switch for paralelled tube

[voivodata]

Hi,

The input tube of my guitar amp is a paralleled ECC 83 (jumped pins 1 to 6, 2 to 7, and 3 to 8). I want to implement a switch for disconnecting half of the tube, in order to be able to lower the gain when i play the clean channel (clean and dirty share the same input stage).

Is it OK to use a SPDT switch to disconnect only the plate of that half of the tube which will not be used?

In such case would the remaining paralleled connections (grid and cathode) affect somehow the performance of the "working" half of the tube? Would grounding the unused plate help?

Thanks! V.

[Salas]

I don't think that you get more gain with paralleled tubes, but more current and lower noise.

[voivodata]

OK, but neverthelless, the "paralelling" works well for me when used with the Dirty channel while the Clean sounds better with a single stage. So can I use a switch as described?

[alexmoose]

i'm afraid it would make some nasty noises if you switched it when the thing was on personally.....

[Salas]

And maybe some pickup of noise from the cabling or possible oscillation. Everything that has terminal pins can be connected to a switch, your tubes included, but I doubt it will work optimally. You can experiment and see. Its very much a practical test.

[alexmoose]

you could build another circuit entirely, and incorperate that through a swtich, that would certainly work

[voivodata]

Thanks guys!

I'm not quite up to implementing a separate circuity cause space is limited and if not properly laid it can be trouble.

I did experiment with a switch for diconnecting pin 1. It works OK - sound changes noticeably. Indeed some popping occurs but it's not loud and I don't plan on using a switch with the amp on anyway.

I also tried disconnecting and connecting back pins 2 and 3 to see if that affects sound. To my hearing there was no difference but I cannot be 100%. I still wonder what theory says about that - I meen if the cathodes and grids are left paralelled, would that affect the "working" half of the tube (the second half - pins 6,7,8).

Cheers! V.

[alexmoose]

Personally, I think it would be really cool if you had an AB switch, where in one mode, the two tubes would act in parelell, however in the other, the tubes would act in Series to give you some added distortion.

Edit!
or, you could put a switch in that would bias the tube two different ways, one for a cleaner sound, and one for a dirtier sound

[Dave Cigna]

Originally posted by voivodata
OK, but neverthelless, the "paralelling" works well for me when used with the Dirty channel while the Clean sounds better with a single stage. So can I use a switch as described?

If you are using the same plate and cathode resistors in both cases, then most of the difference that you hear is probably due to the tubes running at very different operating points. Paralleled tubes would need resistors 1/2 the size to run at the same point as a single tube.

Anyway, if you are running the same resistors in both cases, then you might be able to get some of what you want by simply switching in a parallel cathode resistor. i.e. If you have a single 1.5k resistor for both sections in parallel, then switch in another parallel 1.5k resistor (or some other value....) I would not recommend switching out one resistor and in a different one. Leave one connected at all times and add another in parallel.

Obviously, this does not change the plate resistor, but I really do not like switching high voltages unless I really need to, especially on the same microswitch as low voltages.

-- Dave