Dumbleland Special 150w ser#009 Schematic

[Richard1001]

What doesn't quite make sense to me is 550V plates. To get down to the advertised output power of 150W would require 100V of sag, and then the screens would really like to drop another 100V, down to 350 or so.

I have a theorie on this.

In the schematic drawn by Talbany after the rectifier there are two 100uF caps in series. Then next comes a standby switch and behind that another pair of 100uF caps in series. I don't think this is correct. Using the standby switch will ware out these capacitors fast. Using the switch is much like shorting the first two caps over the ESR of the second two caps in series, and the two caps behind the standby get hit by a 550V DC supply with low internal resistance created by the ESR of the first two caps in series. There is a short but very high loading current. So to me it would seem best not to use the standby switch in this given schematic at all.

Placing a choke after the standby switch will fix that problem because a rapid change will result in a high impedance of the choke, since the load curve of a choke is opposite to the load curve of a capacitor. So using the standby switch now, the caps will no longer get 'shorted' and have to deal with a large current spike.

Looking at the schematic of the Sunn 1200s, which is rated at 120 watts with tube rectifiers, there are also two chokes in parallel after the standby switch. When switching to a solid state rectifier, the chokes are still there. Both chokes are mounted inside the chassis, and are pretty small. There is a 40 volt voltage drop over them leaving 500V on the plates.

I think the Dumbleland 150 would have a similar powersupply with bigger filtercaps than the Sunn amps and one 400 or maybe 500mA choke with something like 100 or 120 ohm DC resistance.

[martin manning]

I guess I have to conclude that the Sunn 1200S 4x6550 UL amp is very conservatively rated. In the silicon rectifier version the power supply reservoir is C-L-C, with two chokes in parallel dropping 10V to arrive at 500V B+1 feeding 3-120T output transformer running in UL. On paper that makes ~190W. The drive signal could be attenuated, or clipped, to keep the clean output power down, I suppose.

The chokes are marked 3-10C, and replacements are available from Triode: http://triodeelectronics.com/c354.html

"Replacement for chokes in Dynaco ST70, Mk2, Mk3 and Mk4. 1 1/2 inches (40 mm) tall on 2 3/8 inch (60 mm) mounting hole centers. 55 ohms, 1.5 henries, 10% tolerance, 2500 volt DC hipot tested, 200 ma DC.
C354 Dynaco Choke Replacement also Sunn 3-10C"

400mA total (for two in parallel) seems a little light to me!

[Richard1001]

Ah, i read the input voltage wrong on the Sunn schematic, I thought I saw 540V at the input of the choke's but it says 510. So the DC resistance is also 1/4 which matches with the choke's you found.

I have been looking for matching Triad choke's Dumble could have used, but do far I have not found one.

[dorrisant]

In the schematic drawn by Talbany after the rectifier there are two 100uF caps in series. Then next comes a standby switch and behind that another pair of 100uF caps in series. I don't think this is correct. Using the standby switch will ware out these capacitors fast. Using the switch is much like shorting the first two caps over the ESR of the second two caps in series, and the two caps behind the standby get hit by a 550V DC supply with low internal resistance created by the ESR of the first two caps in series. There is a short but very high loading current. So to me it would seem best not to use the standby switch in this given schematic at all.

Placing a choke after the standby switch will fix that problem because a rapid change will result in a high impedance of the choke, since the load curve of a choke is opposite to the load curve of a capacitor. So using the standby switch now, the caps will no longer get 'shorted' and have to deal with a large current spike.

I commented earlier about this on the Dumbleand Schematic thread... https://ampgarage.com/forum/viewtopic.p ... 33#p426433

Is it just me, or does that filter set before and after the standby switch look strange? Looks like 50μF before and 50μF after that would combine for 100μF when the switch is is operate.

No one seemed to give a shit.

[Richard1001]

400mA total (for two in parallel) seems a little light to me!

I just have been looking at the Winterland gutshots. It also has a C-L-C powersupply with the choke feeding the centertap of the OT. It uses the Dynaco C492 choke. This is a 400 mA choke. I also found the Winterland poweramp shares a lot in common (copy) with the Dynaco poweramp. So if this amp is using a 400mA choke feeding the poweramp i think the choke in the Dumbleland 150 poweramp feeding the poweramp is the Triad C-17X. With this information, i think it would be possible to draw an accurate schematic of the powersupply and poweramp of the Dumbleland 150. It still can be either UL or non UL though, but that would be a matter of taste.
Maybe a simulation could answer this question for the Dumbleland 009.

