|
SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
|
|
|
SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
|
In Reply to: RE: "you are there" posted by Tre' on December 3, 2019 at 20:01:08:
Yes and no. I'm referring in a general sense to the basic topology of the WE133A which is PP pentode drivers with phase inverting input trans and the use of the two types of FB necessary. I think triode outputs could be fine here, with obvious adjustments necessary. This is why I keep asking about the math so I can try different combos, rather than just trial and error. Because I don't yet get all that, I think sticking to the known values is a good place to start.
You could make a WE133A 6GM5/7591 version which I would recommend, but there's numerous other choices.
There's the Langevin version 6SJ7/6V6, there's the McCurdy version 6AU6/6BQ5 (both from the pro sound world) and the consumer grade RCA RC-10 or RC-20. The later two use no cap in the FB circuit so they stand up the driver cathode on a big resistor. This forces the need for caps from the input trans (McCurdy) or tube PI (RCA) which I don't suggest. UTC even made a kit amp like this using 6AU6/5881 with a 12AX7 PI, but as Crowhurst would say and I agree, "if 2 stages can't get it done, then you need to start over."
If you have 4 good 7591's I'd say use them. Copy the 133A otherwise, but use a 450VDC rail. 10K OPT or close. The spec'd 600/50K split input will be too much gain for your system so use a lesser step up or be prepared to turn down a bunch. These circuits we designed to be driven from a pre-amp step Down OPT, hence the extra gain you don't need.
Put 400VDC on the screens through a dropping R and cap, and use a voltage divider for 275V for the front end. I used a pair of 400 ohm Rk for the outputs. I adjusted the FB resistor by ear to 267K. You may want to play with that value to see how this behaves. You should see about 18-19v at the cathodes, which is the same for 6F6. The test points in the 133A for the drivers is helpful, just roll tubes until you get a decent pair, same with the outputs. The series combo of the cap and R in parallel with the cathode circuit is the 18K throw away filter. Use it. It's because, as the RCA manual states, this type of FB brings a rise in the response at each end of the spectrum, which holds up the bass well, but must be an issue above 18K so "they" decided to chuck it. Makes sense. I truly hope you like what you hear. I got my grid "clips" from one of the old radio dealers, if you can't find any I can send you some. You can also make them from solid wire. You could use 6SJ7, but I didn't. 1620's are ideal here, but all they are is a selected low noise 6J7, and there's plenty of 6J7's that still qualify.
One last reminder also from Crowhurst, is that I believe he said something like, "FB used to make a bad design "better" is a sideways affair at best, while the sparing use of FB applied to a good design can make a good amp excellent"
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- RE: "you are there" - buffy 12:06:40 12/04/19 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
