Kendrick mod to Vibroverb

[rooster]

I just worked on this amp and thought some of you might want to see this. Gerald Weber either did the work personally or supervised it - not clear on this. The Kendrick work order exists.

Of large note is the Solens cap tacked onto the output coupling section. The stock cap is 20uf and under the can, but this is 10uf and added here, grounding to the control panel brass plate, and attaching at the junction of the 100K/82K resistors. I have never seen this done before and am not clear what it brings to the amp. My question to you is this: You seen this before anywhere? The fact that it is a Solens poly cap says it's going to speed up the power supply a bit - and maybe alter the stock Vibroverb deal a bit. Which is actually weird to consider? Who would risk doing this in a collectable amp? He could have easily tagged a 20uf Sprague in there with room to spare, so I think the Solens was a dilberate choice.

He also increased the two stock 1.5K resistors found on the power tubes to a value of 5.6K. Was this just something he does to BF amps?

I also see the other things he is known for done here, too, but the Solens thing really surprised me. Comments/thoughts?

[jjman]

One of the best amps I've heard was a Kendrick. But some of the "improvements" he's advocated over the years have seemed silly to me, at least for guitar amps.

[Cliff Schecht]

Not sure why he's using a Solen there, perhaps it is for speed (aka different feel?) or stability.

Maybe the 5.6k was put there so EL34's wouldn't oscillate in the circuit. Just a guess as this is a typical EL34 grid stopper value.

Also it's good to see that while he did a few modifications to the amp, he in no way butchered it like some of the other modders seem to like to do..

[billyz]

I have it on good authority that Kendrick uses very highly skilled persons other than Gerald to do most of the work.

[rdjones]

Maybe the 5.6k was put there so EL34's wouldn't oscillate in the circuit. Just a guess as this is a typical EL34 grid stopper value.

I see no connection made at pin 1, so ...

I can only guess that increasing power grid stoppers has become quite the popular mod (and design trait), allowing the amp to more tolerate being overdriven.

rd

[phsyconoodler]

Who said it had EL34's anyway? Increasing grid stoppers is not a 'blanket' thing done to fender amps.It's just to help with any oscillation that might occur.
I can only guess what that solen cap is for.??

[dreric]

Mod a Vibroverb????????????????????????

Seems slily to mod one of the most collectable Fenders on the planet. If you didn't like it why not sell it to a SRV devotee and buy three amps?

Did he drill a hole to mount the solen?

What does the added switch on the intensity pot do, vibrato on / off?

Eric

[Cliff Schecht]

Who said it had EL34's anyway? Increasing grid stoppers is not a 'blanket' thing done to fender amps.It's just to help with any oscillation that might occur.
I can only guess what that solen cap is for.??

Nobody said anything about EL34's, it was a guess. I didn't even think about the pin 1 connection missing..

[tictac]

Adding the 10uF to the 20uF Filter for the PI = 30uF, Looks like a 0.02uF on the PI input, then the 5.6k grid stoppers...

Looks like some sort of Marshall /Tweed Bassman Mod; check out an old JTM45 schematic...

TT

[Cliff Schecht]

Adding the 10uF to the 20uF Filter for the PI = 30uF, Looks like a 0.02uF on the PI input, then the 5.6k grid stoppers...

Looks like some sort of Marshall /Tweed Bassman Mod; check out an old JTM45 schematic...

TT

This is why I was thinking el34..

[rooster]

OK, let me clear some things up.

The switch on the vibrato pot is to turn the vibrato off, yes, a Diaz thing for SRV's Vibroverb. The OD PI coupling cap is .001, not .02.

As to modding the amp, well, it's always a mixed bag. Diaz replaced the OT with a BFBassman version, so 4 ohms here, (which always threw me because SRV used an 8 ohm JBL). He also lost the tube rectifier and changed the grid stoppers at the input to 100K, and SRV used a 5751 at V2. Whatever else was done, what caps were changed etc. I can't tell you. But of course I can tell you most collectors would put a much much higher value on SRV's personal Vibroverbs than on any minty version, eh? So here the lines blur. If you are into SRV and want to approach his sound, you have to consider his mods I think.

I should add that the OT on this particular amp seems to be Pacific to my eyes, although the build sticker was removed. What remains are the typical two (three?) small white circular stamps that you see on the Pacific trannys. Also, FWIW, it is a single tap output and a bigger piece of iron than the stock OT. And yes - from what I was told - this was also put in by Kendrick at the time of the other work. If I didn't say it before, the amp sounds pretty good running through an EVM15L, the speaker currently in the cab.