Don't really know why I do these things but over at Hoffman's they were talking about the difference between a Plexi and a Wreck. I looked at the schematics and decided to marry them.
Added a 12AX7 and Wreck components, a four pole switch to change from Plexi to Wreck, tone pot values adjusted to get the proper response with either circuit, tone and volume pots are dual pots so one set of knobs (that was the need to adjust the values, should be close), NFB change between modes. And a split bias switch on input which the switch should have been in Plexi position as all the other contacts are. Oops.
Colossal wrote:Interesting that you chose 100k/100k for the PI plate loads. Was that intentional?
Shoot, I modified another schematic rather than start from scratch and I forgot to change the PI resistor. Might be another error or two in there, I was more concerned with being able to switch between the two with the least amount of trouble.
I do not know much about the Trainwreck and read there are a number of different circuits. I just went with the schematic that was posted. I nay have to do some reading here as this looks ti be an interesting design.
Right on, I wasn't sure if that was a typo or intentional. Some PI designs call for matched plate loads but the Marshall/Trainwreck usually are the traditional values of 82k inverting/100k non-inverting.
If you plan to switch from one mode to another on the fly, you may need to add some high value pull-down resistors (say 2M2 to 4M7) on the common pole of your relays (or switches) to reduce switch pop on the TW side at V1a plate and cathode, as well as at the entrance to the PI.
Also check out the Hall/Mhuss T-rex which is a hybrid of a Marshall 1974 and TW circuit to see the way Mark implemented the switching and input jacks (very slick): http://mhuss.com/18watt/schematics/18wTRex-S.pdf
Doing a 5E3 that goes to a 6G2 and BF and have resistors in to tame the popping. Left them out above just to keep the schematic simple to show what is being done. Separate pots for the BF tone controls though.
Building it right now. I am not expecting to mimic each of the amps exactly but want to get the flavor of them in the same package. I am using 6K6's instead of 6V6's also. This is just a little bedroom amp I am building with a 10".
Colossal wrote:Nice work so far. Good looking cab. I knew CDs were good for something!
Yeah, points for creative use of junk laying around you thought you'd never use again!
Yeah, they have been sitting in a box in the basement for the last 10 years. I needed something to prop up the chassis and they were the handiest thing around.
On a, oh shoot note, I was wiring up the controls and I realized the tone stack is across the normal channel when in Tweed mode. Not sure what how I missed that. I may stick in a push pull switched pot to jump out the tone stack. I would rather it were kept simple but at this point I just want to get it wired up and working.
544]http://i406.photobucket.com/albums/pp14 ... nwreck.jpg[/img]
642]http://i406.photobucket.com/albums/pp14 ... 5G2-BF.jpg[/img]
768]http://i406.photobucket.com/albums/pp14 ... ssis01.jpg[/img]
