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Old 12th May 2016, 02:16 PM   #1
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Default Switch between tubes with relay

Hi,

There is situation that I need help about switching tubes. The situation is I am making a guitar pedal (overdrive) with a tube... The original design has one tube, but I want to use three tubes and switch between them using relays. I know this sounds interesting but I am trying to figure out how I can do that...

Only one tube should be active and by using relays, I need to switch between tubes. My question is, where should I install the relays on this drawing.

Thanks...

PS: Pin 3 is connected to pin 4 on the schematics. And all the tubes are identical.

Click the image to open in full size.


And here is the schematics:
Click the image to open in full size.

Last edited by emretelci; 12th May 2016 at 02:20 PM.
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Old 12th May 2016, 02:31 PM   #2
euro21 is offline euro21  Hungary
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Do you mean, that you want to use 12AT7 tubes from different manufacturers?
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Old 12th May 2016, 02:34 PM   #3
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Quote:
Originally Posted by euro21 View Post
Do you mean, that you want to use 12AT7 tubes from different manufacturers?
No, different but equivalent tubes like 5751, 12AT7 or 12AU7
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Old 12th May 2016, 02:47 PM   #4
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are you thinking of switching all the connections from tube to tube?
heaters would need to see a constant supply otherwise warm up time will be a problem.
in looking at the schematic i'm not sure that plate voltages are adequate for a 12at7 nor does there seem to be any sort of voltage multiplier in the power supply.
interesting concept though.
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Old 12th May 2016, 02:49 PM   #5
euro21 is offline euro21  Hungary
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Quote:
Originally Posted by emretelci View Post
No, different but equivalent tubes like 5751, 12AT7 or 12AU7
These are have equivalent PIN order, but not equivalent tubes.

Maximum anode current:
5751 has about 1mA, the other two capable about 10mA.
12AT7 and 12AU7 not equivalent, but mostly interchangeable (depending of the circuit).
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Old 12th May 2016, 02:53 PM   #6
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Quote:
Originally Posted by euro21 View Post
These are have equivalent PIN order, but not equivalent tubes.

Maximum anode current:
5751 has about 1mA, the other two capable about 10mA.
12AT7 and 12AU7 not equivalent, but mostly interchangeable (depending of the circuit).
Thank you. That's ok actually for me. I have tried and all gives a different tone so all are working for me in same circuit without anything...
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Old 12th May 2016, 02:56 PM   #7
Merlinb is online now Merlinb  United Kingdom
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The easiest way to do that with the three (actually two) single-pole relays you showed, is just to have three circuits and switch the outputs. Dunno if you're trying to switch between tubes in the middle of playing though, in which case you'll need cap coupling to avoid pops.
Attached Images
File Type: jpg relay.jpg (34.7 KB, 130 views)

Last edited by Merlinb; 12th May 2016 at 02:58 PM.
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Old 12th May 2016, 02:57 PM   #8
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Quote:
Originally Posted by turk 182 View Post
are you thinking of switching all the connections from tube to tube?
heaters would need to see a constant supply otherwise warm up time will be a problem.
in looking at the schematic i'm not sure that plate voltages are adequate for a 12at7 nor does there seem to be any sort of voltage multiplier in the power supply.
interesting concept though.
Thank you very much. I don't think I need to switch all the connections. Actually I don't know which ones to switch to make one tube work only... That's the reason I am asking here to figure out which pins I should switch...

You are right about heaters, I was thinking that. So heaters may stay connected I think, without relays...
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Old 12th May 2016, 03:09 PM   #9
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i would go with Merlinb's suggestion.
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Old 12th May 2016, 03:15 PM   #10
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can you give a little more detail as to the heater supply in this pedal?
being that as a pedal the current draw for the tubes would flatten a standard 9v battery pretty quickly wouldn't it?
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