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Discussion Starter #1
Since I had a couple of these big YGL-Mark 3s and this one was quite messed with before I got it, I decided to build it into a Dumble style Steel String Singer.

I was hoping I would save money by using the existing transformers, cab, chassis, and some of the old random components like pots, jacks, mustard caps, etc. I still ended up having to buy a few small transformers: the choke, reverb transformer, and one to provide the high voltages for the cathode follower (post PI).

Here is the Traynor before I got too far ripping it apart:


Here is the finished product after I wired up the new amp:


Here is the new facelift with a roasted maple valence:


I plan to get more of the knobs I have on the right. That's all I had on hand so far.
Anyways, it sounds great so far... A couple of the front controls are actually lies. I have not installed any presence control yet, and the switch labelled cut also is not wired up to do anything yet. I'm still deciding exactly what I'll put in those spots. That was just a couple ideas.
 

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Discussion Starter #3
Ya, I paid $300 for the Traynor several years ago, and then a few hundred more in parts now.
 

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Just how high is the voltage on the cathode follower plates (that it needs own xfrmr)?
Higher than the power tube plates?
Does it exceed cathode to heater rating of cf tube?
 

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Discussion Starter #6 (Edited)
Just how high is the voltage on the cathode follower plates (that it needs own xfrmr)?
Higher than the power tube plates?
Does it exceed cathode to heater rating of cf tube?
No, they aren't that high. They are less than 190V.
The Transformer was actually needed to provide bias voltage because getting it off the original bias tap was not going to work...
It just also happens to provide plate voltage to the cf.
 

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Discussion Starter #7
This is how I had to adapt the power section to work with the Bridge rectifier that is needed when I use my Traynor PT. It has that extra Hammond transformer at the top:
 

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This is how I had to adapt the power section to work with the Bridge rectifier that is needed when I use my Traynor PT. It has that extra Hammond transformer at the top:
For future reference, when you can't use the resistor off the HV node for bias supply because of bridge rect., you can use cap coupled bias like this version of YBA1
yba1bias.jpg
 

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Discussion Starter #9
For future reference, when you can't use the resistor off the HV node for bias supply because of bridge rect., you can use cap coupled bias like this version of YBA1
View attachment 22814
Thanks JP. That is a great point, but because we figured the bias voltage needed for the SSS was actually closer to -370V, we figured that there wouldn't be enough voltage or current available from capacitively coupling a feed from the HT like some Marshalls and the YBA1. I was a little discouraged when I discovered this (Martin Manning from Ampgarage pointed it out), but he also helpfully came up with this extra transformer solution as well.
 

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because we figured the bias voltage needed for the SSS was actually closer to -370V, we figured that there wouldn't be enough voltage or current available from capacitively coupling a feed from the HT like some Marshalls and the YBA1.
I'm a little lost about where the -370V comes in, I'll look at the ampgarage thread.
Agree that you can't get much current with cap coupled bias, but for sure there is enough for biasing 4 power tubes (like in the Marshall's you mentioned, or Ampeg V series).
 

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Ok, I see the -180V to the CF, +/-180 is 370V so I get where you needed the transformer. :)
Where it says -50V at the grid of the upper power tube, is that correct or do you have -180V there?
What class operation does the power amp end up being?
 

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Discussion Starter #12
Ok, I see the -180V to the CF, +/-180 is 370V so I get where you needed the transformer. :)
Where it says -50V at the grid of the upper power tube, is that correct or do you have -180V there?
What class operation does the power amp end up being?
Yes, I am actually getting -50V at pin 5 of the power tubes.
I'm fairly certain this operates in class AB.
 

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Does the 10K pot set the power tube bias? Or, does it set the CF bias or both? It's very different to anything I've seen. No problem getting the B+ to the CF with a standard dropping resistor setup in the PS but the negative voltage would present challenges. You might be able to use a bridge on the negative supply from the PT and tap power tube bias from that as well....or do I have it all wrong?
 

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Discussion Starter #14
Yes, the 10k trimpot sets the power tube bias. The 25k trim is the PI balance pot.... that I'm still trying some different settings... but it might be too subtle for me.
I should say that the schematic I drew there is actually not the same as anything else exactly. It's very much built off of MHartman's layout which he shares here: http://ampgarage.com/forum/viewtopic.php?t=20662&postdays=0&postorder=asc&highlight=sss+filter&start=0&sid=8170fd5cb87b9522b4943671dfa88848
It is very close to 002, but the schematic I have here is sort of David Root's 001, with the B+ dropping of 002, and then adapted slightly to fit with my Bridge Rectifier instead of the Full Wave everyone else has. If you have Twin Iron you don't need to do what mine does with the extra transformer. I found it difficult to find a matching layout and Schematic... unless you want to the John Mayer Version (which is hard to get to sound as good because it doesn't have the cathode follower). After hearing clips of MHartman's SSS, I decided that was good enough for me. He provided a layout, so I use that mostly, and referred to the other schematics when it came time to get technical and do any altercations to fit my transformers. I also had to change the layout somewhat as well in order to accommodate two of my preamp tubes being by the front panel.
 

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Discussion Starter #16
The wiper of the 10K trim is -49.5V
On the CF Pin 2: -45.8V
Pin 3: -47.7
 
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