RT2/50 "humming"

[Eptesicus79]

Hey folks,

I just scored the RT2/50 on ebay a couple weeks ago, & finally got it setup at home. As soon as I switch from standby to play, there is a steady, nerve-wracking hum coming from my cabinet. I have another power amp here & that hum does not exist when the amp is off standby.

Is this just a sign of old tubes? Thanks in advance.

 

[m0jo]

Do you run an RM4 through there?
Then check out the ground lift switch on the RM4..

Is there sound coming through at all or only hum?
Also does the hum get louder when you turn up the volume on the RT/50 (don't turn it up all the way!)

 

[Eptesicus79]

Good call...I tried it & it didnt change anything unfortunately.

 

[m0jo]

Good call...I tried it & it didnt change anything unfortunately.

Hmm, too bad, would've been an easy fix.

But please do awnser the other questions!
I can't make out from your post wether the guitar is coming through or only humm.

 

[Eptesicus79]

Woops, didnt see your other questions!

Yes, the amp is totally useable. It doesnt sound bad at all when played through, but when I usually have silence I now hear this slight hum. It does get louder as I turn the volume up.

 

[Eptesicus79]

Also, when I checked the bias readings, they were off. There are JJ's in there, so Im guessing these arent stock tubes? Channel 1 (6L6) was at around 36mv, while Channel 2 (EL34) was at 32. I changed them both accordingly.

 

[m0jo]

No problem man.

Hmm, now you say "slight".
It's of course hard to judge through a forum
But there's some noise floor that's just due to the fact that you're running a tube rig.

I thought for a second it might be the fan, but then it wouldn't have increased with the volume.
Try changing the preamp tubes in there, they might be picking up something.
A lot of people forget those in tube changes and leave them in for years...


EDIT:
JJ tubes are standard in the RT2/50.
Those values are both not ideal but in the acceptable range.. shouldn't cause hum..

 

[Eptesicus79]

Well, a hum is a hum after all :lol:

Thanks for your input. You might be right about the preamp tubes. Perhaps Ill just re-tube it entirely just to be safe.

By the way, since were talking about the RT2/50 here..Im running it into a Marshall 1960 stereo cab. The mono input is 16 ohms, but I hear of a lot of people running the input to the cab at 8. Is there any benefit to doing this?

 

[Mattfig]

Well, a hum is a hum after all :lol:

Thanks for your input. You might be right about the preamp tubes. Perhaps Ill just re-tube it entirely just to be safe.

By the way, since were talking about the RT2/50 here..Im running it into a Marshall 1960 stereo cab. The mono input is 16 ohms, but I hear of a lot of people running the input to the cab at 8. Is there any benefit to doing this?

There's no benefit that I'm aware of for setting impedance incorrectly...Is there? I'm not gonna experiment...Have you tapped all the connections and such? Usually I'll just kinda fish around in the back of the rack, moving cables a bit just to see if I can make it periodically stop...Just a thought....But I'll give you the same advice I gave the last guy having RT2/50 problems...Your unit is fucked...I'll take it off your hands (for scrap metal mainly) for 100 bucks...

 

[JKD]

Is the hum on both channels and equally loud?

Sometimes bad tubes or bias can cause hum.

 

[m0jo]

Well, a hum is a hum after all :lol:

Thanks for your input. You might be right about the preamp tubes. Perhaps Ill just re-tube it entirely just to be safe.

By the way, since were talking about the RT2/50 here..Im running it into a Marshall 1960 stereo cab. The mono input is 16 ohms, but I hear of a lot of people running the input to the cab at 8. Is there any benefit to doing this?

There's no benefit that I'm aware of for setting impedance incorrectly...Is there? I'm not gonna experiment...Have you tapped all the connections and such? Usually I'll just kinda fish around in the back of the rack, moving cables a bit just to see if I can make it periodically stop...Just a thought....But I'll give you the same advice I gave the last guy having RT2/50 problems...Your unit is f&(%ed...I'll take it off your hands (for scrap metal mainly) for 100 bucks...

Such a kind soul :lol:

I've never heard of this ohmage malarky.
Don't run your amp at the wrong ohmage, that switch is there to match your amp and cab, not for experimenting.
Running it unbalanced will damage your tubes and possibly output transformer.

