[kurtlives]

If you dont know about Dumble amplifiers then here ya go. . Basically they are limited production amps (less than 300 ever made since the 70s) and expensive now a days, $35,000.

Anyways I am building a 50W ODS (Over Drive Special). It's an 80's version and based on the highly documented #124, that was degooped and rev engineered. #124 was a ODS in it's prime. The amp has two 6L6 in fixed bias for its output.

There are two inputs: a "normal" input and FET input where the signal from the guitar goes to a J-FET line level booster pre-amplifier before entering the first tube stage (originally intended for use with acoustic guitars and other instruments with low output levels).

The first tube is followed by a passive tonestack with adjustments for treble, middle, and bass. Typical switching options available in the different models include:

Bright (bypasses the volume potentiometer with a capacitor to boost the high frequencies)
Deep (changes the voicing of the tonestack for a warmer tone)
Mid (increases the value of the treble capacitor to boost the midrange frequencies)
Boost (disconnects the treble potentiometer from the bass potentiometer for a preamplifier level boost)
Rock/Jazz (switches between a Fender-esque voicing and a more "hi-fi-type" of voicing).
The tonestack is followed by another clean preamplifier stage. The resulting signal is either fed straight into the power amplifier ( clean channel), or into the (two-stage) overdrive section. The power amplifier uses a standard long-tail pair phase inverter with negative feedback. It will break up , but only at very high volume levels, or when the preamplifier "boost" switch is engaged.

The "Skyliner" EQ refers to a newer (mid-1980s to present) way of voicing the tonestack. It is said to provide a better clean tone than the earlier voicing of the tonestack. Some lower serial number amps have been retrofitted with this EQ.

Not sure when I am going to finish this build as I have been very busy these days. Also dont have the transformers or cab, and dont know when I can buy those. Going to university in September so it will most likely be a long term build.

Should be a fun build. It is quite big and fairly complex so I wont blow through it. I also dont have a layout to follow really. I am using two layouts and kind of blending them together. I am doing this because I am doing a 50W build and the PSU board I have is a bit different.

Got the chassis today. It's an exact replica of an 80's ODS.





Got a bunch of tubes to try in this build...

JAN-Philips 6L6WGB
TAD 6L6WGC-STR
Winged "C" (SED) 6L6GC
Tung-Sol 6L6GC-STR
Sovtek 12AX7-LPS
Chinese 12AX7-A
JJ ECC83-S / 12AX7
Electro-Harmonix 12AX7

Here are the parts I have as of now...


Waiting on a Mouser order to come in now before I can get started. Going to do some chassis work on it now though.

This post has been edited by kurtlives: 17 July 2009 - 02:26 PM

[AcousticSmash]

Wow, not very often you see Dumble amps these days and I have been curious about them ever since I heard about the SSS model which can be heard on the Electromagnets album featuring Eric Johnson, however he dropped the amp after the power transformers blew out and due to their rarity, getting the replacement parts would cost a fortune so he replaced them with 1960 Twin Reverbs. Looks like someone finally added information to the Wiki page, last time I viewed it there was almost no information. Good luck on the build, hope it turns out great. Are your parents not annoyed at your amp collection?

[kurtlives]

I figured you would know about these amps, the Eric Johnson fanboy you are A bunch of big names used these amps, SRV, Larry Carlton, Robben Ford...

The maker, the nutter Howard Alexander Dumble is a really nutcase. Apparently he and EJ had some falling out and some issues so his amp never got fixed.


The parents dont care too much, they keep remind I'm outta the house in a month and a half. Off to university...

[AcousticSmash]

Haha yeah I guess you could say that, I like his music though and am always fascinated by his sound. I knew SRV used one, never knew Robben Ford did until today. So is that box of tubes just something you ordered in bulk?

And I hear ya, school starts before too long and I still got bills to pay before my courses start, it's driving me nuts how late they were with the acceptance letters this year.

[caprico]

wow that looks good!

so where do you get panels and printing and all done from...
i mean you fenders look like originals.. so does this dumble i suppose.

btw i'd like to listen to the stuff you make.. do you have a soundclick or something?

[kurtlives]

^I do have a soundclick but it is missing a lot of amp soundclips




Did a bit of chassis work. Was kind of over whelming at the start, had so much drilling and such to do. Almost everything is mounted, just a few things left...Still need to mount relay boards, grounds and a few little more things.

