Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on November 07, 2017, 10:35:59 am
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I cannot remember seeing a case where the signal is divided in the following way (see the picture).
Is it recommendable to do in this way?
/Leevi
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That's fairly common. You may consider using a DPDT switch to ground the input to the second tube when the normal gain is selected. Look at Hoffman's Plexi 50 schematic for an example of his "Hot switch" mod.
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Thanks Sluckey,
Why should I ground the input? If the normal gain is selected the second tube is totally disconnected from the signal way.
/Leevi
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Thanks Sluckey,
Why should I ground the input? If the normal gain is selected the second tube is totally disconnected from the signal way.
Because as drawn, that signal is still going through the tube and will be present on the switch. This signal will be between 20 to 50 times bigger than the normal signal. Even though it is not actually selected, it will bleed through the switch and be passed on to the next stage. Think about it. There's probably only about 1/16" inch space between the switch contacts inside the switch body.
There's a very recent forum discussion about this very issue. Shouldn't have to go back more than a week if you want to read about it.
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I would definitely do as Sluckey suggested. You will get popping in the switches though. You can account for that though when the time comes. High value resistors will work but do not put the switch to the left of the coupling caps. Will need to keep the DC off the switch.
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Yes I have to check how to solve this.
The is case is not exactly the same as drawn since there are also tone stacks in both branches before the switch.
The switch I'm using is a big relay that doesn't pop with the current setup.
/Leevi