Modifying a Boogie SOB to a Dumble style amp?

[Mark]

I just thought I'd post up pictures to get some feedback on options to implement the Dumble circuit.

As you can see from the picture the chassis is laid out in a most unusual way.

Thanks for your help.

[drew]

My 2 cents . . . .

How about selling it to someone who wants a Boogie SOB? IIRC, those things weren't supposed to be so great, but still, I assume they were made in fairly low numbers, and it seems a shame to use it as a project if it's still a working amp.

[heisthl]

I used to have one of these - they can sound really great if you can get effects after the "Limit" circuit. Unfortunately the limit works by using a tunnel diode in a variable constant current source arragement for the PI cathodes so there is no way to put in an effects loop.
What I did was hacksaw the spokes off a Peavey scorpion basket and sealed it and its magnet structure in a tupperware container and used that as a speaker load for the SOB, then I took a line out off of that and sent it through some effects (reverb, chorus delay etc.) to a 50 watt tube poweramp (scavenged from an old organ) mounted in the bottom of the amp that drove the regular speaker. Sounds complicated but it worked great, very Dumble like tone.

[Mark]

Thanks for the advice but the PI stage is long gone. I found it was the cause of the SOB's sounding horrible. That PI circuit patent is one that Randall Smith won't have worry about anyone stealing!
Normally you'd expect roughly a milliamp conducting through each triode, The SOB PI only allows microamps to conduct.

The amp is pretty much wired up as a Mark 1. It sounds good provided it is loud!

These factors pretty much make it a candidate for modification, It has been modified before I should mention.

[bluesfendermanblues]

Why don't you just remove the PCB and the wiring harness, and put in point-to-point Dumble instead and see if you like it. No big deal.

If you don't like it just put the old PCB and wiring harness back in, and sell the B(ad) O(od) S(ucker) - Oh sorry SOB .

[tubedogsmith]

On mine I pulled out the circuit board and preamp tube sockets. then put in new sockets and mounted a board over them. Just wire up the sockets first and run wires around.

[heisthl]

You can also make large holes in the baord with a ring of eyelets around each tube like this picture from a Carvin conversion in the files section:
https://tubeamparchive.com/download/file.php?id=1407

[ic-racer]

I would have said don't butcher that thing, but I see your response already.
For a Dumble conversion I would think the thing that needs to be dealt with is the preamp tube location, which is not classic Dumble. Your tube lead dress will be altered from the norm, which may or may not cause an oscillation. So, either new tube holes, or run the wires under the board or through a hole. As suggested if you run the wires under the board to the tubes you could probably use a standard Dumble preamp board layout. Realizing you wires from board to tubes will be a mirror image of the original, but the tube and socket won't be a mirror image.

I have never altered a PC board but if I were to do this project, I would think this would be a fun one to try. Hey if it fails, you were going to remove the board anyway. But the traces look nice and wide. If any PC board could be extensively modified, I would think this one would be a good candidate. You might be able to run the signal from V1B to the tone stack then back over to V1A, then almost totally re do V2 with the circuit pen. In fact those traces look so wide, it looks like you could jump the circuit around with wires soldered right to the traces.

[Mark]

Thanks for the responses, I appreciate the input.

I should point out the amp has had holes drilled in it from a previous crappy mod. I do intend to removed the boards and document it so if it all doesn't work out, then I can put it back together and move it on.

Good point about lead dress Ice Racer, I really hadn't considered that as being a major issue. Where to put the relays is a bit of a problem though?

[ic-racer]

When I did my Fender-Dumble conversion, the preamp tubes were between the tone controls and the board. The resulting component location and wiring to V2 caused a very nasty high frequency oscillation that was eventually cured by multiple trials of different lead dress on V2.

I did not have room for the mini-toggles and the relays to be mounted anywhere near the tone stack (like the real Dumble). I had them way over on the opposite end of the chassis from the input jack. I was not sure if the long non-shielded wires to the relays and mini-toggles would be a problem. In the end it wound up working fine. I just made sure the those relatively long, non-shielded wires ran along the edge of the chassis, where possible.

[drz400]

I made one like that 15 years ago and called it a Bumble never sounded right though, I dont think I like the Boogie transformers
Loose the guts and do a new board IMO

[pamaz67]

And It sounded huge in the clean channel, But too harsh in the od to call it a dumble soundin' thing.
Th power amp was completely rebuilt.
IMHO The best thing you can do with any sob, mk1, mk2 etc in combo version, is to take them out of the box and convert them to heads.
The original combo is way too small to sound good with any kind of spkr you can use.
Ciao

Paolo

[tubedogsmith]

Here's an SOB I basically ended up tearing apart and redoing. Moved the OT and repunched tube sockets, etc... I had originally put a board over the old tube sockets but had some noise issues. I've changed a few parts since this pic but it's essentially done and now sounds pretty killer.

[Mark]

Dear Tube Dog Smith

Thanks for the pictures. That is a well thought out layout. What did you do about the original pre-amp tube holes?

Where did you mount the output transformer?

If my memory serves me well, the pre-amp tubes are where the output transformer normally lives.

I haven't done anything about my SOB yet. It is a combo, a speaker box and head is always a better option. It is way back on the list of priorities.

[tubedogsmith]

You can see mounting screws for the OT between the output tubes and PS board, it's under there. I've got some hole plugs for the old socket holes. Boogie did there layout with the OT way over to one side so they could mount this small head in a combo and clear the speaker. With the OT mounted where I have it the speaker would hit it in a combo box. I'm happy with the way this ended up.