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scrimpu 8th October 2012 10:40 PM

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?

Brion55 10th October 2012 04:41 AM

As long as your switch doesn't change DC levels to the control grid of the 6V6, it should work fine.

ChrisA 10th October 2012 10:39 PM

Quote:

Originally Posted by scrimpu (Post 3194301)
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

DUG 11th October 2012 03:31 AM

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.

ChrisA 11th October 2012 03:49 AM

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".

scrimpu 11th October 2012 04:43 AM

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.


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