Tracing Rick Vito's ODR #58

[rootz]

I have this strange hobby of tracing circuits based on photos. I've had a bit of succes with that, because I've got the tools and skills to enhance photographs a bit and usually can piece things together with several pics.
Now this amp is a bit of a challenge. I've got only one picture and I suppose there are no additional pictures floating online.
Who'd like to join the challenge to make this schematic complete? Yes, that would mean a fair amount of guessing and speculation, but still a lot of fun (or at least I think so).
Have a look at V3a in my hand drawing for example. That looks to me like the mixer stage to me, but not like the one we know from either the tweed mixers like SSS002 or the virtual earth mixer of ODR #60. Interesting right? On the right side of said mixer we see return lug 2 coming in via a resistor to the grid. Then there seems to be a local feedback loop, and from that feedback loop a resistor going out. Where does that one go? To the grid of V3b? Does it mix there with the signal coming out of the preamp? Does the latter come from the relay via a trimmer and resistor/cap combo that can be seen near V3b?

Again, nothing scientific. Just having fun and hope some would join me.

[hitchcaster]

those giant blue 470ohm resistors on the power tubes strapped together... any idea what brand and type those are? i guess you can swap connections on the tubes

[Aaron]

I remember looking at this a while back, and the mixer reminded of the earlier circuit, ie: ODR #013.
This is the only other photo I have.

Thanks,
Aaron

[Guy77]

I have this strange hobby of tracing circuits based on photos. I've had a bit of succes with that, because I've got the tools and skills to enhance photographs a bit and usually can piece things together with several pics.
Now this amp is a bit of a challenge. I've got only one picture and I suppose there are no additional pictures floating online.
Who'd like to join the challenge to make this schematic complete? Yes, that would mean a fair amount of guessing and speculation, but still a lot of fun (or at least I think so).
Have a look at V3a in my hand drawing for example. That looks to me like the mixer stage to me, but not like the one we know from either the tweed mixers like SSS002 or the virtual earth mixer of ODR #60. Interesting right? On the right side of said mixer we see return lug 2 coming in via a resistor to the grid. Then there seems to be a local feedback loop, and from that feedback loop a resistor going out. Where does that one go? To the grid of V3b? Does it mix there with the signal coming out of the preamp? Does the latter come from the relay via a trimmer and resistor/cap combo that can be seen near V3b?

Again, nothing scientific. Just having fun and hope some would join me.

Hi Bas, I may have something to add regarding the V2 preamp. The resistor with the ? mark, on the ODR #057 this was a 56K or 68K resistor feeding from V1 pin 7 or 2 (depending on how the socket was installed). My guess is that this #58 was done in a similar way and so this resistor is either a 56k or 68k. The Bloomfield drive is also done in this same manner. The ODR #013 also has this.

Cheers
G

[rootz]

This absolutely great Aaron; many thanks for that gut shot. Now I can see that V3a has a trimmer and a 220k/cap combo at the input. Looks like a trimmer to control the signal entering the mixer stage.

And I agree Guy. You can see a resistor connected to the grid of V2a. It is pointing in the direction of the 220k/cap combo of V1b. That lightly suggests that it is set up like the Bloomfield drive or #13. Leads me to believe this is an updated amp to a newer 4th gen OD setup (level control on a trimmer, trigger input trimmer, caps from plate to cathode), by the looks of it a classic tone stack in the clean preamp. And an updated mixing stage. A bit like a virtual earth mixer, but with lower feedback? Let me see if I can piece a schematic together.

[rootz]

Concept schematic. Means values are guesstimates and most definitely off. My focus was on the circuit topology and I think this could be it. The trimmer at the entrance of the mixer tube like some kind of hidden clean ratio like you find on ODR #60?

[Guy77]

Concept schematic. Means values are guesstimates and most definitely off. My focus was on the circuit topology and I think this could be it. The trimmer at the entrance of the mixer tube like some kind of hidden clean ratio like you find on ODR #60?

Amazing work, thank you Bas.
Slightly off topic but not too far, I am finally getting around to building something that resembles the Bloomfield drive and will let you know how it goes.

Cheers
Guy