CF driver Va - Vk voltages in SSS consensus?

[rootz]

Richard, how objective is it that Dumble 'cloned' the Macs driver setup? 002 for example is not unity coupled. Is the unity coupled setup harder or easier on the driver tube compared to 002/anodes of the driver a screen grid voltage? There is only one gut shot of 002 I know of and a hand drawn schematic of a previous owner that has got some obvious mistakes. One being the 1k cathode resistors in the DC coupled cathode followers. Another possible one that the chassis won't provide room enough for the power supply caps as drawn in the schematic (but that one is up for debate). In the gut shot there seems to be an orange wire connecting the driver anodes to the screens of the output tubes.

I'm with Martin on this point he made elsewhere: why stick to a design flaw if there is a better option? Why stick to a driver supply that puts a lot of stress on the driver tube if there are better options which do work with less rugged new production tubes?

AN's previous version of the SSS and the Steel String Sultan were all based on a Hi Plains Drifter, which is a clone of previously Eric Johnson's, now Santana's SSS 005. Pictures of the HPD and AN's amps confirm there are dedicated supplies for negative and positive voltages for the driver. The bias tap is not used in those amps and there is no doubler. But why bother, the doubler works and provides all voltage you'd need for the driver.

[Richard1001]

The CF in the SSS 002 is in fact a copy of CF in the McIntosh MC-60 amplifier. The voltage chart of this McIntosh amp shows 430 volt on the plates of the 12ax7 and -45 volt on the grids and cathode. Some of these amps are still working today with the original CF tube. The McIntosh originally uses a Telefunken ECC83 (=12ax7) in that position.

When I was building my SSS, I also was worried to about the high voltage on this tube and tried to lower it in different ways. All of them made the amp sound weaker.
So I just ended up using the original schematic and high voltage.

And there really is no problem at all. No excessive wear of the tube, nothing blowing up. It just works fine.

The cheap Sovtek tube with box shaped anodes works in my amp. I tested the amp with those when i finished it. I changed tubes afterwards and just bought a NOS Telefunken for the CF. For the last two years the amp still works and sounds the same as the moment I put it in there. I do use an open shield on this tube. It gets hot.

Thank you Richard!

So my amp worked flawlessly since 2014. Granted it did not see as much use over all those years as within the last couple of weeks when, as said, I used it as a power amp for testing my Double SSS preamp build, Pentode preamp and ODS preamp build. When I would swap a part in one of the preamps, in the meantime I would switch 002 to standby and on again for testing the preamp and this would go on multiple times. So maybe that led to the failure of the CF? Or maybe it is just coincidence?

Martins bipolar would solve any potential problems, but it would of course leave the original schematic.

Electron

The standby switch in the Japanese schematic is not drawn right imo. It is drawn between two sets of capacitors without a choke limiting the current. As it is drawn, it is bad for the caps before the switch which are essentially shorted and also bad for the caps after the switch that are loaded with a high current. It strains the power supply and power tubes.

I don't know for sure how it should be implemented to reduce the problems (more than one good possibility) but a resistor over the switch would also solve the problem of the bias supply of the CF loading the high voltage caps in reverse.

[Richard1001]

Richard, how objective is it that Dumble 'cloned' the Macs driver setup?

Well objectively the bias supply divider, the tube, the voltages and resistor values are all the same. There is ofcourse a small chance two individuals dreamed up the same design. But i know Mr. Dumble also borrowed from other HiFi amp schematisch. Which is in no way a bad thing, just to be clear. The way he used some of these ideas in guitaramps is unique.

[rootz]

The CF in the SSS 002 is in fact a copy of CF in the McIntosh MC-60 amplifier. The voltage chart of this McIntosh amp shows 430 volt on the plates of the 12ax7 and -45 volt on the grids and cathode. Some of these amps are still working today with the original CF tube. The McIntosh originally uses a Telefunken ECC83 (=12ax7) in that position.

When I was building my SSS, I also was worried to about the high voltage on this tube and tried to lower it in different ways. All of them made the amp sound weaker.
So I just ended up using the original schematic and high voltage.

And there really is no problem at all. No excessive wear of the tube, nothing blowing up. It just works fine.

The cheap Sovtek tube with box shaped anodes works in my amp. I tested the amp with those when i finished it. I changed tubes afterwards and just bought a NOS Telefunken for the CF. For the last two years the amp still works and sounds the same as the moment I put it in there. I do use an open shield on this tube. It gets hot.

