Discussion in 'Tube Audio' started by jaymanaa, May 30, 2010.
Anyone ever use the 6BM8 as a voltage regulator?:scratch2:
I've seen it used in some PS arrangements, but I can not recall which ones, and how/what they actually regulated. Neat concepts, but nothing I've built/played with (yet).
My only problem with using 6BM8 in a PS is that I don't have many of them, and I can't find them cheap ever as they're a semi-popular output tube. Would be nice to find some PS schematic with more obscure tubes.
What'cha building? This for the preamp?
Yep, the preamp PS. I saw a design somewhere that used feedback to the triode grid to regulate. I thought it would be neat to do a different type of tube regualtion, and I think I will only need two.:yes:
That's it I think! What is the heater bias terminal all about??:scratch2:
That is a question for Eric Barbour as I sure as hell don't know.
Whatwould the second valve be?
Oh, never mind. I see iot's the 2nd half.
I had an answer but wasn't sure it was right so I deleted it.
The heater bias allows you to keep the heater-cathode voltage within ratings.
Where can one buy some of these tubes without paying top dollar?
A pass-tube! Looks like a pass transistor in a solid-state regulator...
Russian 6F3P. About $4 or so each.
Here's one based on the 6GV8. Scroll down the page for the schem.
Well you can buy those tubes at about $4.50 but shipping cost puts it out of the running.
Those regulator circuits have a major flaw. The zener diode is a high voltage unit and its temperature coefficient of voltage is high. So the output voltage will climb considerably as it warms up. If I remember correctly, the coefficient runs around .12% per degree C so if there is a 40 degree rise the voltage will climb about 5%. For 250 Volts that will be 12 or 13 Volts drift.
A more stable solution would be to use a VR tube. Their coefficient is very small and they are available in several voltages from 75 to 150 Volts.
On an audio circuit is that an issue? The supply would be stable once it reaches the final voltage, yes?
But where in the circuit does it connect?
You left out the best part, some like the OD3 glow purple -
To the center tap of the filament transformer , if you look in a tube manual it will give the voltage rating for heater cathode,it is 100 volts for a 6BM8
Do you really need a tube to do this? I wouldn't think you'd hear any "tube magic" with a tube regulator.
I've used high voltage power transistors (the sort that were used for the horizontal output in older TVs and computer monitors) to do this.
Just connect a regulated source to the transistor base, like a VR tube or a stack of neon bulbs.
Separate names with a comma.