US Navy 803 tubes for home brew audio amp - opinions wanted

So this is going to depend upon the transformer design. Again, a Class A design is gapped and has a larger core to avoid saturation. Are the UTC output transformers able to handle the full Class AB power rating when operating in Class A? As you noted, no. Because the transformer design is a hybrid between Class A and Class AB. Works fine for Class AB, at a higher price point, but Class A can't run at the same power.

This is conflating single ended with class A as none of this is true of PP class A.
 
When writing "Class A" the context made it clear this was single-ended, as I specifically differentiated by writing "push-pull" when talking about the not single-ended topology. Clear from the context. Engineers and audiophiles don't normally write "Class A single-ended" because the default meaning IS single-ended. Vernacular, shorthand, jargon, and all that.

But this is a distraction. The core issue is that building an amplifier, be it single-ended or push-pull, with ginormous plate voltages (not for hams, but certainly for audio) and peculiar tube characteristics is a very tricky task and not the sort of amplifier built in a weekend..

The OP has an answer and it's been well discussed.
 
What he said.

Once again we circle back to the issue of 2,000 VDC at the plate. Which is going to require custom single-ended output transformers.

Plus the additional issues outlined which are moving into esoteric and rareified design skills.

The 803 is clearly not a project to casually undertake which is what the discussion was intended to address.


You are right here. For that project you need transformer rated (and tested) for 5kV insulation between primary and secondary.
 
Also, when you wrote, "FWIW my UTC OPTs are rated for SE operation as well as PP, albeit at a low power level." I interpreted this to be Class AB push-pull, not Class A push-pull. Because the generally meaning for push-pull is Class AB. The context didn't make it clear which type of push-pull was being discussed
 
You are right here. For that project you need transformer rated (and tested) for 5kV insulation between primary and secondary.

'Zactly.

Can't exactly get one of those at Radio Shack, even with a giant flux capacitor (in any amplifier class) running the car.
 
Also, when you wrote, "FWIW my UTC OPTs are rated for SE operation as well as PP, albeit at a low power level." I interpreted this to be Class AB push-pull, not Class A push-pull. Because the generally meaning for push-pull is Class AB. The context didn't make it clear which type of push-pull was being discussed
Sheesh.

The transformers are rated for power in a PP circuit, whether class A or AB, as I wrote, the whole point being that there is not a difference. Separately they are rated for SE operation at a lower power level.

"Single-ended" can only be class A, therefore it's safe to assume that the latter is implied with the former. The reverse is not true, SE isn't the only topology that class A can be used in, and so it shouldn't be assumed that class A means single-ended. Hence the desire to not conflate them.

My post to you was about PP and PP only, and your claims of special requirements for class A PP.
 
The discussions and designs concerning push-pull Class A describe special transformers. Must be a reason.

I specifically wrote:
This is a complex question because the stages must be perfectly balanced to ensure matching waveform halves else DC will not cancel. The conventional Class AB transformer permits minor amounts of DC, but for push-pull Class A it isn't clear how much arises. The literature on push-pull Class A has not adequately addressed this to the point I could definitively answer the question with respect to the core magnetization and saturation.
 
The only issue I have been able to turn up for Class A PP is the ability to tolerate a much higher idle current. I am running my S265Q's at about 10% over their idle current rating with a 600V B+ to deliver a solid Class A operating point for the finals with 75W Tantalum anodes.
cheers,
Douglas
 
Jack Elliano of Electraprint and I built a single ended version of 803 amp. About 50 W single ended. About 1150 V on the plate. Sounds excellent. We built two versions one with a 6hv5 first stage. The other with an input transformer, kind of like an interstage transformer. The latter sounded better but power dropped about 5 watts.
 
I have several USN 803 tubes from Catoctin. They are circa WWII and were used as audio modulator tubes in high power AM transmitters. I was wondering if anyone has any experience with these, and if so, how they might work in a high fidelity tube amp application. Plates are capable of handling 200 watts so I could probably get 50 watts of audio in a single ended design without pushing them to hard.

Any thoughts?
New
Jack Elliano of Electraprint and I built a single ended version of 803 amp. About 50 W single ended. About 1150 V on the plate. Sounds excellent. We built two versions one with a 6hv5 first stage. The other with an input transformer, kind of like an interstage transformer. The latter sounded better but power dropped about 5 watts.
 
New
Jack Elliano of Electraprint and I built a single ended version of 803 amp. About 50 W single ended. About 1150 V on the plate. Sounds excellent. We built two versions one with a 6hv5 first stage. The other with an input transformer, kind of like an interstage transformer. The latter sounded better but power dropped about 5 watts.
Great! Do you have schematics or a BOM that I could use to follow your design? Did you have to have a custom made OPT? Did you do any testing for distortion/frequency response? Where did you find sockets? Etc.. Would love to hear about this project!
 
Great! Do you have schematics or a BOM that I could use to follow your design? Did you have to have a custom made OPT? Did you do any testing for distortion/frequency response? Where did you find sockets? Etc.. Would love to hear about this project!

The sockets are easy to find both Chinese and NOS. Yes the output transformer was custom made along with the input transformer. Jack builds transformers so a custom job is easy. The circuit is Jack’s design. You will need to contact him here:
electaudio@cox.net

Extensive testing and listening done. Everyone likes it.
 
As a follow on Johnson 275 sockets work. A couple are on eBay for $30/pair. The design without the 6hv5 tube is pretty easy to build.
 
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