Vibro King questions

[MattT]

I was looking at the Vibro King schematic and I have some questions about it.

Am I correct that the signal goes straight into the Reverb circuit...and then the output of the Reverb circuit is blended/mixed with a buffered (but not amplified) version of the input signal...then it goes through the FX loop...and then it goes into the 'first stage' (which obv isn't the 'first' stage anymore...but it's what would typically be a Fender first stage)? And from there it's pretty much a typical Fender circuit (aside from the Tremolo...which may or may not be 'standard' for Fender...I dunno) except a bunch of values have been tweeked?

Just curious if I'm reading this right. It's...different. I have a Fender chassis that I've breadboarded stuff in and I was thinking of gutting it and making something like this. Any help appreciated.

PS - My amp/chassis is much lower voltage than a VK so I'm thinking the EL84-reverb will not be a problem. I've heard the VK takes that EL84 to it's limits in the stock amp...although a friend has an early one that he's gigged with for years and it's still got the original EL84 tube.

[jrfrond]

Yes, the Vibroking splits the input and sends part of it to a full-blown reverb circuit very much like the 6G15 reverb unit, mixing it with the dry signal later on (according to the level you have preset). It's one of the coolest features of one of the coolest amps (in my opinion, anyway) that Fender has ever made.

[cbarrow7625]

That is pretty much correct. They basically were trying to emulate having the old stand-alone Fender Reverb in front of a stock Fender amplifier. While not exactly the same, the Vibroking reverb circuit is essentially the same as the old stand alone unit. The stand alone used a 6K6 to drive the reverb.

There are some other differences in the circuit that are not "typical Fender". The first is that the tone stack follows the second gain stage, like the old bassmans.

The second is the tone stack values: 150pF treble cap, .047 Bass cap & .022 Mid cap with 25K pot. That's different than both Bassmans & the "typical" Fender setup.

The third is that .47uF bypass cap around the 2nd gain stage. Very un-Fender-like to use small bypass caps.

Last is the lack of feedback around the power amplifier.

This is a really unique sounding amp in the Fender line up. I worked in a music store back when they came out & got to play through it now & then. The combination of all the odd circuit design choices (for a Fender) made it kinda cool.

Anybody have one of these that can comment better on the tone?

[MattT]

Thanks jrfrond. How do you think the VK preamp into a no-NFB, cathode-biased, 2x6L6, GZ34 rectified (~390v B+) amp would sound? I've heard the VK doesn't have the most headroom but my intention with this amp is to have it be an amp that gets great overdrive with pedals...so having the amp cooking and 'right on the edge' at reasonable volumes is desired. Not really looking for clean headroom.

This chassis has 6 preamp tube sockets total...so that's why I wasn't considering a Tweed amp (which this power section would probably suit well).

Thanks cbarrow. Regarding the tone...I haven't played my friends VK but I've seen him gig with it many times and he also sometimes uses an early SF Deluxe Reverb for smaller gigs. In this particular case...the VK sounds every bit as good as the DR...IMO the OD (via pedals) is better with the VK.

[mikeboone]

I had a VK and it is a monster!!! I played it with a Fulltone OCD as my overdirve pedal and had the single greatest blues tone I have ever owned.

I got rid of it because it was one of the originals with the EL84 reverb driver and that part of the circuit was very unstable. I didn't want to mod it so I sold it for money to buy parts for some build projects.

[jrfrond]

Thanks jrfrond. How do you think the VK preamp into a no-NFB, cathode-biased, 2x6L6, GZ34 rectified (~390v B+) amp would sound?

I actually think it would sound pretty damn good, though I don't have a VK to experiment with. I would do a mod like this in stages: first the cathode-bias, then the rectifier, IF it needed it, because sometimes cathode-biasing alone will inject enough feel.

Yeah, the VK is way cool, as is the Tonemaster, it's dual-channel "Evil Twin".

[MattT]

I actually think it would sound pretty damn good, though I don't have a VK to experiment with. I would do a mod like this in stages: first the cathode-bias, then the rectifier, IF it needed it, because sometimes cathode-biasing alone will inject enough feel.

Yeah, the VK is way cool, as is the Tonemaster, it's dual-channel "Evil Twin".

The amp is already cathode-biased and tube rectified. The power section and power supply is already in place and I was hoping to not change it. Just remove everything from the eyelet board and redo the preamp per VK (which also involves the Reverb tranny, pan, and phono jacks).

I looked last night and there's just not much room for the Reverb tranny unless I go with 5 preamp tubes (instead of 6) so I think I'm gonna ditch the Tremolo and just put a 220K in it's place.