biasing 1966 BFSR

[tedro]

i have the on/off switch mod on my tremelo intensity pot. does it matter which position this is in when i bias?

[Jazz P Bass]

The Tremelo itself should be Off when adjusting the output tube idle current (bias).

[tedro]

The Tremelo itself should be Off when adjusting the output tube idle current (bias).

yes, the tremolo is OFF, even without the switch set to off it is of course zero'd --as much as hat may be OFF. BUT this [modification] added switch does MORE than just turn it off ...are you familar with this Fender style mod? here some info on what i have:

"Tremolo disconnect mod - More preamp gain in vibrato channel.

"The effect of this mod is similar to pulling the V1 normal channel preamp tube when you only use the vibrato channel. This is also a very popular mod in the AB763 circuit (Super, Twin, Virboverb, Pro Reverb, Deluxe, Vibrolux). The tremolo circuit will draw current from your signal path whether it is in use or not. Hence, it reduces some of the gain that has been added by the preamp tube stages. This mod does not increase the amp’s clean headroom. We would describe the effect as making the tone richer, fuller and more powerful with stronger mids that pushes the power tubes harder. This mod provides a noticable volume increase (and a bump) when enabled.

"This mod is one of Cesar Diaz’ tricks in the Fender Custom Shop. This mod can be implemented in two ways, either by unsoldering/disconnecting the tremolo circuit or replacing the tremolo intensity pot with a swicthable pot, so-called SPST pot."

i have the latter. it's a GREAT mod, very noticeably richer harmonic content (and resultant volume bump, but you can turn it down and retain that richness).

[MWJB]

Jazz P Bass means that the tremolo should be switched off, either at the footswitch, or via your intensity pot switch, when bias is set. Not with the circuit enabled and the pot set to zero, because this is not "off" and you will still see some fluctuation in the idle current.

I don't know that this mod can be traced directly back to Diaz?...It's a very well & widely known mod.

[tedro]

thanks, i'll test both ways. without this "replaced with a 'switchable' pot" mod, of course the trem is "off", i.e., at zero or without the footswitch turned on it won't work, in both of those scenarios it is still in the circuit, from what i understand.

afa the "Diaz" thing, that was a quote. i guess anything related to SRV gets automatic cred., thus i deleted the SRV sentence. :-(
i'm too old, a day late and a dollar short. semantics screw me every time. i can't even answer math questions without questioning the wording.

i'm assuming that i even get the last response. apologies in advance.