BTW good one Mattfig: check all your cables!
Otherwise you're changing tubes, ohmage, bias etc. just because some cable is crapping out on you.

 

[Eptesicus79]

Yes, it happens with both channels. Its definitely not the cables...Like I said earlier, the other power amp I have doesnt hum when it comes off standby & volume is up. In fact its dead quiet, & thats a Marshall EL34 100/100.

I was more curious to see if anyone else's RT did the same thing. Ill probably just change the tubes out & see what happens.

 

[byzon]

Maybe I'm stating the obvious here, but make sure all your modules are screwed into place. I get some hum from time to time when I'm too lazy to tighten the screws down.

 

[Eptesicus79]

Maybe I'm stating the obvious here, but make sure all your modules are screwed into place. I get some hum from time to time when I'm too lazy to tighten the screws down.

Haha, another good point but again, the hum isnt there when I plug into the other power amp! LOL.

 

[muudrock]

You have a ground loop. What else is in your rig? Have you tried the preamp directly into the power amp with no other connections to outboard gear?

 

[Eptesicus79]

You have a ground loop. What else is in your rig? Have you tried the preamp directly into the power amp with no other connections to outboard gear?

Its not a ground loop, I know what those sound like. I just have the RM4 going straight into the RT. Once again, the hum isnt there when I plug it into the Marshall PA, so Im going to bet its the tubes...

 

[m0jo]

You have a ground loop. What else is in your rig? Have you tried the preamp directly into the power amp with no other connections to outboard gear?

Its not a ground loop, I know what those sound like. I just have the RM4 going straight into the RT. Once again, the hum isnt there when I plug it into the Marshall PA, so Im going to bet its the tubes...

Can you record the hum?

Or describe it: very low or not, sizzling, buzzing or just a smooth tone?

 

[Eptesicus79]

You have a ground loop. What else is in your rig? Have you tried the preamp directly into the power amp with no other connections to outboard gear?

Its not a ground loop, I know what those sound like. I just have the RM4 going straight into the RT. Once again, the hum isnt there when I plug it into the Marshall PA, so Im going to bet its the tubes...

Can you record the hum?

Or describe it: very low or not, sizzling, buzzing or just a smooth tone?

Haha, yea I can definitely do that. Where can I upload it when its ready? Its really hard to describe, & perhaps hum isnt the proper description. Ill plug it in again later & see.

 

[m0jo]

You have a ground loop. What else is in your rig? Have you tried the preamp directly into the power amp with no other connections to outboard gear?

Its not a ground loop, I know what those sound like. I just have the RM4 going straight into the RT. Once again, the hum isnt there when I plug it into the Marshall PA, so Im going to bet its the tubes...

Can you record the hum?

Or describe it: very low or not, sizzling, buzzing or just a smooth tone?

Haha, yea I can definitely do that. Where can I upload it when its ready? Its really hard to describe, & perhaps hum isnt the proper description. Ill plug it in again later & see.

Ehm just throw it on filedropper or something no need for a whole soundclick account or whatever.

Yeah that's why I asked for a recording, hum/buzz/noise is very hard to describe.

 

[Eptesicus79]

You have a ground loop. What else is in your rig? Have you tried the preamp directly into the power amp with no other connections to outboard gear?

Its not a ground loop, I know what those sound like. I just have the RM4 going straight into the RT. Once again, the hum isnt there when I plug it into the Marshall PA, so Im going to bet its the tubes...

Can you record the hum?

Or describe it: very low or not, sizzling, buzzing or just a smooth tone?

Haha, yea I can definitely do that. Where can I upload it when its ready? Its really hard to describe, & perhaps hum isnt the proper description. Ill plug it in again later & see.

Ehm just throw it on filedropper or something no need for a whole soundclick account or whatever.

Yeah that's why I asked for a recording, hum/buzz/noise is very hard to describe.

Well this really sucks...I turned the amp on & now channel 1 doesnt work at all! All tubes are lit, I even tried 3 different 12ax7's. Tested tubes fron the front as well, they all get a reading. What the heck!?