Valve amps - odd noises

one of my new monoblocks makes loud hissing noises and pops and bangs whilst warming up. Once fully warm the noises dissapear and the sound is lush. I assume it wont damage my electrostatic, I know its the mono not the pre or speaker as it switches chanels when I swap them over. Quad say give it a couple of weeks to settle down, which I will do but wondered if there was any harm in swapping the tubes between the monos to see if its a valve issue, I know they are tailored to the valves so would put them back in the right places after the experiment - or should I just sit the 2 weeks out?

Thanks

 

only in terms of biasing.... if you switch them without re biasing the tubes you could have even more funny noises. no amp is going to be "tuned" to a specific set of tubes in a more elaborate way than the bias, otherwise it would be a problem when it came time to re-tube the thing.

tubes often make noises when they are warming up. if it sounds fine when hot, then i wouldn't worry about it anyway.

 

I don't think you need to worry, sounds like thermal expansion ...they do get hot. Quads don't need biasing ! well mine didn't [II's] I recall some article that suggested they self biased, or that the curcuit compensates can't remember which.

 

Only one mono does it the other is stoney silent. The quad manual suggests sending back to change valves (it would wouldn't it) which suggests they need biasing. When buying matched valves should I buy 4 or do they only need matching per amp ie. 2

 

Get out of the house now!!!!!!!!!!!

Only jokin. As has been said sounds like standard tubey noise, although Ive never heard hissing noises. Tubes can physically expand when they warm up, In only talking a mm or so but it gives you an idea with whats going on. So long as they sound fine after warm-up I wouldnt worry, you could also have a listen without anything playing, just turn the amps up and see if you get any strange sounds on one channel, this usually points to a dodgy tube.

Im 99% sure that the II 40's are self-biasing. You're fine with a matched pair, in theory a self-biasing amp should be okay with any tube you put in (that fits of course).

 

The noises are coming with the pre turned completely down with no music playing. The Quad brochure reckomends leaving them like this for 15 minutes before playing any music/volume so as not to damage the valves especially if using electrostats.

BTW I just plugged the ESL's into the 8ohm tap and havent experimented with the 4ohm one as I expect quads spec sheet to be accurate.

 

Quad don't give much away do they! Couldn't find anything about biasing at all.

 

If the noises are coming with no music then I wouldnt worry too much. Its when you turn it up with no music playing and you get a howling through one speaker or a high-pitched whine then you know a valve is probbo on the way out. Give it a couple of weeks. BTW I'll get the damper pics for you, been a crazy few days so far.

 

Thanks t-bone I fancy having a go at making them

 

The Quad Forties are a self biasing semi balanced design which allow the use of non matched pair KT88. In theory they can be upto 10% different but would not try it as this will burn one valve quicker than the other.

As has been suggested I would wait about a month before worrying. I would try swapping the valves as this may identify whether it is a valve or maybe a capacitor/resistor in trouble.

 

The noises have got worse, the noises are almost constant and v loud and Im worried about my panels, so I have done some experimenting.

I swapped the valves between amps by type and the noises change sides when i swap the 6SH7 input valves. What should I do now? Should I tell quad and get rplacements? Or are they still likely to rectift themselves?

 

The sounds BTW are a loud hissing similar to pink noise acompanied by pops similar to a digital drum kit.

 

Sorry are the noises your hearing through the speakers....I think thats a yes as you say your concerned about your panels. Can you isolate which input valve is the culprit....run on chanel only [the other electrostatic switched off ] and swap input valves from the other amp. Its likely you may have a rouge valve ....they should all have been tested !
Then give quad a ring and tell them you want a replacment valve because of the symptoms mentioned.... Rather than say the amps faulty. If your close to there HQ its just as easy to pop in !

 

Just noticed your in west yorkshire .....so that not an option.

Give your dealer a bit of hassel they should have some spares let them deal with Quad.

 

rsand,

You have a faulty tube, I've had this happen a few times with input, driver & output tubes. I have a 300B that does the same thing your talking about. Call your dealer asap and get a replacement, The Kt88 don't need to be matched but your input and driver tubes do so get a replacement pair not just one.

cheers

Alan

Ps: no harm should come to your ESL! my ESL-63 have had some poor sounds passed into them from DIY projects gone wrong in the past.

 

Sorry to hear of the problem.

Get it changed by the dealer, but it may need to be looked at. There may be something wrong with one of the resistors and therefore the valve is being over run with too high a B+.

 

If I'm remembering the theory right, they're transformer isolated aren't they? So they're not going to pass any DC to the panel which makes them a pretty safe for exploding DIY projects

 

Thing is now I have located the problem, and swapped them back they seem to have settled down and rarely makes the sounds? Are they really that odd that swapping them about a bit could rectify such an audible defect?

 

Intresting almost sounds like a dirty connection ?