Need help - 2061x hums

[Nihon Jim]

Just took delivery of a 2005 2061x. Great tone however it hums/buzzes. Lead tone above 8 especially with vol above about 4 is very noticeable. Bass channel as well but lead much louder. Not noticeable while playing. Swapped plug in location in the house and power chord. No effect, still makes noise. Noise present regardless of whether or not guitar plugged in (no change either way). Sounds like the background hum/buzz I hear from my DSL100's red channel when it is really cranked.

Any ideas? Need tubes or is it more serious?

[surfnorthwest]

Trouble shooting time. Could be anything from your cables, to your guitar, something in your chain, to your power source. You have to start eliminating things one by one.

It also can be a microphonic tube.

[Nihon Jim]

Surf,

Copy all and thank you for quick input.

Troubleshooting to date: The amp rig was moved to different areas of my home and plugged in. Same noise at different locations. None of the other amps in my home exhibit this symptom. The power cable was also swapped as was the speaker cable and cab. Noise occurs with/without guitar lead plugged in. Two different guitars and leads were tested. No change.

I think I have eliminated the external variables and believe it is something internal to the head. Regarding microphonics, which set of tubes, preamp 12AX7s or output EL84s, would most likely be the culprit?

Thanks,
Jim

[surfnorthwest]

I would start swapping preamp tubes one by one first. If its not the tubes then you will need a tech to look at it as it would be a grounding issue. Take a good look at the amp and cabinet jacks also.

[Nihon Jim]

Surf,

Copy all and will do. I will report tube swap/replace results this weekend.

Many thanks,
Jim

[jboyjams]

Not sure if it's a similar issue - but just in case, check out my post (and pics) toward the bottom:

http://marshallvintagemodern.com/viewto ... =38&t=9634

[Nihon Jim]

jboyjams - very helpful link, thank you.

So here is where I am at this moment. Last evening following the above link recommendations I removed the amp from the cabinet to check out the green wires connected to V1 and V2. The V1 wire had length so I lifted it from the chassis. However, the wire on V2 was way too short and did not budge. While I had the amp out I swapped the Marshall ECC-83 in V1 for a brand new Tungsol 12AX7 then reinstalled the amp into the cabinet. I turned out the lights and looked at the powered up amp (volume and tone dimed). I noticed that V1 was barely glowing. the EL84s looked great as did the Marshall ECC-83 in V2. I powered down and inserted a brand new Mullard 12AX7 in V1. Upon power up it looked the same as did the new Tungsol. See picture below. V1 was glowing dimly but it was glowing. I powered down and reinstalled the stock Marshall ECC-83 and re-powered. Both V1 and V2 were of equal brightness (see picture). I left the Marshall tube installed.

During this cycle I checked for noise. Same noise/hum as I had noted prior to opening up the amp head. (See pics of the inside of the head.)

Today I stopped by a high end guitar shop near me. They happened to have a new 2061X in the shop for sale. It was plugged into a cab and a power source. I turned it on and ran the volume / tone setting to the same levels where I heard the issues at home with my amp. Holy smokes! The same noise. I asked the dude in the shop and he said, "yea, that is normal for these types of amps." He said that he meant amps with no master volume. So now I am thinking that the noise I am hearing from my used 2005 2061X is normal. How noisy should I expect this amp to be? This amp is noisier than any of my other amps (DLS-100, Fender Blues Jr., Blackheart Handsome Gentleman, JTM-1, JMP-1 and JCM-1).


Pic below - New Mullard in V1. Looked same as the new Tungsol in V1 just a few minutes prior. Are both of these new tubes bad?



Re-installed stock Marshall ECC-83 in V1. Looks like V2. I left that tube installed.



Green wire at pin 2 of V1 lifted off the chassis.



No slack to lift V2 green wires off the chassis.