25Z6 Rectifier to Solid State Conversion?
 

Does anyone have a solid state conversion for this dual rectifier? Something similar to https://www.antiqueradios.com/forums...p?f=8&t=225280

I honestly don't know why anyone would bother. They're widely available and cheap, and they last a long time.

You can do it two ways, as a complete drop in or wire in diodes beneath the socket and disable the tube except for the filament. With a drop in you'll have to get your filament resistors right in order to not throw off the others. Either way you'll need dropping resistors or bucking zeners to lower B+.

There are also those (I'm not one of them) who like to delay B+ and say that a SS rectifier will cause cathode stripping of power tubes during cold start.


John

The 25Z6 was usually used in series string heater sets so you can roll your own by downloading the 25Z6 datasheet. Use the heater voltage and current in this equation R=voltage/current to calculate the resistor you need to replace the heater with and multiply the voltage times current to get the wattage that resistor needs to be (it's wise to get a resistor twice that wattage so it doesn't run hot.

Once that's done wire a 1n4007 in place of each diode on the schematic symbol for the tube. You can take the base of a dud tube and install the diodes and resistor in it.
Most commercial replacements are this plus a bunch of bucks to pay someone else to build it.... I'm cheap and usually have all the parts I need to build one so I usually roll my own.

The 25Z6 is not a problematic tube and they're come and reasonably priced.

I'm interested in making a sub is because I want to test a TV while I wait for my tubes to come in.

Looks like at 300mA, the resistor for the filament would be around 83Ω.

Referencing: https://frank.pocnet.net/sheets/127/2/25Z5.pdf

So I have the 83Ω across pins 2, 7
and a 1n4007 across pins 5 (anode), 8 (Cathode/stripe)
and another 1n4007 across 3 (Cathode/stripe) and 2 (anode)

Does this look correct?

1N4007 across pin 3 and 4 (stripe).

Note that the resistor will need to be at least 10 watt, (15 W would be better) .

Unless you have a lot of power resistors, you might get the tube before you get the resistor(s).

Thats correct. I meant the diode across 3/4

Yes, I used 2 10w resistors for 80ohms.

The SS replacement I made seems to work fine! Getting more or less the right voltages, HV and a raster now.

If you didn't add a B+ dropping resistor or bucking zeners on the diodes, your voltage is going to be high. That's generally not a problem short term as long as you aren't stressing the electrolytics or your HV isn't too high.

John

I didn't add a zener or dropping resistors. If anything the LV supplies are 8-14V lower than the numbers I have in my Rider's. May be due to the rectified voltage coming off the Selenium being a little low. I will probably end up dropping a 1n4007 to sub that out too. Will definitely be using a dropping resistor there.