New 70's style build up and running. (Thanks!!)

[crbowman]

Greetings All!
Just wanted to give a big THANK YOU to everyone here, and specifically to Funk, wjdunham, Marcos, and Max for their input via the Lindley sound post, and to Heistl, Gil, and Structo whose ideas I used liberally throughout this build, and of course, to ic_racer and talbany whose layouts and schematic were crucial. (And to anyone else I’ve copped and overlooked).
70’s style, #40 inspired with a few twists such as PAB and full loop, that I felt like I just couldn’t live without.
Nach chassis (I'll probably rub off the "by Dumble" but left it on for now)
Magnetic Comp iron (JTM 45 PT, Bassman OT)
Solid core 20ga Teflon wire and Teflon coax from Steve at Apex Jr.
Tung-Sol short bottle 6L6s and JJ preamp tubes
12AT7 driver
I’m really pleasantly surprised at how good this thing sounds. Nice, fat, and warm while still having plenty of chime on tap. Overdrive, while not quite as harmonically rich and refined as my home brewed D’Lite, is still really great. Not nearly as harsh as I was expecting and really fat and supple.
Can’t really explain it, but this is a particularly great amp for slide guitar.
Overdrive level is a little hot compared to clean channel, I’ll need to tweak that at some point but I’m going to leave it as is for awhile, get to know it, and let it settle in before I start tweaking stuff.
Build might not be the cleanest ever, but I’ve got no sonic problems, no hum or oscillation.
Okay, so here are some pics. Laugh if you must……..

[img537]http://www.coffeesergeants.com/amp/Clone006.jpg[/img]
[img469]http://www.coffeesergeants.com/amp/Clone002.jpg[/img]
[img459]http://www.coffeesergeants.com/amp/Clone003.jpg[/img]

[jelle]

How do you feel your mid pot works?

[crbowman]

Marginally.
Doesn't really seem to be a very wide ranging control, but I don't seem to have the excessive midrange issue with this amp that a lot of people seem to complain about with this circuit so it works for me.....at least for now.

[ChrisM]

That looks great!

Would love to hear clips of a 70's ODS.

[Funkalicousgroove]

Looks good to me!

[crbowman]

Thanks guys!
I'll post some clips if A). I can get my recording setup back functioning again. B). I can get over the feeling of inferiority I've gotten from listening to all the recent dogears clips.
On the FET input circuit, I used a socket for the FET and a 10k trim pot so I can adjust bias. I plan on trying out a few different FET's. Don't know that there will be much difference but I'll report back anyway.
By the way, Funk, you were absolutely right. The FET really rocks on this.
IMHO it is absolutely necessary in this amp.

[Structo]

Cool!

Looks like you did a great job on it!

[crbowman]

Thanks Tom.
Fun and educational too!
I think I learned more researching this one than I have in the past 15 years of building, tweaking, and subsequently destroying.
That's what this place will do for ya.
That and get you in trouble at work.

[Structo]

I suppose if you wanted more control over the overdrive you could install the later generation type with the trimmer on the OD entrance.

But then it wouldn't be a exact 70's model either.

What output impedance does that Bassman OT have? 2 or 4 ohm?

Are those bypass resistors the Vishay 1%?

[crbowman]

Yeah, if you look carefully you can see where I punched eyelets for the OD trim pot just in case I ever wanted to put it in. Main Idea on this one was to start out with a 70's style but leave myself room to slowly take it in the direction of the later models if I ever felt the need to. That way I could kinda get a feel of the overall evolution of the ODS amps. But I really kinda dig it the way it is right now. And yep, Vishay/Dale 2W 1% 1.5K cathode resistors.
OT is actually the bassman/Super Reverb transformer from Mag Comp with 4 and 8 ohm taps.

[crbowman]

Another difference that I just thought of. I couldn't find a source for the old blue Mepco resistors that the 70's models used for plates so I used RN65's.
Can't say for sure, but that may have something to do with the OD on this one being slightly less harsh than what I have heard reported.

[talbany]

GREAT JOB!!... Love to hear it!!


Tony

[BobW]

Nice Job!

[jelle]

Another difference that I just thought of. I couldn't find a source for the old blue Mepco resistors that the 70's models used for plates so I used RN65's.
Can't say for sure, but that may have something to do with the OD on this one being slightly less harsh than what I have heard reported.

The RN65 are very smooth sounding metal films. I have some gray/blue 70's KOA MF that much brighter. Also the beyslag 1W MF are much brighter. All MHO, of course.

[David Root]

+1 on kudos to all those crb acknowledged.

I'd also like to thank Jelle Welagen for all his help, including having two of his great cabs made for me, and answering a grundle of q's I had about a #40 build in a Princeton Reverb chassis and cabinet, which is next after I finish my #124 now in progress.

crb, I have a pair of those Tungsol 6L6s reserved for my #40, how do you like them so far?

Do you use yours on the 4 ohm output into an 8 ohm speaker, as the legend has it about #40??