Pre-Amp Build

[djnagle]

I think the size of the finished amp, foot print wise, will make the 4" look more proportioned
.

 

[Andy Bergstrom]

4”. No reason to fight it.

 

[Wntrmute2]

With a drill press courtesy of DC I managed a pretty good job of hole shooting on a test piece. Bailed on the last through hole cuz I wanted to see how it looked.

 

[paul_b]

I have a remote Khozmo coming, I may consider using your idea rather than a smoked acrylic window.

 

[marantzfan]

That looks pretty slick! Doesn’t take away from the classic good looks your going for either.

 

[Wntrmute2]

I've ordered my chassis. Next up are the capacitors. I cannot afford real boutique ones everywhere and I know I don't need them everwhere either. I currently have in stock:
Output Caps = 3.3uf Obbligato Gold @ 630V
Between Plate and Grid = 0.22uf Jensen PIO Cu. 630V (old)
Feedback Loop = 1uf Hovland MusiCaps 200V (old)
Cathode Bypass = 100uf Sprauge Atoms or 100uf Jensen electrolytic
Across B+ to GND by VR tubes = 0.1uf Russian PIO 630V
Ground Breaker 0.1uf of questionable parenthood
Heater Voltage Divider = same as above
PSU 100uf X 4 Jensen electrolytic 500V (Really 2 double cans)

So my question is are there improvements to be made in cap choice that won't break the bank? I am reading that thread about the K75-10s with interest and I've used some Jupiter caps in the past with pleasant sonics. Also those Miflex ones look promising but get stupid big in diameter.
All opinions welcomed.

 

[paul_b]

The ground breaker should be a Z5U or other similar ceramic cap, not something from the audiophile parts bin.

A 3.3uF 630V cap will be far bigger than it needs to be. I'd look for a 3.3uF 250V cap and use that instead. Same with the 1uF cap, it could be a 50V cap if you have one that seems promising. There are some nice loudspeaker crossover caps with low voltage ratings that sound excellent and would work well here.

 

[MrEd]

A lot of progress here, things are looking good.
i need to go back and re read all the latest posts I just skimed through.

 

[djnagle]

Is that schematic the updated one with all the changes?

 

[Wntrmute2]

Is that schematic the updated one with all the changes?

Very close. I have two OC3s instead of the one 0D3 for looks and to get to my B+ to 210V. I have a 0.1uf cap across the 100K voltage divider and I have changed the cathode resistors to 47K from the 33K on the original schematic per PB. The last change was in response to bumping the B+ to 210V from the original 150V.

 

[Wntrmute2]

Oh, the 2 100uf caps in the PSU are now doubled up to 200uf each and the 270 ohm resistor between them is a choke with 270 ohm resistance.

 

[djnagle]

Thanks Dave. I've never been completely satisfied with my preamp so I'm interested what you think over time.

 

[Wntrmute2]

Thanks Dave. I've never been completely satisfied with my preamp so I'm interested what you think over time.

I'm forgetting which preamp you are using and what things are you not satisfied with?

 

[djnagle]

Pete millett low mu pre. I've got hum issues and I can work through those but it doesn't sound very dynamic. Kind of a dud. It can take a number of output tubes and I'm going to play with that. Right now I'm running a 6080 tube.

 

[Wntrmute2]

Thought regarding these caps? Supposed to be "High Quality". I have them in 0.1uf, 1uf and 3.0uf.
Vishay Caps

 

[djnagle]

Everyone knows green caps are the best color.😁

 

[paul_b]

I would give them a shot!

 

[Wntrmute2]

Everyone knows green caps are the best color.😁

IKR

Actually, different values are different colors. The 0.1 and 1uf's are white.

 

[djnagle]

Agreed. Vishay makes very good caps without being all boutique on your ass.

 

[Wntrmute2]

The changes I made to @paulbottlehead's schematic are outlined in red. I have not documented the voltages but will get to that when I can tear the Gadget out of the system.