Head change?
- Thread starter dread31
- Start date
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keep an eye on the European auction sites, the whole headblocks are frequently available there. Its a lot easier to change the headblock than individual heads! Alignment after replacement could be a problem and requires a calibration tape, and a scope to do it properly. Dont think of new heads tho! In the UK the three would set you back around $1500.00. from a ReVox agent!!
The service manuals give the info you will require and are available for free on the web.
Persil
SaSi
Seriously Illogical
There are headblocks available for the A77 but they are rather rare (at least compared with the B77 ones for which there appears to be a steady and unlimited supply of 1-2 blocks per week).
The B77 headblock is very similar to the PR99 (lacking the right hand side tape meter and motion sensor wheel) but a lot different to the A77 one. So you cannot use a B77 headblock on an A77 and vice versa.
The good thing is that the A77 and B77/PR99 heads are interchangeable as they are the same item.
The bad thing is that although I agree with Persil that the head block replacement is much much simpler than head replacement (for the same reasons plus the need to desolder and solder the leads on the heads - something that can burn the coil if you are not careful and relatively fast) most headblocks that come with heads come with already worn out or almost worn out heads. Many sellers advertise the mirror flat area at about 3mm, which is marginal as 4-5mm is the limit for proper operation.
And, more important, this mirror makes head alignment a pain if not impossible. And, it causes the tape to travel over the head rather irregularly which generates phase modulation. I have tried to align such heads and I could never get a straight line on the scope. All I got at best was a relatively narrow ellipse for anything above 1kHz.
I have replaced my PR99 heads with brand new ones I got from Joe Dundovic and worked with him on producing a suitable kit of materials and instructions on the head replacement for PR99, B77 and A77.
I have several pictures from that process which you can have a look at http://www.pbase.com/sidiropoulos/pr99 Look at them and if your deck's heads look anything like the ones in pictures 2 and 3 then your heads are marginal.
My PR99 was easy to calibrate with the new heads and sounds fantastic.
If you really need to replace the heads and don't want to have it done by a service center, it *is* possible to achieve this with a lot of work and some shortcuts.
You can get calibration tapes that are both expensive and cheap or you can make your own, provided you take as granted that your current A77 is well aligned. Or you have access to someone with a well calibrated deck that can record a few test tones for you.
If you have a scope than all you need is time and a couple of simple tools. And patience for the first time. If you don't have a scope then you can use some piece of s/w that produces Lissajus patterns on the screen from what is input in the left and right channels.
But, it's a lot of detailed work for the first time since you need to discover how to dismantle your deck, reach the cables and remove the heads. Believe me, second time around it becomes really fast (2-3 hours including dismantling and bringing it back together and calibration).
The B77 headblock is very similar to the PR99 (lacking the right hand side tape meter and motion sensor wheel) but a lot different to the A77 one. So you cannot use a B77 headblock on an A77 and vice versa.
The good thing is that the A77 and B77/PR99 heads are interchangeable as they are the same item.
The bad thing is that although I agree with Persil that the head block replacement is much much simpler than head replacement (for the same reasons plus the need to desolder and solder the leads on the heads - something that can burn the coil if you are not careful and relatively fast) most headblocks that come with heads come with already worn out or almost worn out heads. Many sellers advertise the mirror flat area at about 3mm, which is marginal as 4-5mm is the limit for proper operation.
And, more important, this mirror makes head alignment a pain if not impossible. And, it causes the tape to travel over the head rather irregularly which generates phase modulation. I have tried to align such heads and I could never get a straight line on the scope. All I got at best was a relatively narrow ellipse for anything above 1kHz.
I have replaced my PR99 heads with brand new ones I got from Joe Dundovic and worked with him on producing a suitable kit of materials and instructions on the head replacement for PR99, B77 and A77.
I have several pictures from that process which you can have a look at http://www.pbase.com/sidiropoulos/pr99 Look at them and if your deck's heads look anything like the ones in pictures 2 and 3 then your heads are marginal.
My PR99 was easy to calibrate with the new heads and sounds fantastic.
If you really need to replace the heads and don't want to have it done by a service center, it *is* possible to achieve this with a lot of work and some shortcuts.
You can get calibration tapes that are both expensive and cheap or you can make your own, provided you take as granted that your current A77 is well aligned. Or you have access to someone with a well calibrated deck that can record a few test tones for you.
If you have a scope than all you need is time and a couple of simple tools. And patience for the first time. If you don't have a scope then you can use some piece of s/w that produces Lissajus patterns on the screen from what is input in the left and right channels.
But, it's a lot of detailed work for the first time since you need to discover how to dismantle your deck, reach the cables and remove the heads. Believe me, second time around it becomes really fast (2-3 hours including dismantling and bringing it back together and calibration).
ledinhaccweb
New Member
Dear Sasi! Can you note all step of calibration new head.