Got my Mouser order in so I basically have everything I need. Still waiting on an order for wire, socket covers, OT, pots and a few other random things. Once I have the wire I can start really building.

Forgot to post pics of these before. These are the choke and footswitch I got.



Progress pics...

[Fillmore_East]

this should be a tough one. I always hear how sensitive D style amps are to good lead dress

This post has been edited by Fillmore_East: 21 July 2009 - 11:35 PM

[kurtlives]

^it's not overly sensitive. There are things in it that are much more sensitive.



Did a bit of work a while back, then went away for a while. Came back yesterday and got a bit more work done today. So far I have done all chassis work. Well actually I need to grind the chassis under all the 1/4" jacks but o well. All hardware fits and there is no problems! Mounted and tightened all the back hardware but not the front yet. Still missing an 18mm 250K(A) pot!!!

Also started work on the PSU and main board eyelet. Still not total complete on either of them. Still have to do more research and figure a few things out. Also wired the heaters, did them in the true HAD ODS style.

O also got a 50W Bassman OT, it has 4R, 8R and 16R taps.


Bias jacks added. All nuts tightened like the real #124 I know





Note how the heaters go vertical almost immediately, that's how the original ODS did them.




Wire color coding same as real #124. Really like this solid core teflon wire.

[improviduto]

let me know when you're ready to build me one.

[kurtlives]

But I was going to mail this one to you

[Fillmore_East]

so in the last year, a tweed deluxe, deluxe reverb and onto an ODS? a lot of amps!

speaking of which, i'm actually interested in building a tweed deluxe myself.

[improviduto]

But I was going to mail this one to you

Hah! I think it better you get this one sorted out so we can talk about fine tuning one for myself.

Also, what's next? A Trainwreck clone?

[kurtlives]

But I was going to mail this one to you

Hah! I think it better you get this one sorted out so we can talk about fine tuning one for myself.

Also, what's next? A Trainwreck clone?

Haha, yes what's next.

I was thinking about a "Wreck" as the next one (next summer). Will probably build an Express as both the Liverpool and Rocket are EL84 based, I already got a bunch of EL84 based amps. Those are "interesting" amps to build. Very simple but super finicky, incrediblty sensitive.

Been thinking about a standalone reverb unit for the amps that don't have reverb. I am a sucker for reverb.

[improviduto]

Build an all-tube standalone reverb unit.

[kurtlives]

^ya, if I did build one it would be all tube for sure.

I started wiring the the PI and OD tube. Here is where I am so far...

Going over my lead dress now and having some other people overlook it as well. I tried to follow the layout, the real #124 photos and "Funk's" lead dress.

Doesn't seem like the lead dress is anything special. But the layout of the wires is fairly crucial. This is more or less how HAD wired the amps. It wasn't super neat but he definitely had a idea of what he wanted from it.

[kurtlives]

Did a bit more work. Wired up V1 and added the relay boards, also wired them up. Wired up and test the voltage doubled which powers the relays. It works perfectly when tested under load, gives a steady 12V DC. Also wired bias jacks and power tubes. The mini switches and control pots are also being wired.

[kurtlives]

Did some more work this afternoon. Right now I am about as far as I can go with this build. I still need to order some more parts to finish it (PT, trimmers, a pot, footswitch jack and other random ######). O well gives me time for a new amp I am design.

Right now the power supply and the OT's leads are a bit loose, leads to a bit messy look. It is just like this because the dropping string needs to be adjusted according to the PT and also because I am not sure if the OT is in phase. I might need to reverse the OTs leads, the NFB could make the amp into an oscillating mess.

[improviduto]

have a cab in mind that you're going to pair it with?

[kurtlives]

Not sure exactly what I am going to use cab wise. May be a 112, could be a 212 though. I will most likely build the cab. The real Dumble's used EV12L or G1265 so Ill probably use them or some similar speakers.

Not sure where I will get the replica head cab, know a few places.

Got a few final parts on the way so hoping to finish the amp up soon and test it.


Once September comes around the amp and any plans for the head/cab will be on hold as I go off to school. I am hoping to build the cab when I come back home at Christmas time.

[kurtlives]

Got the power transformer yesterday, it's a beast.


FET board installed and input jacks wired


PI trimmer installed


DIN jack installed and wired



Power transformer installed





Going to install ground buss and add the coax tonight. Tomorrow will test it and do the startup procedures.