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Stephen, here's what I'm thinking about that foot switch mod.

Add a rear 1/4 inch jack for the footswitch input.

Use the MV channel input for an indicator light which would light when the MV channel is selected, go with the relay internal in the amp to switch from normal to MV channel.

The two remaining input jacks to the far right would be where you plug the guitar in for either channel. One for singlecoils and one for humbuckers.

How best to pull this off?

1. Adding a rear 1/4 inch jack for the footswitch input is not a problem

2. Use the MV channel input for an indicator light which would light when the MV channel is selected - doable and an interesting idea.

3. I would go with an internal relay in the amp to switch from normal to MV channel. For simplicity, use Webers switching kit: https://weberspeakerscom.secure.powweb.com/store/chansw1.htm Since it is a DPDT relay, it should have an extra set of contacts for an indicator of some sort.


4. The inputs on the TMB are already set up as a "low" and "high" input on the Normal channel. The TMB and the Normal channel go to different pins of the Phase inverter 12AX7. I think Webers DPDT relay switching will work, and I think you'd get an indicator. This scheme would actually give you a low & high input to BOTH Normal & TMB channels.

Has anyone else done channel switching between the TMB and the Normal channel

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I haven't done a stock 18 watt, but my channel switcher is based on an 18/20 watt PI and power amp.

I think it would be very doable on a TMB 18 watt. The trick is shutting up the channel that isn't in use. You could switch at the inputs, but I think a better way of doing it would be to send both inputs into the normal channel and tap the output with a .022 cap (or .01 if that sounds better to you) and feed the screen of the TMB's first stage. You'll want a 470k screen resistor and a 1 meg (or less if you want to dump some gain) grid leak resistor on the screen. Then use the relay to ground which ever channel you are not using. I would suggest right after the coupling cap of the new second (original first) stage of the TMB channel. For the normal channel I'd ground it at the "top" of the volume pot, between the volume pot and the 100k in the tone control.

If you wanted to, you could also switch at the input of the phase inverter, sending both channels to one side of the PI. The other side would go to ground through a .1 cap. This is the quietest way of doing it, but you could get by without it. This would take up both sides of the DPDT relay.

However, the channel indicator can be hooked up to the footswitch jack. Simply hook an led in series with a 1k resistor from the ring to the tip of the footswitching jack. Hook up the relay so that the TMB channel is on in the NO (Normally Open) position and the LED will light when the TMB is active. When the footswitch is closed the light will go out.

This will get you a channel switching 18 watt. Plus the TMB channel will gain another triode for even more distortion!

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Richard Johnson
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Playing an insturment doesn't make you a musician, listening does