okay friends, need help:
intermittent buzz in sound. comes and goes and sounds like a mosquito bzzzzzt lasts for about 20sec then goes away. comes back 3-5 min later...

heres the set up:
Dynaco ST-70 w/ EH EL34s matched quad and less than 40 hours; 2 sylvania 7199 unk amount of hours; and sovtek 5ar4 rectifier less than 40 hours.

Juicy Music Audio BlueBerry less than 100 hours, but had to replace 6DJ8, now has new Ei 6DJ8.

Buzz started one hour ago after playing most of the day flawlessly...

any suggestions what might be causing the buzz?

:thumbsdn:

Perhaps its the source components?? :scratch2: Seriously though, does the buzzing increase or decrease with the volume level or is it constant? Does the buzz occur with ALL of your sources?


Mike

My tube amp had a grounded (3 prong plug) plugged into a power strip with other gear and when I lifted the ground (3 prong to 2 prong adapter) the buzzing went away ;)

that was a good one! its the Maverick!
the buss is not constant. it really is like a mosquito buzzing around ones head, comes and goes. i first heard it on Stevie Ray Vaugn and Albert King "Bumble Bee," and thought it was part of the song! but then it came back when i put in the Coconut Song.


thor, the amp is modded and has new 3 pronged power cord that is not detachable. i shall try degrounding it and see what happens.

I know this is a shot in the dark, try putting in the old rectifier and replacing the Ei tube. I've heard some Ei tubes can have horrible microphonics. Either they sound great, or they really sound....bad. Hopefully, your old 6DJ8 tube is still servicable? Not sure if that's causing that "mosquito buzz" or not, Thor sounds like he's probably right about a grounding issue, but if that don't work try swapping that tube.

Try pluging your amp directly into the wall socket. You may find it works best that way.

"intermittent buzz in sound. comes and goes and sounds like a mosquito bzzzzzt lasts for about 20sec then goes away. comes back 3-5 min later..."

Likely a capacitor breaking down somewhere in your system. It will unquestionably get worse as time goes on.

Translation:

The component (undoubtedly a cap) partially breaks down and allows an unacceptably large amount of alternating current to flow through it for about 20 seconds and then slowly recovers and then fails again a few minutes later.. That is typical behaviour for a failing cap.... Eventually it WILL fail outright and the result will be serious indeed because when that happens it will short to ground and burn out the rectifier and/or output tubes and/or transformers.

Contact the manufacturer of your Blueberry. I don't think the problem is with the Blueberry itself but Mark Deneen the designer will unquestionably be able to help you track down the problem

thanks lynnm. yeag tried all prior suggestions to no avail. put a whole new set of tubes in pre-amp and that made no difference. sound is out of both channels. yeah marks been great help before. was worried that it might be a bad Ei tube, but replaced all with BN EH tubes and still there. swapped out all tubes on ST-70 and still have hiss, and its already worsening. have brand new orange drop caps on ST-70. damn i hate and love tube gear. when it all works, its pure pleasure, but seems like once every few eeks i'm hunting down a problem!

If you have a variac you can pull all the tubes except the rectifier in the ST-70, set it at 30V and leave it over night. You use a volt meter and put the neg on the chassis and pos on the + of your PS cap(s), turn the power off and watch the voltage drop. A cap that isn't forming right will drop fairly fast while a good one drops real slow. Without a cap tester and knowing how to use it this is the only method I know of to check on the health of the big litic filter caps.

Also depending on the age of the Orange Drops, if they were not brought up with a variac there is a chance that some damage might have occured.

ST-70s do need to have the bell bolts on the transformers torqued pretty regular. The PS will buzz, but it is mechanical and won't come out the speakers.

I have had more than one ST-70 give me problems with the RCAs being set close together and putting new ICs on them. That usually caused a ground loop and a LOUD 60 cycle hum, but it is worth checking.

A cold solder joint can cause this too. Make sure you drain the caps before you go tugging on things even if it hasn't been powered up in days.

Is the CB a new mod or an old one rebuilt? They are tough on the 7199s and the old boards tend to suffer from years of heating and cooling.

Jusr reread your post. I take it the Maverick is a source so it isn't the ST-70, but I will leave the info anyway.

thanks for all your help, but its worse and off to repair.... like car talk, we'll play "stump the chumps" when it gets back and see who was right/closest to te prob!

Since it's getting worse I'd have to go with Lynnm about the capacitor. One of your electrolytics are about gone and leaking AC through it.