Here are the Dynaco schematics and and specs of the transformers /chokes

Dynaco_01.pdf

[Roe]

400mA total (for two in parallel) seems a little light to me!

yes, but the tube rectifiers should limit the current to 450ma or so?

[martin manning]

...I also found the Winterland poweramp shares a lot in common (copy) with the Dynaco poweramp. So if this amp is using a 400mA choke feeding the poweramp i think the choke in the Dumbleland 150 poweramp feeding the poweramp is the Triad C-17X. With this information, i think it would be possible to draw an accurate schematic of the powersupply and poweramp of the Dumbleland 150. It still can be either UL or non UL though, but that would be a matter of taste.

Thanks for the link. If this is basically the Sunn/Dynaco power amp, why would it not be UL? Running in conventional pentode mode without a separate screen supply would require other circuit changes that would compromise its performance or reliability, IMO.

[Max]

... If this ... [Max: "this" = Winterland #003 power amp] ... is basically the Sunn/Dynaco power amp, why would it ... [Max: "it" = Dumbleland Special 150W #009 power amp] ... not be UL?

For example: Perhaps because Alexander Dumble was of the opinion that Dumbleland Special 150W #009 would most closely match the personal taste of his client (according to some reports: Merle Haggard) not beeing UL?

... Running in conventional pentode mode without a separate screen supply would require other circuit changes that would compromise its performance or reliability, IMO.

IMO, the block diagram of ODS 150W #0121 https://ampgarage.com/forum/download/fi ... &mode=view quite obviously shows only two (BLU and GRN) connections between "POWER OUTPUT" and the primary side of the output transformer. Or am I missing something?

And as far as I understand this correctly, the connection between "POWER OUTPUT" and "+ Ebb2" shown in this block diagram does not seem to be particularly unconventional or complex? Or did I get this wrong?

And this article https://www.vintageguitar.com/31567/dum ... -od150-wr/ doesn't sound to me like Todd Sharp and the current owner have had any problems with performance or reliability?

Best regards,

Max

[martin manning]

And as far as I understand this correctly, the connection between "POWER OUTPUT" and "+ Ebb2" shown in this block diagram does not seem to be particularly unconventional or complex? Or did I get this wrong?

No you have that right, as I said above: https://ampgarage.com/forum/viewtopic.p ... 97#p427297

And this article https://www.vintageguitar.com/31567/dum ... -od150-wr/ doesn't sound to me like Todd Sharp and the current owner have had any problems with performance or reliability?

As shown, the only option to get the screen voltage under control is to use very large screen resistors, which tends to make most amps lose their punch, so to speak. That is the loss of performance I am referring to. With normal size screen resistors, the screen current draw is going to be excessive, which creates the reliability issue. I suppose that unmarked dropping resistor could be made quite large to lower the screen voltage, but then the PI voltage would be getting quite low.

[Max]

Thanks again for your explanations.

If I understand you correctly, then we have the following facts:

ODS150W#0121 has an output transformer that - at least in appearance - is the same as the output transformer of DLS150W#009.

According to the block diagram for ODS150#0121, the primary side of its output transformer is only connected to the plates of its four 6550A tubes, but not to their screens. Their screens are connected to +Ebb2. So the output stage of ODS 150W#0121 is - at least according to this block diagram - apparently not an output stage with a UL circuit.

The article now says:

… Second rehearsal, though, I had both Dumbles and plugged them into some white-painted Marshall 4×12″ cabs – everything on Rod’s stage had to be white – and in short order took care of the volume disparity. That was really the only band I ever played with where my Dumbles fit, power-wise,” Sharp said. … https://www.vintageguitar.com/31567/dum ... -od150-wr/

And in terms of reliability, according to this article, ODS150W#0121 has been reliably performing for around 35 years now.

In my opinion, these facts allow the conclusion that Alexander Dumble has probably found a way not to use the UL taps of this output transformer without having to accept compromises relevant in praxis in terms of performance and reliability.

And in my opinion this leads to the conclusion that he could (in the sense of: not impossible) have succeeded in doing this with the Dumbleland Special 150W #009 too, which he built in 1978 - 10 years after Winterland #003 - for (AFAIR) Merle Haggard.

Best regards,

Max

[martin manning]

It's still a mystery to me. The block diagram I have for 121 is a machine drawn copy of the one posted above for OD-150W s/n 012. There is no s/n included on the drawing itself, only in the file name. Can anyone post what is recognized as 121's block diagram? Is this the diagram that is said to be in the 4th edition of "The Tube Amp Book" by Aspen Pittman? My copy of this book is the "New Deluxe Revised Edition," which has no such diagram. The one posted above is incomplete, as some of the resistor values are missing. Could it be that it is a proposed arrangement that didn't survive? How do we know this diagram also represents 009?

