Unison Research 845 monos

bonneville

Wammer
Wammer
Oct 21, 2008
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Merseyside.
AKA
Vinnie
Since moving house and in a much smaller room,I have noticed a squeal from one monobloc when starting up from cold this can last up to a minute or so,then it settles down and is as quite as it's partner,which into 99db speakers is pretty good.

I have swapped the valves around ,first the ecc 82's then 83's and then the 845's,and thought I had sorted it only for it to reappear when started from cold.

I was going to sell them and did have a buyer who understandably got cold feet but is still sort of interested if the problem could be fixed.

UKD serviced them last year( £400 plus) and since then they have had moderate use only.I don't mind keeping them as they are the best amps I have ever owned,so my question is can I continue to use them as is or could I be storing up trouble and risk damaging my speakers.

Also any repairers near to Merseyside that could take a shuffty?

Vinnie

 

SMEagol

Middle Earthed
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Aug 13, 2008
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Lancashire
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Chris
HiFi Trade?
  1. No
I'd reapproach UKD after such a thorough service judging by the price, and particularly given the light use, should be good for at least another year! That's a lot of dough for it to go the shape of the pear.

 

bencat

Amplifier Destroyer
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Feb 6, 2010
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Hi Vinnie

Mike will look at valve equipment as well he did a service / repair on my Concordant pre . I can recomend Mike as being very good and reasonable in price . Quality of work is first class and he has done work for me from Dac,s to the Krell and as above.

 

take5

Wammer
Wammer
Jul 17, 2008
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lancs
AKA
brian
Vinnie, Mike will look at valve work.

If you need to borrow something whilst these are being fixed, just let me know.

However, Im with Chris. Such a short time after a £400 service, I would be looking for some back up work from the folks who serviced them.

 

bonneville

Wammer
Wammer
Oct 21, 2008
616
3
0
Merseyside.
AKA
Vinnie
Vinnie, Mike will look at valve work.If you need to borrow something whilst these are being fixed, just let me know.

However, Im with Chris. Such a short time after a £400 service, I would be looking for some back up work from the folks who serviced them.
thanks for offer Brian!I do have other amps to use.

 

Tel

Wammer
Wammer
Aug 13, 2006
30,258
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Hove Actually
AKA
Kevin
HiFi Trade?
  1. No
This squealing noise from cold start might be an indication of a problem with the slow start circuit if it has one. Often you can hear a relay click in after about 30 secs but I am not familiar with this amp. Basically the valve heater circuits are switched on and after the delay the audio circuits get switched in. If this isn't working then it could cause the problem you are describing and would also explain why the problem goes away when the valves get up to working temp.

A minute does seem like a long time though.

 

bonneville

Wammer
Wammer
Oct 21, 2008
616
3
0
Merseyside.
AKA
Vinnie
it seems to be a two stage warm up there is a second surge after about 20secs it is then when the squeal starts.When the amps are warmed up they are very quite and do sound very good

 

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