E88CC in the microphone.

[vmanj]

I welcome everyone.
I use an E88CC (half triode) in my mic.
It will not work to turn off the heating for an unused E88CC triode (as in C-12 with 6072).
Could this ruin the sound somehow?

 

[ruffrecords]

The E88CC does not have separate connections for the heaters of the two triodes. Therefore both are always on for the tube to work at all. You could improve noise by operating the two triodes in parallel.

Cheers

IAn

 

[vmanj]

Thanks, I already tried that, but I liked the sound more with a half triode. Perhaps this is due to the drain transformer СAD Trion 8000 .

Maybe E88CC is not designed to work half of the triode?

 

[Tubetec]

By the time you've parralelled the electrodes across the socket the extra incidental capacitance might well affect the tone .

 

[ruffrecords]

Thanks, I already tried that, but I liked the sound more with a half triode. Perhaps this is due to the drain transformer СAD Trion 8000 .

Maybe E88CC is not designed to work half of the triode?

You cannot simply parallel them. You would need to adjust the cathode resistor to set the bias correctly. On the other hand, if the output transformer has dc flowing through it then it may not be designed to carry the current of two triodes in parallel so this may not be an option. I think the E88CC was designed as a front end tube for VHF and UHF tuners in a cascode configuration which uses both triodes so there would have been no need to design it to power just one of the triodes.

Cheers

Ian

 

[vmanj]

You cannot simply parallel them. You would need to adjust the cathode resistor to set the bias correctly. On the other hand, if the output transformer has dc flowing through it then it may not be designed to carry the current of two triodes in parallel so this may not be an option. I think the E88CC was designed as a front end tube for VHF and UHF tuners in a cascode configuration which uses both triodes so there would have been no need to design it to power just one of the triodes.

Cheers

Ian

Here is my circuit, according to which I tried the E88CC in the mode of parallel connection of triodes.

 

[ruffrecords]

OK, it is clear from your schematic that the output transformer is ac coupled so there is no issue with dc current flowing through it. I also see the tube has fixed bias created by the potential divider R4 and R5. As this is fixed bias it should be correct for both triodes. However, because the plate current will be doubled you will need to make the value of the plate resistor R6 half what it was for a single triode. This should maintain the original operating point for both triodes. You also need to verify that the HT supply is capable of supplying this current.

Cheers

Ian

 

[vmanj]

OK, it is clear from your schematic that the output transformer is ac coupled so there is no issue with dc current flowing through it. I also see the tube has fixed bias created by the potential divider R4 and R5. As this is fixed bias it should be correct for both triodes. However, because the plate current will be doubled you will need to make the value of the plate resistor R6 half what it was for a single triode. This should maintain the original operating point for both triodes. You also need to verify that the HT supply is capable of supplying this current.

Cheers

Ian

Thanks, I'll try to do that !