Dumbleland update (was SSS) :D

[ElectronAvalanche]

Hi there,

so here is a bit of what a have. Please be reminded, that I can only share what I personally have found out. Some other stuff remains secret due to request.

The SSS I had a chance to look at used EF86 tubes. The preamp used the same Tone stack values as most Dumbles (0.1uF, 0.047 Tone caps, 250pF). Deep Switch, Rock-Jazz, Bright. Usual stuff.

The first Pentode was wired as a triode, the second as a pentode. Think of the normal Dumble Clean channel but using two EF86.

The Reverb was the same as used in some ODS Reverbs. Somewhere on the Web there is a schematic from a guy called Ben I think.

Tremolo as in Fender amps, using Silver Mica caps.

The PI was standard stuff, but there was a directly coupled CF after the PI driving a quartett of 6550s.

Look at the SVT schematic. For the CF Dumble used a 12BH7.

I do not know much about the SSS with active EQs or filters. I think the trick is the hot preamp and the CF after PI.

Here is schematic of the preamp attached.

See ya,

Electron

[Funkalicousgroove]

Right here or in the files section you pick!!

[ElectronAvalanche]

Up for Funkalicousgroove

[oldmacman]

The reverb schematic is in the Files section under OD Reverb #13.

A couple of questions:

You said that the second pentode is wired like a pentode. In your schematic, it looks like both pentodes are wired like triodes.

The SVT schematic shows each output of the PI feeding a triode driver stage, which then feeds the direct coupled cathode follower. Is the SSS like this, or do the outputs from the PI go directly to the direct coupled cathode followers?

Ben

[ElectronAvalanche]

Indeed, the schemo I posted has the second EF86 wired as a triode.

Only later on did I find out, that the second EF86 is wired as a pentode. The screen has a 0.1uF cap going to ground and a 680k resistor tapping of the B+ for the screen. Think standard Pentode stage.

You have to omit the stage before the CF of the SVT schematic.

Electron

[oldmacman]

Thank you so much for the info!

I take it the amp you looked at was one of the newer ones without the filter, like the one at http://homepage.mac.com/bill_jpn_morgan ... e/sss1.jpg ?

I have a couple more questions:

What's the PI tube? 12AT7? 5751?

What's the value of the grid resistor into V2?

What is the B+ for the pre/power amp? About the same as the ODS/ OD Reverb?

What does the footswitch do? Preamp boost like on an ODS?

[ElectronAvalanche]

That is the amp. Silver alligator.

The PI tube is a 12Ax7a. PI values are as in an ODS, Prescence knob is 5k though, prescence cap is 3.3uF.

Iron: MM Power transformer (MusicMan). The CF after the PI needs a large negative voltage (bias) around -150V. Look at TUT for details on this circuit.

Look at the block diagramm of the 150W ODS in the Groove Tubes book to see the PowerSupply.

Output Iron from Sunn amp me thinks.

One Fender style choke, a small 6.3V transformer to supplement the MM PT heater voltage.

NO relays in the amp. FS is for Tremolo (plain vanilla Fender style Tremolo).

Grid resistor is 220k.

See ya,

Electron

[jelle]

ElectronAvalanche, Thanks for sharing the information!!!!!.

This is will be speculation and a couple of questions on the SSS schematic:
The early SSS used 6l6 and 12ax7 tubes:

SSS data sheet:
http://homepage.mac.com/bill_jpn_morgan ... e/sss.html
The 6l6’s are clearly visible in this amp:
http://homepage.mac.com/bill_jpn_morgan ... /sss4b.jpg
http://homepage.mac.com/bill_jpn_morgan ... /sss4f.jpg
Is there any knowledge available on these early amps?


