SSS#002 low voltage in original drawing

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larsvictor
Posts: 152
Joined: Wed Sep 23, 2009 12:00 pm
Location: Germany

SSS#002 low voltage in original drawing

Post by larsvictor »

Hi Everybody,
still working on my second Dumble build (SSS #002 - scratch build). I´m trying to collect some information about the voltages in SSS #002 and was surprised about the low voltages listed in the original drawing. I´m sure this has been discussed elsewhere, but I can´t find it with the search function. The voltages measured by TAG-Members who have already built a SSS are significantly higher and in a range one would expect with a twin reverb PT. Is there an explanation for this? Somewhere I read that this reverse engineering was done in Japan (?). So might this be just because of the lower wall voltage (100 VAC) in Japan?
And again the question for the SSS User concerning the very high plate-cathode voltage in the cf driver tube. Now - after some years experience with the circuit: Does a 12AX7 stand that high voltage over years ?
Thanks
Lars
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dcribbs1412
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Location: Arizona Desert

Re: SSS#002 low voltage in original drawing

Post by dcribbs1412 »

Interesting idea.
the lower voltages might make sense using 100V mains
assuming HAD used twin iron.
As far as the 12ax7 at higher voltages I changed to a 12AT7 CF
Not sure about tube longevity but amps seems to be running fine
Love to see your amp progress if you get the chance

here's Ceriatones SSS voltages not sure about the 100v reference at the top

SSS 100V 29/05/2012

Tube Type Pin1 Pin2 Pin3 Pin4 Pin5 Pin6 Pin7 Pin8 Pin9

V1 12AX7 228 1.75 231 1.7

V2 12AX7 235 1.68 238 1.65

V3 12AT7 357 6.75 357 6.75

V4 12AX7 250 1.53 250 1.5

V5 12AX7 301 35 56 298 35 56

V6 6L6GC 35mV 444 -45.8 442 35mV

V7 6L6GC 35mV 444 -45.8 442 35mV

V8 6L6GC 35mV 444 -45.8 442 35mV

V9 6L6GC 35mV 444 -45.8 442 35mV

HT 347
HT 347
OT CT 447 (low wall, optimal = 460V)
larsvictor
Posts: 152
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Location: Germany

Re: SSS#002 low voltage in original drawing

Post by larsvictor »

Hey dcribbs, thanks for the additional data from ceriatones version of this amp. I´m not familiar with their circuit. Regarding the voltages of the preamp tubes it seems to me that they omitted the cf-driver stage completely. Cannot see the negative cathode voltages in the bias range. V3 is reverb driver and V5 is PI. V2 could be the reverb send and recovery gain stage and V4 the “mixer” tube that merges the signal from the filter section and reverb, designed as a recovery gain stage like M. Hartman did it in his version.

On the original drawing of #002 the PT is listed as L022756 CSA827 – 606 – 5 – 42. That should be a vintage Woodward-Schumacher twin iron.

Is the 12AT7 rated for more than 300V plate voltage? D. Root suggested 12BZ7 for the driver tube. Never heard of that tube :shock:

Lars
Synchu
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Re: SSS#002 low voltage in original drawing

Post by Synchu »

I did mhartman's layout that is sort of mixed from 2 and 4 and some TR John Mayer. Using 12AT7 for the reverb driver and 12AX7 is doing just fine at CF position. It is either Sovtek LPS or JJ803 there. The amp sounds amazing.
Can't find the voltage chart :(, but can take some measurements once back home in a week or two.
Niki
larsvictor
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Location: Germany

Re: SSS#002 low voltage in original drawing

Post by larsvictor »

Thanks Niki. That would be great. I will try to get one of the named tubes for the CF.
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martin manning
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Re: SSS#002 low voltage in original drawing

Post by martin manning »

D Root used a small auxiliary transformer for the bias supply and customized the component values for the 12BZ7 tube type. I don't like the idea of that high voltage potential across the CF driver stages. I designed a self contained bias and plate supply for a 12AX7 driver using a small flat-pack transformer, which bcmatt recently built: http://ampgarage.com/forum/viewtopic.ph ... 489#361489
larsvictor
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Location: Germany

Re: SSS#002 low voltage in original drawing

Post by larsvictor »

Thank you, Martin for that hint. I am already a reader of that thread and I like your solution. Without any doubt it´s less stress for that poor tube.
I know there is at least 1 builder who had trouble with the high voltage across that tube, but others had not.

I have to go with an extra PT for the bias supply as well, because the main transformer has no CT in the HV winding and the extra secondary bias winding has only 50 VAC which is still too low for the bias circuit in the #002 schematic.

I will give the scratch build a try since I have already etched the boards. If it failes I can use the extra transformer (secondary 2 x 115 VAC) for your design. Thank you again for the input.

I´ll post some pics (after cleaning up :? )

Lars
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mhartman
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Re: SSS#002 low voltage in original drawing

Post by mhartman »

The original drawing was done in Japan. The wall voltage is lower there hence the unusually low voltages on the original schematic.
lovetone
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Re: SSS#002 low voltage in original drawing

Post by lovetone »

I did some repairs on an amp built by Spade amps made in Italy. The voltage on the CF was high around 430v it was killing the 12ax7 in about 10 days. I changed the dropping string to give 380v

As far as I know it has worked ok since, I do remember that this also improved the overall tone of the amp.
larsvictor
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Re: SSS#002 low voltage in original drawing

Post by larsvictor »

Thanks lovetone, you where the one I was refering to in my last post. I thought of supplying the CF Driver from the node of the reverb driver tube. That should be around +380V.

I cleaned my workbench. Here are some pics. Not much to see and a long way to go. I´m a very slow builder. Don´t expect too much in the next weeks (month)...

Lars
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Aaron
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Re: SSS#002 low voltage in original drawing

Post by Aaron »

Nice circuit boards Lars. What capacitors are they???
Synchu
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Re: SSS#002 low voltage in original drawing

Post by Synchu »

Looks very good. No worries with the speed, I built like 5 other amps while contemplating the SSS endeavour. Looked so complicated. But when you approach it with respect, it pays back enormously.
Unique amp once again.
Caps look like WIMA to me. I am very curious on how they will sound.

Did you do the chassis yourself?

Niki
larsvictor
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Location: Germany

Re: SSS#002 low voltage in original drawing

Post by larsvictor »

The caps are WIMA MKS4. They are cheap here in Europe and have a good reputation in audio circuits. Jelle mentioned them in an old thread. Unfortunately the legs are too short for point to point wiring. I´m curious too on how they will sound...

Yes, I did the chassis myself. Just two L-sections and an aluminium plate for the base. The sides are wood.

Lars
lovetone
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Re: SSS#002 low voltage in original drawing

Post by lovetone »

Nice work these big projects do take some time.

:)
larsvictor
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Location: Germany

Re: SSS#002 low voltage in original drawing

Post by larsvictor »

Update. Heater wiring for the preamp tubes, B+ wires to the boards and output and reverb tranny secondaries. Still a long way to go...

Lars
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