Fender Vibro King circuit

Fender

collins_ji--(at)--andem.com (Jim Collins)
wrote:
CO>fat. I love it. Anyway, the biggest knock on the amp when it first came
CO>out was that the FAT feature was not footswitchable. Imagine my surprise
CO>when I unboxed the beast to find that our friends at Fender have been
CO>reading their mail. The FAT feature is now footswitchable. The amp comes
CO>with the same dual footswitch that the reissues come with, only the two
CO>features that are footswitchable on the Vibro King are the tremolo and the
CO>FAT. Reverb is not footswitchable.

I have studied the schematic for the Vibro-King at length, and it might
be of interest to the more technically inclined readers of this group
that the famous FAT switch is nothing more than a switch that grounds
a 22 uF bypass capacitor across the cathode of the first gain stage.
This is an OLD trick, although I'm not implying that that makes it any
less useful. A good tech could convert the #2 input jack into a foot-
switch jack for the FAT function in minutes... something you owners of
Vibro-Kings might want to consider, once your warranty expires.
It's also easy to make the reverb footswitchable without altering
the amp in any way. All you need to do is rig up a pedal to ground
the hot lead of the return from the spring tank. You could use a
"Y" adaptor to hook up the switch in parallel with the reverb
return cable.
Here are some more comments on the Vibro-King's circuit:
1) In a break with Fender tradition (at least Fender tradition since
the late '50s), there is NO negative feedback loop. This might explain
why the amp is gaining a reputation for volume and harmonic richness.
2) The reverb section is NOT an exact copy of the old standalone Fender
reverb unit, although it's close enough. It uses a 6BQ5 for the reverb
driver and one triode preamp before the driver, unlike the original
with two triodes before the 6K6 driver. The recovery circuit is also
slightly different. But like I said, it's close enough; it embodies
the overall "spirit" of the original.
3) The tone stack is an inspired variation on the old "Blackface"
circuit. It uses a 150 pF treble cap instead of 250 pF (something I've
been doing to my stock Fenders for a while, since I think the 250 pF
emphasizes the high mids too much) and a larger-value midrange pot
(25K, I believe, although I don't have the schematic handy). The
volume control comes BEFORE the tone stack, and is separated from it
by the second gain stage. The treble pot wiper is connected (via
a coupling cap) to the grid of the phase inverter.
Overall, it's a surprisingly simple circuit.

---
þ OLX 2.1 TD þ /\/\Dr.Distortion/\/\/ , New York

Index:

1974 prices	3 Spring Reverb Tanks	3 Wire Cord installation	5R4 not enough current
5V4 in BF Deluxe	6550s in Super	68 Princeton Rectifier	68 Super Reverb
6L6 in Champ Again	6L6 in Deluxe LV	6L6 in Deluxe Reverb	6SC7 to 12AX7
6V6 In 6L6 Amp Test	6V6 in Showman Test	6V6s in Super	AA vs AB 763
AA763 vs AB763	Alternative Switches	Bad Fender Mods	Bandmaster Cathode Bias
Bassman 10 info	Bassman Head Running 2ohms	Beef Up Tweed Champ	Birth of Fender Reverb
Blackface Cabinet Dates	Blackface Pro	Blame UL	Blues Deluxe review
Brown Bassman Transformers	Brownface Trem Pulse	Brownface Tremolux Cabinets	CBS Deluxe Reverb Changes
Champ 8ohms	Champ problems	Champ speakers	Champ Transformers
Choke Specs	Clean Ckt Board	Concert Head Footswitch	Dead Amp Checkout
Deluxe Cathode Bias Mod	Deluxe reissue vs original	Deluxe Tweed vs BF	Design Eras
Detailed AB568 test	diy	Dr Z Harp Amp Mods	Early Blackfacing
Ed Jahns Xformers	Eyelet Board Problems	Faceplate Restoration	Factory Mistakes
Fender 6V6 Overvoltage	Fender AA568 circuit	Fender Alternative Footswitches	Fender Amp Covering
Fender Amp Dating	Fender amp tremolo	Fender Amp Tremolos	Fender bad Supers
Fender BF Bassman mods	Fender BF SF changes	Fender Bias Pot Failures	Fender Bias Schemes
Fender Blackface	Fender Blues Deluxe Settings	Fender brownface topology	Fender Cap Replacements
Fender Channel Coupling Caps	Fender Combo Reverb trick	Fender Concert Reissue	Fender Concert Tremolo
Fender Correct Tubes	Fender coupling caps	Fender decrease reverb mix	Fender Deluxe Power Trans
Fender Deluxe reissue	Fender diodes	Fender Ext Spkr Jack	Fender Grill Cloth
Fender ID circuits	Fender Input Jacks	Fender Midrange Knob	Fender neg feedback
Fender Normal Channel	Fender replacement parts	Fender Reverb Both Channels	Fender Reverb FX loop
Fender Reverb Reissue	Fender Reverb Transformer	Fender RI Reverb mods	Fender RI Reverb Tube
Fender RI Reverb Tweaks	Fender SF vs BF	Fender Silverface facts	Fender speaker recs
Fender Super 60 price	Fender Super pricing	Fender SuperChamps	Fender The Twin
Fender tone circuit boost	Fender Tone Circuit	Fender Tone Circuits	Fender Transformer Codes
Fender Treble Caps	Fender Tube Chart Dates	Fender Vib Rev Pedal	Fender vibrato pot
Fender Vibrato Ticking	Fender Vibro King circuit	Fender Vibrolux RI review	Fender VibroVerb
Fender Was Dumb	fender	Footswitch specs	Grid Blocking
Homebrew Vibroverb	Invert normal channel	Knob Changes	More Pro Reverb
Narrow Deluxe Chassis	No 5R4s	Normal Channel Delay	PA 100
Pot Tapers	Princeton Adjustable Bias	Princeton driver mods	Princeton Mods
Princeton PI Headroom	Princeton PI Heater Cathode v	Princeton PI Mod Layout	Princeton Reverb Power
Princeton Reverb Tweaks	Princeton tone bypass	Princeton Vs Deluxe	Princeton with 5881s
Pro Reverb baffles	Pro Reverb History	Pro Reverb Orig Speakers	Pro Reverb Parts
Pro Reverb Questions	Pro Reverb Speakers	Pro with a 15	Proper Blackfacing
Pull Boost Failures	Red Knob Twin problems	Reduce Champ Screen Voltage	Replacing Glued Baffles
Restoring Grille Cloth	Reverb Amp Effects Loop	Reverb Fixes	Reverb Pan Bottom
Reverb Trans Specs	Reverb Unit Mods Page	RI Bassman Mods	Rivera Designed Fenders
Scrape Vibrato Pot	Screen Resistors	SF Deluxe mods	SF Deluxe Reverb Questions
SF Reverb Cathode Resistor	SF Vibrolux Changes	Shielding Plate Problems	Showman vs Twin
Silverface Changes	Silverface Pro Reverbs	Small Trannys Sometimes Better	Super Champ 6C10
Super Molestation	Super Too Much Bass	Tolex Repairs	Tremolo Tick Tips
Tweed Champ Filter Caps	Tweed Deluxe Bypass Cap	Tweed Deluxe Transformers	Tweed Twins
Twin Reverb History	Twin Reverb overdrive	Twin Reverb Variants	Vibrato Click Fixes
Vibrato Tick Svc Bltn 9	Vibro King fat switch	Vibro King info	Vibroverb tone
What is Hi Pot	What Makes Fender Sound	What Was Ice Cube	Why 68K Input Resistors
Why No More Cloth Wire	Why Silverface Changes