Another 36 watter lives.

Post by **Plexi** » Mon 07/05/04 10:38 am

I finally got around to getting my 36 watter wired up. Still got a few things to tweak,experiment with and try,but it sounds great,and it is LOUD..
Mine is quite a bit different than a stock amp. It has a Trainwreck channel.
And had to use a switch to go between it having a feedback circut.
Richie

bnwitt · Post by **bnwitt** » Mon 07/05/04 11:34 am

Richie,
way to go. Now start doing some drawing to share with the rest of us. I want to see that trainwreck circuit. I just finished another Hoffman Plexi 50 watt yesterday morning, and I had forgotten how loud those suckers are. I also forgot how trebly the hi treble channel is with that .68uf bypass cap and how bassy the normal channel is with the 220uf cap. I think I'm gonna change them both to bring the channels a little closer together. Any suggestions on values you like? Part of my motivation is a little pig squeal on the treble channel with the volume and presence maxed.
Barry

bnwitt · Post by **bnwitt** » Mon 07/05/04 4:00 pm

Richie,
I do have the .002 coupling cap on V1b. I'll try that change. I have shielded wire on the inputs but not on the mixer 470K's. I'll change that. I was running the 12AX7's without shields so I'll put the shields on and see if that helps. I'm using Groove tube 12AX7M's (Mullard replicas) in all three Novals. As far as removing the bypass cap on the mixer, are you talking about the 500pf cap? I don't have a treble cap on the volume pot.
thanks,
Barry

bnwitt · Post by **bnwitt** » Mon 07/05/04 8:21 pm

Richie,
I changed the .002 cap to a .022 and the treble channel is much better. It is actually useable now. I also put shielded wire to the mixing resistors and shields on all of the 12AX7's but I still get the squeal when the presence and high treble volume knob are both full up. Of course I couldn't play the amp that way anywhere but in an auditorium or bigger venue. I didn't remove the 500pf bypass cap yet. I am finding that these GT 12AX7M tubes are not as warm as others and seem to acentuate the mids and highs so I might try some EI's in the amp before I pull the cap. I have a feeling that will fix it. Thanks for the help.
Barry

Post by **Plexi** » Mon 07/05/04 8:27 pm

Yep the 500pf cap over the 470k resistor.

WOW this trainwreck kills,i had a couple weird problems,i had this weird noise crapping out in the speaker,and it was doing it in both channels. I knew it had to be in the driver or power section. I was very surprised i had a bad recto tube causeing it {New VA tube] That was 2 of these that turned out bad out of the box.
I used a different recto tube..and it worked fine.All is smooth,and no noises. I'll post a few pics below.
It was a give and take between the 2 circuts,to make both work in the amp. As to keep the stock 18, but i can say i like this even better than the TMB..
How to describe this.. it has a great clean sound,set the volume just right on the amp and tone controls to the guitar,and you can just roll the volume control on the guitar,and it has a pure sustain. I've been playing it most of the day. It is fantastic,i never dreamed it would sound like this,or turn out so good.
You have to have the feedback switch,for what ever channel you want to use,to make them work like they should. The feedback has alot to do with how the amp sounds. I still have to finish the box tolex,and put the cream chicken head knobs on it,and labeling for the speaker jacks,and feedback switch. When i get it all done,i'll try to post some sound files.

Oh..the pics may be a bit of a mess,i haven't put tie wires or dressed it up any yet.

Richie

bnwitt · Post by **bnwitt** » Mon 07/05/04 8:35 pm

Richie,
She looks well built. I can't wait to hear some clips and see the layout.
Barry

Post by **Plexi** » Mon 07/05/04 10:21 pm

A while back SteveUK built his 36,and he had to use a screen resistor for each tube. i only used 1-100ohm for each set of EL84s.And 1 each cathode resistor for each set of tubes 125 ohm.

My EL84s are running 330v plate 318v screens.

Richie

Post by **Plexi** » Tue 07/06/04 12:37 am

i forgot a pic

2BDH · Post by **2BDH** » Tue 07/06/04 12:41 am

Looks good to me

. That chassis looks very nice.
What transformers are you using?

Brent

dboul · Post by **dboul** » Tue 07/06/04 12:45 am

Very cool Richie!!

Will we have sound clips soon?

Take care buddy!

bubba2 · Post by **bubba2** » Wed 07/07/04 8:49 am

Looks great, I want one or two or three ... I guess I'll keep on dreaming
till I sort my finances.
Hey Richie, I recall in a thread somewhere that you prefer NOS 'orange drops'. Which ones should I keep an eye out for?
thanks

myker · Post by **myker** » Wed 07/07/04 8:55 am

That is a fine looking amplifier! Impressive craftsmanship! Clean work! When do we get to hear it? I would really like to hear what you have done with the trainwreck channel too..
mike..

Post by **Plexi** » Wed 07/07/04 11:08 am

"""I recall in a thread somewhere that you prefer NOS 'orange drops'."""

The ones i have are or have 6PS on them. I still try to use some current made caps like mallories 150 and others.
The thing is,I really used nothing special in this amp for parts. And some things i used i did because i was out of the others,and didn't want to wait.

I need to get some new preamp tubes,i'm just running some test tubes ..which are good,but not as good as they should be. And the thing still sound fantastic with these in it.

As with most proto type amps..i already see things i'd do different,not to make the sound better,just things like a smaller width board.And once i got started,i tried many things . So i changed from the layout i had drawn up..lol
But the thing is,its perfect..and i don't want to even try to change or mess with it. Just some new preamp tubes. Its got a new set of JJEL84.
Once i finish my box,i'll try to get some sound files made of it.

Richie

Ian · Post by **Ian** » Wed 07/07/04 11:58 am

Hi Richie â€“ the 36 looks really nice

, although I have to admit I havenâ€™t kept up with any of the 36watt stuff at all. The Trainwreck bit is interesting,....I thought maybe the circuit in those was pretty much a â€œsecretâ€

stevesuk · Post by **stevesuk** » Wed 07/07/04 1:35 pm

Well done Rich,
My 36 watt has clocked up probably a dozen or more gigs, plus practices and finally needed something doing to it.
I replaced the 1 meg, MV pot which was secondhand and had started crackling. I also had a microphonic Mazda EL84, the combination of those two things really made it unuseable, the last gig was finished using the normal channel which doesn't drive everything so hard.
I think the moral is, as Richie suggests use new valves because this thing has the tone without the NOS valves. I have ordered up some new gold EL84 Marshall valves because they are really cheap and tested. I don't care about the matching crip. But to match them means somebody must have tested them. I might rest the prized Mullard ECC83s gracefully and try new Marshall ECC83 valves as this amp is a real workhorse. (two more nearing completion with different OTs etc.)

Whoever volunteers to draw the layout I am ready with my four penny worth (as they say in blighty).
Steve UK

Post by **Plexi** » Wed 07/07/04 3:57 pm

"""I thought maybe the circuit in those was pretty much a â€œsecretâ€

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