79 SFVR

[Smokebreak]

This is my main gigging amp, and I cracked it open today to see what's going on, as I love it. I also wanted to see what was going on with that awful pull boost, out of curiosity. So the PI seems like a mishmosh of various designs, and I can't find a schematic that matches. 330K grids, 680r cathode, and both grid caps are .01. Standard 820r/22K/100r FB. I'm curious as to what the circuit designation is, if anyone knows...

The pull boost- so the 220K grid leak on the vibrato channel's 3rd stage has a series 10K to it, and then to ground. At the junction of the 220K/10K the pull boost connects that junction to the reverb input, the green lead on the reverb tranny. Is it basically sending the signal through the reverb recovery stage?

Cheers,
J

[PaisleyTube]

'79 schematic shows the same pi-values, gotto look for the pull-circuit-values...

[Smokebreak]

Ah I found the push -pull circuit on a deluxe of the same era http://www.studiosoundelectronics.com/s ... _schem.pdf so it's just adding the reverb recovery stage? I imagine that .003 coupler isn't helping

[PaisleyTube]

most energy/signal passes the reverb-recovery-stage if I do remember correctly, reverb ain't working no more if the boost is on?

[Smokebreak]

oh duh, that's right. Not sure about the reverb working or not with the boost. I actually never use either..well, reverb and trem sometimes. I was just curious about the boost circuit. It effectively lifts the 220K to ground maybe? I'm just not quite sure what connecting the reverb tranny's sec to the 220K accomplishes

[rdjones]

Ah I found the push -pull circuit on a deluxe of the same era http://www.studiosoundelectronics.com/s ... _schem.pdf so it's just adding the reverb recovery stage? I imagine that .003 coupler isn't helping

As long as the pull boost switch is not pulled out, it's completely out of the circuit and will not effect the tone.
No need to remove the components (contrary to "Google Voodoo").
The implementation on the Vibrolux is only very slightly different than the Deluxe but yes, the 'boost' signal is taken from the reverb drive stage.

regards,
reddog

[tictac]

I had Jim Campalongo's (Nora Jones) main amp, a SF Pro-reverb in for repairs years ago. It had that SF PI with the 33k plate loads. I offered to "Blackface" it but he was like..."don't change the tone of this amp! I like it the way it is!"

He really liked the natural compression the amp had when he cranked it up.

I believe the 33K plate loads were a better choice for the 12AT7 used in the PI...would that be correct?

TT

[PaisleyTube]

not all silverfaces suck

"better" is pretty subjective but lower plate-resistors give give a slightly better/sturdier current drive to the outtubes

mxing bf and sf stuff is also cool and/but I also know a lot of players loving their stock SFs.......