trinityamps.com

another question from the "apprentice"amp builder,looking for info on how to change the VRM circuit to control B+ to PI and PA tubes only and leave B+at normal level to preamp tubes,have not installed VRM yet in my chassis would like to look at options now before soldering everything up,I will be using this amp at very low volume most of the time and read on 18watt.com alot of people prefer VRM on PI+PA tubes only

Have a look at my recent build photo's and you can see the layout and almost all the schematic. 18watt/Trinity? member named Conger has a few schematics at 18watt and one is for an sIII.
http://s188.photobucket.com/albums/z265/kersanov/18%20Watt%20S111/
I think the only thing that is missing on the schematic that Conger had uploaded and my pencil mud-map is the preamp filter cap resistor was changed from 2K2 to 8K2 for the PA-PI VVR to get the preamp voltage on spec.

thanx for the info,this is my 1st amp build so all this is one big new learning curve.Looking over your pics really helped me trace out path for B+ and VVR dropped B+,all makes alot more sense now,better for me to learn how all this works than just plug in the iron and"connect the dots"
by the way nice looking amp,like the front and rear plates

see photo VVR board going by cap can,gonna make "B+ routing board"similar to what you used and mount between VVR board and output selector switch

Hello Zircontweezer

I am interrested by your single off-standby-on switch. Can you tell me more about it. Type of switch and wiring to achieve this function with a single switch. Must be a special on-on-on switch.

Thank you

Sorry for the hijacking, but here's some info on the progressive switch used for the Triwatt...
viewtopic.php?t=1468

Pretty elegant solution

Joe G

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Thank you very much for the info.

Hi Serge, I hade made the plates up with the switch in mind but not in stock. I believe their are a couple of suppliers that I was going to import from. Weslabs carry a DPTTP double-pole triple throw progressive? and AES have a Carling that does a single pole? version. The one in my pics is just a standard on-off-on with the mains connected and no standby.

Thank you very much for the answer.

I think I will contact Stephen as suggested by Joe G in the thread about the new Triwatt double duty switch. The Carling progressive on-on-off will do the trick for me. Just need to add 220K 2W resistor to discharge the power supply cap.

couple questions here regarding PI+PT VRM only,
1)do you need to do the scratchy pot mod,.1uf caps at input if not regulating B+ to preamp tubes(following congers schematic,noticed the caps are not on schematic and 1 meg resistors still on inputs)
2)cannot source 16uf cap locally,only 10+22uf can I use 2 8uf(450v)caps in parallel?(should be 16uf with 450volt rating still right?)

I have not added any mods for scratch sounds and cannot hear any issues. I believe that related to a different VVR setup. If you don't have a 16uf then the 22uf would be fine or parallel the 8's.

thanx,going to leave out the .1uf caps at v1,running 2x8uf in parallel

No, you do not need to add the 0.1uF caps at the inputs if you're not scaling the preamp rail. That's another advantage of that particular approach.

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