DeArmond R-15 x 2 , A Need for Tweed

[David Root]

I have been wanting to build this one for a few years, for two reasons,

1) I never built a 5E3 circuit, and

2) Ever since I saw this amp reverse engineered and offered as "the best 5E3 circuit ever" by Tonequest magazine and offered at a princely $2,000 for a 15W 1x12, I have wanted to build it as a 4x6V6, but also set up to use 2x6L6GB/5881 instead.

I'm doing it in a modified Weber 5E3x2 chassis drilled out for 2x5Y3GT rectifiers in parallel. Pull one for some serious sag, or pull both, put in one 5AR4 and pull 4x6V6 and replace with 2x6L6, maybe a sniff of Neil Young tone.....???. In a Weber 2x12 cab that looks like a low power Twin cab.

Here's a Watts Audio 5E3 board slightly altered to accomodate the above operation, now wired up and with the PS caps in the right sequential order (!).

[M Fowler]

David,

Sounds like a great project and everyone should have a 5E3 around.

Mark

[David Root]

Thanx Mark, it is an interesting variant on the 5E3, uses 12AX7 in V1 not 12AY7, two channels with different cathode Rk and coupling caps, different operating points on different load lines.

I'm incorporating some hints from reading about 5E3 builds--1) tone cap to ground changed from .005 to .0007 (680pF). 2) 10 uF instead of 25 on channel 1 Ck.

Here's the original schematic if anyone's interested. This is the R-15T, I'm not doing the tremelo, no space left!

[XgamerGt03]

Was it the DeArmond amps that used the P.E.C parts? I remember some amp using potted parts that was apparently the best deluxe tweed clone or something like that.

[M Fowler]

I have this DeArmond Schematic.

[David Root]

Xgamer, that's the one. Look at this gut shot. The one potted board is easily visible.

[David Root]

Mark, that SE 6V6 schematic I have not seen before! I'll trade you this R-25T schematic!

[M Fowler]

Thanks David I added it to my collection

[ER]

I built that SE one for my nephew, it sounded great so now I need to do one for myself. Left out the tremelo and used 6aq5 to stick with the small bottle theme. I may do mine with paralleled octals (6sl7, 7408's and 6x5) and adding a speaker tapped lineout with level to the front panel to run to a bigger amp like Kimock does with his for lap steel.

Why would anyone who owns 2 dumbles and has their own signature two rock plug into a single ended dearmond from 1960 for lap steel? Build one and find out!

I used a webster wire recorder power tranny a choke and $17 edcor OPT and a pair of alnico 8" speakers from the thrift store. With the 2x8" the thing sounded like a little plexi, and way louder than you would think, to tape I think one of these would fool a lot of people.

My nephew's I ended up putting in an old bell and howell (we call it the "bell and howl") projector 12" speaker extension cabinet with a cable holder and clip on back it's pretty cool.

Savage amps used this for their Macht 6 amps but I think they went in the wrong direction not using the 6x4 (replaced with a 5ar4). With this and with their speaker choice they lost some of the charm of the original dearmond. Adding a paralleled SE for the macht 12 they strayed even further. Stick to the original recipe for best results, or at least start there before you think it can be improved.

Everyone thinks the secret is the big OPT on the deluxe style PP amps, I think mercury made the one for the tonequest amps and it's available on their website under "miscellaneous amps". Not cheap but seems to be a big part of what makes these amps so special.

some good clips of both types here; http://www.youtube.com/user/doofusmania#p/u

-ER

[David Root]

Here it is, 2x5Y3GT, '50s, 4x6V6GT/G, VT107A, '40s, and 2xTungsol long plate 12AX7, '62.

Fair amount of chassis rework, and tweed chassis are a pain to wire, no room to work in.

Sounds great thru a pair 1x12s with Altec 417Bs in them.

However, the PT puts out too much voltage, I need to lose 40V on the plates and 30 on the screens. Used a Hammond 290DX tweed Bassman because it fit the chassis cut out.

Haven't tried it yet in its combo cab w/two Alnico Blues.

[David Root]

Have to order a faceplate for it, but other than that it's done. The 4x6V6 sound great especially on Channel 2. Tried 2x6L6 but prefer the 6V6s.

[M Fowler]

Nice looking amp David, I like the use of old resistors and caps.

[David Root]

Thanx Mark. There are lots of old carbon comps and mylar caps out there that are still very good and just raring to go in the right old circuits!

The brown coupling caps are Arco Difilms, probably '70s vintage, but were made from '62 on. They are a combination paper and Mylar that bridge the period between all paper and all mylar dielectric. The orange 20 uF bypass caps are '79 no-names, 30 cents each.

The tone circuit .002 uF to ground I changed to a 680 pF (.0007 uf) on the advice of someone, thank you for that it works great! Instead of ceramic I used a polystyrene cap, for a change.

The only new resistors are the 6V6 cathodes, they are 12W Mills wirewound. Oh there are two Riken 1W CFs, the 820R on channel 2 cathode and the 470K on the PI grid, to suppress those nasty frequency doublers when you push a cathodyne PI hard.

All the tubes are vintage UOS except the JAN Sylvania 5Y3GT, NOS. I changed the 12AX7s from '62 Tungsols to Amperex short plates, a '66 in V1 and a '70 in V2. Mo' better harmonics fo' sure!

Channel 2 is awesome thru my pair of Altec 417Bs, I hope the G12s in the cab can get close, haven't tried them yet.

[Structo]

Did you use a power zener to drop the voltage?
I think I see one there.

[David Root]

Tom, you have a keen eye! Yes, there is a 39V 25W Zener on the PT CT, between the standby switch and ground.

It doesn't do anything until you crank the amp. I have 370v on the plates vs. 330 schematic at idle so that's why I did it. Used a Hammond 290DX PT which is a tweed Bassman PT, because it fit the chassis. I knew it would probably be high but I figured if I can control the grid voltage it doesn't make much difference.

Unfortunately the preamp/PI voltages are 20V high at idle but I haven't measured them when the amp is cranked, volume does not increase much when cranked so I guess it's working.