using common tube triodes as rectifiers

[thebadtall]

hello, having a truck of triodes,sleeping at warehouse, i thought that i might use some of them, to make a rectification bridge.

is this possible? I was thinking to feed their filament, tie the grid to anode and feed ac 12v to the cathode. unfortunatelly i dont have any tube diodes :/

can you suggest some way? utilising 12ax7

thank you

 

[tpetar]

You will get small current. I think is best to get back in 2012. year.

:wink:

 

[thebadtall]

i know how hard it is to stand when time is running.
but, id like to put some tubes in one of those enclosures i have since so long ago, and id like to know that the dc out is going to be from tubes.... (maybe i will ruin all the concept with a regulator)
so all in all, i want to fill the enclosures

 

[tpetar]

I have lots of electronic tubes from my father and uncle, some of them are very rare and expensive today, but I dont have will to struggle with these. We should accept technology improvements and to move on.
I have first IBM PC XT, I keep motherboard. I was kid when father bring that PC to our home. In that time price for that tech was very very high, but today ..... :-?
Also I have lots of old and today rare semiconductors from US and SSSR with gold and made from other noble metals inside but I just keep them.


:wink:

 

[rfredel]

Hello thebadtall,

12AX7 and other triodes are not good for rectifying, because the internal resistance ist very high with ~50-60kΩ . Also the current will be very low (~1mA). Look for other datasheets of rectifier tubes. You can not use reservoir capacitors with high capacity. This is one of the reasons, why I don't use tube rectifiers for my tube amplifiers only normal silicon rectifiers.

Regards

Rainer

 

[thebadtall]

dear tpetar, i have an ibm ps2 386 with win3.1 wich my bro brought home(and i partially destroyed) in 1993 , i still use it sometimes(reminds me forgotten and valuable childhood unstressed memories),it has a new psu! those rare tubes you own, is legacy, me either would never sell them(maybe would do a test some day!)
anyway, i personally, can only deal with "new" economy-financial technologies, as my studies and income is rely on.
however, i admire those engineerers that can design their own digital circuits.

as about my question, i will not use the 12ax7's as my german friend rainer informed that is high impedance.
maybe can use kt88's i got somewhere,but i think when i return from vacation to start a pushpull amp with this pair.

i found some tube diodes on ebay, cheap, but.. this experiment can wait.
thank you all..

 

[chuckey]

If you are using a valve (tube)amplifier with a HT of 300V, after switch on, by the time the valve rectifier has warmed up the other valves are drawing current. If you replace the valve rectifier with silicon diodes, they work from cold, so at the instant of switch on, the HT line is 450V until the other valves warm up. This can cause the reservoir capacitor to explode!!! :-(
Frank

 

[rfredel]

Hello Frank,

normaly it's right what you write about warm up and that the HT slowly rise up with valve rectifiers. But in the event of a fault in the following circuit, the HT line also will rise up.

This can cause the reservoir capacitor to explode!!!

This is also right, but a good design engineer will never calculate the capacitor to the operation voltage of the circuit, but to the peak voltage of worst case. This means, the highest input voltage from line that can appear.

Regards

Rainer