January 6th, 2010, 08:21 AM
I tried posting this in AmpCentral, maybe here is Better.
I would like it to be slower on the slowest setting, and less strong overall. Should I put in a lower gain preamp tube? Which one, not sure if both triodes are used for the trem, or how to tell looking at the schematic. Is this as sinple as popping out the 12AX7 and putting in a 12AT7 or AU etc? Also with a tub wit lower gain effect the speed ?
Not that I know how to read a schem., but it looks like both side are used for the trem circuit. Do is a 12DW7 something to consider for what I want to accomplish ?
January 6th, 2010, 10:27 AM
It's a Viibro Champ?
January 6th, 2010, 12:22 PM
Valco made Airline from the early 60s
January 7th, 2010, 09:09 AM
I gotta say, I am very surprised at the lack of help on this. I know there are tons
of savey amp modders that could help with this.
Y'all afraid to help me risk blowing up my amp I guess.
January 7th, 2010, 12:31 PM
Actually, after studying your schematic, I don't see any reason that you couldn't try to tame the tremolo with a tube swap. the second 12ax7 is only used by the trem circuit and both halves are being used. I'd suggest a 12at7 or 12ay7 as those tubes would be used in other amps should you not like what the tube swap does for the trem. tube swapping is probably the safest mod you could try.
January 7th, 2010, 01:40 PM
Tube-swapping will probably bring the intensity down quite a bit, if not too much. The speed depends on the .01/.01/.03uF caps and the resistors attached to them. The math is quite involved, you might want to just try clipping resistors and caps in parallel to experiment and find something you like.
January 7th, 2010, 01:44 PM
That circuit uses a bias-vary against the cathode of a preamp tube, extremely similar to how the Vibro Champ works. The biggest difference is that your amp has no intensity control.
It might be possible to simply replace the on/off switch with a 1meg pot to control intensity. It definitely won't blow it up, but I'm not certain how effective it would be.
Now for a proper intensity control:
See the connection marked as "C" that goes from the cathode of the first preamp stage to the cathode of the second tremolo triode? In a vibro champ, there is a 68k resistor and a 25k pot inbetween those two. The cathode of the preamp connects to one of the outer lugs of the pot, the other outer lug goes to ground. From the center (wiper) of the pot, a 68k resistor goes to the tremolo cathode. Done!
To slow down the trem a bit, try replacing one or both of the .01uf capacitors in the trem section with .022uf caps. It's a commonly used trick on the very similar Vibro Champ circuit.