Fender custom Vibrolux Reverb

[trem]

This is one of the "Modern Day" amps with a PCB. It belongs to a friend of mine that plays.

First of all... Pardon me, but it has been a long time since i worked on a guitar amp. I have forgotten a lot of what little i did know.
Anyway..... two things.

1. There is no reverb.
What HAVE i done or checked.?
Tried different cables
The crash test, is that what it is called. Shake the amp, and i can hear the springs (a little bit) through the speakers.
I changed V3 and V4 a couple of times.
I tried a known working tank.
I actually still have a spare reverb tranny. I did not TRY that in the amp, i simply put an Ohm Meter on the new tranny and compared it the the reverb tranny in the amp. One side is almost shorted and the other side was 1.5 or 2k..... something like that.? Is that kosher, or do i need to install it.?
One side of the tranny (in the amp) has high voltage. Is that B+ from the phase inverter.?.....and then the other side has little or no VDC. That is normal... isn't it.?
The Cat resistor for V3. The schem says it should be 2.2k. This amp is 1k and there is about 3.5 VDC across it.

Do you guys have any ideas what i might Check/Do to fix the reverb.?

2. Power tubes.
My friend wants new power tubes. He gigs with this amp a lot and they have not been changed in 2-3-4 years maybe.
This might be more Academic than practical, but.......
Looking at the schem, i was going to change (If Needed) R58. But it is not on the main PCB. I am thinking that circuit is on the little PCB for the Tremolo circuit... with the pots for the Trem. I would rather not get into if i do not have to.
The power tubes grids are at about -41 VDC. Probably a little "Cold" for most players, but i should probably be OK with that.
Should i just install the power tubes and leave the bias where it is.?
That is all part of that Bias-Vary trem circuit....right. I should just leave that be.?

Thank You So Very Much.!

Sorry..... the schematic

https://el34world.com/charts/Schemat...lux_manual.pdf

[Randall]

Does this amp have reverb in/out jacks? If so, try swapping them, hearing the "crash test" only a little can be a symptom of reversed jacks. If that doesn't work, unplug the cables at the tank. Touch them both with your finger with the reverb control turned up a bit. If one of them makes a good buzz in the speaker, then you have a good recovery stage. Then connect the other cable to the input of another amp. Any signal applied to the Vibrolux input jack will appear at the second amp if the reverb send stage is working. If both tests are good, it's the tank. If one test fails, concentrate on that stage.

[vintagekiki]

There is no reverb.
What HAVE i done or checked.?
Tried different cables
The crash test, is that what it is called. Shake the amp, and i can hear the springs (a little bit) through the speakers.

Remove the footswitch from jack on amp (J5)
Check that the in and out RCA/Cinch connectors on reverb tanks are not mutually replaced.
Check that some of the cable reverb are not open or shorted.
RCA/Cinch connector with 1.5 or 2k goes to reverb out connector on amp.

[trem]

Sorry..... i can hear the reverb springs A Lot. I was just being too wimpy with the crash test.
I have looked at all the connections and swapped the cables.
Let me try some of these other things.

The foot-switch, for the reverb, that just turns the verb Off and not On.?
That is to say, the verb will work without the foot-switch.

The reverb is also VERY noisy after the knob hits the half way point.
Is that indicative of anything.?

Thank You

[vintagekiki]

Question

- Does the reverb work when the guitar is playing.
- If you disconnect the reverb cables from the amplifiers, does the noise change when the reverb knob is moved.
- Check the RCA / Cinch connectors on the reverb tank in reverb bag for no oxidation. At the same time check the thin wires on in and out coils in reverb tank that they did not break off.

[trem]

Question

- Does the reverb work when the guitar is playing.
- If you disconnect the reverb cables from the amplifiers, does the noise change when the reverb knob is moved.
- Check the RCA / Cinch connectors on the reverb tank in reverb bag for no oxidation. At the same time check the thin wires on in and out coils in reverb tank that they did not break off.

With the Verb all the way on, there is just a Slight amount of reverb.
I have swapped in a new tank, and tried new cables, and they do not work either.

Just to clarify... i have changed the tubes twice, and i have normal VDC on the Cats and Plates of V3 and V4.

" If you disconnect the reverb cables from the amplifiers, does the noise change when the reverb knob is moved."
I will give that a try and let you know.
Thanks Again

[vintagekiki]

" If you disconnect the reverb cables from the amplifiers, does the noise change when the reverb knob is moved."
I will give that a try and let you know.

Don't try it
Now I've seen that reverb cable is soldered directly to the PCB.

Disconnect amplifier from the AC outlet.

Disconnect reverb cable from reverb tanks.
Check that the reverb cables shield is not interruption.
Check with ohmmeter that the reverb cables is not shorted or interrupted (page 7 reverb cable detail)

[trem]

Well, you were on the right track. I should have seen this sooner, sorry for wasting space on The Forum.
He needs a new RCA Jack. Not sure what you call it, but the jack that gets The White Cable from the amp to the tank...that is loose and the two solder lugs were touching down at their base on the jack.
They had slowly moved around, toward each other and were shorting out.
Kind of embarrassing, but i have not done this for awhile, i should have checked all the "simple stuff" first.....but i guess i have forgotten what the simple things are.
I feel bad for wasting your guys time.
Thank You All Very Much

[g1]

It's never a waste of time as long as you post your resolution, that way it's there for others who could come up against the same issue.

[J M Fahey]

Glad you solved it

[trem]

Glad you solved it

Yes... Thank You.

[vintagekiki]

Should i just install the power tubes and leave the bias where it is.?

Each change power tubes implies the adjust bias (quiet current) for changed tubes.
Adjust quiet current is made by changing resistor R59 to required value.

https://music-electronics-forum.com/showthread.php?t=8291
About biasing tube guitar amplifiers

[trem]

Right..... but Fender did not make it easy. You have to pull the two Trem Pots off the front of the chassis and turn the little PCB over so you can get at that resistor.
It is not the end of the World. But for a fixed-bias amp, you would think Fender might have put the bias circuit somewhere that was more accessible.?
I was thinking to install the new power tubes and see where the bias is at. If they are not too hot or cold, it should be fine.
I was thinking that with -41 volts on the grids, i am probably not in danger of red-plating the new tubes. So i should have time to check without doing any damage to the new tubes.?

[vintagekiki]

If original Fender Tube (5881/6L6WGC PART# 039214) is used, re-biasing is not required (Custom vibrolux parts list/ page 4)

[trem]

If original Fender Tube (5881/6L6WGC PART# 039214) is used, re-biasing is not required (Custom vibrolux parts list/ page 4)

Other than those being a 6L6.........
My friend bought a matched pair from Ruby Tubes. They are a tall bottle 6L6 made by J/J