The later SSS evolved into 150w amps:

On the same site there’s:

SRV first came to know Dumble amps when he recorded "Texas Flood" in Jackson Browne's Studio. For the guitar tracks on "Texas Flood" he used Jackson Browne's "Dumbleland" that he found in this studio. He was so impressed by this "Dumbleland" that he contacted Dumble to order an amp. So Dumble made for him a "Steel String Singer" with a preamp that is a bit different than the preamp of a usual Steel String Singer. Let's hear what Dumble says about Stevie's Steel String Singer in a interview for "Guitar Player"/September 1985:
"There are some different things about Stevie's. His is set up more like a bass amp, modified to accommodate the guitar range. It's not the usual lead guitar 'singer' approach. One thing he liked was that he could turn the volume control all the way up, and it didn't distort - it just got louder. He does make it distort sometimes because he has about 50 megatons of pressure when he attacks the strings (laughs). He gets an incredible amount of signal out his guitar, and most amplifiers can't take it. He did his first album with a bass amp I'd made for Jackson Browne."
http://homepage.mac.com/bill_jpn_morgan ... ble-e.html

I’ve seen internal shots of the Winterland with 4x KT-88.
I’m not sure but I think it has a buffered phase inverter.
Maybe HAD borrowed his Winterland output stage for the later SSS.

The same site mentions the use of the Ampeg svt and V-9 poweramp schematics with the 12ax7/7025 like ElectronAvananche mentions. The Ampeg schematic use different tubes for the pi. Are there any values (resistors/caps) changed?
Is it like a schmidt into the second half of an isodyne? See:
http://www.bonavolta.ch/hobby/en/audio/split.htm

I also noticed that the 300sl uses taller preamp tubes for the pi:
http://homepage.mac.com/bill_jpn_morgan ... l300-r.jpg
Can anyone shed a light?

The high and low step filters perhaps are seven step rotating switches.
http://homepage.mac.com/bill_jpn_morgan ... /sss4f.jpg
I found the output cap of v1b to be crucial for the bass response of the ODS especially with different speakercabs. Perhaps HAD is messing around with different values on a rotating switch here. Anyone?

Is there any information on the jfet circuit and the way it is blended into the preamp circuitry? Some SSS have a jfet volume on the front panel. The Silver Alligator doesn’t have the jfet volume.

On the net many people have mentioned that the EF86 has a high internal impedance of 2.5 M and that an extra 12ax7 stage is required to connect it to a tone stack. With the Triode mode and a 47k plate resistor (output imp 2.5M//47K => 47K) this would possibly work as a 7025 with a 220K plate load. But with a gain factor of 5000, cool!

Any information would be appreciated.


Maybe it’s getting obvious, but I’d really like to build a SSS.....I like it clean and big.

Jelle
The Netherlands

[tonelab2]

I also noticed that the 300sl uses taller preamp tubes for the pi:


Could be 12bz7.
12bz7 is a taller version of the 12ax7. heater current = 6.3v/0.6A.
Put out slightly more wattage, 12ax7=1.2w, 12bz7=1.5w.

[v00d00blues79]

That was my guess for the PI tube. I ran one in my BF Bandmaster in the PI slot for a while and it really did wonders for headroom.

[ElectronAvalanche]

Hi there,

I only know of 12BH7 being used as the post PI CF driving the grids of the output tubes. I doubt that Dumble uses 12BZ7

Electron

[glasman]

Hi there,

I only know of 12BH7 being used as the post PI CF driving the grids of the output tubes. I doubt that Dumble uses 12BZ7

Electron

i would agree, I think the 12BH7 would be the tube of choice for this application.

Gary

[Bear]

What's the info on the filter circuit?

Bear

[jelle]

Hi,
With the buffered pi research in progress, I thought it would be a good idea to test the EF 86 preamp.
Last weekend I bought 3 NOS philips EF86's and this weekend I hope to find enough time to build it into my selfbuild AB763 vibroverb.
Anybody tried this?


I'll keep you updated!

Jelle

[oldmacman]

http://homepage.mac.com/bill_jpn_morgan ... e/sss.html

This one uses 5751s.