NAD with problems

[CR]

Hey everybody, I just picked up a used VHT Special 6 Ultra head. I was looking for something with an effects loop that wasn't too big. I was interested in the wattage control but it wasn't a requirement since I have a Jet City attenuator that works pretty well. I tried it out and it has a great tone, a little less boxy sounding than my Marshall Class 5. However, I was putting it through its paces on the Ultra channel and right away I noticed some strange volume spikes/drops accompanied with a crackling sound. I am by no means an expert on amp troubleshooting but I'm hoping it is an easy fix, like replacing the tubes or something. Anybody have any ideas?

 

[wlewisiii]

Not sure. I've been having similar crackling issues. I need to record it, perhaps with my phone? and email it to tech support. It did go away for awhile but it came back worse. This bums me badly as its been a great amp till this.

 

[wildeman]

I would imagine that they dont use the greatest tubes from the factory so this is where i would start. Maybe take them to a tech who can test them for you.

 

[jtcnj]

If you are comfortable and review the safety precautions, re-seat your tubes in the sockets a few times - when they are cool. they are friction connections and can get oxidized. Wash the oils off your hands first and wipe the glass clean after.

If you poke around the socket pin wiring or rock the tubes slightly with the amp on with a chopstick or small art paint brush, With Your Other Hand In Your Pocket, you may get some symptoms. the tube socket terminals can be re-tensioned with a tiny screw driver. This is getting deeper in however; dont do this if you are unsure of yourself.

Remember the voltages stored in the power capacitors can kill you even with the amp unplugged.

 

[CR]

I cracked it open to take a look today. It has a JJ 6V6 and some no-name 12AX7s. Does anybody know if the problem I am having comes from the preamp side or the power amp side, or not necessarily one or the other?

 

[DPaulCustom]

From your description,
"I tried it out and it has a great tone"
Then you switched to the ultra channel, & found that problem.
I might be wrong, but I wouldn't think it was tube related, or it would do it on both channels.
Are there separate inputs for the different channels, or just a switch?

If separate inputs, you might want to check the 'bad' one.
If it's a switch, some cleaner might do the trick.

Does this model have a 'pull' volume knob?

 

[CR]

That is a good point. I was playing at much louder volumes when on the Ultra channel so I wasn't sure if it was an issue that was volume related or channel related. There are separate inputs for the clean and ultra channels as well as a pull "boost" feature on the volume knob.

 

[IGRocker]

Could be as simple as a faulty volume or tone potentiometer. But I'm certainly no amp tech.

 

[Ken Rose]

Sounds to me either bad tube or bad cap.

 

[wlewisiii]

Mine just went away with pulling the back cover off
Looks like the RF shielding is hosed. I don't know how similar the heads are to the combos.

I found this link useful : http://www.300guitars.com/articles/tube-amplifier-crackling-noises-what-to-look-for/

 

[Caddy]

If this is a new amp, as the thread states, then I would take it back and get a replacement. I sure wouldn't mess with it.

Oops, I see it was actually a new 'used'amp day.