Traynor YBA-1A OT Protection-those old GE parts are Selenium!

[nevetslab]

While still in the 'work-in-progress' mode of restoring my 44 yr old Traynor YBA-1A, and had pulled all the rectifiers off the fiber eyelet component board while replacing all the older film caps, I had moved those blue-colored Transient Protection devices back into place, without yet researching just what they were. Two different parts....the smaller one is a 6RS20SP7B7, a unidirectional 296V breakover part with a 20A rating, and is a Selenium-based part. The longer one is a 6RS20SP20-B20, carrying a 848V breakover rating, also 20A rating, and also Selenium-based part. I didn't see any polarity marking on the parts, but I did manage to install them wired opposite of how they were installed. Opps. I found that information from American Microsemiconductor's listing, which called them unidirectional parts. Are they really? If they were, I'd think there would be polarity markings on the package. But, following recommendations to remove and replace them before they cause damage, they're being removed and replaced with some Littelfuse MOV's

After reading thru the long threads on OT protection, and found excellent information in the thread 'What's a good rating for MOV Suppressors?' R.G suggests a voltage rating of 2.2 to 3.3 times the B+ value of the plate voltage.....which at idle is around 570VDC, and low in capacitance, I think using a pair of the LIttelfuse P/N V07E420P in series would do the trick. Its' 1mA DC Varistor Voltage rating is between 612V min to 708V max (660V nominal?), 55pF @ 1MHz, and has a max clamping voltage rating of 1120V @ 10A for insulation protection. 2 parts installed in series between plate-to-plate connections at the tube sockets.

Original installation vs revised installation:



I hope I understood the information in the thread 'What's a good rating for a MOV Suppressor.

[nevetslab]

No Vendor inventory...1500 pc min qty.

Isn't that typical in this day and age. If you're a manufacturer, you can usually get anything, including samples. That does, of course, also hold true with engineers who do OEM designs, and might not be a bad thing to have on hand, as at least 50% of what we inventory in our backline gear rental dept are tube amps. Granted, I've only had to replace one output transformer so far over the past 5 years, but it makes for good cause to have LIttelfuse send out samples.