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Post subject: Blackface Concert 120 hz hum
Posted: Wed Jul 16, 2014 8:04 am
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My 1964 Concert has developed a 120 hz hum. It is present with or without a guitar plugged in. Also, the amp pops-once-when I take it off standby. The filter caps were changed about 5 years ago, however, the 2 68uf/450v Aero M caps look like pulls from another amp. Would bad filter cap(s) cause these problems?


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Wed Jul 16, 2014 8:11 am
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Sounds like bad filter caps. At least, I would rule this out, first. Replacing the first stage (two 68mfd caps) maybe all you need to do. What is the conditions of the other main filter caps, under the doghouse?


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Wed Jul 16, 2014 12:29 pm
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BMW2002Ti wrote:
Sounds like bad filter caps. At least, I would rule this out, first. Replacing the first stage (two 68mfd caps) maybe all you need to do. What is the conditions of the other main filter caps, under the doghouse?


+1

I would never install "pulls" in such a critical area as the filter-cap array. Or the bias-supply circuit.

Do as Steve suggests and inspect every component under the doghouse. Replace anything that looks wonky. Dittos with the bias cap and the bypass electrolytics.

Arjay

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Post subject: Re: Blackface Concert 120 hz hum
Posted: Wed Jul 16, 2014 12:37 pm
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If filter caps are bad you may read more than few volts AC ( yes AC volt ) on filter caps,

Few days ago I had some bad filter caps on Super reverb ; I could read 250 VAC yes AC and 340 DC


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Wed Jul 16, 2014 1:01 pm
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BMW2002Ti wrote:
Sounds like bad filter caps. At least, I would rule this out, first. Replacing the first stage (two 68mfd caps) maybe all you need to do. What is the conditions of the other main filter caps, under the doghouse?


The 3 20uf/500 Sprague Atom caps look like the have been installed more than once. I ordered a complete set of caps-Sprague. I'll get back in a couple days. Thanks


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Wed Jul 16, 2014 2:06 pm
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Krankster wrote:

The 3 20uf/500 Sprague Atom caps look like the have been installed more than once. I ordered a complete set of caps-Sprague. I'll get back in a couple days. Thanks



F & T caps are best buy .


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Wed Jul 16, 2014 2:29 pm
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stratele52 wrote:
F & T caps are best buy .


+1

I use F&T's exclusively now.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Wed Jul 16, 2014 4:00 pm
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Retroverbial wrote:
stratele52 wrote:
F & T caps are best buy .


+1

I use F&T's exclusively now.

Arjay


+1K...I told my amp tech "F&T's Only" the first time we talked when he was recapping my Bantam, he just looked at me and smiled! He knew!
:wink:
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Post subject: Re: Blackface Concert 120 hz hum
Posted: Fri Jul 18, 2014 8:18 pm
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I replaced all filter caps, resistors and cleaned eyelets. She's totally quiet and sounds great. I can't believe any tech would used old caps. That's why I do it myself. Thanks guys.


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Fri Jul 18, 2014 8:25 pm
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Rawk on!

8)

Arjay

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Post subject: Re: Blackface Concert 120 hz hum
Posted: Sat Jul 19, 2014 6:57 am
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Krankster wrote:
I can't believe any tech would used old caps. That's why I do it myself. Thanks guys.


No tech would do this. Bet, he charged you new cap prices.

JOC... where is this "tech" located?


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Sat Jul 19, 2014 9:35 am
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BMW2002Ti wrote:
Krankster wrote:
I can't believe any tech would used old caps. That's why I do it myself. Thanks guys.


No tech would do this. Bet, he charged you new cap prices.

JOC... where is this "tech" located?


Yup, $120. He's in Cincinnati.


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Post subject: Re: Blackface Concert 120 hz hum
Posted: Sun Jul 20, 2014 1:25 am
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Krankster wrote:
He's in Cincinnati.


Give that clown a wide berth.

:roll:

Arjay

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