36 watt tmb lite
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marcrochotte
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36 watt tmb lite
i built the 36 watt tmb lite (http://img.photobucket.com/albums/v173/ ... mblite.jpg) and would like to add a half power switch to make it break up at lower volumes. ive been searching through the forum, but im not sure how to do it correctly
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cGil
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A VVR would always be a good choice, I think.
Seems to me that tying the inputs of a pair (outside or inside opposing pairs) of power tubes would be a quick way to cut power in half.
Also, since it's cathode biased, and because you're using split bias resistors and caps, might want to look into the quarter power-der mod that lifts the cathode bypass caps. The half power position on the quarter powerder switch doesn't mess with the tone very much. That mod, combined with tying the inputs of a pair of power tubes to ground should result in maybe 10watts of output, with pretty much the same basic tone (minus OT compression, of course).
And there's also triode mode accomplished by tying the screen grid to the plate, but that'd change the power tube's signature "pentode" tone.
Gil...
Seems to me that tying the inputs of a pair (outside or inside opposing pairs) of power tubes would be a quick way to cut power in half.
Also, since it's cathode biased, and because you're using split bias resistors and caps, might want to look into the quarter power-der mod that lifts the cathode bypass caps. The half power position on the quarter powerder switch doesn't mess with the tone very much. That mod, combined with tying the inputs of a pair of power tubes to ground should result in maybe 10watts of output, with pretty much the same basic tone (minus OT compression, of course).
And there's also triode mode accomplished by tying the screen grid to the plate, but that'd change the power tube's signature "pentode" tone.
Gil...
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marcrochotte
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CurtissRobin
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[Ya gotta love a double post.]
KennyO
KennyO
Last edited by CurtissRobin on Mon 12/07/09 12:47 am, edited 1 time in total.
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CurtissRobin
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VVR = variable voltage regulatormarcrochotte wrote:what is the VVR? is that just putting a switch between a pair which connects the pair to ground when switched?
The 18 watt amp is LOUD so instead of using volume reduction techniques that screw up the sound (poorly designed master volume circuits or power attenuators) we use the super-simple VVR to reduce the B+ voltage which drops the volume while keeping our sweet sound intact. It's adjustable with a knob like volume, tone, drive, & al. Member UR12 is the master of all things VVR so search the forum for author UR12. If you search for VVR you'll get way too many hits to be useful. Start with his first post in this thread http://www.18watt.com/modules.php?name= ... highlight=
When you're new on a site it's always a good idea to browse a bit before posting a question because on many subjects you'll find that your questions have been asked/answered many times.
HTH and welcome!
KennyO
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