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Discussion Starter #1
I recently picked up a vibro king. Sounded great testing it out. I ended up leaving with it. Loaded it into the trunk of my car and drove 2 hours home with it.

Fired it up once I got home. Johnny Marr jaguar plugged into channel 1, dwell, mix and tone at 3 o'clock and volume at 9 o'clock. It's sounds like shit. So distorted and not in a good way. Turn all the reverb controls off and the amp sounds wild, super clean and crisp.

Start slowly adding the dwell and it starts breaking up at about 1 o'clock.

I bought a new 6v6 reverb power tube, replaced the RCA cable and checked the reverb tank for any broken solder joints. Still the reverb distorts. A bias issue?
 

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Very unlikely to be a bias issue. I take it that it did not sound this way when you tested it out.
Most likely culprit is the tank, like you suspected.
Did you check that all the springs in the tank are still connected at both ends?
None of the little wires to the transformers inside the tank are broken?
These are the most common things to go wrong with reverb during transport.
Do you have an ohm meter that you can check the resistance at the tank jacks? Or another tank you can swap in?
 

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I dont understand this...."I bought a new 6v6 reverb power tube".
Im the last guy on earth to offer advice on tube amps cause I only know when they are working right.
BUT a 6v6 power tube that runs a reverb doesn't sound right to me.

Someone else will have to explain it.
G.
 

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Discussion Starter #4
Yes I have a meter and will be testing the reverb tank tonight. Also the 6v6 is the stock tube that powers the reverb. You can run a 6k6 like the original 63 reverb stand alone tanks had also.
 

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Discussion Starter #5
What also strange is that when I put it in channel 2 with all 3 reverb controls full on it doesn't get distorted even when I increase the volume. The reverb with a single coil guitar in the 2nd channel is definitely not as splashy/crashy as it should be with full on reverb. The 1st channel is but distorted.
 

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I don't know that this schematic is identical to your amplifier, but it shows an EL84 as the driver for the reverb pan. It is unlikely you could have inadvertently installed a 6V6 where an EL84 should go because the pin spacing/layout is different. But that said, clearly a low-power power-tube is used as the driver.

https://farm1.staticflickr.com/661/22292660395_97df52628b_o.png

I'm not especially well-versed in the tube arts, but while a 6V6 may be able to simply plug and sub for a 6K6, perhaps the manner in which the gain/output of the driver tube is set makes a 6V6 push the pan too hard in some way.
 

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Discussion Starter #7
The stock tube that comes in this version of the vibro king is a 6v6. The older version used a el84. I think it is a tube that's being driven to hard and that's why its breaking up. For the reverb there's only 3 tubes. 6v6 and 2 ax7's. The 6v6 had been replaced with a new jj tube, the ax7's have been swapped around with the other 3 that are used in this amp also. I'll have to get the meter out tonight and check it out when I get home.
 

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My understanding is the earlier EL84 reverb tube ran very hot. Fender changed it out to the 6V6 for longer life.
Here is my old Vibro King, a 1994 year, if I recall. Check out the heat signs around the EL84.



In terms of fixing the reverb, you should start with schematic. Follow the reverb path. It's unique design, not like any other Fender combo amps that I know of. They plunked the 6G15 reverb tank circuit in the Vibro King.
Trace out the reverb path in your chassis and measure every component to see that it is in spec. Don't forget the pots too. Check resistance and voltages where shown on the schematic. Check all wires. Re-flow any suspect. Replace any old suspect e-caps. Remove and inspect the tank, all connections.

While you are in there, this below needs to be addressed. These two need to be separated. The white block resistor gets dang hot, and will damage the adjacent cap. Before and after, below.

Saying all this, If you have little experience around high voltages, you
have no business going into the amp. Lethal voltages are present.




Just for fun, here is what you are getting into.

 

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Discussion Starter #10
I'm going to swap the tank with my brothers hot rod deville and see what that does.
 

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Discussion Starter #11
Hey cool I will take a look tonight with my meter. I pulled the chassis out last night just to inspect and see if I can find anything obvious. I'll separate that resistor and cap as you have pictured. Just weird that the reverb works and does not distort with the same guitar plugged into the 2nd channel. Obviously I don't have the same volume but even when I turn this monster past 3, the reverb doesn't break up.
 

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I grabbed the schematic listed above. It shows the earlier EL84 reverb tube. If you look you'll see that input 1 and 2 do the same thing. They go into V1. Input 2 only, has a 1M resistor across it to tame an overly hot guitar like my smoking humbucker equipped ES335. (If wanted. However I still like to use input one for plenty of gain on tap).

The symptoms you tell me, about it only distorting in channel 1, indicate an overly high gain signal may be happening in your pre-amp. The 1M resistor on channel 2 might be pulling things down a little closer to normal, and not driving the reverb circuit too hard? Not causing distortion? Just a guess. There are better techs here than me. A failing e-cap, (a cathode cap), or cathode resistor on one of the pre-amp, or reverb tubes could be a culprit. This could add more gain. The signal line, I partially traced in red. The items I circled in green, I would start out checking. Especially the caps shown. That's a good start, then go from there.

An even better start would be to get the correct 6V6 equipped schematic and use it. Not the one shown below for the EL84.

You'll also see the line in signal splits before V1A. Part of it goes to V2A. I did not trace this, however I'd be inclined to also check cathode cap and resistor there.




PS: You may or may not know that you cannot test a resistor that is wired in parallel to a cap. The cap holds voltage and the meter cannot read the resistor. Best to lift one end the resistor to check it's value. These conditions are found at the cathode resistors.
 

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Discussion Starter #13
Wow, thank you! I have a good time a head of me tonight. Your guess is as good as mine for channel 1 having a issue with gain. I mean it's a signal coil jaguar but again it's the Johnny Marr signature with the bare knuckle pickups. I'll let you know how I make out. I'll first swap reverb tanks and then preamp tubes, then I'll pull the chassis out if it's still messed up.
 

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This is interesting: Look at the cathode resistor for the EL84, the reverb driver tube, in my schematic above. R69 is the reference. This resistor, is 680 ohm at 5W. Circled in green on my schematic above. Look at the cap, labeled C3 parallel to it. 100uF/100V.
Guess which two I suggested you move apart? Yup, these very two. Maybe, just maybe, C3 is cooked from the heat from the 5W resistor right beside it as I mentioned. This sets the gain for the reverb tube. Might as well line up a new proper resistor and cap, replace and separate them regardless of what the fix turns out to be.

The circuit board on my '94 Vibro King has the schematic reference numbers printed beside the components. So its pretty easy to find the part location, as referenced on the schematic.

The correct 6V6 reverb equipped schematic can be seen here: https://schematicheaven.net/fenderamps/vibro_king_manual.pdf
 

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Discussion Starter #15
I had the chassis out last night and looked at the cap and resistor you are talking about. I'll definitely be replacing those and get them away from each other either way.
 

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Discussion Starter #16
I did take a few pics last night, that cap and resistor are already separated like the pic you posted. I can't post pics for some reason.
 

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Discussion Starter #19
It's fixed! Easy fix at that. Just swapped out the reverb tank from my brothers deville. It's such a killer reverb. I gave up my bassman and reverb tank for a guitar deal. Then traded a cs tele for this vibro king. So kind of disappointed when it didn't work!

I'll have to pick up a reverb tank. Any suggestions on what brand or just pick up a stock replacement?
 

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I've had really good luck with MOD replacement tanks. To my ears, they just sound sweeter than OEM tanks supplied by Fender...
 
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