Re: Selenium rectifiers in Tek equipment


On Fri, Feb 5, 2021 at 02:29 PM, Morris Odell wrote:
I have a 127 too and had no compunction in replacing the Se rectifiers with
Si. Nobody can tell you how long it will be before the Se rectifiers fail and
you will probably always have it in the back of your mind every time you
switch on the 127. It's not a diffcult or expensive modification to do and
gives you peace of mind.
An update on my 127. I got the power supplies running (one 6080 and a 12AX7/ECC83 were down to air) and the rails were all within spec, though +225V was a whisker low at 221V.

While I was testing the output amplifiers, the rectifier for the -150V rail started cracking and sparking and there was, to quote my wife, a "strange smell". I switched off quickly!

This was after about an hour of running, in total. I had a handful of 800V/4A bridge rectifiers in stock so have replaced all except the heater rectifier. I'll check the DC heater supply voltage.

All rails are now even closer to their correct voltages, so the +225V rectifier was clearly a bit marginal.

I haven't added any additional series resistances. There is a few ohms in series with all the rectifiers anyway, and I figure the 6080s can take the strain!


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