SSS #2 Started

[stelligan]

I get a hernia just looking at that bad boy! Looks good - a real man's amp.

[greekie]

How did you make the faceplates? Looks real good!

[dreric]

Hi , are you sure to use red/blu wire for bias?

Thanks for questioning my work. I'm kind of counting on having many eyes on this project.

Based on the schematic for the transformer:

Red / Blue (50V) = bias tap = bias
Red / Yellow = center tap = to ground
Red + Red = secondaries with 690v 310ma = to rectifier
Orange = shield = to ground

Did I miss something?

Eric

[dreric]

How did you make the faceplates? Looks real good!

I didn't make the chassis or faceplate. About two years ago in a fit of SSS zealotry rj made up some chassis before the true nature of the SSS had been revealed. I had him make up a custom faceplate sometime later. Consequently, not everything matches the layout. I think there's a few dozen of these chassis out there.

Unfortunately, rj has been out of commission for the past few months, I'm hoping he comes back to his previous service, he's a great resource and a heck of a nice guy.

Eric

[grtamp]

Dreric , I think the red/blu wire is not used( like SSS #2 layout show) , the bias comes from B+ red tap.

[dreric]

Dreric , I think the red/blu wire is not used( like SSS #2 layout show) , the bias comes from B+ red tap.

I understand that my build differs from the layout. The PT in the layout shows what I take to be a red/ yellow center tap and a green / yellow 6v heater winding center tap. All we have is Aaron layout as the 1 picture of #2 doesn't show the full amp so I don't know the specs on the PT.

The PT I'm using has different taps so I'm using them the same way I have in past builds.

I used the bias circuit values and wiring from #124.

I used 100ohm artificial CT for the heaters, this is shown on the schematic but not on the layout.

Anyone see something funky about the first filter caps and the standby wiring?

I plan to describe where I differ and hopefully to point out errors in the layout and schematic.

Thanks for the input, keep it coming!

Eric

[ToneMerc]

Dreric , I think the red/blu wire is not used( like SSS #2 layout show) , the bias comes from B+ red tap.

I understand that my build differs from the layout. The PT in the layout shows what I take to be a red/ yellow center tap and a green / yellow 6v heater winding center tap. All we have is Aaron layout as the 1 picture of #2 doesn't show the full amp so I don't know the specs on the PT.

The PT I'm using has different taps so I'm using them the same way I have in past builds.

I used the bias circuit values and wiring from #124.


Eric

I might be wrong but I was under the impression that voltage was taken off the HT tap so that you can get bias in the range of 125 to 150 neg volts for the driver. When I faintly thought of doing one of these I thought of having a PT made with a 100v bias tap, but then realized HAD used stock transformers when we started to analyze the SSS further here.

TM

[Aaron]

Hi Eric,

On the bias board, the is a connection from one of the red wires to the bias supply. The yellow/green and yellow/red wires would have been an earth and centre tap.

Just wondering, if using the standard bias tap, would a voltage triple circuit work there? I started wiring up a Marshall PT, but it is the LV style. So I would use the voltage double circuit for the B+, but was wondering can the same be down for biasing?

Thanks,
Aaron

[ToneMerc]

Just wondering, if using the standard bias tap, would a voltage triple circuit work there? I started wiring up a Marshall PT, but it is the LV style. So I would use the voltage double circuit for the B+, but was wondering can the same be down for biasing?

Thanks,
Aaron

No, you will need a complete bias winding( start & stop) not just a single tap. However, yes you can use a doubler supply for the bias, provided it's winding current is designed accordingly.

TM

[talbany]

Eric
A word of advice on that 100 NOS Bassman OPT.. Try some different GNFB resistors on that one..If memory serves it generates a bit more signal going back than the regular Twin style. That's a GREAT transformer BTW..

Good Luck with that build

Tony

[dreric]

Dreric , I think the red/blu wire is not used( like SSS #2 layout show) , the bias comes from B+ red tap.

