[philco4me]

Hello all
Got a 51-934 and I want to replace the selenium rectifier. I want make sure i get the positive correct so on the schematic there is an r28 resistor off the rectifier is that the positive ?

Thank you.

[morzh]

Yes the left of R28 is the Positive Rectified Voltage. That is, this is the Diode's Cathode (Negative), and the Anode (Positive) is the one connected to the plug. The rule for the diode symbol is, The Triangle is A, the Bar is K. The confusion comes from the fact that the rectified Positive Voltage always comes from the Diode's Negative (K). On most diodes "K" is marked with a bar.
You might need to increase the R28 value if using a diode (like 1N4007) to compensate for what used to be the SR losses.


BTW, I am also formerly from West Milford (Hewitt, to be exact and worked at Upper Greenwood Lake). That was my first place in NJ that I went to live to.
Still have a friend in there.

[philco4me]

Thank you so much. It is a little confusing but I’m willing to try it. Glad you’re from here. That’s very cool and thanks again.

[David]

The old selenium rectifier  drops the voltage 7 volts the silicon will drop voltage only 7/10 of a volt so need to add more resistance. Fun with math. David

[philco4me]

Here is what I  will be using and thank you fr the replies

[morzh]

Yep.
And, looking at the sch, the banded end goes to the right, and the black end to the left.
As for the resistor, see what it drops. The wattage should be sufficient.

[Arran]

I looked up this model, it's an AM/FM AC/DC set. in all honesty the extra 7 volts using a silicon diode over a selenium probably won't hurt anything. The .7 volts is the forward drop across the rectifier diode, but that does not mean that the B+ will be seven volts higher under load, however this is something you would want to take into account in a three way portable where the tube filaments run off of the B+ supply.
Regards
Arran

[easyrider8]

If the voltages are good after the selenium there is no need to replace it. If you do replace it with a 1N4007 the small increase in voltage wouldn't make any difference.

Dave

[morzh]

Arran

Keep in mind, there will be an additional few volts due to the AC Voltage today being 5-10VAC higher, so together with extra 7V it, though won't hurt anything short-term, will contribute to some extra wear.
Of course, this is not that important if the radio is not used as it was in the old times, that is often and for prolonged periods of time.