Dumbleland Special 150w ser#009 Schematic

[martin manning]

Ok, thanks. So a couple of cases where large resistors (2700 vs. your 510) are used to protect the screens, and the early Marshals had very saggy power supplies IIRC.

[Richard1001]

... Looking back at the gut shots of SSS #002 it appears the color bands are indeed brown-black-yellow.

Could you please post a link to these gut shots so that this 100K hypothesis can be checked against these?

Thanks and best regards,

Max

The way i came to this conclusion is explained in my last two posts of the ' Ryan and Erwins sss002 Madness' topic.
Gutshots of the sss001 and 002 are also found in this topic.

[talbany]

Yes, that is what i mean, together with the role the local feedback loops play in the sound and workings of the tonestack and filters.

Sure the loops can effect the T.S & filters, however ,not all SSS's are the same. The Later 150W singers, has only 1 Local feedback loop, the earlier ones like Henry Kaiser and the one John Mayer has are 100W, those amps have inductors and several feedback loops. E.J & L.C's SSS"s have just 1 loop and therefore a more raw sound to them.. I removed 1 of mine from 002. That amp compressed enough without both them

Tony

[rccolgan]

... Looking back at the gut shots of SSS #002 it appears the color bands are indeed brown-black-yellow.

Could you please post a link to these gut shots so that this 100K hypothesis can be checked against these?

Thanks and best regards,

Max

Hey Max,

https://photos.app.goo.gl/h2EXCbaaToxjiXLu8

[Max]

@Richard1001 and @rccolgan: Thank you for directing me to these pictures.

Marshall also produced bass amplifiers in the 80's with 6550's with the screens on high voltage. There were two models i believe one with 4 power tubes an one with 8 6550's producing 375W RMS .

... the early Marshalls had very saggy power supplies IIRC.

Marshall schematics “2000-250W- …” (guitar) and “2001-375W- …” (bass): https://www.vintageshifi.com/repertoire ... rshall.php

Best regards,

Max

[Richard1001]

Today i came across some old topics on the Todd Sharp OD special 150 amplifier. This amplifier uses the same transformers as the Dumbleland special and also uses 4 x 6550 tubes. The PI and driver diverse from the Dumbleland amp and is closer to the SSS002 12ax7 PI and DC coupled driver.
I also found a block diagram. This shows both Ebb1 and Ebb2 going to the power tube section. This (in my opinion) could well mean the powertubes in this amp are wired as regular penthodes with high voltage on the screens. Other than that, the block diagram shows the complete powersupply. An other thing is that it shows a way to wire two bias pots for both powertube sections which could be implied on the SSS002 using a 10k pot between the (probalbly 820k/120k) voltage dividers. Dr.D apparently also felt the need to lower te voltage on the 12ax7 driver tube in this amp, creating Ebb3a.

I still don't know which wiring was used on the Dumbleland amplifier powertubes, but this also seems to be an option.

Here is the block diagram:

IMG_5058.JPG

[talbany]

#121 is basically an ODS preamp coupled with a SSS-style power section,and some unique features, such as the 4 knob OD section , additional pots for OD entrance trim and h.f. taper(tone control), and a 7247 tube in the OD circuit.
https://thesubjectmatter.com/dumblearch ... efault.htm

A few questions would be what do they mean by "The Same" could the same mean they are both labeled Triads?. It would be nice to get a shot of 121 out of the cabinet so we could get a number from the transformer and confirm the voltages.
Diagram
In the block diagram? He has Ebb1 which feeds the plates after the choke? (If so that must be a big ass choke) If Ebb2 feeds the screens then what is the value of that resistor (dropper?) regulating the screen voltage? (It's the only one he didn't label?) Also a 6K dropper from the screens feeding the P.I doesn't exactly scream high voltage there? ( a standard ODS fare for an AX would be 22K @ 450VDC?) Also the last 2 droppers at the end are 470ohm (Would those drop any voltage at all?) Looks like it ran out of voltage?...Who drew this?
Tony

Dumble Overdrive 150 Special #121 010.jpeg

Triad R-25A.jpeg

[Max]

#121 is basically an ODS preamp coupled with a SSS-style power section, ...

...One of the amps … [Max: 2 x SSS150W] … (newer) had what looked to be mercury Dynaco Iron at the OT, as well as the 12AU7/12BH7 Driver setup, it also had a lower gain type preamp. It was a 150W amp with 4 6550's and definitely said "Steel String Singer" on it.
The PT in one of them put 525 on the plates, in the other it was around 495. https://ampgarage.com/forum/viewtopic.p ... 244#p66244

Best regards,

Max

[Max]

#121 is basically an ODS preamp coupled with a SSS-style power section, ...

Plate voltages in 2 SSS 150W amps:

...One of the amps … [Max: 2 x SSS150W] … (newer) had what looked to be mercury Dynaco Iron at the OT, as well as the 12AU7/12BH7 Driver setup, it also had a lower gain type preamp. It was a 150W amp with 4 6550's and definitely said "Steel String Singer" on it.
The PT in one of them put 525 on the plates, in the other it was around 495. https://ampgarage.com/forum/viewtopic.p ... 244#p66244

Best regards,

Max

[talbany]

Max
I am not following you? I am basically quoting from the article I posted?

