Tremolo Thump - 64 Deluxe

[Valvehead]

Got a 64 deluxe reverb up and running and it has a loud thumping in the tremolo---not the usual Ticking sound. Ive tried everything i could find online to fix it =

moved all wires around v5/v6
tried a .01 cap across the bug and across the 10 meg res.
installed a shielded cable from v5 to the bug
re-routed the 3 wires from the trem circuit to the 2 pots
swapped out the v5 tube

adding that .01 cap makes it worse!

So , could it be a noisy bug/light ?? or maybe the caps in that circuit ?

[SoulFetish]

Two things: did you try swapping out either the oscillator tube (V5) or the mixer/recovery tube (V4)?
the other thing I’ve made a strange discovered when chasing this symptom around some Fender amps. I’ve had some wild trouble shooting sessions, but they are usually models of the wax board era.
And it’s this: I believe this to be caused by a pulse loop in the AC ground currents. I think Fender’s design and layout in the Tremolo switching, make some amps susceptible to this problem.
Okay, try this; the Oscillator cathode resistor on V5 is 2k7 and bypassed by a capacitor. This is grounded to the same node as both cathodes on V4. Lift the Bypaas capacitor, or both 2k7 cathode resistor and bypass cap, and ground them at the ground lug in the Vibrato Switch RCA jack at the back of the chassis. This will kill that thump.
Now, here’s the obvious observation, obviously having gone through those experiences, I now understand why fender actually built some of their later models using this particular ground location for that triode. I can only imagine some of their techs scratching their heads and going through all the steps both you and I have done.
But earlier on in my tech career, I could not figure out why Fender did that in some amps. It seemed counterintuitive and anathema of what I understood to be the modern corrected approach to physical ground layouts in audio amplifiers. I would actually often change the layouts back when i would see it.
I wonder the fiber boards start to suffer some contamination in amps that are sensitive to this and develop the problem.
Anyways, hope this helps you out. Try this and report back

edit: i was able to fix the last amp by just grounding the bypass capacitor to the RCA jack after trying everything else I could think of.
I actually took a video to demo the audio, what we were trying, and ultimately the fix so we could catalog the repair, and post it for the others who might encounter this problem as well

[Valvehead]

Thanks for the info !!!

ive swapped several tubes at v5

the v5 cathode cap is already grounded to the trem jack.

i moved the 2.7k to ground at the same spot


no change at all .

cant upload a vid for some reason........ sounds like rumble strips on a highway...not a ticking.

[Helmholtz]

As it's very low frequency I suspect coupling via the power supply.
Especially check the filter cap after the choke which connects to point B.
To test just parallel a known good cap.

Are output tubes balanced?

[Valvehead]

As it's very low frequency I suspect coupling via the power supply.
Especially check the filter cap after the choke which connects to point B.
To test just parallel a known good cap.

Are output tubes balanced?

im out of 6V6 -ive got 3 here and can only get the bias at about 20ma one side and 10ma the other.....always 10ma difference. ( 3 different brands and all are used)

Ill start clipping in filter caps today --they are all original in the doghouse and none are visibly leaking. i do have some .02 / .01 caps for the trem circuit i wanted to try also

[Helmholtz]

If the tremolo is working there's no need to replace LFO components.

My theory is that the LFO plate current is modulating the supply voltage at point B.
This is possible if the filter cap there either has high ESR or lost capacitance.
A modulated supply voltage at point B modulates the screen voltage and if power tubes are not balanced, the LFO signal will be amplified and appear at the output.
With balanced tubes this common mode signal would be suppressed.

[Valvehead]

Found another 6v6 , bias is pretty close now 20/22ma

clipped in a 22uf across each 16uf filter cap 1 at a time = no change in noise at all

[Helmholtz]

[Helmholtz]

I hate to mention it, but it might even be a conductive board.

[Valvehead]

https://www.youtube.com/shorts/vv5BdV7_nuA

[Tom Phillips]

https://www.youtube.com/shorts/vv5BdV7_nuA

Maybe there is another way to view this video. I get

[Helmholtz]

Neither allows me to view the video.

[Helmholtz]

Scuse me if I missed something already mentioned, but..
- Does the thumping frequency correlate with the tremolo frequency?
- Does the thumping disappear with the tremolo off or intensity at zero?
- Does the thumping disappear with V5 pulled?

[Valvehead]

Try this =

https://www.youtube.com/shorts/vv5BdV7_nuA

[Valvehead]

- Does the thumping frequency correlate with the tremolo frequency? yes
- Does the thumping disappear with the tremolo off or intensity at zero? it goes to a tick , no low end and quieter , but still there
- Does the thumping disappear with V5 pulled? Yes

also , the noise is there with volumes on 0