Tube noise - Help

[pollypocket]

Hi;

I am looking for some advice on tube noise...

I am running a Radford ESA225 amplifier with EL34 outputs. I am getting noise in the left channel which seems to be getting worse. It sounds like the wind blowing through the trees. Very distracting. I tapped the cage and there is no microphonics. The tube heaters light up fine and look normal. The noise isn't constant but seems to come and go... but seems to be there more than not. I am using the new Mullard EL34's. Is this an output tube problem or a front end tube?

Any advice is appreciated.

thanks,

Paul

[sreten]

Hi,

The obvious - swap tubes between channels.

/sreten.

[pollypocket]

thanks...obvious test...should have thought of it

will give it a try

thanks

[kevinkr]

Further thought, with the exception of output tubes swap one at a time, this will help you eliminate all but the specific tube if indeed it is a tube.

Bad resistors and sometimes bypass electrolytics in low level stages can also account for this problem.

There does not seem to be any information on this amplifier out there on the web, at least not anything I can find quickly. So fill us in on the details - is this an integrated amplifier or a power amplifier?

[pollypocket]

Kevin;

It is a power amp outputting 25wpc Class A. It is based on the Radford STA225 design and was manufactured by Woodside Electonics in Wales. There is a convoluted story around Radford and Woodside, neither of which are in business any longer. I could post a schematic although I don't know the rules in this regard on the site. Some of our brethren from the UK would know the Radford equipment well and could comment on the design further.

I swapped out the EL34's and still have the noise comming through, so it isn't an output tube.

Paul

[aletheian]

Originally posted by pollypocket
...I could post a schematic although I don't know the rules in this regard on the site...

i think you should be fine since the companies in question are defunct.

[kevinkr]

Interesting, I don't think there should be a problem posting the schematic here, if in doubt ask a moderator..

I doubted very much that the problem stemmed from the new output tubes, it is more likely that one of the small signal tubes is the culprit, particularly if they have been in the amplifier for a while. I would swap one at a time.

Other possible causes are dodgy tube socket contacts, a bad resistor or a bad electrolytic bypass cap in the first stage if present.

[planet10]

Go ahead post the schematic...

dave

[pollypocket]

I haven't posted any photos to this site...can you point me to some instructions? I couldn't find anything in the FAQ's or on a quick search.

thanks

Paul

[aletheian]

Originally posted by pollypocket
I haven't posted any photos to this site...can you point me to some instructions? I couldn't find anything in the FAQ's or on a quick search.

thanks

Paul

When you hit the "post reply" button, a screen pops up where you type your response. There is a field at the bottom that says "Attatch file". Just click on the "Choose File" button to the right of it and browse through your hard drive until you find it.