Single triode version of 12BH7?

[RMckay]

Hello.
I was wondering if there is a single triode version of the 12BH7?

Or, are there any 7-pin equivalents to the 12BH7?

Thanks.

 

[Eli Duttman]

AFAIK, the answer to your questions is no. However, you can wire the 2 channels of a stereo project asymmetrically, with channel 1 only using system 1 and channel 2 only using system 2. When signs of wear appear in the working triodes, exchange the bottles for doubled tube service life.

 

[6A3sUMMER]

Eli Duttman,
Good idea.

But consider wiring only the filament section that corresponds to the triode section that is used in one tube, and the other tube's filament section with the triode that is used on the other tube.
If paralleled, that would need a 6.3V filament transformer.
Or you could wire 4-9 of one tube in series with 5-9 of the other tube (12.6V).

The purpose of this technique would be to prevent Cathode Poisoning.
A cathode that is heated but that is not conducting plate current for a very long time may suffer degredation.

 

[Eli Duttman]

But consider wiring only the filament section that corresponds to the triode section that is used in one tube, and the other tube's filament section with the triode that is used on the other tube.

That is a given. Let the non-working section's heater "float". Ground the plate, grid, and cathode of the non-working section.

 

[RMckay]

Thanks for the input Eli and 6A#sUMMER.


The issue I have is that my amp uses 7 tubes in total (4x EL84, 3x 12BH7) and I only have two heater windings at 6.3v/2.5A.
I currently have 2x EL84 and 2x 12BH7 on one winding, and the other 3 tube's heaters on the other winding. This gives me a 2.4A load on one, and 1.8A on the other. My heater voltages are now uneven.

I just want to load the heater circuits evenly, that's why I was asking about single-triode tubes. That way I could power the heaters evenly.

Can I power each half of of the heater of a 12BH7 from different windings? If no, (which I suspect) I guess my other option is to add a small 12v transformer to power just the heater circuit of one 12BH7.

Any easy solution I've failed to see?

Thanks

 

[Eli Duttman]

Phase up the filament windings and connect them in parallel. Wire all the heaters to the composite.

 

[waltube]

One solution is to put the trafo winding in series so you have 6.3-0-6.3 volt
2+2 EL84 in series then connected to 12.6 volt (0 to ground) + 3 12BH7 in parallel to them.


Walter.

 

[RMckay]

Ah, both sound like easier options. Thank you!

Eli, when you wrote "phase up the windings," do you mean just just check that I'm connecting them in-phase with each other?
Complicating it a bit, my amp has two potentiometers for "hum control," which are connected in parallel to each transformer winding. The 2 wipers are connected. Will I still need this circuit, or can it be omitted?

Thanks

 

[waltube]

If you haven't the 0 central you need a pot.


Walter

 

[RMckay]

Nope, no center tap on heater windings.

So, both 6.3V windings in parallel, with one pot. Sounds easy enough.

Thanks