Hey there all,
Recently I have been documenting my Boogie Mark 1 so I can convert it to use 12AX7 optimally, instead of the current "ok for 12AX7 but really made for Fetron" circuit, I made a thread here about that, I am learning a lot with all you guys helping.
https://boogieforum.com/threads/help-with-my-1978-mark-i.86559/
In the process or tracing the amp's schematics I got interested in the workings of tube amps, and in tweaking a bit myself. But I won't do that on the Mark 1 !
So I searched for either old tube organ (unsuccessfully) or stereo console, and a couple days ago I found a fully working Sparton 64N5-D stereo console, seems to date from early 60s, all tube.
As a bonus, this exact console had the full schematic available online! That will make it easier than tracing everything.
http://pacifictv.ca/schematics/sparton64n5-data.pdf
I am on a steep learning curve since the last couple weeks, it is a bit early to tell you all what type of amp I'll be doing exactly, but I am sharing the start with you in case you have some advice and to discuss stuff. I also posted this on another forum, but since I really am a Boogie nut I guess this is the place for that
The tubes in the console are:
1x 6GY8 (RF FM stuff, triple triode but with jumped pins for RF specific use, maybe I can use 1 or 2 thirds of it that does not have the funky jumpers)
1x 6BA6 (might be useable, not sure yet, remote cutoff type instead of sharp cutoff like 6AU6, I read it was no good because of odd harmonics)
1x 6AU6
1x 6BE6 (RF AM stuff, but seems to be used for tremolo on 12W Playmaster amp)
2x 6GW8 (ECL86)
It has treble, bass, volume (loudness) and the input switch for AM, FM, FM stereo, phono. I think I'd prefer rebuild an entire circuit more optimal for guitar than just take the the shortest route of minimal mods.
This is one very interesting example I am seriously considering since it uses the exact tubes I have in the stereo:
https://www.thegearpage.net/board/i...d-photos-and-schematic.2221422/#post-36177306
The two 6GW8 are not matched, they are different brand. But I don't think I will exclude a push pull setup only because of that. I guess having them not matched is less than ideal but it won't matter for that small experience project.
Also the amp being stereo, I guess it has what I'd call two single ended amps (please correct me if wrong). Two pics below are the complete circuit from the online PDF. Lots of RF AM - FM crap I will get rid.
The main reason why I am still unsure to do a push pull is because the two independent output transformers that probably won't take well the combined push pull power. So one idea for push pull would be to combine them in parallel or in series, but I don't think that will be ok for the tubes since it completely messes the impedance seen by the tubes. I don't really see how else I can run a push pull configuration with those two separate OT. Thoughts on that?
Alternately I could go single ended with two independent circuits, kind of like it is currently. But I would like to add adjustable negative feedback, and I'm unsure how to go about that in single ended, dual output. Would I just choose one of the output to feed the NFB? I am not yet at the point of looking up single ended schematic examples since I'd like first to make sure if there is a way to go push pull with my current OTs, with a phase inverter and NFB like the one member V2Racing did in the thread linked above.
Any thoughts welcome! I have a long way to go still to understand enough to start dismantling the amp, and it works so it is currently in the living room, playing some SRV, Deep Purple, Janis Joplin and Led Zeppelin LPs I already had, but couldn't play cause I did not have an LP player
Fred
Recently I have been documenting my Boogie Mark 1 so I can convert it to use 12AX7 optimally, instead of the current "ok for 12AX7 but really made for Fetron" circuit, I made a thread here about that, I am learning a lot with all you guys helping.
https://boogieforum.com/threads/help-with-my-1978-mark-i.86559/
In the process or tracing the amp's schematics I got interested in the workings of tube amps, and in tweaking a bit myself. But I won't do that on the Mark 1 !
So I searched for either old tube organ (unsuccessfully) or stereo console, and a couple days ago I found a fully working Sparton 64N5-D stereo console, seems to date from early 60s, all tube.As a bonus, this exact console had the full schematic available online! That will make it easier than tracing everything.
http://pacifictv.ca/schematics/sparton64n5-data.pdf
I am on a steep learning curve since the last couple weeks, it is a bit early to tell you all what type of amp I'll be doing exactly, but I am sharing the start with you in case you have some advice and to discuss stuff. I also posted this on another forum, but since I really am a Boogie nut I guess this is the place for that
The tubes in the console are:
1x 6GY8 (RF FM stuff, triple triode but with jumped pins for RF specific use, maybe I can use 1 or 2 thirds of it that does not have the funky jumpers)
1x 6BA6 (might be useable, not sure yet, remote cutoff type instead of sharp cutoff like 6AU6, I read it was no good because of odd harmonics)
1x 6AU6
1x 6BE6 (RF AM stuff, but seems to be used for tremolo on 12W Playmaster amp)
2x 6GW8 (ECL86)
It has treble, bass, volume (loudness) and the input switch for AM, FM, FM stereo, phono. I think I'd prefer rebuild an entire circuit more optimal for guitar than just take the the shortest route of minimal mods.
This is one very interesting example I am seriously considering since it uses the exact tubes I have in the stereo:
https://www.thegearpage.net/board/i...d-photos-and-schematic.2221422/#post-36177306
The two 6GW8 are not matched, they are different brand. But I don't think I will exclude a push pull setup only because of that. I guess having them not matched is less than ideal but it won't matter for that small experience project.
Also the amp being stereo, I guess it has what I'd call two single ended amps (please correct me if wrong). Two pics below are the complete circuit from the online PDF. Lots of RF AM - FM crap I will get rid.
The main reason why I am still unsure to do a push pull is because the two independent output transformers that probably won't take well the combined push pull power. So one idea for push pull would be to combine them in parallel or in series, but I don't think that will be ok for the tubes since it completely messes the impedance seen by the tubes. I don't really see how else I can run a push pull configuration with those two separate OT. Thoughts on that?
Alternately I could go single ended with two independent circuits, kind of like it is currently. But I would like to add adjustable negative feedback, and I'm unsure how to go about that in single ended, dual output. Would I just choose one of the output to feed the NFB? I am not yet at the point of looking up single ended schematic examples since I'd like first to make sure if there is a way to go push pull with my current OTs, with a phase inverter and NFB like the one member V2Racing did in the thread linked above.
Any thoughts welcome! I have a long way to go still to understand enough to start dismantling the amp, and it works so it is currently in the living room, playing some SRV, Deep Purple, Janis Joplin and Led Zeppelin LPs I already had, but couldn't play cause I did not have an LP player
Fred
