UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players

Notices

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

Reply
 
Thread Tools
Old 25th May 2024, 11:37 am   #1
Linnovice
Hexode
 
Join Date: Jun 2014
Location: Chelmsford, Essex, UK
Posts: 396
Default PR99 Voltages

Hi all, I'm underway recapping my PR99 MkII and have a (hopefully) small query. I've recapped the power supply/tape transport control board/speed regulating board and am in the process of getting them set and stable before moving onto the audio boards.

My question; the Service Manual specifies an unregulated 24V supply at resistor R34 on the tape transport board. I'm getting 27VDC (it quotes 24V . . . 26V). Is this extra voltage critical and, if so, how do I adjust it? There doesn't appear to be any trimmers for this purpose.

Any advice would be gratefully received.

Mike.
__________________
Small Scotch, New Aids and Happy Ears
Linnovice is online now   Reply With Quote
Old 25th May 2024, 12:11 pm   #2
Welsh Anorak
Dekatron
 
Welsh Anorak's Avatar
 
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,997
Default Re: PR99 Voltages

I found this on a PR99 I was restoring.

There's no adjustment and when the machine is idling it does hit 27v. This varies with demand, so as long as the +24v is spot on there's no need to worry.

You probably know this (I didn't!) but there's a RIFA cap hidden behind the mains input panel just lying in wait....
__________________
Glyn
www.gdelectronics.wales
Welsh Anorak is offline   Reply With Quote
Old 25th May 2024, 1:28 pm   #3
Ted Kendall
Dekatron
 
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,718
Default Re: PR99 Voltages

Quote:
Originally Posted by Welsh Anorak View Post
You probably know this (I didn't!) but there's a RIFA cap hidden behind the mains input panel just lying in wait....
I didn't on the first B77 I tackled - but I soon found out!
Ted Kendall is offline   Reply With Quote
Old 25th May 2024, 2:27 pm   #4
Linnovice
Hexode
 
Join Date: Jun 2014
Location: Chelmsford, Essex, UK
Posts: 396
Default Re: PR99 Voltages

Thank you chaps, I suspected as much but it is good to have it confirmed.

Re the RIFA (and Frako) . . . all in the bin not one to be seen.
__________________
Small Scotch, New Aids and Happy Ears
Linnovice is online now   Reply With Quote
Old 25th May 2024, 2:39 pm   #5
Linnovice
Hexode
 
Join Date: Jun 2014
Location: Chelmsford, Essex, UK
Posts: 396
Default And another PR99 question

Following on from my query this morning re my PR99 MkII.
I have the transport side all finished now but on testing I've found that the Brake Solenoid is not working. I've traced it back to a transistor on the Tape Drive Control Board, Q13 which is listed as a BD 135 Medium Power NPN.

Would a NPN TO126 45V 500mA 6.5W from Cricklewood constitute a 'Medium Power' transistor?

Thanks in anticipation
Mike
__________________
Small Scotch, New Aids and Happy Ears
Linnovice is online now   Reply With Quote
Old 25th May 2024, 3:40 pm   #6
Welsh Anorak
Dekatron
 
Welsh Anorak's Avatar
 
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,997
Default Re: And another PR99 question

To be honest I'd use a BD135 - 500mA / 6.5W seems a bit on the low side to me - the datasheet suggests 1.5A/12.5W.

The genuine transistor is a staggering 9 pence from CPC!
However the minimum order might be a problem...

Quite a few on eBay from trusted sellers with no minimum order.
__________________
Glyn
www.gdelectronics.wales
Welsh Anorak is offline   Reply With Quote
Old 27th May 2024, 11:02 am   #7
Linnovice
Hexode
 
Join Date: Jun 2014
Location: Chelmsford, Essex, UK
Posts: 396
Default PR99 Board Confusion

Hi all, again. I've got a bit further with my refurbishment of my PR99 MkII and have discovered something odd. AFAIK it is a IEC machine with corresponding boards thoughout the audio section with one exception. For some reason it has a NAB board in the SYNC. Amplifier board slot. Instead of the 1.177.872 board it has a 1.177.871 in there.

My question is, does this make a significant difference? I have never to date used the Sync facility on the machine. I've looked at the service manual and there seems to be quite a bit of difference with additional circuitry and IC's to the IEC version. Is it possible (or even worth) changing my board to the correct spec?

Any advice would be gratefully received. I cannot understand why anyone would swap the IEC for NAB boards.
__________________
Small Scotch, New Aids and Happy Ears
Linnovice is online now   Reply With Quote
Old 27th May 2024, 5:32 pm   #8
theredhouseinn
Hexode
 
theredhouseinn's Avatar
 
Join Date: Jan 2013
Location: Kelvedon, Essex, UK.
Posts: 278
Default Re: PR99 Voltages

I might have a bd135 Mike.
I will have a look tomorrow when I am in the cave.
John.
theredhouseinn is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 2:39 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.