[Max]

The block diagram I have for 121 is a machine drawn copy of the one posted above for OD-150W s/n 012. There is no s/n included on the drawing itself, only in the file name. Can anyone post what is recognized as 121's block diagram?

On page 730 in the 4th edition of his book "The Tube Amp Book" Aspen Pittman published a picture of the handwritten original. This handwritten original is initialed (“HD” = Howard Dumble) and dated (“1-11-87”) by A. Dumble in the upper right corner. Here is this picture: https://ampgarage.com/forum/download/fi ... &mode=view

For the serial number “OD-150W, s/n: 012” there is the following explanation:

Alexander Dumble built two more or less identical amplifiers for Todd Sharp in the mid-80s, namely ODS 150W #0120 and ODS 150W #0121. And because the handwritten block diagram published by Aspen Pittman refers to both serial numbers (# 0120 and # 0121), the last digits (0 and 1) of the two serial numbers are omitted in the picture published by Aspen Pittman.

Is this the diagram that is said to be in the 4th edition of "The Tube Amp Book" by Aspen Pittman?

Yes.

The one posted above is incomplete, as some of the resistor values are missing. Could it be that it is a proposed arrangement that didn't survive?

As Todd Sharp reports in the interview with Tonequest Report published in "A Dumble Book by Jesse Schwarz" (page 263 ff.), A. Dumble delivered #0120 around 1985 and #0121 around 1987. Because of this period of around 1 ½ years between the delivery of #0120 and #0121 IMO it would be conceivable in principle that the power supplies of the two amplifiers may differ slightly and that A. Dumble has therefore omitted the values for the perhaps somewhat different components in this block diagram initialed by him on January 11, 1987, so around the time of delivery of # 0121. But of course this assumption in regard to the missing resistor values is based on pure speculation.

How do we know this diagram also represents 009?

On the contrary: We know for sure that this block diagram for ODS 150W #120 and #121 by no means represents Dumbleland Special 150W #009, because Dumbleland Special 150W #009 has neither FET nor Overdrive nor Reverb nor Tremolo, and also no possibility to measure and adjust the idle current and the power amp symmetry on the back without removing the chassis from its cabinet and no footswitch etc..

So the only thing that results from this block diagram in regard to the Dumbleland Special 150W #009, which was built in 1978 - about 10 years before ODS #0120 and #0121 - is, in my opinion, the following:

This block diagram of ODS 150W # 0120 and # 0121 shows - in conjunction with the unreserved praise of Todd Sharp and the current owner of #0121 - that Alexander Dumble obviously knows some way not to use the UL taps of this output transformer without having to compromise in terms of performance and reliability to an extent that is practically relevant for guitarists.

In principle, IMO it would therefore be possible (in contrast to: sure) that he also took this route (no connection of the UL taps) with Dumbleland Special 150W #009.

So for the topic "Dumbleland Special 150w ser # 009 Schematic" discussed in this thread IMO it only results from this block diagram that both options may be conceivable in regard to Dumbleland Special 150W #009: An output stage with connected UL taps and an output stage without connected UL taps.

Best regards,

Max

[martin manning]

Ok, thanks for the explanations, Max. It's a shame there aren't any supply voltages included on that block diagram, as that would help to explain things a bit better.

[talbany]

Sorry for not keeping up with the discussion as my wife has been in the hospital all last week
So before I make any changes or alterations to the schematic I do have a question for Max?

AFAIR #009 is a Dumbleland Special for bass, but with very nice guitar tones, too (I've never perceived that much of an important difference in a practical sense between those for bass and those for guitar anyway.

Here you specifically call out #009 "for bass" classifying it as a 'Bass amp" that can be used for guitar, correct?

So Max? Do you know (or can find out) why you designated his #009 Dumbleland Special specifically? for use with bass guitar?..Put simply? why did you write?

#009 is a Dumbleland Special for bass

Thanks!
Tony

[Max]

I was told ("for bass") by someone who at the time I thought, for a variety of reasons, that he knew (as opposed to: that he assumed).

Apart from that, I - as well as some other guitarists who once (about 25 years ago) had the opportunity to compare the tone and feel of DLS#009 with the tone and feel of DLS#008 - also had the subjective personal impression that #008 was more likely built for a guitarist and #009 more likely for a bass player. But as far as I know, Merle Haggard isn't a bass player.

And - as you already quoted:

I've never perceived that much of an important difference in a practical sense between those for bass and those for guitar anyway.

Best regards,

Max