Weber 6a14hp buzz when reverb is on.

[Suprolofi]

I have a weber 6a14hp that has a weird buzz on the low notes. The buzz goes away when the reverb cables are disconnected or the reverb tube(12at7) is pulled. This is new build. The amp builder is a skilled tech and could not figure out what the problem is. All of the obvious things have been tried - a different reverb pan, tube, driver, connections and resistors in the reverb circuit, speaker. Two other techs have checked it out and cannot find the cause. Any ideas?

[slowhand]

Hi Suprolofi,

how is the reverb tank mounted? Is it mounted with screws to the bottom of the cabinet or is it tucked into a bag?

I tuck my reverb tanks into a bag (like a tuki) and staple that to the bottom of the cabinet.

[Suprolofi]

It's in bag on the bottom of the cab.

[Suprolofi]

I forgot to say that the ot on this amp is different than the standard 6a14hp - it's Allen Amps to25. The buzz is like a farting out sound on low notes when the volume is above 5 and a half. Im running nos tung sol 6v6's and a gz34 rectifier.

[Diablo]

Try plugging the chassis into an extension speaker to isolate the chassis, tubes and reverb pan from speaker vibration. See if it still makes the buzz.

[Suprolofi]

I have plugged into a couple of different cabs and the buzz remains. Could this be a grounding problem perhaps?

[tubeswell]

Couple of thoughts:

Did you try another 12AT7 reverb driver?

Is the signal cable to the reverb driver grid shielded?

Is the tank cover connected to the chassis ground by one cable shield only?

Are both the RT and the OT covered with end bells?

Where is the RT primary grounded?

How is the OT mounted w.r.t. the RT laminations?

(Sorry that's more than a couple)

[Suprolofi]

I know I tried a couple at7s in there... The cables look like normal braided ones. The rt is basic little fender rt with no bell. It was replaced with a heyboer. As far as the other things go I am not sure. I am not a tech but I can open her up and check. Thanks alot for the suggestions!

[Jazz P Bass]

Reverb Tank

Did you try to reorient the tank position?
Accutronics uses a string of characters to indentify there tanks.
The last character identifies the orientation.
When they go from open side Down to open side UP, they move the (4) little hold down springs to keep the pan from rubbing the chassis.

[tubeswell]

If the RT hasn't got any end-bells, it could be sharing EMR with other trannies. The 'verb is the most sensitive circuit in the amp, so interference is more likely to be picked up there, and basically anything you can do to improve shielding helps