Strange but true...?

[Rino odorico]

Hey all,

Ok, this is strange. I have this little EL84 push/pull amp running in my bedroom, she's worked flawlessly for years untill a few weeks ago. Started to notice a slight 60Hz hum, not that big of a deal I thought. Trying to figure out where this hum is comming from, so I pulled the CD players RCA's off (running the CD's output directly into amplifier...CD has variable output) and BAM...really loud 60Hz hum!

My question is, why would this start to happen all of a sudden? Bad tube or something? Parden my ignorance...still learning how tube amps work.

Going to check out things further tonight. I do know that the amp is not grounded to a centre tap for earth. Just a two prong plug. This is prob. # one I fear.

Rino

 

[karma]

do you have anything that you can try on the amp besides the cd player? if so try it or try a diferent rca cable. do you have the hum in one channel or two?


mines 2 prong and its fine

 

[fdegrove]

Re:Strange but true.

Hi,

I have this little EL84 push/pull amp running in my bedroom, she's worked flawlessly for years untill a few weeks ago.

Boy, do I love the way you describe all this.

Could be a number of things, Rino...a dried out PS cap, a loose cinch connector...?
The cable itself?

And of course since it's a "she" it could be that time of the...oops.

Cheers,

 

[karma]

heh

ya

heres a link that may help if your new to tube amps be carefull

http://www.members.cox.net/archangele666/vaud.htm#howto

 

[Rino odorico]

Hey guys! Long time no talk, thanks for the reply/s!

Ok, just for fun I attempted to look at her lastnight. Noticed that the noise gets louder as it warms. I was able to add a small jumber from chassis ground to earth ground. I would say that half of the noise went away...cool. The only thing is, since the - of the spk output is tied to the chassis, I used that as the temp grounding point. Now this is the strange part, the channel that has this jumper has the noise, the other doesn't. Pull the jumper and both channels have noise. Also as mentioned, as she warms up (about an hour or so after turn on) the noise gets louder. Starting to wonder if I have (like you said Frank) a bad PS Cap or something...maybe even a bad tube.

I love playing with this stuff...power off of course

Thanks guys,

Rino

 

[Gregm]

Just an idea: don't stroke her caps even when she's off (the mains)

I know you hadn't done that a few hours ago, I saw you were still in posting mode, but still

You've tried changing cables, of course???
Cheers

 

[Rino odorico]

Hey Gregm,

Yup, tried that...no difference. Grounding did make a difference, but for the noise to get louder as it warms bothers me. Sounds like something is out of tolerance. Just have to figure where to start.

Rino

 

[fdegrove]

KABOUMMM...

Hi,

Rino, is this amp relatively young or is this a vintage sixtier still running on the original PS caps?

If the latter is the case I seriously suspect the PSU...
The tubes usually run like for ever once they make it through the first weeks.

They have never told them what MBTF means, see.

 

[Rino odorico]

MBTF....

Yup, I'm thinking caps as well. The amp is between new and old (well in the tube world), I suspect that she's an 80's vintage. The amp is actually a prototype of a small independant manufacturer (basement type). Baught it at a pawn shop for 60 bucks, they wanted 200 originally, so what the heck right. Cleaned it up a bit, re-tubed it, touched up some solder joints and have had her working for a number of years. Guess it's time to replace some parts...been really lucky thus far with it (and yes- I can be a cheap S.O.B sometimes

Thanks dude,
Rino