You know Max, I'm glad you brought this up. We now have basic topologies for three SSS's, and every one of them are very different. My appreciation of the talent of Mr Dumble is growing exponentially looking at these schematics.
I think we may ultimately find that unlike the "generations" of the ODS, every SSS is going to be completely different.
I tried to redraw it into a preamp section & then an LTPI to PA section. My effort was to just recreate the topology for us to look at. I wanted something easier to read then the original hand drawn schematic.
I presume that this schematic has ERRORS in it. I would encourage you to assume there are ERRORS!
This is NOT intended as a correct guide to build an SSS type amp.
So I am simply reposting what LeftyStrat posted for the purpose of discussion.
Anyone who has a better idea of what might be correct, please feel free to use the attached editable version to redraw a correction.
I have no interest in building this amp. I simply redrew it to help contribute to some constructive conversation.
Corrections noted and made ! Revision #6 4-18
With respect, 10thtx
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Last edited by 10thTx on Thu Apr 19, 2012 1:16 am, edited 3 times in total.
martin manning wrote:Markus, I'm interested in the LTSpice file... I though about doing one myself, and found a 12BH7, but it needs a little work to create a symbol, etc. I'm working on something else right now, but following along with interest, and will be glad to help where I can.
Anyone have a link to info or schematic of another amp with that type of power stage topology?
Martin, I found two 12BH7 models and realised it's not that hard to integrate them into LTSpice as ".inc" files. As a symbol I used the "generic" triode symbol from Duncan's site.
Interestingly, with both models the voltages on the 12BH7 cathodes are way off (~ -17V to ~ -21V compared to ~ -40V indicated in the hand drawn schematics of SSS #002) while the grid voltages are quite OK (~-44V).
With the 12AX7 model for the CF driver the cathode voltages are in the range of ~ -41V.
Is it confirmed that the CF driver is indeed a 12BH7 in SSS #002?
Max wrote that "AFAIK Alexander Dumble usually specified a 7025 phase inverter and a 7025 driver for the 100W SSSs with such a phase inverter / driver configuration. "
On the B+ rail, the H node needs a 270K balancing resistor across the lower cap.
I doubt that the driver in 002 is a 12BH7. That spice simulation strongly suggests that the driver position is set up for a 12AX7/7025.
I used a 12BZ7 in my 001 build, and I tried a 12BH7 in it just for giggles and it did not work right, gave wrong bias voltages just like the spice simulation did. There is just so much difference between the 12BH7 and the 12AX7/12BZ7 that it's not surprising to me.
HAD used the 12BH7 in the 150W SSS like SRV's, which is really a Dumbleland bass amp with a guitar preamp. Bass power amps need extra current draw from the driver and the 12BH7 is a very good way to get that.
David Root wrote:On the B+ rail, the H node needs a 270K balancing resistor across the lower cap.
I doubt that the driver in 002 is a 12BH7. That spice simulation strongly suggests that the driver position is set up for a 12AX7/7025.
I used a 12BZ7 in my 001 build, and I tried a 12BH7 in it just for giggles and it did not work right, gave wrong bias voltages just like the spice simulation did. There is just so much difference between the 12BH7 and the 12AX7/12BZ7 that it's not surprising to me.
HAD used the 12BH7 in the 150W SSS like SRV's, which is really a Dumbleland bass amp with a guitar preamp. Bass power amps need extra current draw from the driver and the 12BH7 is a very good way to get that.
Good to know that the Spice simulation appears to be right!
Thanks a lot!
For all images bass, mid, treble, volume and level were set to 50%.
Frequency response is shown at the OPT.
First the high and low filters.
For high filter stepping the low filter was at position 4, for low filter stepping the high filter was at position 2.
Below the deep switch, once with a 1Meg volume pot, once with a 100k volume pot.
With a 100k the deep switch has barely an influence on the frequency response.
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A few posts back I listed the tube complement that HAD advertised at one time. The only noval other than the 12ax7 was the 5751. I'm assuming he used this as the reverb driver. Nice to see the simulation predicting that.
This is simply a DRAFT idea. It has NOT been built and is not a proven design.
I thought I'd post it strictly as a discussion point. It eliminates the reverb and buffer from the #002. I'd rather have an active FX to insert a delay pedal. Reduces the 100w to 50w. Adds a PAB.
The smoothing cap across the PI plate resistor works. I use this on my amps. Also I found that placing the smoothing cap after (vs. before) the LTPI coupling caps does make a significant difference in tone. Placing the cap between the LTPI and coupling cap muffles the tone, IMO.
I am not sure the filter is drawn correctly? And I don't know if the bias would need to be changed? (I am thinking it would need a change?) The attached SCH file has the PT & B+ rail draft.
With respect, 10thtx
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