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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Tue Sep 10, 2019 11:50 am
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Fluke set on kOhms I get 109 for that resistor.

More later.

RB3988


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Fender Play April 2019
Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Tue Sep 10, 2019 1:10 pm
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109KΩ is a little on the high side but still within spec (assuming a 10% tolerance).

Arjay

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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Tue Sep 10, 2019 9:17 pm
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Just to be sure, measure a known, good, 1% resistor in the 100K range with that Fluke.


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Wed Sep 11, 2019 8:46 am
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BMW2002Ti,

Fry's Electronics is the only local spot I can find that sells this type of resistor, they list several 100K ohm types with different "watt" specs...1W etc.

https://www.frys.com/search?search_type ... Name=false

Which is the one to buy?

Thanks,


RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Wed Sep 11, 2019 8:51 am
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You don't have a precise resistor around the 100K-ohm range? Like anything between 50-220K-ohms? You are just testing the accuracy and precision of your Fluke.

If you are going to buy that resistor, go with the 1/2 watt one. You maybe able to use it later.

:)


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Wed Sep 11, 2019 9:03 am
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BMW2002Ti,

I'll double check to see if I have any resistors at all...otherwise I'll make a trip to Fry's.

Thanks,

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Wed Sep 11, 2019 12:48 pm
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vinyl wrote:
FWIW, a 16V rating on the second stage cathode bypass capacitor of a tremolo oscillator is inadequate IMO. It should be at least 25V, 50V would be better.

If you look at the schematics of most AB763 amps, the tremolo oscillator is identical, and the voltage at the cathode of the second stage of the tremolo oscillator is 17 volts.

Image



The whole point of this post was to point out the inadequate voltage rating of a 16 Volt capacitor, which is what is actually in your amp. The only thing that will kill a capacitor faster than a reverse voltage is an over voltage application.

Even if you don't replace all of the electrolytic caps, you should replace this particular one.

BMW2002Ti wrote:
Just to be sure, measure a known, good, 1% resistor in the 100K range with that Fluke.

Mostly a waste of time IMO. Certainly, you want to know your meter is calibrated.

The big question here is after a period of time, the tremolo takes some period time before it works. In your first post, it takes 1-2 minutes, then in your next post that mentions a time for the tremolo that only takes 30 seconds, then in the next post it only takes 15 seconds.

I realize you are trying to learn something here, and that is admirable, but change this capacitor:
Image

And change it with one that is rated for at least 25 Volts, not 16.

We'll go from there.


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Wed Sep 11, 2019 1:07 pm
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vinyl wrote:
I realize you are trying to learn something here, and that is admirable, but change this capacitor:
Image

And change it with one that is rated for at least 25 Volts, not 16.


+1

And change any of the other cathode-bypass caps that have that chintzy voltage rating. They all need to be 25/25's.

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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Wed Sep 11, 2019 8:09 pm
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Vinyl and Retroverbial...

Also...what is it in the photo that somehow lets you know the voltage is 16 rather than 25?

Sooner or later I'll get this done...

Thanks,

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 12, 2019 9:36 am
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royb3988 wrote:
Vinyl and Retroverbial...

Also...what is it in the photo that somehow lets you know the voltage is 16 rather than 25?

Sooner or later I'll get this done...

Thanks,

RB3988


It's denoted on the left side of the capacitor. 22uF 16v. Easier to see on the right edge of this photo.

Image


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 12, 2019 9:48 am
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Roy -- If you can hear a faint ticking in the speakers, then the oscillator is working. And you've already replaced the opto-coulper. The lamp driver cathode bypass cap has also been replaced (although should be upgraded as previously stated) -- but one thing I have not heard mentioned is the Vibrato Intensity control. If the wiper of this control loses contact with its carbon track either because it's dirty, or the simply worn out, then the effect on the tremolo effect will be much like that of dirty volume control -- sometimes it works, sometimes not, and sometimes, take time to kick in.

The control can be checked by turning it up to maximum intensity, and then using a jumper with clips to short the middle Intensity control terminal to the outer terminal of the control that is NOT grounded. If the control was the issue, then the tremolo effect should begin the moment the oscillator starts.

Dave


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 12, 2019 3:46 pm
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Image


Cap on left is a 25mF/25V, on right is a 22mF/25V...I was unable to find a resistor yet.

Which cap is the one to use?

Thanks,


RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 12, 2019 3:48 pm
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The schematic specifies 25/25.

Arjay

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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 12, 2019 3:54 pm
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Ok,

The guy who sold me the caps asked..."For the 100K resistor...how many watts?"


RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 12, 2019 4:15 pm
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1/2 watt or 1 watt would be fine.


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