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Old 30th August 2013, 12:24 PM   #1
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Default help with a power amp

hey everyone im new here and have a question for anyone in the know I have an old ev 7300 amp its in a rack with 3 bgw amps and I have not used it for about 7 years the bgws work fine but I have not had a need for the ev well I hooked it up the other day and it powers up but nothing is coming out with the power all the way up I hear a low sound but that's it any ideas whats wrong I moved all the cables to one of my bgws and the sound is fine what could have happened to this amp from not being used thanks for any help
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Old 30th August 2013, 01:04 PM   #2
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If it has not been switched on for 7years, it is likely to require new capacitors as they, much like a car battery, dry out and go high impedance or leaky.
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Old 30th August 2013, 03:11 PM   #3
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thanks I will have them checked
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Old 31st August 2013, 08:43 AM   #4
dangus is offline dangus  Canada
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It might just be bad contacts in the input jacks. I had one channel of an AB amp that didn't work because the Normally Closed contacts in a 1/4" jack were oxidized. The speaker protection relay is another possibility, though if those contacts are bad you shouldn't hear anything from the speakers (no hiss, no hum).

Filter caps in my experience only go bad if they're run at painfully high temperatures for extended periods. I'm using a power amp that has 30 year old filter caps and works fine.
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Old 31st August 2013, 08:50 AM   #5
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The filter caps are probably not the problem as they are fairly reliable. Small value coupling capacitors go leaky and the line in/out sockets have issues.
I had a client with a Crown VZ5000 with a dead channel, (protection was activated). He took it away with out a repair, powered it up with no speakers for a few hours and the capacitors reformed. Lucky or what!
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Old 31st August 2013, 01:55 PM   #6
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thanks guys I going to have it checked out I just don't want to put more into it than its worth like I said before I can hear a very low sound with it turned all the way up so I hope its not to bad im going to use it to drive the monitors as I have 3 bgws for the mains
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Old 3rd September 2013, 04:16 PM   #7
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Quote:
Originally Posted by tamaman View Post
hey everyone im new here and have a question for anyone in the know I have an old ev 7300 amp its in a rack with 3 bgw amps and I have not used it for about 7 years the bgws work fine but I have not had a need for the ev well I hooked it up the other day and it powers up but nothing is coming out with the power all the way up I hear a low sound but that's it any ideas whats wrong I moved all the cables to one of my bgws and the sound is fine what could have happened to this amp from not being used thanks for any help
I have a bunch of those old 7300's.
They all have an intermittant somewhere on the circuit board.
If I bang on the amp the sound comes back proper but then eventually fade-crackles back to the lower level.
Try banging on the amp while it's running -and by banging I don't mean to beat the **** out of it, but gentle taps by a rubber mallet on the front panel while in a rack.
I've since narrowed them all down to one spot on the Ch2 circuit board -and since they are near sequential in serial number, it might have been just a glitch in soldering the day they were made.
(It's not like they've run flawless for 20 years before developing the problem -I "rescued" them at the point where the fans had stalled due to excessive dust pile-up so they were definitely heat-stressed for the last few years of their duty!
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Old 3rd September 2013, 10:32 PM   #8
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Hi Tamaman,
That Ev amp is identical to an Altec 9444B and a QSC1400 (QSC made both amps for Altec and EV). The problem areas in those amps were always bad (cold, or cracked solder joints). De-case the amp, flip the board over and look at the solder mask under a magnifier, You should easily be able to see which joints are bad (especially around the driver and output transistors, emitter resistors, and the main electrolytics). Also, clean and burnish the contacts on the protection relay (another weak spot on these amps). Otherwise these are great-sounding old workhorses!
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Old 3rd September 2013, 10:40 PM   #9
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tamaman,
I'm thinking the speaker relay contacts have gone bad. If you're lucky they're in sockets and you could try pulling them out, removing the cover and clean the contacts with a burnishing tool. If that fixes the problem, I recommend replacing the relays if reliability is important.

Mike
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Old 4th September 2013, 12:34 AM   #10
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Quote:
Originally Posted by Robbie42 View Post
Hi Tamaman,
That Ev amp is identical to an Altec 9444B and a QSC1400 (QSC made both amps for Altec and EV). The problem areas in those amps were always bad (cold, or cracked solder joints). De-case the amp, flip the board over and look at the solder mask under a magnifier, You should easily be able to see which joints are bad (especially around the driver and output transistors, emitter resistors, and the main electrolytics). Also, clean and burnish the contacts on the protection relay (another weak spot on these amps). Otherwise these are great-sounding old workhorses!
Totally different amps, I think you're confusing the QSC model number.

EV 7300 looks just like this except level controls on front:
Click the image to open in full size.

QSC 1400 looks just like this:
Click the image to open in full size.
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