Thank you Richard!

So my amp worked flawlessly since 2014. Granted it did not see as much use over all those years as within the last couple of weeks when, as said, I used it as a power amp for testing my Double SSS preamp build, Pentode preamp and ODS preamp build. When I would swap a part in one of the preamps, in the meantime I would switch 002 to standby and on again for testing the preamp and this would go on multiple times. So maybe that led to the failure of the CF? Or maybe it is just coincidence?

Martins bipolar would solve any potential problems, but it would of course leave the original schematic.

Electron

The standby switch in the Japanese schematic is not drawn right imo. It is drawn between two sets of capacitors without a choke limiting the current. As it is drawn, it is bad for the caps before the switch which are essentially shorted and also bad for the caps after the switch that are loaded with a high current. It strains the power supply and power tubes.

I don't know for sure how it should be implemented to reduce the problems (more than one good possibility) but a resistor over the switch would also solve the problem of the bias supply of the CF loading the high voltage caps in reverse.

There is an even simpler solution, and I'm going to 'pollute' this thread again with a digital gut shot: IMHO there shouldn't be a dual mains filter setup like in the hand drawn schematic. It simply wouldn't fit with TVA 1906 and 1620 caps, unless two of those caps are located somewhere else in the chassis. The pt is lay down style. You'd see a standing transformer in pics of the back of the amp otherwise. The screen prints/faces of the 002 check out with a chassis 23 3/4" wide. Same as many ODR's from that time. The only known gut shot gives a clear indication of where the PSU PCB is in the chassis: the left side is roughly lined up with the left most output tube socket in that pic. With a lay down PT to the right of the PCB there simply isn't space for more than 5 caps. I should add that 2x100uF in series can be seen in more amps from the same time period and those amps are also 100W.

[Richard1001]

A logic place for the first two caps could be the side of the chassis next to the hv supply board. Are you sure the ODS is the same length as the SSS? The SSS 002 looks a lot taller and longer to me.

[rootz]

A logic place for the first two caps could be the side of the chassis next to the hv supply board. Are you sure the ODS is the same length as the SSS? The SSS 002 looks a lot taller and longer to me.

That's why I've written ODR, not ODS The Overdrive Reverb chassis are bigger than the ODS chassis, mostly a fair bit wider. The spacing of the knobs is different also and there are many more differences.

The HPD has two caps on the side of the chassis, where the HV diodes are. Then again, with the stb switch between the pairs of caps just is not a good way of doing it. ODS's have the switch after the main caps, but before the choke. That is a much better way.

[martin manning]

Some voltages on the CF (from simulation) for the bipolar and original type power supplies, along with maximum ratings for 12AX7 from GE data sheet. “Cold” is at main power turn-on (modeled by removing the driver tube from the circuit), “hot” is after the heater is up to temperature (driver tube in circuit). There are four states for the original type CF supply, and just two for the bipolar. A 1N4007 is placed across the screen filter to limit the negative voltage there to 600 mV for the original type negative supply in standby.

[ElectronAvalanche]

Thank you Richard!

So my amp worked flawlessly since 2014. Granted it did not see as much use over all those years as within the last couple of weeks when, as said, I used it as a power amp for testing my Double SSS preamp build, Pentode preamp and ODS preamp build. When I would swap a part in one of the preamps, in the meantime I would switch 002 to standby and on again for testing the preamp and this would go on multiple times. So maybe that led to the failure of the CF? Or maybe it is just coincidence?

Martins bipolar would solve any potential problems, but it would of course leave the original schematic.

Electron

The standby switch in the Japanese schematic is not drawn right imo. It is drawn between two sets of capacitors without a choke limiting the current. As it is drawn, it is bad for the caps before the switch which are essentially shorted and also bad for the caps after the switch that are loaded with a high current. It strains the power supply and power tubes.

I don't know for sure how it should be implemented to reduce the problems (more than one good possibility) but a resistor over the switch would also solve the problem of the bias supply of the CF loading the high voltage caps in reverse.

There is an even simpler solution, and I'm going to 'pollute' this thread again with a digital gut shot: IMHO there shouldn't be a dual mains filter setup like in the hand drawn schematic. It simply wouldn't fit with TVA 1906 and 1620 caps, unless two of those caps are located somewhere else in the chassis. The pt is lay down style. You'd see a standing transformer in pics of the back of the amp otherwise. The screen prints/faces of the 002 check out with a chassis 23 3/4" wide. Same as many ODR's from that time. The only known gut shot gives a clear indication of where the PSU PCB is in the chassis: the left side is roughly lined up with the left most output tube socket in that pic. With a lay down PT to the right of the PCB there simply isn't space for more than 5 caps. I should add that 2x100uF in series can be seen in more amps from the same time period and those amps are also 100W.

