Multivibrator circuit with vacuum tubes

Thread Starter

popcalent

Joined Mar 17, 2018
49
Hello all,

I have a box full of vacuum tubes that I bought about 20 years ago for an old radio that needed replacements (I only needed a few tubes, but I had to buy the full box). Anyway, I recently came across these circuits, and I thought I'd be interesting to use the extra tubes that have been sitting around for 20 years:

multA.gif multB.png
I'd like to implement either circuit to do something like this: 12SN7 Dual Triode Vacuum Tube Astable Multivibrator

I have never used vacuum tubes before (except for replacing the ones in my radio), and I'm not sure how they work. Here's the possible candidates I've found (ie. I already have in my possesion):

For circuit 1:
6FJ7 - Dissimilar double triode
6EA7 - Dissimilar double triode
6CY7 - Dissimilar double triode
6FD7 - Dual triode
6J6 - Double triode
6EM7 - Double triode
6B10 - Duplex-diode twin triode (I'd ignore the diode part)
6211A - Twin triode
10GF7 - Dual triode

For circuit 2:
6HQ5/4HQ5 - Sharp cutoff triode
6FH5 - High Mu triode
6DZ4 - Medium Mu triode

My questions are:

1) Will any of the tubes I listed work? I know they are all dual triodes (circuit 1) or single triodes (circuit 2), but I'm not sure how the differences will affect the circuit (dual vs twin, high mu vs medium mu, etc.).

2) What's the margin of the heater voltage in a vacuum tube? For instance, if the datasheet says 6.3V, can it be 6V? If it says 8V can it be 9V or 7V?

3) Can I supply the heater voltage to the rest of the circuit. For instance, circuit one uses a tube with a heater voltage of 6.3V and supplies 200V to the rest of the circuit. Can I just use 6V for everything?

4) Finally, once I decide what tubes I will use, I'd like to buy sockets. How do I find the right socket? Obviously, the socket needs to have the same number of pins, but what about diameter, etc. In oder words, what parameters do I need to find the right socket?

Thanks!
 

Audioguru again

Joined Oct 21, 2019
3,534
Vacuum tubes are obsolete and are not used anymore.
Vacuum tubes use a high voltage that can kill you.
Vacuum tubes burn out and wear out.

Does anybody sell a high voltage power supply or sockets for antique vacuum tubes that are not used anymore?
 

crutschow

Joined Mar 14, 2008
27,735
1) Will any of the tubes I listed work?
Chances are any of the single or not-dissimilar dual/double triodes should work.
2) What's the margin of the heater voltage in a vacuum tube?
It will likely work on a volt or so less, but the life will be shortened if you run them at a higher voltage.
3) Can I supply the heater voltage to the rest of the circuit.
You can run all heaters with the same voltage in parallel.
4) Finally, once I decide what tubes I will use, I'd like to buy sockets.
You find one with the same number of pins and pin circle diameter.

You likely need a plate power supply of at least 100V for the tubes to operate.
If you accidentally touch that, you will remember it for a long time. :eek:
 

Thread Starter

popcalent

Joined Mar 17, 2018
49
Thanks for your responses!

You likely need a plate power supply of at least 100V for the tubes to operate.
If you accidentally touch that, you will remember it for a long time. :eek:
I saw a video on YouTube of a guy who was running the tubes with 24V. I can't find the video now... Anyway, 100V can't be worse than 220V which I touched many times by accident.

The idea is to use a battery for the heaters, and the 220V from the power outlet for the plates, but I was wondering if I could use much less than 220V and 100V...
 

crutschow

Joined Mar 14, 2008
27,735
The idea is to use a battery for the heaters, and the 220V from the power outlet for the plates,
Bad idea.
It is dangerous to use 220V from the power outlet, as it subjects you to lethal voltages to ground.
And rectifying that to get the required DC for the plates would give about 1.4 * 220V = 308Vdc.

Much better to rectify the output of a lower voltage (100Vac or so) isolated transformer.
 

Audioguru again

Joined Oct 21, 2019
3,534
You can survive certain types of electrical shocks (between the fingers on one hand for example ) but if a shock stops your heart from beating then you will be dead within a couple of minutes.

Since you do not know anything about vacuum tubes and their shock hazard then do not use them. Use safe low voltage transistors instead.
 

Ian0

Joined Aug 7, 2020
3,249

Thread Starter

popcalent

Joined Mar 17, 2018
49
Bad idea.
It is dangerous to use 220V from the power outlet, as it subjects you to lethal voltages to ground.
And rectifying that to get the required DC for the plates would give about 1.4 * 220V = 308Vdc.

Much better to rectify the output of a lower voltage (100Vac or so) isolated transformer.
Alright. As AlbertHall suggested (and as I recall seeing on a YouTube video), the circuit might work with lower voltages. I will use an AC26V/300mA and a DC30V/400mA power adapters that I have. All I need are the sockets. I'll report back. Thanks!
 

Ian0

Joined Aug 7, 2020
3,249
I got my sockets from HifiCollective
https://www.hificollective.co.uk/components/valve_bases.html
You can download the datasheets for your valves here:
https://frank.pocnet.net/
GE datasheets tend to be the easiest to read.
Imagine that you are dealing with a JFET and you'll be going in the right direction.
All yours are triodes, so you won't have to worry about Grid2 and Grid3 that a pentode has.
Heaters are nearly always insulated from any of the "working" electrodes, but the insulation will only withstand 200V. Heaters generally use AC but work perfectly well off DC.

Of the various parameters, Gm is the same as Gfs in a JFET
mu is the voltage gain.
The datasheet lists the bases B7A, B9A, Octal, etc. and that is how you find the right socket. There are chassis sockets and pcb sockets.
If you want a good book on the subject or some articles to download look here:
http://www.valvewizard.co.uk/

I just have to share this picture:
"Arthur, have you seen the tin I cookScreenshot at 2020-05-20 14-50-29.png the roast potatoes in?"
 

Thread Starter

popcalent

Joined Mar 17, 2018
49
I got my sockets from HifiCollective
https://www.hificollective.co.uk/components/valve_bases.html
You can download the datasheets for your valves here:
https://frank.pocnet.net/
Thanks for your response.

I'll use 6211A twin triode (base E9-1) because I have six of them, which will provide some window for error in case I break one of the tubes.
I will also order a couple of E7-1 bases because all single triodes I have use that same one (4HQ5, 6HQ5, 6FH5, 6DZ4).

I've notices that some of the tubes are "burned" on one spot or two. I imagine that's just a sign of usage. However, it doesn't mean the tube is totaled, does it? I can't tell...

tube.jpgtube.jpg
 

crutschow

Joined Mar 14, 2008
27,735
Heaters generally use AC but work perfectly well off DC.
They typically used AC since that's readily available (wait for it) from a filament transformer.
But some old HIFi audio amps (especially preamps) rectified the AC to provide DC to the filaments, to reduce hum pickup (which was a common problem in tube amps).
 

Ian0

Joined Aug 7, 2020
3,249
They typically used AC since that's readily available (wait for it) from a filament transformer.
But some old HIFi audio amps (especially preamps) rectified the AC to provide DC to the filaments, to reduce hum pickup (which was a common problem in tube amps).
And if you've ever wondered why there are so many 6.3V transformers in electronics surplus suppliers. . . .
 
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