Steel String Singer #001/#002/#004 Layout/Schematics

[erwin_ve]

Hi Ryan, dont burn your tubes
The tail resistor on the bias circuit can be higher, try a 47k or even higher.
What are the bias readings when you apply the RAW bias voltage(without the pot and tail resistor?
Edit removed some useless question.

[rccolgan]

Hi Ryan, dont burn your tubes
The tail resistor on the bias circuit can be higher, try a 47k or even higher.
What are the bias readings when you apply the RAW bias voltage(without the pot and tail resistor?
Edit removed some useless question.

Yes!! That would be an awful and expensive mistake. I went immediately to playing instead of checking voltages and then I noticed things were starting to get toasty no red plating thank goodness.

I'll disconnect the pot and tail and see what I get for bias when I get home. Thanks for the input! I'll grab a higher tail resistor value too afterwards.

[martin manning]

Do you have a schematic posted somewhere that matches your build?

[rccolgan]

Do you have a schematic posted somewhere that matches your build?

Yes, The Japanese Hand Drawn: https://ampgarage.com/forum/viewtopic.php?f=5&t=17827

I didn't change any values other than the bias trim pot and tail resistor.

[martin manning]

You didn't redraw it? It's hard to read, and some have suggested that there are errors in it.

[erwin_ve]

You didn't redraw it? It's hard to read, and some have suggested that there are errors in it.

This is the redrawn version. https://ampgarage.com/forum/download/file.php?id=54132

Concerning errors, at several building reports there were concerns on the bias voltages,
So Martin if you see any errors or questionable things in the circuit, we can make a list of possible changes.

Still Ryan is making a good attempt with his chassis and eyeletboard drawings and I have basically all the PCB drawn for this project, which hopefully fit in Ryans future SSS002 chassis.
I hope this will be the beginning of a accessible SSS, just like the many ODS projects that came along.

[martin manning]

Sure. I ask because it is helpful to have a schematic to which the hardware supposedly conforms, to help with troubleshooting.

[erwin_ve]

Sure. I ask because it is helpful to have a schematic to which the hardware supposedly conforms, to help with troubleshooting.

I know

[rccolgan]

Sure. I ask because it is helpful to have a schematic to which the hardware supposedly conforms, to help with troubleshooting.

Martin, I appreciate your willingness to assist and I apologize for not having a schematic to compliment the layout I made. I see where it could be helpful with troubleshooting. I'm going to try a few things tonight based on Erwin's suggestions. The end goal is to have a working layout of SSS #002 to share since I don't think there is a 100% working one to date without some corrections or forum reading needed?

[rccolgan]

Good news!! As Erwin and Bombacatotal has originally suggested (and I was too stubborn to listen the first time) I removed the bias trim pot for the raw bias voltage and I'm getting a stable 30mA @ 440v! Everything is much, much cooler now and the tone is incredible! Exactly the "SSS tone" that I have in my mind with WGS ET65s. The bias is pretty cold now at 13w dissipation which is ok, but I'll experiment more with tail resistor values per Erwin's suggestions to see if I can get an appropriate range. It's too early to compare my SSS #004 build to this one but this #002 is incredible! Reverb is strong with 5751 tubes but very warm and deep. I'm going to experiment with different tanks.

[rccolgan]

Bias is all figured out. I am removing the bias pot from the layout and suggesting either original 3.3k or 4.7k bias resistor on the rectifier board. 3.3k for 26w 6L6's and 4.7k for modern 30w 6L6's to dial in ~50% of max dissipation. Obviously different tubes may yield different results so I need to think that through. The amp is very stable and I played it at decent volumes for 4 hours or so total so far. Next is troubleshooting very low output from the FET board and that's it for the electronics. Sergio's build included changing the voltage divider so I'll look into that as a starting point.

[rccolgan]

Extensive tone demo up of my SSS #002 build using the layout I posted.

https://youtu.be/0FQV7AY33o0

[rccolgan]

Very warm welcome to all! Update on my SSS #002 build which ties into layout/schematics (I think).. I bought a AmpRX Brown box and I dropped the line voltage down to 104v (Japanese schematic was 102v) and all of my voltages measured up to the Japanese schematic within a few percent except V1 with an 12AX7. The voltage was about 20 to 30v higher than the 185v measured and I found this thread https://ampgarage.com/forum/viewtopic.php?t=28331 where CHIP changed the dropping resistors to accommodate the voltage difference, but I tried a 5751 in v1 (like the SRV rumor) and sure enough, the v1a voltage was exactly as the Japanese schematic at 185v but my v1b is 20v higher than v1a.

Questions for the group -

• Is it possible that the cathode resistor on v1b is actually a 100ohm and not a 1k so the voltages line up? SSS #001 had 100ohm on both v1a and v1b.

• Any effect to LNFB by changing 1k to 100ohm?

I'm attaching the Japanese schematic I'm referring to and a marked up collage to aid the discussion.

sss voltage question.jpg

[dorrisant]

I think you are right about the V1b cathode resistor... it would match what is going on with V1a. I would think that the NFB will different with a 100R in there. Also the gain of V1b would change.

[martin manning]

Since the supply voltage and plate voltages are the same I would think the cathode resistors should be the same (true if the triodes match exactly, which is the unknown here). I think it’s likely that the 1k is a mistake, since plate voltage for a nominal 12AX7 with 100k and 1k6 is 198, and with 100k and 2k5 it’s 220; just about 20V higher. 1k would result in 10x the feedback as 100R.