Hi Rootz,

interesting analysis you did with the Fusion and Eagle technique regarding the similarities between some ODRs and SSS.
Looking at the power supply of SSS002 (also briefly touched upon by Richard re the Standby switch) I can not comprehend why there is a first filter (2x47uF in series) followed by the Standby switch then by two 100uF in series. Usually one would expect the larger filter node to come first in line. So in essence: 2x100uF in series, then Standby followed tby the choke then into the subsequent filter nodes. The setup as in 002 does not make sense and there is quite the current inrush into the 2x100uF in series (50uF in sum) once the standby switch is switched. So in essence you say that either the 2x100uF or the 2x47 do not really fit into the 002 chassis (we also do not have a pic of the power supply of 002). So could this be a mistake in the hand-drawn schematic? Could the 2x47uF be part of a node for the CF driver somewhere on the side of the chassis?

Here is a pic of ODR 03x (in the low thirties) I took myself. Two 100uF (do not know if in series, I see no balance resistors) followed by three 22uF. The other pic shows a three-section can cap. Unfortunately I did not take a general view pic, or at least I can not find it. AFAIR the preamp tubes were all in a row on the back, 2 power tubes (50W amp) with holes for two more output tubes. So essentially a chassis that could fit either a SSS or a ODR.

I will look for some more pics.

So again the question: is there also a mistake in the Japanese schematic regarding the power supply for the CF driver? Is there a dedicated power supply node for the CF? How could this look like? Would this node simoply have a way lower B+? Yet the bias supply seems to still have a high neg voltage derived by tapping the B+winding as in the Macintosh amp. So no real bipolar circuit in 002. So many questions. Maybe John Mayer would be so kind as to have his tech take a better pic of 002 next time they service the amp.

I need to upload the whole lot of pics I have someday. I had some pics posted here many years ago.

Electron

[ElectronAvalanche]

ok, found some more pics:

The chassis is 60.5 cm (23.75 inch) wide and 20.5 cm (8 inch) deep (not my socks in the pic btw!).

[bepone]

nice pics.. small bandmaster output transformer for a lot of compression, 6L6GC Sylvania..early fender ala vibroverb values..1k-100ohm in nfb loop..100k in output tubes leak , indicating 12AT7 for PI (also seen from the short plates on Pi tube)

[ElectronAvalanche]

Some more pics:

[ElectronAvalanche]

more

[rootz]

Hard to tell if the hand drawing of the PSU of 002 is definitely wrong. There simply isn't much reference to double check things. However, there are other ways, which are arguably better, to do things, without much adverse affects on the sound of the amp (if any). 002 has no 12V for relais. There is a whole side of the chassis open for diodes and other PS parts. Not saying Dumble must have used that space, be he sure could have.
I don't think its is wrong to use the hand drawn schematic as a guide though. Comes from someone who owned the amp and has been in it. That is more than most of us can say.

I'd love to see all your pictures you have of Dumbles haha. But this is already great. Let me guess: front is 2 1/2" high?
Man, there is so much to see in these pictures! Finally I can see the value of the blue resistor for the reverb driver supply node: 10k. I've seen some of these pictures before.
Anyway, it looks so 2nd/3rd gen in the parts selection. That is one of the thing I also see in SSS001 and 002. MF7C, MF6C, '70-ies Pihers, etc.

Also looks like Dumble had a whole bunch of these chassis made. I've seen with 2 slide switches between Volume and treble; SSS001. With three; SSS002 (with addition of a level pot next to the MID switch), this amp, ODR008x IIRC. With toggle switches; ODR60, ODR58, ODR59? Between all of them I see more similarities than differences.

[Guy77]

Thanks for posting these pics ElectronAvalanche. Especially this one here!
The famous 68k resistor feeding the reverb circuit from V1 to V2 (seen on far right of the pic below). Dumble must have been very found of doing his reverb like this.
The fact that builders like 2 Rock now use this in several of there models tells you they like it a lot too .

IMG_0462.JPG

Cheers
Guy

[ElectronAvalanche]

and some more since this seems to bring you guys some joy. As said, I posted some of these some years ago, but found them again. So happy to share