|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
|
|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
In Reply to: Melody 3 stage M845 amp posted by Jim D. on February 20, 2019 at 09:06:51:
While you're thinking about your breadboard, you'll need to plunk some serious money down on output transformers. If you aren't prepared to spend $500-1000 on just the output transformers, then you'll need to lower your expectations significantly.
I don't really recommend an interstage transformer with the 845. Pushing into A2 isn't particularly necessary, and I'd spend the money you saved by not buying ITs to get better output transformers.
As far as the schematic goes, the 2A3 is probably setup "by the book", and the 845 is very likely running fixed bias with a hair over 1000V on the plate and maybe 80mA or so of current. The 6SN7 could be setup as SRPP, a cascode, or cascade (or potentially others). How you might run the 6SN7 depends on how much gain you need, and whether you plan to use a little feedback around the amp. In these amps, you'll either see a big dropping resistor from the ~1kV supply to feed the rest of the amp, or a different power supply that makes 300-400V for the driver stage.
DC heating of the 845 tubes is pretty mandatory, and this is a time to remember that all those schematics that you see with a 10V/4.5A winding feeding a bridge rectifier with a cap at the output are not trustworthy! This is probably the most annoying part of the design to do correctly.
You'll notice that vendors sell both 5K and 10K output transformers for the 845. The value you use will depend to some extent on your operating point, but also whether you plan to use any feedback around the amp. There is certainly some sense to buying a 5K transformer (it's far easier to wind a high performance 5K transformer compared to a high performance 10K transformer) and using a bit of feedback to straighten out performance and potentially lower the noise-floor of the amp.
If you can tolerate less power, there's a lower voltage operating point available that calls for a 3.5K load and still makes 15W.
If you have worked a lot with single ended 2A3 amps and you have one that you like, you can replace the output transformer with a plate choke and you have an adequate driver for an 845 amplifier. When I built my first one, I used a #27 driving a #45. It wasn't particularly sensitive, but it worked just fine for my purposes at the time.
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- RE: Melody 3 stage M845 amp - Caucasian Blackplate 16:05:24 02/20/19 (1)
- Thank you! - Jim D. 04:21:46 02/21/19 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
