6505+ Combo Not Outputing

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surjer
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6505+ Combo Not Outputing

Post by surjer » Sat Jul 15, 2017 3:44 pm

So my 6505+ Combo has a very strange problem. At first I thought all the symptoms were pointing to a bad standby switch. But then while the amp was on and I bumped it, i could hear the reverb tank! So with the amp on, you can bang it and hear reverb. But no matter what channel it is on, there is no signal. No amp noise at all! No hiss, nothing. I have reseated ALL of the tubes, and have used known cables and different speaker cabinets with no success. Whats could possibly be causing this?

Classic30inCincy
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Re: 6505+ Combo Not Outputing

Post by Classic30inCincy » Sat Jul 15, 2017 4:38 pm

Are you sure power tubes are ALL WORKING ?

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surjer
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Re: 6505+ Combo Not Outputing

Post by surjer » Sun Jul 16, 2017 5:05 pm

Yeah, the power tunes and the PI are all lighting up but the tubes in the front are not. So... After doing a bunch of reading it sounds like I will need to dig into the amp and check out some fuses and diodes inside. :(

surjer
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Re: 6505+ Combo Not Outputing

Post by surjer » Fri Jul 21, 2017 1:36 pm

Got the board out. Since the burn marks are around D24, D23, D18, D19 and C83, would you agree that is where I should start with replacing? Found an electronics store about an hour and a half away and I will be picking up the parts tomorrow. (Anything else I should grab while I am there?)
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Enzo
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Re: 6505+ Combo Not Outputing

Post by Enzo » Fri Jul 21, 2017 2:04 pm

Start replacing??? How about start checking? Are any of those diodes shorted? Does the amp blow the associated fuses? Do they rectify the incoming AC into reasoanble DC?

Replace parts because they are defective. Don;t replace them hoping you hit the lottery.

surjer
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Re: 6505+ Combo Not Outputing

Post by surjer » Fri Jul 21, 2017 2:20 pm

ok, So I should snap this thing back together and fire it up and start pulling test voltages? Sounds easy enough. What voltages should I see ya think?

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Enzo
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Re: 6505+ Combo Not Outputing

Post by Enzo » Fri Jul 21, 2017 7:06 pm

Whatever the schematic suggests, your B+ is several hundred volts, the bias supply is maybe -60v, the low voltage supplies are like +/-15v, etc. Are all the tube heaters lighting?

surjer
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Re: 6505+ Combo Not Outputing

Post by surjer » Sun Jul 23, 2017 7:40 pm

Replaced the four diodes and i am back up and running.. Was not so easy getting the old parts out.

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