PR99 Head Confusion - UK Vintage Radio Repair and Restoration Discussion Forum

Linnovice · 29th May 2022, 5:54 pm

I've recently been having problems whilst changing the heads on my PR99. During the course of sorting out the problem I had to take all the audio boards out of the machine. On doing this I discovered a weird anomaly. I have a standard 7.5/15ips machine. It has the NAB label on the back but when I first bought it seven years ago I was told it was CCIR. On taking out the boards today I discovered that the Sync, Record Amp and Repro Amp are all labelled NAB 3.75/7.5ips!

It's been a very reliable machine and until now, I've had no need to go inside and fettle. It calibrates easily and sounds great so my problem is, what have I got? I was told it was CCIR 7.5/15 so I'm assuming that these three boards have been changed but I cannot find any evidence of work being done. All the solder joints look normal 'flow' soldered joints. Is there an easy way of a) checking them to see what they are and b) if necessary, changing them to what I want at 7.5/15 CCIR.

I'm on a steep learning curve but going through a mass of components trying to decifer what is what is just too much for me. Any suggestions or information would be very gratefully received.

Restoration73 · 29th May 2022, 10:41 pm

Only a small number of components differed on each board, and can easily be identified
using the service manual. For example on the record amp pcb only I cannot see any
difference in the IEC and NAB versions, apart from the actual drawing style of the
schematics.
Note the BV version was only made with IEC eq.

Linnovice · 30th May 2022, 7:45 pm

Excuse my ignorance but what does BV mean?

I think I know what?s happened. The glass fibre boards are I presume made up in large quantities. These boards all have a part number embedded in the glass fibre and the components then installed make up the finished board. I?m guessing here, but I would think any later revisions to the circuitry would not involve making new boards. They make the revision and then stick a small label on the board noting the revision. Problem being, over time the labels fall off! That?s where I am now. My boards have been revised but whatever labels were stuck on have now fallen off and so it?s hard to identify what board revision I have. I realised that this morning as one of the boards has a small sticker noting it as an IEC board.

The life of a hobbyist tech is not easy. I discovered the new playback head I?d fitted previously is open circuit on one channel!

Restoration73 · 30th May 2022, 10:15 pm

BV = Broadcast Version = no tempting knobs to adjust ;
http://www.gbaudio.co.uk/data/pr99iii.htm

So many years after production ended I expect some boards may have been modified.
Note that on the online manuals, the components lists can be a bit hard to decipher, but
the schematics are OK. Good luck with the head.

29th May 2022, 5:54 pm	#1
Linnovice Hexode Join Date: Jun 2014 Location: Chelmsford, Essex, UK Posts: 386	PR99 Head Confusion I've recently been having problems whilst changing the heads on my PR99. During the course of sorting out the problem I had to take all the audio boards out of the machine. On doing this I discovered a weird anomaly. I have a standard 7.5/15ips machine. It has the NAB label on the back but when I first bought it seven years ago I was told it was CCIR. On taking out the boards today I discovered that the Sync, Record Amp and Repro Amp are all labelled NAB 3.75/7.5ips! It's been a very reliable machine and until now, I've had no need to go inside and fettle. It calibrates easily and sounds great so my problem is, what have I got? I was told it was CCIR 7.5/15 so I'm assuming that these three boards have been changed but I cannot find any evidence of work being done. All the solder joints look normal 'flow' soldered joints. Is there an easy way of a) checking them to see what they are and b) if necessary, changing them to what I want at 7.5/15 CCIR. I'm on a steep learning curve but going through a mass of components trying to decifer what is what is just too much for me. Any suggestions or information would be very gratefully received. __________________ Small Scotch, New Aids and Happy Ears

29th May 2022, 10:41 pm	#2
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: PR99 Head Confusion Only a small number of components differed on each board, and can easily be identified using the service manual. For example on the record amp pcb only I cannot see any difference in the IEC and NAB versions, apart from the actual drawing style of the schematics. Note the BV version was only made with IEC eq.

30th May 2022, 7:45 pm	#3
Linnovice Hexode Join Date: Jun 2014 Location: Chelmsford, Essex, UK Posts: 386	Re: PR99 Head Confusion Excuse my ignorance but what does BV mean? I think I know what?s happened. The glass fibre boards are I presume made up in large quantities. These boards all have a part number embedded in the glass fibre and the components then installed make up the finished board. I?m guessing here, but I would think any later revisions to the circuitry would not involve making new boards. They make the revision and then stick a small label on the board noting the revision. Problem being, over time the labels fall off! That?s where I am now. My boards have been revised but whatever labels were stuck on have now fallen off and so it?s hard to identify what board revision I have. I realised that this morning as one of the boards has a small sticker noting it as an IEC board. The life of a hobbyist tech is not easy. I discovered the new playback head I?d fitted previously is open circuit on one channel! __________________ Small Scotch, New Aids and Happy Ears

30th May 2022, 10:15 pm	#4
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: PR99 Head Confusion BV = Broadcast Version = no tempting knobs to adjust ; http://www.gbaudio.co.uk/data/pr99iii.htm So many years after production ended I expect some boards may have been modified. Note that on the online manuals, the components lists can be a bit hard to decipher, but the schematics are OK. Good luck with the head.