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Post subject: Cleaning and maintenance of an older SS Amp
Posted: Wed Sep 19, 2018 6:01 am
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Hi All
I am working on a 89 Deluxe 85 and have a few questions.
1) Why do I have three stereo jacks? They are inputs 1 and 2 plus headphone. Guitar input chords are mono.
2) I have 11 pots should they have a flat washer then a nut? Are the pots 12mm or 7/16
3) What the the cheapest device i can but that will put out a 1khz i assume audio signal for test points?
4) Can i use my speaker for the 8 ohm dummy load or a large resistor?
thanks


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Post subject: Re: Cleaning and maintenance of an older SS Amp
Posted: Wed Sep 19, 2018 7:06 am
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I suggest you check that speaker's impedance with a VOM -- you may find that it's a 4-ohm driver.

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: Cleaning and maintenance of an older SS Amp
Posted: Thu Sep 20, 2018 9:48 am
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The stereo jacks are to accommodate more switching capability, not to run stereo. When two guitars are plugged in and for a muting circuit, I think.
The pots are metric. Washers optional if they're missing.
The cheapest signal injector is your finger. 60hz. SS amps are mostly low voltage. Feelin lucky? On sensitive circuits, you can safely inject a signal from earbuds placed near a circuit.
Its an 8ohm on the 85. Rather than buy 100 watt dummy loads, I scrapped out an old space heater and cut the heating element down to 8 ohms. Mount it on a piece of board or in a water jar for cooling.


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Post subject: Re: Cleaning and maintenance of an older SS Amp
Posted: Fri Sep 21, 2018 4:31 am
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Thanks Tim
Is the 1khz signal injected into the FX loop power amp jack?
I can just use the speaker for a load correct?
What voltage is required for the input signal?
Are the test points taken on the top of the board?
Voltage is higher if the board is not grounded to the chassis.


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Post subject: Re: Cleaning and maintenance of an older SS Amp
Posted: Fri Sep 21, 2018 7:15 am
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The test points for audio signals are marked in ovals on the schematic.
Test points for dc voltage are marked in rectangles.
Most are on the board, but the input tp is the input jack, showing a 9mv ac rms input signal.
The controls need to be set according to the notes. Only 1 khz will give the right levels. The other signal levels should match up then.
Yes you need to ground the chassis to keep the shielding.
The voltages may vary depending on the ac voltage from the wall. Normally, I would adjust the ac voltage with a variac to set the correct b+ voltage, so the rest line up.
If you run it with the board pulled, be sure to heat sink the output transistors.
The speaker will be pretty annoying at that level, but as I described earlier, the output stage voltages will be different if you use a dummy load. Put a rug over the cabinet to quiet it down.


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Post subject: Re: Cleaning and maintenance of an older SS Amp
Posted: Tue Sep 25, 2018 5:07 am
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Thanks Tim
Does the 1khz input go into the channel one guitar input jack?
I thought I read on the schematic to use the power amp jack


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Post subject: Re: Cleaning and maintenance of an older SS Amp
Posted: Tue Sep 25, 2018 7:08 am
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The power output test does use the power amp input. The rated output is 65 watts @ 5% distortion. This is past clipping and can only be accurately determined with a distortion meter. Not to worry though, if it runs its probably fine. These power stages are bulletproof and seldom fail.
The preamp levels are based on signal input to the ch2 input jack. This is where you need all the controls properly set to make sense of it.


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Post subject: Re: Cleaning and maintenance of an older SS Amp
Posted: Tue Sep 25, 2018 7:45 am
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Oh I see that is a different test all together. So i need to inject my 1khz signal into the 2nd channel to get to the pre-amp signals correct? What is the input impedance of my passive fender strat?
Did you say a 9mv signal where did you find that info?
Is it better to use a SS signal generator that a tube?
Thanks for all your help


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