Push Pull 2A3

I have only one on a board right noe, listening in mono for a lot of hours as I've made changes and tried many combinations.
I ready to build the two final iterations and call myself have.
It is dynamic, balls with good solid base, midrange and extended highs.
Pretty much check all the boxes I am looking for.
That last experiment was a shunt regulator on the driver type power supply.
Nice little improvent.

Sounds great, ive been using a borrowed diy 300b set for the last two weeks and its nice but its not got great bass and not that good in highs either, the other amp i have had recently is a quad 2 and thats sort of the opposite but not quite what im looking for, fingers crossed for this PP2a3
 
I have a bit of an update, for a while now i have had a friends diy d3a > 300b stereo amplifier and breadboard lashed up as an approximation of the amplifier im planning on building. Sounds good but so far its been mono and im not used to that! The plan now is putting togeather the amplifiers using my parts and working out the final configration in the chassis (ive had to return the borrowed 300b amplifier).

I should have the pair of chassis ready for drilling in the next week or two so hope to speed this process up and have this completed by the end of October, or even sooner.

I wanted to ask about this:
I have been recommended to add a cathode resistor (with its own bypass capacitor) to each 2a3, do i need to change the value or just add another of the same value? Ill need to check what value was used as i think my friend added a resistor to the 500R one i originally planned not sure if the value we used ended up lower or higher, i did write it down but seem to have misplaced the details.
 
If I understand you correctly, you are talking about changing from a single cathode resistor connected to both cathodes in a PP pair to separate cathode resistors for each tube. If so, each separate resistor should be twice the value of the common resistor. The cathode resistor is setting the bias voltage for the tube, so to get the same voltage when you have 1/2 the current you’ll need twice the resistance.
 
Thanks Salectric, thats exactly what i wanted to know!

I have 8 Mills 1800R 12w resistors that will get to 900R, and if im right that when it was a shared resistor it was a little under 500R that might do nicely.
 
If you're going to use separate bias resistors for each tube, you also need a separate filament winding for each tube.

I got that covered, i have the appropriate split bobbin filiment transformers, Dave Slagle filiment modules and rod coleman reg boards. I heard the coleman boards on the 300b amp vs AC and i liked the DC better, hope it works as well for my amplifier.
 
The lack of progress is frustrating!

I have all the parts so have given the layout a bit of thought and have come up with what’s below. The transformers on top of the chokes and PT would go below, as would the rod coleman dc supplies and ccswith the heatsinks. I think the output transformer and interstage splitter transformer are ok like that but I can rotate if needed?

450B8722-0DB4-4EA3-BC0C-C40E9E2F5E19.jpeg9FDE3D01-BE36-4A6A-9C0F-4904DE24C91E.jpeg


feedback would be much appreciated.

thanks guys!
 
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Certainly looks worthy of construction!
Thanks! I was a bit unsure about the output transformer oriented the same way as the interstage splitter transformer but have seen other amplifiers where it’s the same so maybe not a problem.

I’m thinking about outsourcing the top plate to someone else but will need to learn how to design it for the CNC machine. There is a good chance that might end up taking longer than just waiting for my friend to have a free weekend where I can have a go with his drill press.
 

Thermionics

Post Whore In Training
The lack of progress is frustrating!

I have all the parts so have given the layout a bit of thought and have come up with what’s below. The transformers on top of the chokes and PT would go below, as would the rod coleman dc supplies and ccswith the heatsinks. I think the output transformer and interstage splitter transformer are ok like that but I can rotate if needed?

View attachment 37150View attachment 37149


feedback would be much appreciated.

thanks guys!
Wait, I thought you wanted a zero feedback design? :D
 

Wntrmute2

Not So Mediocre Member
Thanks! I was a bit unsure about the output transformer oriented the same way as the interstage splitter transformer but have seen other amplifiers where it’s the same so maybe not a problem.

I’m thinking about outsourcing the top plate to someone else but will need to learn how to design it for the CNC machine. There is a good chance that might end up taking longer than just waiting for my friend to have a free weekend where I can have a go with his drill press.
I THINK you can design it in Front Panel Express and export the file wherever you want. I believe that is a CNC compatible file.
 
You might want to take the time to learn a more flexible CAD tool. I use QCAD and I think that is what Paul uses too. It is 2D (what we need for panels etc.), doesn’t take long to learn the tools you will use most, and it has a good manual/tutorial.

I’m still learning how to use it more effectively, but using CAD is now so much faster for me than hand drawing (then sending for conversion at the shop) or manually hacking the panels myself that the investment up front is well worth it. Wish I’d done it years ago.
 
You might want to take the time to learn a more flexible CAD tool. I use QCAD and I think that is what Paul uses too. It is 2D (what we need for panels etc.), doesn’t take long to learn the tools you will use most, and it has a good manual/tutorial.

I’m still learning how to use it more effectively, but using CAD is now so much faster for me than hand drawing (then sending for conversion at the shop) or manually hacking the panels myself that the investment up front is well worth it. Wish I’d done it years ago.
That’s a very good point, I do have plans for building a phono and I’m not that old so maybe lots more to come! I think it makes sense to get to grips with it now then. I just looked it up and QCAD should run on my laptop (wiped the hdd and committed 100% to freebsd in a fit of frustration last year).

I should have a lot to learn in the next few days.

thanks!
 
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That’s a very good point, I do have plans for building a phono and I’m not that old so maybe lots more to come! I think it makes sense to get to grips with it now then. I just looked it up and QCAD should run on my laptop (wiped the hdd and commuted 100% to freebsd in a fit of frustration last year).

I should have a lot to learn in the next few days.

thanks!
And learning something foreign to me was enjoyable. You can run the free Community Edition, which has a reduced toolset, but certainly enough for what you might need to do.

Feel free to PM me if you’d like to chat more about the tool etc.
 
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