|
Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc. |
|
Thread Tools |
2nd Jun 2020, 2:41 pm | #1 |
Hexode
Join Date: Feb 2011
Location: Newcastle upon Tyne, Tyne and Wear, UK.
Posts: 280
|
Revox A77 preset pots question
I intend to replace the trim-pots on the all of the plug in PCBs but do not have the gear to re-calibrate. I understand that that you can measure the resistance between the wiper and terminal 3 then transfer that result to the replacement pot. Whilst that might work where they are a variable resistor such as in the oscillator board, but where they form a voltage divider may not work as the trim-pot will have a different spec example: 25K instead of the original 20k (which is actually about 22k rather than 17K in this case between pin 1 and 3)
However if the original measurement is converted into ratio and then applied to 22k for instance, the result would be higher but in proportion. Would that get me into the ballpark area at least? |
2nd Jun 2020, 7:13 pm | #2 |
Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,675
|
Re: Revox A77 preset pots question
Yes, I'd say so. The ratio is the important thing for a potential divider.
|
3rd Jun 2020, 11:27 am | #3 |
Hexode
Join Date: Feb 2011
Location: Newcastle upon Tyne, Tyne and Wear, UK.
Posts: 280
|
Re: Revox A77 preset pots question
|
6th Jun 2020, 12:00 am | #4 |
Hexode
Join Date: Jan 2016
Location: Ramsgate, Kent, UK.
Posts: 298
|
Re: Revox A77 preset pots question
Hi Pentoad,
I have replaced the presets on my A77, see my post on it, "Revox A77 refurbishment advice please" #46 describes how I did the record amps, probably the most difficult ones to do. As Ted says the ratio is the important thing.
__________________
Andrew Illegitimi non carborundum Last edited by MeerKat; 6th Jun 2020 at 12:16 am. Reason: spelling |