[rosgr63]

Guilty!
 
If I remember well you mentioned something about the face plate before?

 

[Silent One]

I did I did! 

 But I was just funnin' with Glenn about getting my amp Blacked out. I really am falling in love (deeper) with my vintage 1980 Pioneer SX-D7000. Would have loved to sent that back too, for enhancements. But @ 50 lbs!!! 

 That'd be an extra $200+ round-tripper which could better be spent on caps...

 

[Xcalibur255]

You are getting your volume pot swapped too right?  That's basically mandatory for running the 5998 full time anyway.  The old pot isn't very accurate.
 
If I had to do it over again I would have skipped the switch and had the amp wired for 5998 operation only, and asked Glenn if there were any further steps that could have been taken to reduce power supply hum further to compensate for the higher gain.  I can't see any reason to ever use 6AS7G tubes these days, the 5998 is superior in almost every way to my ears.

 

[Silent One]

Quote:

You are getting your volume pot swapped too right?  That's basically mandatory for running the 5998 full time anyway.  The old pot isn't very accurate.
 
If I had to do it over again I would have skipped the switch and had the amp wired for 5998 operation only, and asked Glenn if there were any further steps that could have been taken to reduce power supply hum further to compensate for the higher gain.  I can't see any reason to ever use 6AS7G tubes these days, the 5998 is superior in almost every way to my ears.

 
Yup, we're going "Step" baby! While the amp is in transit, do you think it's a good time and idea to ask Glenn to wire it full-time for the 5998's? No matter what power tubes I roll, the 5998's roll right over the swap and back into their rightful place. 
 
You brought me along this far, don't leave me now! 

 

[Xcalibur255]

I would say if, and only if, there is further improvement in doing so.  I think in my implementation the 5998 still isn't biased optimally, just more so than it was before the mod.  This I'm guessing was the maintain 6AS7G functionality.  Glenn told me it bumps the plate current 20mA.  Technically you can run the 6AS7 with the switch in 5998 mode, this makes the amp behave the way john's does but it runs hotter and most American 6AS7 tubes scream uncle.  I tried this with a pair of RCAs, they started humming 3 seconds after I flipped the switch.  A tap on the glass actually settled it back down and indeed I thought they sounded better this way, more full sounding just like the 5998 does, but the 5998 itself sounds better still.
 
I never actually asked but I'm guessing Glenn did this for safety sake so a person couldn't accidentally nuke a 6AS7 by having the switch in the wrong position.  Since the extra cathode resistors only change the plate current by 20mA it is technically still safe for a 6AS7 tube in either mode.
 
Glenn posted in here a few days ago that the ideal bias on the 5998 tube was 125mA which is considerably higher than what he told me my amp is running even with the mod, so maybe there is still room for further improvement.  A PM to the man himself would clear everything up I'm sure. 
 
One note though, and an important consideration for you in particular:  if that 125mA number is actually true as opposed to 80mA which is what my amp is supposed to be running, then it likely rules out the 596 as a rectifier in the amp post mod.  You would be at 268mA current draw, uncomfortably close to the 275mA max of that tube.
 
The guru himself will probably chime in and correct any errors in my logic here. 

  I don't want to pretend to be an authority when I clearly am not, I'm just re-posting numbers that have been quoted to me in the past.

 

[Silent One]

I believe you're right. And it would make perfect sense for our designer to make improvements; seek improvements, as we go forward. And the fate of my beloved United Electronics USAF-596 (The Mighty 596)?
 
Officially down-the-street (finished)!

 
Nothing is forever. Will simply make the 5U8C/3DG4 recs do what they do! 

 I've got four USAF-596 and will move to sell two and keep two for display and future implementation. 
 
After further thought, Glenn might be able to use a '596' for future testing with various amps. If he no longer got it, he gonna get it...will gift him one! 

 

[Xcalibur255]

Well, don't take my word as gospel on the subject until we know it is right.  I may have misunderstood something along the way.  Plus the rectifier might hold up just fine, it is still within the rating even if just barely.  Better to wait and see.

 

[rosgr63]

By not having the 6AS7G option you will not be able to try the MOV 6AS7G tubes which are worth trying.

 

[Silent One]

This is why Glenn is installing a switch, so that we won't lose the option to run tubes in standard mode. A few times a month, I'll get to hear the Mighty 596 still! Just not in '5998' mode. The Russian 6AS7's are safe in '5998' mode though.
 
Now, if I could just learn more about the MOV 6AS7G you speak of...

 

[rosgr63]

Marconi Osram Valves, such as the MWT, Osram, GEC brown and black base variants with straight or curved bases.

 

[Silent One]

In audio, looks aren't everything. But I love the way Osram glass looks with the silver metal base! I'm sure now, only sticker shock awaits...gonna look anyway.

 What kinda dough am I lookin' at for a pair?

 

[Silent One]

Fun! Fun!! Fun!!!
 
My custom built OTL amp has now been modded. And speeding its way toward the listening room. It's going to be fun revisiting some of my most recent impressions. Wednesday, a new chapter begins!

 

[wotts]

This is very exciting to hear! I can't wait to read your impressions.
 

 

[Silent One]

Uh-oh! I hear your amp will be shipping in the immediate future. We're gonna have to have an OTL block party! 

 

[wotts]

Quote:

Uh-oh! I hear your amp will be shipping in the immediate future. We're gonna have to have an OTL block party! 

 
Everyone is invited to timmeh's (my house)!