U47 TUBE Issue

[sr1200]

another

 

[Moby]

Pic's are blurry so I can't see damned thing, but here we go. In attachment you can see original Neumann's VF to Nu mod. if you like to have the same output level as with VF than change the 6,8pF capacitor between the grid and the anode to 3,3pF 500V highest quality, or you can put it out too. Typical cap type is Styroflex (Polystyrene) but you can use some other to taste. Also, you can  change R2 from 60 M Ohm to 100 M Ohm . With R2 don't go over 250 M Ohm because the tube is not stabil with high pressure level, with 100 or 200 M Ohm all is fine. Cheers

 

[sr1200]

You're the best man, i can't thank you enough!  Out of curiosity, why did they not just use .25 watt resistors all around?  Why the .1 watt?

 

[Moby]

You're the best man, i can't thank you enough!  Out of curiosity, why did they not just use .25 watt resistors all around?  Why the .1 watt?

As I can see your U47 is pretty old (i presume it's from the end of 1940's). Those days resistors were double or triple sized compared to present production. I can't see any other reason than dimension to go with lower W rating :/ Also, don't be lazy and check all the values of resistors. If the are within 5% then OK but it's possible that thy changed the values over the time.

 

[sr1200]

I know this is an old thread, but does anyone have the schematic for the power supply.  I had a copy of if, and for the life of me cannot find it!

 

[sr1200]

I just found 3 schematics, that have no identification as being neumann, but one has 4 caps, one has 5 and one has 6.  lol

On none of them do i see this guy... (attached pic)  Any thoughts?

 

[Moby]

It's possible that it's just an "upgrade" but can you post the pic so we can see the guys around?

 

[Walrus]

I just found 3 schematics, that have no identification as being neumann, but one has 4 caps, one has 5 and one has 6.  lol

On none of them do i see this guy... (attached pic)  Any thoughts?

That is the rectifier bridge.

 

[sr1200]

Guess the look of some of these components has changed over the years huh?