I understand that my build differs from the layout. The PT in the layout shows what I take to be a red/ yellow center tap and a green / yellow 6v heater winding center tap. All we have is Aaron layout as the 1 picture of #2 doesn't show the full amp so I don't know the specs on the PT.

The PT I'm using has different taps so I'm using them the same way I have in past builds.

I used the bias circuit values and wiring from #124.


Eric

I might be wrong but I was under the impression that voltage was taken off the HT tap so that you can get bias in the range of 125 to 150 neg volts for the driver. When I faintly thought of doing one of these I thought of having a PT made with a 100v bias tap, but then realized HAD used stock transformers when we started to analyze the SSS further here.

TM

First, Thanks for the input and I'll going to remind evryone that in my intial post I stated that I was not qualified to do this build alone. That said I misunderstood the need for a higer bias due to the driver tube and move ahead as if this was an ODS circuit. I've corrected the board and done some tests:

1. Corrected bias rect board. It now matches the #2 schematic (primary, 3k3 2 watt, diode, tap, 10uf@450 cap) but not the layout which shows the cap at 100uf@25. Due to the tap coming from the primary, I'm assuming that the schematic is right on the cap value. (??????)
2. Board mounted in situ

Brought her up on the variac............NO SMOKE!!!!!!!!!

3. Testing B+ at 120v AC B+ measures 426v DC
4. Testing bias, at 120v AC bias measures - 455v DC. This seems way high to me!! Does this drop when there are tubes in the amp? Does the 3K3 value need to be increased????

Thanks to all for their support, kind comments and suggestions.

Eric

[ToneMerc]

Eric, looking at the schem I would say you do need the big negative voltage for the cathode driven PI, the question is how much. Whereas, if you where using the plate driven LTP config like what's seen in the Odyssey diagrams, your bias could be obtained from the normal 60V PT bias tap.

TM

[dreric]

Eric, looking at the schem I would say you do need the big negative voltage for the cathode driven PI, the question is how much. Whereas, if you where using the plate driven LTP config like what's seen in the Odyssey diagrams, your bias could be obtained from the normal 60V PT bias tap.

TM

Thanks for the feedback TM.

I looked closer at the hand drawn schematics and found that there are voltages an transformer codes on them that didn't get transferred over to the pdf / type versions.

I know that the scuttlebutt is that there are errors in these documents and ................. it's all the info we have. If you are aware of or suspect an error, rather than perpetuating the myth please, by all means point them out, offer suggestions or corrections. I'd like to believe that whoever spent the hours it took in #2 to come up with the schematic was smart enough to do it accurately. My goal in this project is to have some fun, learn more and hopefully come up with a working amp. I'm choosing to post a lot in a step by step fashion to aid in the learning process. Being self taught, I find that I have large gaps in my knowledge and it helps me to work this way.

That said, the transformers in 3 are stock Schumacher Twin Reverb and I'm guessing by the component selection mid-late 70's.

PT: 022756 = 125P34A
OT: 022889 = 125A29A
Choke: 022669 = 125C1A

The schematic says the secondary (red leads) off the PT are putting out 565.5 VAC. (this seems low, my PT puts out 669 VAC approx 100 volts more)

Bias stated at - 328 VDC (my value is -456 VDC approx 120 volts more)

Seems like the problem, for now, is that my PT puts out too much voltage (it's rated at 690 VAC). I could switch over to a Hammond, rated at 620 VAC. Does that seem like a good idea??

I'm aware that I'm comparing voltages from a completed amp to a small section of the circuit. Are these values expected to change as the rest of the circuit fills out?

Thanks for reading.....

Eric

[ToneMerc]

Don't change the PT, it's right where it should be for an 022756 thats unloaded.

TM

[dreric]

Don't change the PT, it's right where it should be for an 022756 thats unloaded.

TM

That's exactly what I wanted to know............... your transformer knowledge is awesome!

Now onto the other side of the amp........... reverb.

Eric