorch marks behind the two dummy load resistors shown in the photo.

Lawrence.
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Old 7th Nov 2018, 12:19 pm   #63
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Default Re: Revox A77 calibration.

You can set up tape recorders with all sorts of instruments.

I prefer an oscilloscope as my first look at anything because it allows you to see everything that's going on. DVMs are more accurate on voltage, but can be misleading if something funny is going on and stuff usually winds up on my bench only if other people have failed to find problems.

For setting up tape bias on 3-headed machines, I use an HP 3580A audio spectrum analyser. Set to slow sweeps and a wide resolution bandwidth the it's tracking generator is still within the analyser's bandwidth even after the tape delay and I have the luxury of looking at updating frequency response plots as I adjust.

It's a new area to you and you're still finding your way around, so you may be best sticking carefully to the printed setup routines to start with and then getting more adventurous when you have a bit of spare time on a machine of your own.

THose adjustment routines are usually well written and carefully thought out, they don't usually explain why some things are done the way they are, but the Sony ones suggested above make informative reading.

Those adjustment procedures weren't handed down on tablets of stone, someone had to design them. Someone had to pick operating levels and bias levels by looking at the effects on flatness and on overall distortion and then pinning the tail on the donkey by picking a good compromise bias setting and planning out how someone in a service centre with limited test equipment can arrive at that level.

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Old 7th Nov 2018, 12:21 pm   #64
NorfolkDaveUK
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Default Re: Revox A77 calibration.

Quote:
Originally Posted by ms660 View Post
A known good test set is good for tape deck setups etc if you do a lot of them, back then the Ferrograph RTS2 was a popular choice, I see you are aiming for one of those, that's the type I used, you can just see the left hand end of one set into the bench panel in the photo, that was my old bench at Sony, the 'scope was nothing special (single trace B&K) shortly after the photo was taken I upgraded to a better spec dual trace job in preparation for Sony Betamax servicing as the Betamax had just been launched, needless to say there were scorch marks behind the two dummy load resistors shown in the photo.

Lawrence.
I had a 60MHz analogue scope and that was much simpler to use but the darn thing packed up on me (tube went) so I got this Fluke and it's overly complicated for what I need really, it's all push button and menus and, uggh so I may end up selling that and getting a regular one again although i dont really want to be defeated by it ..lol, but for now the Siemens meter should do what I need it too. If I can find a good RTS2 at a good price that's what I will end up with yes.

Quote:
Originally Posted by Radio Wrangler View Post
You can set up tape recorders with all sorts of instruments.

I prefer an oscilloscope as my first look at anything because it allows you to see everything that's going on. DVMs are more accurate on voltage, but can be misleading if something funny is going on and stuff usually winds up on my bench only if other people have failed to find problems.

For setting up tape bias on 3-headed machines, I use an HP 3580A audio spectrum analyser. Set to slow sweeps and a wide resolution bandwidth the it's tracking generator is still within the analyser's bandwidth even after the tape delay and I have the luxury of looking at updating frequency response plots as I adjust.

It's a new area to you and you're still finding your way around, so you may be best sticking carefully to the printed setup routines to start with and then getting more adventurous when you have a bit of spare time on a machine of your own.

Those adjustment routines are usually well written and carefully thought out, they don't usually explain why some things are done the way they are, but the Sony ones suggested above make informative reading.

Those adjustment procedures weren't handed down on tablets of stone, someone had to design them. Someone had to pick operating levels and bias levels by looking at the effects on flatness and on overall distortion and then pinning the tail on the donkey by picking a good compromise bias setting and planning out how someone in a service centre with limited test equipment can arrive at that level.

David
Yes thats why I like using the scope you can see noise and "weird stuff" happening on the scope that a needle just can't show you, but once you have hooked it up to the scope an seen nothing is ary it is then simpler to just use a needle probably.

Last edited by NorfolkDaveUK; 7th Nov 2018 at 12:35 pm.
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Old 7th Nov 2018, 2:06 pm   #65
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Default Re: Revox A77 calibration.

BTW , these are all my machines , I have about 12 - 14 at the min . I dont do work for other people incase you got the impression I did , when I say "customer" i refer to the person that buys the machine when its all finished and I always let them have a good pl\ay with it before selling them and never had one back . I didnt want people to think I was taking money for doing shoddy work on other people machines . When I sell them I sell them as part calibrated and state clearly that I`m no expert just a hobbiest and the machine will more that likely need tweaking .
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