Dumbleland Special 150w ser#009 Schematic

[talbany]

Here is the schematic of what we believe to be Dumbleland Special 150w ser#009 collected from the Amp Garage and other reliable outside sources who are familiar with the Dumbleland topology,unfortunately no detailed gut shots of an actual specimen have yet to surface, so we are calling this version unverified for now? ,however, all of these circuits used were imported from other amplifiers from the Dumble line, Odyssey,Winterland, and the Steel String Singer.
We believe Dumble used these similar type circuits in his Dumbleland Specials .So for those out there who wish to share any detailed knowledge about #009 or any Dumbleland Special we would be grateful and honored to update our schematic.. Feel free to PM me if you wish to be discreet...Here we go....

REVISED SCHEMATIC.jpg

Here are some specs from ser#009 Built in 1978
7025/ input/tone stack recovery
7025/Filter recovery
12AU7 L.T.P Phase inverter
12BH7 A.C coupled Driver
4X6550 Output tubes
Classic tone stack
Hi/Lo Filters 7 step
Deep/Rock-Jazz/Bright
Accent
Output power rated @137 watts continuous
Inputs/Normal no FET
4-8-16 Ohm Selectable
Pre amp out

Power transformer looks to be Triad R-25A made 42nd week of 1968
Output transformer Schumacher OT. EIA code 606 is from a Sunn 1200S (4x6550) amp. The Sunn original part# is 28-1312, 3-120T output transformer.
Date of Mfg says 1971

Schumacher.jpeg

Some History
Dumble manufactured the Dumbleland amp from 1966 to around 1986 some voiced for Bass others guitar and was the forerunner to the later SSS model amplifier for lead guitar
Dumbleland Bass 150W $ 3,145.00
Dumbleland Special 150W $ 3,390.00
Dumbleland Special 300SL $ 3,935.00

For those builders planning to use the schematic as a baseline for their Dumbleland inspired build.Here are a few other ideas for modifications that would be easy to implement or change!
1. 2nd or 3rd generation tone stack
2. Martin Mannings filter array (voiced for guitar)
3. Convert the unused triode in V2B to a DC coupled cathode follower to help drive any outboard gear.
4.Different power and output tube combinations
5.footswitchable FET to drive the front end
https://ampgarage.com/forum/viewtopic.p ... 23009+pics

IMG_0140.jpeg

IMG_0139.jpeg

PI and Driver setup
As far as the various parts and circuits that make up the Dumbleland design The early 200W (4xKT88) Winterland has been the forerunner of the Dumbleland for guitar and bass and the Dumbleland for guitar has been the forerunner of the SSS.The SSS uses a completely different PI/Driver structure than the Dumblelands. The SSS style PI/Driver section commonly uses 2X 7025 preamp tubes, consisting of a LTP style PI, with an S.V.T style Driver section, whereby, the grids of the power tubes are D.C driven by the low impedance side of the cathodes of the 7025's,(correct terminology being "cathode follower driver"). The Odyssey's is similar to a L.T.P phase inverter are A.C driven to the grids of the power tubes via the plates of a 12BH7 driver tube. Benefits of the BH7 come with an increased current handling capability, therefore delivering a smooth, punchier more responsive,sound and feel.The Odyssey which was also used for guitar by players like Eric Johnson (who owns a very early Odyssey) As far as we know Alexander Dumble used this (12AU/BH7) PI driver structure in a lot of his amps.
Pictures and a schematic of the Odyssey
https://ampgarage.com/forum/viewtopic.p ... seyFilters
https://ampgarage.com/forum/viewtopic.p ... +schematic
FILTERS
Filter values were taken from SSS# 002 from this hand drawn schematic https://ampgarage.com/forum/viewtopic.php?f=5&t=17827, #002 also used a Triad SP-118 inductor to feed the filters. This is considered optional Read here: https://ampgarage.com/forum/viewtopic.p ... r&start=15
The filters in 002 have been known to cause complaints by several builders that has used the same values. Because of these complaints a different filter array was developed better suited for the frequency range for guitar, by member Martin Manning..Thank you MM
http://ampgarage.com/forum/viewtopic.ph ... 57#p378857

