Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on March 02, 2017, 05:17:46 pm
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I have a J20 Ampeg, made in Vietnam a few years ago, they are no longer made but were PTP with a board rather than a CB. I want to change the amp to more of a Tremolux 5G9 layout but want to keep the original faceplate, drill no holes. The Ampeg has two inputs, bright and normal, one volume and one tone along with speed and intensity for the tremolo.
I changed the Fender schematic (5G9) preamp to work with the faceplate, taking out one volume and one input. I plan to put a switch in the normal input for a cascade effect (on/on/on) and eliminated one volume. I'm changing the trem circuit to a 5G9 using both sides of a 12AX7.
I attached the original schematic, J20 along with what I plan to, any mistakes seen?
Maybe, I should just change the input to cascade and one volume and half a 12Ax for the trem as in the original J20, a lot sell work..?
al
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Your On-On-On switch isn't drawn correctly. That's usually a Double-Pole device.
Regardless, I'd recommend ditching it and using a shared plate load & coupling cap for paralleled input triodes.
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take the switch out and run to volume?
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To be clear, the On-On-On switch can be made to work.
However, I'd simplify. Use a single plate load resistor (50-100kΩ) for both triodes, one coupling cap, then the Volume pot.
I suspect the switch won't find much use once you hear the amp. You'll get a bit more gain (~30% more) by simply having parallel triodes for the input stage.
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Forgive my ignorance, do you mean like this:
Or maybe the HV should go before the coupling cap to volume, in otherwards run the .022 after the 100 ohm plate load?
Maybe I should just run the input to a single gain stage, then to a second gain stage then volume?
I'm not too good on designing a preamp, just want a decent sounding amp without a ton of gain, blues tone is my goal.
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Forgive my ignorance, do you mean like this: ...
I don't think you will need the 220kΩ resistors of the voltage divider before the Volume pot. Otherwise, yes.