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Post subject: Re: 100th post need some opinions with photos
Posted: Fri Dec 13, 2013 1:47 pm
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Retroverbial wrote:
mud wrote:
First of all I do believe its a AA1069 circuit not sure if that matters
Second would it be this resistor I need to check
Image

Or these
Image

or all 4 and the pot

Thanks
mud


I'd check everything in the biasing circuit, including the incoming voltage from the power supply.

Arjay


Thanks Arjay I do know how to check the resistors but where would I put my meter to check the incoming voltage from the power supply
mud


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Post subject: Re: 100th post need some opinions with photos
Posted: Sat Dec 21, 2013 9:30 am
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Check all voltage points, as illustrated in the schematic & layout. VDC will prolly run 10-25% higher than listed, as the wall voltages run around 10-25% higher than when the schematic were drawn.

Start with main power supply and bias supply circuits. B+ and all taps off the power supply. And the negative VDC off the 10k-ohm resistors (off balance pot) branch point.

You must read negative VDC off pins #5 of the 6L6GC's.

http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: 100th post need some opinions with photos
Posted: Sat Dec 21, 2013 9:57 am
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BMW2002Ti wrote:
...as the wall voltages run around 10-25% higher than when the schematic were drawn.


A bit of an overestimation, Steve.

The highest voltage I've ever seen from a residential wall socket measured 124 VAC -- only a seven-volt deviation from Fender's original spec.

Arjay

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Post subject: Re: 100th post need some opinions with photos
Posted: Sat Dec 21, 2013 10:24 am
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Arjay, yeah make that 5-10%.

So Sorry. :(


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Post subject: Re: 100th post need some opinions with photos
Posted: Sat Dec 21, 2013 10:33 am
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BMW2002Ti wrote:
Arjay, yeah make that 5-10%.


+1

And Leo always over-spec'd his iron by 20% (or more). Which is why I never get my panties in a wad about plugging a blackface into a "hot" wall socket or diddling around with power supplies or swapping rectifier tubes. Now were I to own a primo, all-numbers-matching, vintage tweed model, that'd be another story. I don't think the Triad's were quite as beefy as the Schumacher's.

Arjay

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Post subject: Re: 100th post need some opinions with photos
Posted: Sat Dec 21, 2013 11:01 am
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mud wrote:
First of all I do believe its a AA1069 circuit not sure if that matters
Second would it be this resistor I need to check
Image

Or these
Image

or all 4 and the pot

Thanks
mud


Given the '69 date code :shock: on the bias board cap, I'd consider replacing it on general principle. Pay attention to the polarity if you decide to replace it.

Bill


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Post subject: Re: 100th post need some opinions with photos
Posted: Sat Dec 21, 2013 11:44 am
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vinyl wrote:
Given the '69 date code :shock: on the bias board cap, I'd consider replacing it on general principle. Pay attention to the polarity if you decide to replace it.


+1

That component is well past its prime. The remaining electrolytics are likely of similar age and condition.

Arjay

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Post subject: Re: 100th post need some opinions with photos
Posted: Sat Dec 21, 2013 12:00 pm
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vinyl wrote:

Given the '69 date code :shock: on the bias board cap, I'd consider replacing it on general principle. Pay attention to the polarity if you decide to replace it.

Bill


Like all of 6 ( ? ) bypass caps .


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Post subject: Re: 100th post need some opinions with photos
Posted: Sat Dec 21, 2013 11:52 pm
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stratele52 wrote:
Like all of 6 ( ? ) bypass caps .


That might not be a bad idea either. Or at a minimum, inspect them for tell-tale signs of leaking electrolyte. Replace as necessary.

Arjay

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Post subject: Re: 100th post need some opinions with photos
Posted: Sun Dec 22, 2013 2:33 am
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Retroverbial wrote:
stratele52 wrote:
Like all of 6 ( ? ) bypass caps .


That might not be a bad idea either. Or at a minimum, inspect them for tell-tale signs of leaking electrolyte. Replace as necessary.

Arjay


On these small by pass caps I never see ( can we they are so small ? ) a sings of leaking electrolyte.

Testing many with my Heatkit capacitor Checker IT 28 I found most of all leaking and /or discharge problem .
Even if this was not the problem at the origin, have replaced them have revived the amplifier.
Obviously I put only good quality, Sprague Atom.

These " tests " were performed recently on a few Fender Blackface and Silverface amps.


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Post subject: Re: 100th post need some opinions with photos
Posted: Sun Dec 22, 2013 3:17 am
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Note the cardboard-hulled Mallory's of this '64 Concert Amp.....

Image

If/when these caps begin to leak or bleed electrolyte, a visual inspection will instantly reveal that fact.

Arjay

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Post subject: Re: 100th post need some opinions with photos
Posted: Sun Dec 22, 2013 3:29 am
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+1, these are big enough to see leakin signs, mine are not so big .

IMO no leaking signs do not mean they are good


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Post subject: Re: 100th post need some opinions with photos
Posted: Sun Dec 22, 2013 4:08 am
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True.

But signs of oozing or seeping are an indication that they're definitely bad and need to be replaced.

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: 100th post need some opinions with photos
Posted: Sun Dec 22, 2013 4:57 am
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Retroverbial wrote:
True.

But signs of oozing or seeping are an indication that they're definitely bad and need to be replaced.

Arjay



Sure , like if you see they are broken in half :lol: But more important , no sings do not mean they are good.

As you know the value of these capacitors affects the tone. Same thing if these capacitors malfunctioning. The amp will still work "well" but does not get its full potential.
As a guitar with old strings.

An old capacitor is likely to have these problems.

Any time I replace them , I hear a better sound from the amp . My customer heard it too .
A Fender BF sound more like a NOS Fender BF

I do some A / B test with some NOS Fender BF.


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Post subject: Re: 100th post need some opinions with photos
Posted: Sun Dec 22, 2013 9:01 am
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For any amp over 15 years old with original electrolytic caps --- or amps that have caps which haven't been changed in 15 years (but amp has been constantly used) --- I replace all the lytics. To me, it helps the owner know when the caps were changed out. All were done at the same time.

Replacing only those that leak or are dry risks failure to the remaining caps, due to added stress applied by the extra voltage and current delivered by the new caps.

If the amp has been in storage, unused for 5 years --- I ramp up the amp, inspect the caps and listen for issues related to failing caps. Taking B+ measurements can ID bad caps in the power rail, too.

I always change BIAS supply caps. Esp if they are original or cheesy aftermarket brands. It just doesn't pay to keep old ones in the circuit. IMHO.

I figure that it really doesn't cost that much to have a nice quiet, consistent PSU that should last another 15-20 years.


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