Switching the dual voltage PT taps

[Souelle]

Hello,

I have read the previous post, but I still don't understand totally...

What happen when the switch is set to full power ? How can it bypass the resistor on the switch since that resistor is between the pin that have the bias tap coming from the PT and the bias tap going to the board?

Here's what I mean :

Habitually, when you don't have a low / high option, and using only a 2 position switch, the bias tap goes directly from the PT to the board 27 k resistor

This is that same tap that we remove from the board, to connect it to the switch, is that correct ?

But the connexion must still go from the PT to the board (via the switch) even in high mode, right ?

So how can it go from A: the PT to the switch and then B: the switch to the board without being affected by the extra resistor is that resistor is set exactly between A and B ?

I don't know if it's clear, or if you understand what I'm trying to say because I'm not that good in english, but visually, I don't understand it.

Here's what I see in a graphic

Let say that the bias tap coming from the PT is attached to pin 6 of the switch, and that the switch bias tap is going to the board from Pin 3 (don't know how they are named, so we will use number...

PT bias TAP -> Switch Pin 6 -> Resistor -> Switch Pin 3 -> on Board 27k resistor

But on high power it should go from :

PT bias TAP -> Switch Pin 6 -> Switch Pin 3 -> on Board 27k resistor

is that right ? But how can it bypass the resistor on the switch if Pin 6 is link to Pin 3 with that resistor ?

I hope you will understand what I'm trying to say

[Billy Batz]

Its basics of how the switch works. When the switch is set in the one position the 2 lugs that the resistor is soldered to are directly connected by a connector inside. It doesnt matter what you have between the lugs at that point. 5k, 10k the whole Armenian army. Its the same point electronicaly. That resistor is bypassed. So the bias tap is then basically directly connected to the wire going to the resistor on the board. In the other position the two lugs are not connected so the bias tap is connected to the board only through the resistor there.

This is that same tap that we remove from the board, to connect it to the switch, is that correct ?

Yes

But the connexion must still go from the PT to the board (via the switch) even in high mode, right ?

Yes. But, like I said, set one way the PT bias tap goes directly to the board bypassing the resistor by the connector inside the switch. The other way it does not and the bias tap only gets to the board via the resistor which, being in series with the 27k resistor on the board, makes the total resistance higher.

[Souelle]

ok, I understand now..

One last question : The higher the value of the extra resistor is, the lower the tubes bias will be when the switch will be set to low, is that right ?

Thanks a lot

[mightymike]

yes

It's just like changing the bias range resistor.

Same rule applys

[45auto]

does anybody use like dual trimmers?

[mightymike]

edited

[pongo316]

does anybody use like dual trimmers?

Bit Late here But I have use dual Trimmers mounted on the board works great

[John_tucker66]

I know this is an old thread but I was wondering if anyone could send send me the schematic George had created for the dual voltage switch. When I click the link it says attachment unavailable.... it would be greatly appreciated! Btw this is for a JTM45 build

[danman]

Here is a link from the Valvestorm website to our member SDM's page with some of the old layouts. Check under the "1959" file and I believe you may find what you are looking for.

https://drive.google.com/drive/folders/ ... jdaSFNBOGM