Hoffman Plexi 6V6 - New project

[JPK]

Edit: After discussion in this thread I decided to just build Doug's Plexi 6V6 instead of the Robinette JCM800 6V6. More to come.

[dwinstonwood]

Hello JPK, I built Hoffman's Plexi 6V6 and added his "Hot Switch." The power amp section is basically the same as the amp you intend to build, using 6V6's.

I went with the Hammond 290AX PT, the 1760H OPT that has 4, 8, and 16 Ohm speaker taps (my drawings show the 1750H that only has an 8 Ohm tap), and the 194A choke.
I have about 380VDC on the 6V6 plates with the 290AX, which I think is just right.
I build the amp in a JTM45 chassis.

Take a look at my schematic for voltages and my layout. There might be something useful there that you can use.

[tubeswell]

Ask Rob

[JPK]

Hello JPK, I built Hoffman's Plexi 6V6 and added his "Hot Switch." The power amp section is basically the same as the amp you intend to build, using 6V6's.

I went with the Hammond 290AX PT, the 1760H OPT that has 4, 8, and 16 Ohm speaker taps (my drawings show the 1750H that only has an 8 Ohm tap), and the 194A choke.
I have about 380VDC on the 6V6 plates with the 290AX, which I think is just right.
I build the amp in a JTM45 chassis.

Take a look at my schematic for voltages and my layout. There might be something useful there that you can use.

Thanks. That's going to be very useful. I'd prefer to use a 4 8 16 ohm selector switch. I'll take a look at your docs. The Hot Switch sounds interesting. How do you like the sound? What speaker cab are you running?

[dwinstonwood]

JPK, the switch adds an extra triode so that you have three gain stages before the cathode follower and tonestack. With the switch off it's very similar to the low gain input (top input in your schematic) of the RR800 you want to build; with the switch on, it's like the RR800's high gain (lower) input. So, you flip a switch instead of moving the guitar cord between input jacks. The hot switch is our host, Doug Hoffman's design. The main differences in tone will mostly have to do with the coupling and bypass caps in each amp. You can play with the preamp B+ voltages by changing the dropping resistors.

I originally built the amp with the switch, but later removed it so that the amp is always "hot."  Right now, I don't own a speaker cabinet, so I either play it through the Celestion Creamback in my AC15 cabinet, or the WGS G12C/S in my 6G3 cabinet. But, a coworker has chosen to give me a broken Fender Stage 160 solid state amp sometime soon. It has two Celestion G12T-100 speakers at 4 Ohms. Since I used the 1760H OPT, I can match the amp to that. I have no idea how that will sound, other than loud. 

[JPK]

Sounds like the Hoffman Plexi 6V6 without the switch is more what I'm looking for. I don't need the low gain option since I rarely play clean. Then I can buy all the stuff from Doug. Turret board with turrets installed, chassis pre-punched, and most of the parts. Cool. I edited the thread title and my first post to reflect my change of plans. Excited to have a project picked out. 

[dwinstonwood]

Excellent choice! 

I recommend following the grounding scheme in my layout with only the one ground point: the input jack. My amp is very quiet.

[labb]

You will love this amp. Takes a little tinkering to get the normal and bright mix just right but once you do it really sings.

[Bieworm]

Anybody checked out the Trinity Thor for a 6V6 plexi build? Looks like a killer amp if you check the YouTube clip with that overly happy dude presenting his build

[RoadShow]

Take a look at my schematic for voltages and my layout. There might be something useful there that you can use.

I realize in your statement further down you aren't using the switch, but is the DPDT in your schematic correct?

[dwinstonwood]

Hi RoadShow,

I literally copied Hoffman's Plexi 50 wiring diagram.

I originally had the switch installed and it worked perfectly. But, since I always kept it on, I just removed it.

I just like keeping amps as basic as I can. If there are too many switches and knobs I don't know how to stop fiddling with them and start playing. 

[RoadShow]

Hi RoadShow,

I literally copied Hoffman's Plexi 50 wiring diagram.

I originally had the switch installed and it worked perfectly. But, since I always kept it on, I just removed it.

I just like keeping amps as basic as I can. If there are too many switches and knobs I don't know how to stop fiddling with them and start playing. 

What you display now is correct, you were missing the middle diagonal connection in the schematic you originally posted.  Check it out. I like the schematic and was checking it out and noticed the missing connection.

[dwinstonwood]

Yes, I just figured out what happened.

In DIYLayoutCreator (the program I use), when you copy and paste an object made from multiple shapes it will change the positions of the layers.

The "S" shaped wire between On and Off was in the drawing all along. But the layers changed positions and the rectangular switch body was covering it up.

All I had to do was select the rectangle and move down its layer order. It's a weird glitch in the program. I've seen it happen before with turrets.

Here's a screenshot of what happens when I copy and paste the switch. The wire is still there, but it's hidden under the rectangle.

I fixed the PDF. I'll upload the new version with the wire on top of the rectangle. A really big thanks for catching that!

[labb]

You may want to take a look at this: http://sluckeyamps.com/6v6plexi/6v6plexi.htm