The power amp is similar to a 150 W Dumbleland (same transformers), but the phase inverter and driver tubes both are 7025s as in a Steel String Singer

Are you saying that Brandon was reffering to one of those as 121?

BTW. I don't know about you but I tend to not want to lump in Dumble in with Marshall and especially Boogie..I am sure Dumble insisted on a bias pot.

Tony

[Richard1001]

#121 is basically an ODS preamp coupled with a SSS-style power section,and some unique features, such as the 4 knob OD section , additional pots for OD entrance trim and h.f. taper(tone control), and a 7247 tube in the OD circuit.
https://thesubjectmatter.com/dumblearch ... efault.htm

A few questions would be what do they mean by "The Same" could the same mean they are both labeled Triads?. It would be nice to get a shot of 121 out of the cabinet so we could get a number from the transformer and confirm the voltages.
Diagram
In the block diagram? He has Ebb1 which feeds the plates after the choke? (If so that must be a big ass choke) If Ebb2 feeds the screens then what is the value of that resistor (dropper?) regulating the screen voltage? (It's the only one he didn't label?) Also a 6K dropper from the screens feeding the P.I doesn't exactly scream high voltage there? ( a standard ODS fare for an AX would be 22K @ 450VDC?) Also the last 2 droppers at the end are 470ohm (Would those drop any voltage at all?) Looks like it ran out of voltage?...Who drew this?
Tony

I agree it does leave questions. I can however not agree with your conclusion about the voltages based on this block diagram. In the 121 amp the PI and CF are both 12ax7 tubes. The maximum anode voltage on the PI is not the same as the voltage feeding the tube. There is significant voltage dropping over the anode resistors and tail resistor. In the SSS002 with 430 Volt supply the dropping resistor in the powersupply is 1K8 feeding the PI. Here it is 6K. Further the reverbdriver in the SSS uses a 22K dropping resistor, here is a 56K used. And the 12ax7 CF driver in the SSS002 got 430V on the plates and - 46 on the kathode which we all know now is copied from a McIntosh amplifier using the exact same wiring and voltages on their 12ax7 CF driver. In this amp Dumble however felt te need to lower the anodevoltage of the CF driver using a 47k dropping resistor. So my conclusion is that the Ebb1 and Ebb2 votages are higher than those in the SSS002 and +/- 500 V

But that is IF the block diagram is correct. It does say HD in the corner

[talbany]

Thanks for the clarification!

This along with Brandon's listing would put it @ either 495VDC or 525V.
then the remaining questions are?. Did he run the screens out of spec? and why use an O.P.T with U.L taps on both amps if he didn't use them. (and I understand you can just tie off the taps? )
Any Ideas?
Tony

[Max]

... Are you saying that Brandon was reffering to one of those as 121? ...

AFAIR Brandon‘s referring to:

"the other it was around 495" = SSS150W Eric Johnson (many pictures online)

"525 on the plates" = SSS150W Colin James/Kirk Hammett = copy of SSS150W SRV (special order by Colin James)

Colin James/Kirk Hammett:

SSS 150W Colin James.png

SRV:

SSS 150W SRV.png

The two transformers in this SRV SSS look quite similar to the transformers in ODS # 0121 (in my personal impression).

Best regards,

Max

[Richard1001]

Thanks for the clarification!

This along with Brandon's listing would put it @ either 495VDC or 525V.
then the remaining questions are?. Did he run the screens out of spec? and why use an O.P.T with U.L taps on both amps if he didn't use them. (and I understand you can just tie off the taps? )
Any Ideas?
Tony

It is no problem to wire a UL transformer as a regular output stage without using the UL taps. As long as the primary impedance matches the tubes. There are output transformers that have multiple taps / primary impedance's so you have the option to use the transformer with different types of tubes. This also leaves taps unused.
Much like a powertransformer with different taps you get more options but don't have to use them all.

As to why he used this transformer i can only guess, but maybe he wanted a big iron core transformer for that paticular sound and extended lows and this was what he could get at the time. Normal guitaramp OT's usualy have an undersized iron core that is not realy suited for low frequency transfer. And this thing, even for 4 x 6550 putting out 137 watts looks massive. I also bought a big core transformer for my SSS build for this very reason. (Classictone 40-18072)

[martin manning]

Since the Ebb2 is fed into the power amp in the 012 diagram, that says it is conventional pentode operation. At 500V Va, Raa has to be around 2k to avoid over dissipation on the plates, which puts the load line well below the Vg1=0 knee. It could be that large screen resistors are used to keep the screen current under control as in the examples cited above. I don't think these amps would be designed to operate in a way that would make them unreliable at high power. Indeed the choke in the 012 power supply schematic would need to have a high current rating, something like [edit] 1A. There is what looks like a choke between the PT and OT in the photos. It doesn't look to be very large physically.