Need help with bias switch

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MBDR1987

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Mar 26, 2022
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Hi,

it appears the bias switch of my 2000s dual rectifier does not work properly.
i swapped tubes form EL34 to 6L6, I switched the bias switch, but the re EL34 led keeps lit. in this position the green 6L6 led should be lit right?

I opened it up and tested the switch, when I flick the switch to the left, both middle and left terminals make connection, when I flick the switch to the right, both middle and right terminals make a connection, all 0 Ohm.
so the switch should be fine.

now when I look at the wire connection, this looks odd, I can see some solder traces, and to my (limited) knowledge, there should be one grey connected to the middle position in order to make switching work.
To me this explains why it doesn't switch anything. (again, with my limited knowledge).

If you look at the last picture, its very obvious to me that the yellow is originally connected to middle(Yellow), and the blue to middle(blue), as demonstrated. but I can't confirm it with the original schemes.


it doesn't look to a bias pod mod to me because I can't find a bodged pod anywhere, it looks like a mod to keep is on EL34 (which makes zero sense to me).



I truly want to reverse this, because I want to run it with 6L6.

anybody who can help with this?

https://www.dropbox.com/sh/r9pdbuslqwmdifu/AAAIbb8HQFzqE5azkKIxp94fa?dl=0

see pictures in link.

cheers fellow amp lovers!
 

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