Selenium rectifiers

[Bill Cahill]

This set doesn't have a power transformer. It's series string.... I still have the concern for the wattage. I didn't realize you were saying baxically the same thing as I. But, I still doubt it will be as low as 30 ohms..In any case, there is the surge factor... I prefer to start high, and, work my way down.. Perhaps ten watts is plenty, but, Tim is afraid to even try that. He is afraid he will dammage the set. I tried telling him that wouldn't happen, the worst that could happen is the resistor prematurely fail.. I can understand why he refuses to spend sixty dollars on twenty watt resistors, but, I tried even telling him to put resistors in parallel to get the desired wattage...
Bill Cahill

[Findm-Keepm]

Even if it is a series string, the filaments do not come into play - they are a separate leg/circuit. The total load coming from the doubler cannot exceed the ampere rating of the original seleniums, which Tim stated was about 320mA.

Second, the voltage drop across the selenium is rarely above 5V, and with the 7/10s of a volt that a silicon diode drops, you only have to drop the additional 4.3V or so. You aren't dropping tens or hundreds of extra volts, so the resistance and wattage are going to be low.

I stand by the calculations - two previous posters also weighed in, saying 25 watts is overkill - and I too have never used more than a ten watt resistor. In any case, it is imperative that the set be fused, and adding a B+ fuse would also be recommended.

60 bucks for a 20 watt resistor(s)? Where? Three 5 watt resistors could be had for a buck-thirty plus shipping.

I too can sense Tim's confusion -and a good reference for replacing seleniums is nowhere on the web. It's all Ohms Law and Kirchoffs Law, but no one on the web applies either to a selenium replacement scenario. I guess someday they'll all be replaced, making this thread obsolete.

Cheers,