BeePree2 Done...

[Ivan303]

Up and running.  And running fine.

Tried it with a number of 300B tubes.  Pair of KR tubes from olden days when Riccardo Kron was still alive. Never used much as they were WAY too microphonic,  And still are.  Causes acoustic piano to sound more like an electronic one.  Tizzy, in a word.

With the EH tubes supplied as well as some late 90's-early2000 era WE 300B re-issues from Charlie Whitner, a slight tizzyness or 'hardness' in the upper range remains.

Not sure why.   Easy to change tubes.  They are running with so little current/voltage that you don't have to let them cool off in order to safely touch them.

Maybe the Stepped Attenuator/Constant Current Source upgrade will help?  Plan to do at least the constant current source part of that upgrade leaving the pots as they are for a time.  Really need the balance control due to seating issues in the room. That said, betting a Big Fat Choke on that 300B would tame the tizzyness/upper register hardness!   That's a story that will sadly never be told. 

Also am a bit confused on what the Constant Current Source actually is or does.  On the blurb of the product page for the upgrade, all of the blurbbing is about the 'sweet whispers' part of the upgrade and little or nothing on the Constant Current Source part  (which from prior posts here seems to be doable in two steps)?

Is it really a Constant Current Source (below the cathode controlling the current) or is it an active load (a solid state choke, as it were)?  Guessing active load as the picture shows the cathode circuit intact and the big ugly sand-cast resistors are no longer in the picture.   

Not so sure about possible output cap upgrades being easy(if larger and fatter) as the upgrade board seems to be sitting right on top of the stock Dayton cap?

And maybe the BeePree2 is producing more 'high frequency detail' than my current tube PS/tube regulated 6SN7 pre-amp and it's all in my head?

The BeePree2 also produces more than a bit of background HUMMMM when cranked, but maybe that's easily curable.  I have two DACs I like and for some reason the Audio-GD produces about 3dB more output than the Denafrips which is currently in the system, and that on the RCA outputs.

Why?  Who knows?  I like them both so have no problem switching.

Also, I padded down the MonAmours about 3-dB or so in order to eliminate any and all pre-amp noise from the  6SN7 pre that the BeePre2 is doing its best to replace.   MonAmours have a bit more gain than the 300B monoblocks they replaced and that did the trick. 

As the volume control INCREASES ambient noise on the BeePree,  being located at the output, an increase in both input level along with an increase in gain in the amp it is driving should fix this as that would seem to mean the BeePre2 output will be cranked down about 6dB from where it's currently set?

So, C+ for sound (so far) but certainly an A+ for looks!

[Paul Birkeland]

You would definitely want to allow for some break in to mellow the sound out a little bit.

The first upgrade uses a constant current source as an active load on the plates of the 300Bs. 

You can decrease the noise floor of the BeePre at full volume by swapping out the four 130 ohm resistors for 27 ohm ones.  The second upgrade also tames this down a bit. 

I would definitely remove any padding on your amplifiers, as the BeePre 2 does not benefit from these treatments. 

[Ivan303]

You can decrease the noise floor of the BeePre at full volume by swapping out the four 130 ohm resistors for 27 ohm ones.  The second upgrade also tames this down a bit. 
 

Wouldn't changing those resistor values by such a large percentage also change the voltage across the 300B filament?

[Paul Birkeland]

Nope, the voltage across the 300B filament is set by the regulator on the filament supply board and the 0.51 ohm dropping resistors that go to pins 1/4 on the 300B sockets.

[Ivan303]

Nope, the voltage across the 300B filament is set by the regulator on the filament supply board and the 0.51 ohm dropping resistors that go to pins 1/4 on the 300B sockets.

Guess I'm having a problem understanding the schematic in the manual I downloaded a few weeks ago when I ordered.

It's a .pdf and my free version of Adobe won't let be post a picture but...

It doesn't look quite right.   It's the schematic that has me confused.  Looks like the 130 ohm resistors are attached directly to the socket pins.

Even left and right side of the filament are different and while I agree with what you you say as the resistors do go directly to the pins of the 300B as I assembled it the schematic is confusing.

[Paul Birkeland]

Yes, the resistor values are swapped in the schematic, but correct in the assembly directions and all the photos of the build.

[Ivan303]

Yes, the resistor values are swapped in the schematic, but correct in the assembly directions and all the photos of the build.

That was my guess but still...

And assuming that, as the left and right side of the filament circuit in the schematic are wired differently, at least on my schematic, that the left side is the way it should be drawn out?

If that's the case, it look to me as if the Regulated  6.3 V comes in on the outside end, away from the  filaments, of the 130 Ohm resistors and then attached to the two filament pins through the .51 Ohm resistors?

A better drawing would help but I am assuming the purpose of the two 130 Ohm resistors is to drop the voltage from a regulated 6.3V to the 5V that the 300B would like to see?

And if the 6.3V is indeed regulated at 6.3V then changing the 130 Ohm resistors would change the voltage on across the filaments?

A more accurate drawing might help me understand and I might be missing something?

[Paul Birkeland]

The 0.51 ohm resistors drop the regulated 6.3V to 5V.  The 130 ohm resistors create a center tap for biasing.

[Ivan303]

The 0.51 ohm resistors drop the regulated 6.3V to 5V.  The 130 ohm resistors create a center tap for biasing.

Then there is clearly an error on the schematic in my manual as to where the 6.3V is applied even with the resistor value swap.

[Paul Birkeland]

There is an error in the schematic.  There is not an error in the manual.

[Ivan303]

Thanks, that's exactly what I was looking for!

Makes all the sense in the world now.

[Paul Birkeland]

If it makes you feel better I had to redraw it twice 

[Ivan303]

If it makes you feel better I had to redraw it twice 

What makes me feel better that that I'm not losing my mind.