Selenium rectifiers

[Findm-Keepm]

Tim,

Attached is a simplified schematic of what you are doing - I drew it from memory - if you want a marked up copy of the Sams, I can scan that tomorrow, noon-ish. The Sams is out in my shop, and I am in for the evening.

As you can see, the silicon 1n5408's are simply installed where the selenium was removed - cathode (banded end) to the "+" connection, and anode to the "-" connection. Off of the cathode of the output (rightmost) rectifier, we add in a series resistance. At 39 ohms/5W, you are good for up to about 12V of voltage drop across the resistor. I LOVE those RH-series Dale resistors you've chosen, as they make for easy mounting, and the chassis can sink some of the heat. Some purists want only axial or old ceramic resistors in their sets.


Sams (IIRC) says the B+ should be about 195V for your set.

If the B+ is low, (lower by 5-8 volts or more) add some Parallel resistance to bring it up. I don't think that will be the case, as 17 to 75 ohms is my experience for most series resistors in tube sets.

If the B+ is high, (higher than 5 volts or more) add some Series Resistance. Doing so will not only drop more voltage, it will also decrease the power dissipated by the (each) resistor.

Your "fusistor" is the 4.7 ohm 15 Watt resistor under the chassis in one of your photos.

Hope this helps - I'm up for another hour or so - I have to take my daughter to school in the morning, so an early evening for me.

Cheers,

[Findm-Keepm]

I re-read what I wrote above, and I wasn't clear that each selenium rectifier is replaced by one 1N5408.

Cheers,

[Kamakiri]

Originally Posted by Findm-Keepm

I LOVE those RH-series Dale resistors you've chosen, as they make for easy mounting, and the chassis can sink some of the heat. Some purists want only axial or old ceramic resistors in their sets.

That to me was an obvious choice in this case. That resistor replaced a resistor that used to be in the lower right corner of the second picture. There was so much heat there that it ended up burning the terminals right off the phenolic strip, and the old resistor was just dangling. I also upped the rating on it, and used a 25 watt instead of a 15 IIRC.

I fully believe in over-building a circuit, especially when it's apparent that the way it was made just wasn't good enough over the long haul

I'll be doing this job today, after all the housework I just ran out of steam last night....

At the risk of sounding like an idiot, B+ is checked across the first filter cap, yes?

[Findm-Keepm]

B+ is measured at the point I marked on the schematic. B+ refers to the main DC supply in most sets - it's a carry over from the old battery days when they had A and B batteries - A Batteries were for filaments and low voltage bias, and B batteries (45V, 67.5V and 90V) were for the plate and other high voltage needs.

I marked up the schematic for you - hope it helps. Start with a 39 ohm 5W resistor and measure your B+, and follow my previous advice if it is high or low.

The Sams should carry you forth from here.

Cheers,