SSS_Step_Filters1_MPM.png

Tone Stack
Although the transformer codes on ser#002 latest reads 1977 and uses what's known as the "Classic" tone stack and Ser# 009 Dumbleland was AFAWK built in 1978 there seems to be some discrepancies as to when Dumble implemented his "Classic". The 78 time frame would perhaps more accurately coincide with either 2nd or 3rd generation tone stack which you can find Dumble used in his earlier 2nd/3rd Generation ODS amps. This is why the tone stack is still not yet verified.

https://ampgarage.com/forum/viewtopic.php?f=5&t=12870
https://ampgarage.com/forum/viewtopic.php?f=5&t=12871

Be aware that these type stacks used in these 2nd or 3rd gen amps w/james configuration used different pot values and therefore respond differently and can have a slightly narrower ranging E.Q than the later Classics. AFAIK in 1978 Dumble did not equip his Dumblelands with a Skyliner tone stack.
There are also several different versions of these earlier type tone stacks you can read about here.https://ampgarage.com/forum/viewtopic.p ... 75#p126317
(BTW.for those members looking for something closer to that of a Fender AB763 sounding stack? the Classic would be better suited to this taste)
ULTRA LINEAR
The Dumbleland's Output transformer is equipped with ultra linear taps, this enables you to run the output tubes at higher plate voltages for increased power output, given that the screens of 6550 are not designed to handle these higher voltages under load, the U.L taps provide a kind of negative feedback which helps regulate the screen supply under heavy load conditions for extended periods. So if one is to run these output tubes plates at 540/550 VDC ultra linear operation is recommended. (The earlier model Winterlands were also equipped with U.L taps) #003
https://ampgarage.com/forum/viewtopic.php?f=5&t=3668
U.L operation also lowers THD% and increases the damping factor..If one decides to go with the standard Fender/Twin style off the shelf and run 6l6's@ 450VDC there is no need for the taps, although, this could also alter the sound, performance,feel of the amplifier,

Many Thanks to Aaron Griffin Sleepwalk studios for drawing up the schematic and anyone else who posted and contributed to get this project started!!

[martin manning]

Great start! The schematic image won't open full size for me. :^(

Remember! 8) This amp utilizes its ultra linear taps and runs above 500V on the plates 320 on the screens.

Might be closer to 550VDC on the plates? Also, in UL plate and screen voltages are essentially equal at zero signal.

[talbany]

Great start! The schematic image won't open full size for me. :^(

Remember! This amp utilizes its ultra linear taps and runs above 500V on the plates 320 on the screens.

Might be closer to 550VDC on the plates? Also, in UL plate and screen voltages are essentially equal at zero signal.

Martin
Thanks for the review.
My math on the Triad in the amp shows 535V DC under load on the plates and a close guess would put the screens at or around 330V DC.
Do you concur?

Tony

[martin manning]

I can't read the schematic (it won't open), but I can see that it shows a UL power amp, so the screens will be within a few volts the plates. Without more info, I think an estimate somewhere around 540VDC is reasonable.

[talbany]

I can't read the schematic (it won't open), but I can see that it shows a UL power amp, so the screens will be within a few volts the plates. Without more info, I think an estimate somewhere around 540VDC is reasonable.

I don't know why they won't open will check with Phil?

[Max]

... Dumble manufactured the Dumbleland amp from 1966 to around 1980 ...

This ( "... to around 1980 ...") isn't correct (typo?):

Guitar Player Magazine - September 1985:

“… I actually started making a series of amplifiers called the Dumbleland in about '66, and I still make them. …” source: https://ampgarage.com/forum/viewtopic.php?f=4&t=22012

And AFAIR these are the prices listed in the 1986 Price Schedule:

Dumbleland Bass 150W $ 3,145.00
Dumbleland Special 150W $ 3,390.00
Dumbleland Special 300SL $ 3,935.00

And these are the prices listed in the “Schedule of Pricing & Terms of Business Effective April 15, 1990”:

Dumble Price Schedule 1990.jpg

Picture source: https://www.thegearpage.net/board/index ... t-29284471

And as you can see in this price list from 1990, the amplifier listed as "Dumbleland amplifier" is listed with the same "standard" price with which the "Dumbleland Special 300SL" is listed in the price list from 1986. Therefore, in my opinion, one could perhaps assume that the models "Dumbleland Bass 150W" and "Dumbleland Special 150W" may have expired sometime between 1986 and 1990, and Alexander Dumble from 1990 on (at the latest) possibly only offered the "Dumbleland Special 300SL". But the latter is of course pure speculation - even if perhaps not entirely out of thin air.

