BRAUNER VMA

[rock soderstrom]

Do you want to see the PSU as well?

Would be nice!

 

[kingkorg]

Sorry for the delay! Here’s the guts of a VMA. I know I know, we should get a fancier tube, pretty sure that’s been replaced before I started working here. Do you want to see the PSU as well?
View attachment 90300View attachment 90301View attachment 90302View attachment 90303View attachment 90304

Thanks for this. Quite a lesson to be learned from the images. Notice the foam between the dome and the board to damp resonance, and the dome itself. Although i would make the dome cover the whole area all the way to the edge, and make it out of another type of material that would absorb reflections as well. I would make sure that foam under the dome doesn't touch gate connection of the tube.

 

[moamps]

I see only one 470uF cap, so the switch may probably change more significantly the LF response.

If we refer to the schematic from the first post, neither the vacuum tube used is 6922 but probably EF86.

 

[abbey road d enfer]

If we refer to the schematic from the first post, neither the vacuum tube used is 6922 but probably EF86.

??? I see a dual triode, both sections paralleled, not a pentode...
Check post #18.
The plot thickens...

 

[Gus]

Looks like wing C EF86 tube
SO maybe the schematic in this thread is another version of the VMA

 

[bobtheninja]

…and the PSU

 

[rock soderstrom]

Thank you for the photos. The mains transformer is apparently shielded with mu metal! This is probably also from Pikatron. ( but Haufe also build such models). Would be interesting to know if this and the output transformer are also sold separately by Pikatron.

 

[Jesper Findshøj]

Sorry for the delay! Here’s the guts of a VMA. I know I know, we should get a fancier tube, pretty sure that’s been replaced before I started working here. Do you want to see the PSU as well?
View attachment 90300View attachment 90301View attachment 90302View attachment 90303View attachment 90304

thx for these great pics, makes it clear to me that my VMA is a totally other version...
can you se the value of the cap to the left of the tube ? the caps on each side of the tube is the to decoupling the cathode, and the mode switching is putting them in series..
thx in advance

 

[Gus]

thx for these great pics, makes it clear to me that my VMA is a totally other version...
can you se the value of the cap to the left of the tube ? the caps on each side of the tube is the to decoupling the cathode, and the mode switching is putting them in series..
thx in advance

The schematic in the first post has the caps being switched in parallel.
Can the person who traced the schematic check the voltages?
I am curious if I guessed close the correct voltage readings

bobthenija

Can you post the color codes on the resistors in your microphone pictures?
I am not sure of some of the colors (maybe my monitor is off in color rendering)

Also is a component behind the two orange caps?

 

[Gus]

So is the 6DJ8 version a revision of the VMA or a special build or?

 

[Gus]

I forgot to ask does the B+ voltage change when changing from VM1 to VMX mode?

 

[Gus]

any updates