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Old 8th October 2012, 11:40 PM   #1
scrimpu is offline scrimpu  United States
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Default DIY multi champ amp

I have an early 1950's amp from a reel to reel tape recorder that I have converted to a champ 5C1 since it had a 6SJ7 preamp tube into a 6V6. The amp originally had a 5879 tube as a mic preamp that I have coverted to a 12AX7 and now I have it wired as a 5F1. I would like to be able to switch from the 6SJ7 preamp to the 12AX7. Can I do this with a simple switch just before the 6V6 of is it more compex that that?
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Old 10th October 2012, 05:41 AM   #2
Brion55 is offline Brion55  United States
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As long as your switch doesn't change DC levels to the control grid of the 6V6, it should work fine.
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Old 10th October 2012, 11:39 PM   #3
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by scrimpu View Post
I have an early 1950's amp from a reel to reel tape recorder that I have converted to a champ 5C1 since it had a 6SJ7 preamp tube into a 6V6. The amp originally had a 5879 tube as a mic preamp that I have coverted to a 12AX7 and now I have it wired as a 5F1. I would like to be able to switch from the 6SJ7 preamp to the 12AX7. Can I do this with a simple switch just before the 6V6 of is it more compex that that?
The only problem is if the extra wire picks up hum and noise. That canbe prevented by using shielded wires to and from the switch. Be sure and ground just one end of the shields.

Be sure and post here to tell what happens, how does each preamp sound when you flip the switch and A/B compare them
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Old 11th October 2012, 04:31 AM   #4
DUG is offline DUG  Canada
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Low level signal relay.

Control lines can go wherever they need to be without worrying about signals being on them.

And yes, watch the DC levels.
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Old 11th October 2012, 04:49 AM   #5
ChrisA is offline ChrisA  United States
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One more thing. Are you planning to switch this while playing or only between songs. If you need to switch it while playing then you will get a "pop" noise if you use a toggle switch.

To avoid the pop you need to use some LDRs, Light Dependent Resistors. You use them a little like volume controls. When you flip the switch one goes up and one goes down and you get a smooth fade over with no "pop".
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Old 11th October 2012, 05:43 AM   #6
scrimpu is offline scrimpu  United States
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Well I installed a switch it is really a night and day differance. The 6sj7 is dark and really quite nice, but not as much gain as I would like. The 12ax7 is very bright and giives much more distortion when cranked. Unhappy with the extra wiring and crappy switches I had on hand I decided to rewire yet again. I dumped the 12ax7 for the original 5879 pentode and wired it into the 6sj7 to give it the boost it needed. Its super dark and dirty and may take a while to fine tune but I think Ill like this setup better the either champ circuit.

Last edited by scrimpu; 11th October 2012 at 05:46 AM.
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