Studer A67 (B67) motor capacitor replacements - UK Vintage Radio Repair and Restoration Discussion Forum

MarkSimms · 22nd Jul 2021, 4:50 pm

Hello,

I'm in the process of replacing capacitors on a Studer A67 tape machine and I'm trying to source some new motor caps as the original electrolytic dual section 6.5uF+1.5uF caps have splurged.

These are obviously very specific caps, value-wise, for the motors to run correctly and I was intending to use two individual caps instead.
The Studer circuit drawing has these drawn with no polarity, but being electrolytic I was a little confused about the polarity implications of using two new electro replacements. I have read elsewhere that some people are using polypropylene caps instead. Are there any advantages or disadvantages to using polypro vs/ electros in this application?

Thanks in advance!

DMcMahon · 22nd Jul 2021, 5:06 pm

Hello Mark and welcome to the Forum.

Motor capacitors are non polarized, i.e. they are not electrolytic and have no polarity.

Modern motor caps are generally Polypropylene. Need to make sure they are rated for continuous usage, most will be.

David

barrymagrec · 22nd Jul 2021, 5:31 pm

Are there two different caps to cater for 50 / 60Hz operation? If so you only need a single 8uf for UK operation.

MarkSimms · 22nd Jul 2021, 7:06 pm

Thank you both for the quick replies and clarifications!

That's a good point about an 8uF cap as the 50Hz switch just puts them in parallel, ta.

Out of interest why were Studer using electrolytics in the 70's/80's for motor caps? Was this just because film caps available at the time were physically too big?

Michael Maurice · 22nd Jul 2021, 9:10 pm

Quote:

Originally Posted by MarkSimms

Out of interest why were Studer using electrolytics in the 70's/80's for motor caps? Was this just because film caps available at the time were physically too big?

They were not using electrolytics, they were paper I believe, but had to be rated at least 150 volts AC.

DMcMahon · 22nd Jul 2021, 9:33 pm

I see from the Service Manual that these are used for the Supply and Take Up Spooling motors. A 3.5uF is used for the Capstan motor.

David

22nd Jul 2021, 4:50 pm	#1
MarkSimms Diode Join Date: May 2020 Location: Newcastle upon Tyne, Tyne and Wear, UK. Posts: 4	Studer A67 (B67) motor capacitor replacements Hello, I'm in the process of replacing capacitors on a Studer A67 tape machine and I'm trying to source some new motor caps as the original electrolytic dual section 6.5uF+1.5uF caps have splurged. These are obviously very specific caps, value-wise, for the motors to run correctly and I was intending to use two individual caps instead. The Studer circuit drawing has these drawn with no polarity, but being electrolytic I was a little confused about the polarity implications of using two new electro replacements. I have read elsewhere that some people are using polypropylene caps instead. Are there any advantages or disadvantages to using polypro vs/ electros in this application? Thanks in advance!

22nd Jul 2021, 5:06 pm	#2
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Studer A67 (B67) motor capacitor replacements Hello Mark and welcome to the Forum. Motor capacitors are non polarized, i.e. they are not electrolytic and have no polarity. Modern motor caps are generally Polypropylene. Need to make sure they are rated for continuous usage, most will be. David

22nd Jul 2021, 5:31 pm	#3
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,560	Re: Studer A67 (B67) motor capacitor replacements Are there two different caps to cater for 50 / 60Hz operation? If so you only need a single 8uf for UK operation.

22nd Jul 2021, 7:06 pm	#4
MarkSimms Diode Join Date: May 2020 Location: Newcastle upon Tyne, Tyne and Wear, UK. Posts: 4	Re: Studer A67 (B67) motor capacitor replacements Thank you both for the quick replies and clarifications! That's a good point about an 8uF cap as the 50Hz switch just puts them in parallel, ta. Out of interest why were Studer using electrolytics in the 70's/80's for motor caps? Was this just because film caps available at the time were physically too big?

22nd Jul 2021, 9:33 pm	#6
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Studer A67 (B67) motor capacitor replacements I see from the Service Manual that these are used for the Supply and Take Up Spooling motors. A 3.5uF is used for the Capstan motor. David Last edited by DMcMahon; 22nd Jul 2021 at 9:36 pm. Reason: Typo correction