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my 300B SET project

I read this whole post...and to me, at times, sounds like Charlie Browns teacher talking. Whatever the tech was, and for as dumb as I felt reading it, I loved it all and am amazed with your amps. Simply beautiful.
 
I just finished a 1:15 min listen to them. Very dynamic sounding, stump pulling torque! Even with new tubes they performed very nicely. The lamp shining on that pearl paint sure looks nice also.
 
I live in Dave's neighborhood and had the opportunity to listen to these amps! They are absolutely wonderful sounding and look as good as they sound! Dave has a pair of winners here!:music::thmbsp:
 
I've got a couple hundred hours on the Pearl amps now. While I was listening to them I put the chrome amps under the knife and installed K&K audio constant current cascode supplies to the first 7193 tube and converted to diode biasing. I brought them back up and put them in the system. The improvement in these amps was so great (and they were fantastic anyway) I decided to part with some cash and ordered a pair of Sophia Electric Royal Princess 300B tubes. It's only money right! These amps sound so good, depth and width of sound stage that I thought they were worth the investment. I also have a few mods I want to do on the pearl amps. More to come in a week or so.
 
I'd be interested in hearing more about those constant current sources. You left the 2nd 7193 as-is for now?
 
Jeffery I ordered 3 of the current cascode units from K&K audio http://www.kandkaudio.com/accessories.html I bought the cascode current source kits over a year ago. I built them and played around with them but decided at first that I would postpone using them until I learned more about them. I saw a great benefit in my mind if I would use them on a diode biased tube as that would hold the flow of current very precise going in and coming out. The first tube in my design also operates at a lower voltage, less voltage means that any variation is a larger percent than the same variation would be at a higher voltage. Also I like to do a benefit analysis of things thus making only one change at a time. I don't know how I would diode bias the second tube as of now because of the higher voltage there and I'd need to order some more CCS units. I'm waiting now for those Royal Princess tubes to arrive and sit down and enjoy the music. Cheers!
Dave
 
Yep, same thing I was wondering on the 2nd tube, need to drop nearly 100v worth of diodes in there.

So you just hook the CCS up to the plate instead of the plate resistor? What did you power it off of, the same plate voltage as was going to the resistor? Does it come with any instructions :D ?
 
Jeffery, I just removed the plate resistor and installed the CCS in its place. There is a trimmer resistor on the CCS that allows voltage adjustment to what you want it to be. It may also be necessary to vary the resistance in the circuit right after the trimmer to get the range you need for the draw of the tube, the unit comes with a jumper wire and also a 1.5K resistor for this position. A 1K worked best for me here. I spent a few evenings with these things before I got what I wanted from them. It's a tinkerers project for sure but once you get them dialed in they produce.
 
Thanks, Dave, I'll get a couple just in case. Did you use the Cascode Current Source $12 unit (2nd one down on the price list)?
 
It's been freezing cold in Wisconsin this winter, March first and it's below zero. Makes working at the bench seem like time well spent. I opened up one of the pearl amps this afternoon and installed a B+ delay box. I should have done that in the beginning but got a little lazy I guess. I also swapped out the 12BH7A and put a trusty 12AU7A in its place. I don't have good speakers for doing this testing at the bench but the 12AU7A got rid of the darkness the 12BH7A tubes seem to produce.
 
A chrome amp update. The CCS units I installed on the 7193 tubes brought so much more detail and life to the music that I thought I should upgrade my 300B tubes. I ordered a pair of Sophia Royal Princes tubes. http://www.sophiaelectric.com/pages/se/royal_300B.htm I researched and read everything I could find about them, most said they did everything very nice. I have to say that after about the first dozen notes I could hear that my amps had been put on steroids! I have about 15 hours on these tubes now and the sound stage width and depth have really increased. The CCS units and all the upgrades I've done send these tubes a very clean signal, the results I will place with the best I've ever heard. Now if I can find some time to get back to working on the pearl amps and get their potential fully unlocked.
 
Yes Jeff, I used the 1A 600V units. I bought a bag of them and daisy chained a bunch together and then tapped between them until I got the voltage drop I wanted. I've done this before and I don't remember the count exactly but I think 7 or so was the final number.
 
That's the ones I have. :thmbsp:

I thought I read that someplace, or it might have been Maxamillion, he used them in a diode-biased 7193 preamp.
 
A few weeks ago I put the pearl amps back under the knife and installed B+ delays and decided to replace the 12BH7A tubes with the 5814 version of the 12AU7A. I hooked them back into my "A" system today for a listen. I'm here to tell you that in my circuit this is THE tube! It totally outshines the 12BH7. From everything I read I wouldn't have believed this without hearing it myself. The 5814's I used were random tubes salvaged from a couple of old aircraft radios I had laying under the bench. More listening tonight!
 
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