Diana Moe Hum (Reverb)

[treelifeUK]

My on-board reverb mark IV b, has developed a serious hum! What's a good valve/tube replacement and what position does it occupy? Maybe it's humming 'cos it doesn't know the words? Any ideas, anyone?

 

[Russ]

On the B version it sends from the second triode of the V4 and returns back to the second triode of the V3. These two tubes share the first two stages of Lead high gain also V3 (first) and V4 (second). For these two positions you really want a good quality tube with decent gain that is screened. Try the GT12AX7C. That tube has good gain for your Lead stages and will be decent for a reverb tube also. V3 and V4 are the tubes closest to the reverb cables. They are numbered counting away from the shielded V1. Your PI tube (V5) is the one sitting by itself not in the line.

 

[lento]

I've just bought Treelifes MkIV and a fine amp it is !

However, it's still humming. It creeps in around level 3 of the reverb knob.
This is regardless whether or not any guitar is connected and what channel setting.

I've changed both the v3 and v4 valves as suggested, but no luck.

I will call their service centre here in the UK, but just in case anyone has any insight .......

regards
Lyn

 

[Russ]

You might try cleaning the contacts of the reverb tank and the amp where the cables plug in. Also clean the RCA's themselves. You might also try a different RCA cable to check to make sure if your RCA cable isn't causing the hum.

 

[lento]

While removing the tank to outside of the cabinet, to look at the RCA lead, the hum stopped ! And upon relocating it started again.
After checking inside for any bad contacts and replacing the lead, there still wasn't any improvement.

Next thought was to swap the tank with one from a Musicman combo.
This one also hummed in the Boogie, while the Boogie's was silent in the Musicman !

So, at least I've narrowed it down to nothing wrong in the tank, cables ok and valves ok.

Doing a Google search did reveal potential problems regarding stray magnetic fields being picked up by the reverb pick-up. Usually position related to the transformer. I don't see this applying here, though.

Just a thought, could this be capacitor related ? The amp is about 12 years old but well looked after.

 

[Monsta-Tone]

This might seem silly, but maybe you could try swapping the RCA plugs that are on the chassis side of the Reverb Cables. If these were reversed, I've done it before, you would have funny noises and no Reverb.

You could also try moving the cables around to see if the noise disappears. It may be that the cables are simply passing too close to the power transformer or power cord.

Was the original Tank still connected when you removed it and noticed that the hum disappeared? This would support the theory that you just need to move the wires to a place that is not picking up hum.

Usually, the Send is the unshielded wire, and the Return is the shielded one. This will prevent any unwanted noises from entering the Return circuit.

 

[lento]

When the tank was moved it was still connected as this was how I noticed the hum reduce. It would seem that moving the cable and tank is the cure but, from the original post, it's only just started happening and was perfectly fine before.

The cables do pass very near to the transformer but this is how they were designed to.

And, as I've changed the cable with no improvement and tested the tank in another amp ......
:?

 

[lento]

Well, just after posting about the fan noise for recording, I disconnect the fan and not only wallow in the silence, but also revel in pure reverb, without the hummmmmmmmmmmmm !!

Can anyone explain a link between the fan and the reverb ?

Anyway, if anyone has a similar reverb issue, be sure to try disconnecting the fan !

 

[disassembled]

Try to reroute the cable for the fan so that it is farther away from the tank bag.

Greg