Tape speed adjustment on a Revox PR-99 MK3 - UK Vintage Radio Repair and Restoration Discussion Forum

themisk · 18th Mar 2010, 6:47 pm

Hello to all ,

Recently I bought a Revox PR-99 MK3 HS. Near mint condition with low hours. By playing tapes from my other revox machine I noticed that it plays them a little slower.
Before I go to audio calibrations with the milivoltometer I have to adjust the speed.
The service manual writes to connect a digital counter on TP1 and P5 to measure the frequency of 800Hz.
What type of electronic device can measure this frequency? Have in mind that I'm not experienced with oscilloscopes.

Regards

dseymo1 · 18th Mar 2010, 10:26 pm

I believe that your mains frequency is 50Hz. As long as the speed isn't too far out, and you have a reasonably good musical ear, you could mix the signal from the TP and the 50Hz hum, and adjust the speed to eliminate 'beats'. Otherwise, use the 'measured tape' method I've desribed here before.
If you don't need absolute speed accuracy, but just to match the two machines, simply feed tape directly from the faster machine to the slower, and gradually adjust the speed of the slower one until no tape is gained or lost in the loop between them.

Michael Maurice · 18th Mar 2010, 10:46 pm

You really need a frequency counter to set this up accurately, the specification is 800Hz +/- 1Hz. An oscilloscope really isn't accurate enough.

allanhaynes · 19th Mar 2010, 12:12 am

I have a cheap yellow plastic multimeter from that nice Mr. Maplin that seems to measure frequency fairly accurately ... (Usual disclaimer !)

themisk · 19th Mar 2010, 8:49 am

Thank you for your answers!

Do you have any model info about a multimeter that can do this measurement? Thank you in advance.

18th Mar 2010, 6:47 pm	#1
themisk Retired Dormant Member Join Date: Sep 2009 Location: Athens/Greece Posts: 8	Tape speed adjustment on a Revox PR-99 MK3 Hello to all , Recently I bought a Revox PR-99 MK3 HS. Near mint condition with low hours. By playing tapes from my other revox machine I noticed that it plays them a little slower. Before I go to audio calibrations with the milivoltometer I have to adjust the speed. The service manual writes to connect a digital counter on TP1 and P5 to measure the frequency of 800Hz. What type of electronic device can measure this frequency? Have in mind that I'm not experienced with oscilloscopes. Regards

18th Mar 2010, 10:26 pm	#2
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: Tape speed adjustment on a Revox PR-99 MK3 I believe that your mains frequency is 50Hz. As long as the speed isn't too far out, and you have a reasonably good musical ear, you could mix the signal from the TP and the 50Hz hum, and adjust the speed to eliminate 'beats'. Otherwise, use the 'measured tape' method I've desribed here before. If you don't need absolute speed accuracy, but just to match the two machines, simply feed tape directly from the faster machine to the slower, and gradually adjust the speed of the slower one until no tape is gained or lost in the loop between them.

18th Mar 2010, 10:46 pm	#3
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: Tape speed adjustment on a Revox PR-99 MK3 You really need a frequency counter to set this up accurately, the specification is 800Hz +/- 1Hz. An oscilloscope really isn't accurate enough.

19th Mar 2010, 12:12 am	#4
allanhaynes Retired Dormant Member Join Date: Mar 2010 Location: Norwich Posts: 2	Re: Tape speed adjustment on a Revox PR-99 MK3 I have a cheap yellow plastic multimeter from that nice Mr. Maplin that seems to measure frequency fairly accurately ... (Usual disclaimer !)

19th Mar 2010, 8:49 am	#5
themisk Retired Dormant Member Join Date: Sep 2009 Location: Athens/Greece Posts: 8	Re: Tape speed adjustment on a Revox PR-99 MK3 Thank you for your answers! Do you have any model info about a multimeter that can do this measurement? Thank you in advance.