SWR Studio 220 Squealing Sound/Intermittant

[Hawk]

Thanks. Still the siren sound. Tomorrow will take the boards out and check for cracked solder joints. I'm sure others have experienced the siren sound I'm talking about... I'll also check The caps. Maybe try applying heat to components to see if I can duplicate the siren sound. .

[phatt]

Its already been mentioned, Dirty contacts are highly likely with older gear.

Just saw the picture of the board and all the chips are socket mounted and I would consider those prime suspects. :trouble

Sockets do make for a quick change of component but it does introduce another contact point and the cheaper sockets are often a problem as they get old.
Just by removing and reinserting can resolve the surface corrosion as it scrapes the crap off the pins

It would be wise to leave all those other caps alone until you establish what is actually wrong otherwise you might introduce a whole pile of new problems which will make trouble shooting a nightmare.
Phil.

[Enzo]

Sockets?  If nothing else, gently pry each IC halfway out of its socket and push it right back down, that will refresh the contact within the socket.  If that makes a difference, then you know you are on to something there.

[Hawk]

Thanks gents. Pried sockets half way out and all the way but no difference. Took out preamp board and saw limiter pot was loose so resoldered. Used deoxit on all pots. Noticed that when I turn on amp light bulb limiter stays on for awhile then goes normal. Subsequent turn ons and the light only flashes momentarily and all appears normal. Something at cold startup is eating lots of current--but, as I say, lamp dies out, amp works, and bass sounds good through amp....siren sound occurs when limiter bulb is normal(unlit)..hmmm

[Hawk]

Should I try replacing the op amps? Are they expensive?  TL072CP. Internal shorting?

[Hawk]

My conclusion. One fader cuts out at a certain level. Tried Deoxit and lithium grease but no luck. Other than this fader issue and the loud pop/sometimes squeal at start- up the amp sounds good. Found another SS post that talked about large inrush current being normal for some amps--the Renown has gone as high as 12 amps. It has been suggested to put a standby switch on the speaker, wait for the inrush current to subside, then turn on the speaker. I put a thermistor (7.5 ohms) on primary and that reduced the inrush current to an average of two amps but still get the loud popping. Tried the cap/resistor across AC switch but still heard pop/siren sound. So, basically after 5 seconds this amp is very playable (minus the fader issue of course). .....so is it fair to say that the 6800uf caps are creating this large inrush current and the amp is amplifying the poppingl/siren sound produced by the cap and its mechanical imperfections during inrush? And if that is normal then can we say that the speaker standby switch is a simple effective solution?   

[phatt]

Which pot cuts out?

Re the 5 second squawk problem
Last I looked,, there is a compressor in there somewhere ,,maybe look around that section.
better minds will know more. :tu:
Phil.

[Hawk]

Friend picked up amp. It will have to do in its present state--I invested a ton of time on this one...as you say better minds....