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Tube noise - Help

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

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.
 
pollypocket said:
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.
 
planet10 said:


maximum 1000 x 1000 pixels, 100 kB

dave

i hate to thread-jack, but Since you popped up here Dave, I wanted to pick your brain. I have read every letter on both your websites, and I am interested in building up some transmission line speakers... probably something simple at first like a TQWT. Can you suggest some decent drivers that are pretty efficient and forgiving of construction flaws? ;) I'd like to drive them with a couple low-wattage SE monoblocs.
 
aletheian/ dave;

Thanks for your help getting the graphic of the schematic loaded.

The schematic is for a modified Radford manufactured by Woodside electronics in Wales. As stated earlier, it is rated at 25wpc class A. I enjoy the sound however, the noise problem is very distracting. I have yet to swap tubes on the front end to see if I could isolate one. One note of interest, on power up, one of the front end tubes glows very bright for the first 1 or 2 seconds and then returns to normal. My repair guy told me not to worry about it as it is probably a shorted heater and won't effect the sound.

Opinions are welcome.

thanks,

Paul
 

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pollypocket said:
One note of interest, on power up, one of the front end tubes glows very bright for the first 1 or 2 seconds and then returns to normal. My repair guy told me not to worry about it as it is probably a shorted heater and won't effect the sound.

Rubbish. It is perfectly normal behaviour. Some valves (particularly some Mullards) were designed to do this to speed warm-up.

There are various possibilities for the hiss. It might help if you were able to measure and compare DC voltages between the good and bad amplifiers.
 
Gentlemen;

I swapped the front end tubes (ECC81 and ECF82) between channels looking for the problem to move but I have seemed to have resolved the noise issue alltogether. I have been running the amp all day and the noise has not returned. Either I bumped something during the swap or there were some dirty contacts on the tube pins.

Thanks to everyone for the opinions and suggestions.

Paul
 
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