Kind regards,

Max

[talbany]

Great Thanks Max Updated

[Max]

... Nor/FET inputs ...

There's no FET input visible on the pictures of the DLS150W#009 posted here.

Perhaps it would be helpful in the sense of better orientation and thus also to avoid misunderstandings if one could make clear in the circuit diagram proposed by talbany from which Dumble amplifiers known and documented in this forum the individual parts of this proposed circuit diagram originate. For example: green = SSS # ..., yellow = ODS # ..., red = info from jfs322, black = picture of DLS#009, blue = Odyssey # ..., brown = anonymous source, violet = Winterland #... etc. Then maybe one could post here direct links to the schematics / layouts of these 'donor amplifiers'?

BTW: Schematics still don't open in their full resolution.

Some more pictures:
Picture showing DLS150W#009 in the early 90ies with its original knobs: https://ampgarage.com/forum/download/fi ... &mode=view
The knob on the back (speaker impedance selector switch) visible on the pictures posted by talbany seems to be still the original one.

Picture of DLS150W#008: https://ampgarage.com/forum/download/fi ... &mode=view

Best regards,

Max

[Max]

Corresponding "Dumble Discussion" thread: https://ampgarage.com/forum/viewtopic.php?f=4&t=34389

Best regards,

Max

[talbany]

... Nor/FET inputs ...

There's no FET input visible on the pictures of the DLS150W#009 posted here.

Perhaps it would be helpful in the sense of better orientation and thus also to avoid misunderstandings if one could make clear in the circuit diagram proposed by talbany from which Dumble amplifiers known and documented in this forum the individual parts of this proposed circuit diagram originate. For example: green = SSS # ..., yellow = ODS # ..., red = info from jfs322, black = picture of DLS#009, blue = Odyssey # ..., brown = anonymous source, violet = Winterland #... etc. Then maybe one could post here direct links to the schematics / layouts of these 'donor amplifiers'?

BTW: Schematics still don't open in their full resolution.

Some more pictures:
Picture showing DLS150W#009 in the early 90ies with its original knobs: https://ampgarage.com/forum/download/fi ... &mode=view
The knob on the back (speaker impedance selector switch) visible on the pictures posted by talbany seems to be still the original one.

Picture of DLS150W#008: https://ampgarage.com/forum/download/fi ... &mode=view

Best regards,

Max

BTW: Schematics still don't open in their full resolution.

I know Martin already pointed this out and I responded. I do not run the website and have a PM to Phil concerning this..He has not opened my PM yet.
Thanks for the clarification on the FET and will consider your request to post the various circuits we used

Thanks!

Tony

[Max]

... Dumbleland Filter values were taken from SSS# 002 (This is confirmed by the hand written schematic from Japan that many SSS amps built) ...

Just to avoid misunderstandings:

AFAIK, the schematics of the SSS #002 circulating here in this forum are more legible copies of this handwritten schematic from Japan.

And a comparison of a more legible copy with the handwritten original can of course only confirm that the copy agrees with the handwritten original, but not that the contents of the handwritten original (and thus also its copies) match the reality (reality: circuit of SSS #002).

Best regards,

Max

[jfs322]

.

[Max]

... Dumbleland Filter values were taken from SSS# 002 (This is confirmed by the hand written schematic from Japan that many SSS amps built) ...

... a comparison of a more legible copy with the handwritten original can of course only confirm that the copy agrees with the handwritten original, but not that the contents of the handwritten original (and thus also its copies) match the reality (reality: circuit of SSS #002).

So maybe it would be a little better to write in order to avoid misunderstandings:: "Dumbleland Filter values were taken from the hand written schematic of SSS#002"?

Best regards,

Max

[Roe]

Any idea what the specs of the OT should be? 2.4k primary impedance?

[talbany]

Any idea what the specs of the OT should be? 2.4k primary impedance?

Yes.I am thinking around 2k should be about right
Tony