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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Aug 29, 2019 12:39 am
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Arjay,

I cannot say to a certainty if those items have been checked. The last time a tech had the amp was in early 2017...due to fuses blowing. While I waited and watched he put in a new fuse, picked up the chassis and twisted it while he watched his scope. On the second fuse he turned the chassis upside down and shook it...a small piece of what he called "old solder" fell out. On the 3rd fuse he replaced the V2 12AX7 with a new Tung-Sol and we played the amp for 10 minutes...but at that time the Tremolo was not a problem. He charged me $20 including the tube and fuse.

I need to get it back to him and mention the suggestions in this thread.

Thanks for the follow up,

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Aug 29, 2019 6:12 am
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Image

Check the lead of this cathode bypass cap. Looks like it's barely connected. Use a wooden chopstick or some other "insulated" tool to see if it's really soldered to the eyelet on the board. If not, re-solder.

Check the solder joints of the other cathode bypass caps as well.


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Fri Aug 30, 2019 3:41 pm
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Vinyl,

I unsoldered both ends...the Tremolo still operates with that cap out...is it supposed to? I then re-soldered the cap securely, tried the wooded prod routine throughout the chassis...no loose or cold solder joints that I could find. The amp is back up and running and sounding like it should.
I'll Google those other caps you mention and check them one at a time. My experience inside this...or any amp's...chassis is very limited and elementary but I learn something each time I get into a thread like this.

Thanks,

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Fri Aug 30, 2019 7:26 pm
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RB,

After re-soldering, are you saying there is still no change? Still takes 30 seconds for the tremolo to work? Still motorboats if you crank the speed up?

Here is a couple of links to help you with your education "quest".

http://www.valvewizard.co.uk
http://www.geofex.com/tubeampfaq/taffram.htm


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Sat Aug 31, 2019 10:05 am
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Vinyl,

Yes, no change to the Tremolo issue at all.

I will check out the links you provided.

Thanks,

RB3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Sun Sep 01, 2019 3:07 pm
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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

Changing back to 25uF might also give you a slightly slower low speed setting. (very slight)

Cheers,

RB,

Please let us know how all this works out.

The loudness issue is a whole "nother can of worms"


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Sun Sep 01, 2019 9:28 pm
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These three caps control the rate of the tremolo. They are lined-up on the circuit board (see red arrows). I usually replace them in older amps, as I have a bunch of 1KV 0.01mfd and 0.02mfd Sprague ceramic disc caps. If you change the middle cap to 0.02mfd from 0.01mfd --- you will slow the rate of the tremolo. They are arranged on most vintage Fender amp circuit board: 0.02mfd/0.01mfd/0.01mfd --- going from the tube side of the board to the pots side of the board.

Image

Image


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Tue Sep 03, 2019 4:35 pm
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Vinyl,

The area you have encircled in red...how to best identify that when I open up the chassis?

Thanks,

RB3980


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Tue Sep 03, 2019 6:15 pm
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RB,
A fair and reputable supplier of replacement parts:
https://www.tubesandmore.com/products/capacitors?filters=Type%3DElectrolytic
6 Sprague 25uf x 25vdc @ $2.25 each =$13.50
1 F&T 100uf x 100vdc @ $3.06
3 F&T 22uf x 500vdc @ $ 3.55 each =$10.65
2 F&T 80uf x 450vdc @ $6.26 each = $12.52
Total= $39.73 + shipping
You should probably replace them all, as has been recommended. Especially if you plan to do the work yourself. Your amp will thank you, by lasting another 10 years w/o much worry.
PS: I would still recommend you check the ground reference on your opto-isolator and shorten the leads on the bright switch.


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Tue Sep 03, 2019 7:18 pm
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"The area you have encircled in red...how to best identify that when I open up the chassis?"

The resistor next to the yellow arrow is the 100K-ohm cathode-tied one to pin 8 of V5.

Image


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Wed Sep 04, 2019 2:59 pm
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royb3988 wrote:
Vinyl,

The area you have encircled in red...how to best identify that when I open up the chassis?

Thanks,

RB3980


Been away for a bit. It's the same cap I asked you to check the soldering on.

Image

Technically, it's the one tied to pin 8 of V3.

sfceric64 wrote:
RB,
A fair and reputable supplier of replacement parts:
https://www.tubesandmore.com/products/capacitors?filters=Type%3DElectrolytic
6 Sprague 25uf x 25vdc @ $2.25 each =$13.50
1 F&T 100uf x 100vdc @ $3.06
3 F&T 22uf x 500vdc @ $ 3.55 each =$10.65
2 F&T 80uf x 450vdc @ $6.26 each = $12.52
Total= $39.73 + shipping
You should probably replace them all, as has been recommended. Especially if you plan to do the work yourself. Your amp will thank you, by lasting another 10 years w/o much worry.
PS: I would still recommend you check the ground reference on your opto-isolator and shorten the leads on the bright switch.


I agree with sfceric, but you will only need 5 Sprague 25uF X 25V for a Dual Showman.


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Wed Sep 04, 2019 4:17 pm
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I apologize for the totally incorrect comment I made previously, :oops:

I still maintain that a 16V rating for the second stage of the tremolo circuit is inadequate.
The tremolo circuit consists of 2 parts, the first tube stage is the oscillator, the second stage provides the gain to drive the neon bulb of the trem roach.

What I should have said is the 25uF provides a slightly lower frequency response than a 22 uF capacitor for the second stage.

It won't really make the tremolo rate slower.

Please feel free to call me whatever name you choose.
<edit>
Some of my favorites are obstinate, obstreperous, or obtuse. :lol:
I love alliteration.


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 05, 2019 10:08 am
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Well...
Yesterday I opened up the chassis again, looked at all connections mentioned by members in this thread and I then re-flowed all those connections.

This morning the Tremolo come on instantaneously after hitting the foot switch as soon as I took the amp off Standby! Plus...THE MOTOR BOATING IS GONE! This amp has not worked properly for more than 2 years!!

The only thing I can say is...if any of you have ever been embroiled in an attempt to fix an amp issue and its inherent frustrations, and my guess would be many of you have been, you know the level of my pure, unadulterated JOY when the amp and Tremolo came on properly this morning. I don't know which connection or connections it may have been but...at the moment I do not care! Again let me say...THE MOTOR BOATING IS GONE!

To all of you who stuck with me on this I cannot thank you enough!

Royb3988


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Post subject: Re: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 05, 2019 11:05 am
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Outstanding.

NOW GET OUT THERE AND RAWK!

:wink:
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: Fender 1967 DUAL (in block letters) Showman
Posted: Thu Sep 05, 2019 12:24 pm
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royb3988 wrote:
Well...
Yesterday I opened up the chassis again, looked at all connections mentioned by members in this thread and I then re-flowed all those connections.

This morning the Tremolo come on instantaneously after hitting the foot switch as soon as I took the amp off Standby! Plus...THE MOTOR BOATING IS GONE! This amp has not worked properly for more than 2 years!!

The only thing I can say is...if any of you have ever been embroiled in an attempt to fix an amp issue and its inherent frustrations, and my guess would be many of you have been, you know the level of my pure, unadulterated JOY when the amp and Tremolo came on properly this morning. I don't know which connection or connections it may have been but...at the moment I do not care! Again let me say...THE MOTOR BOATING IS GONE!

To all of you who stuck with me on this I cannot thank you enough!

Royb3988


That's good news. Don't be a stranger.

What about the loudness issue? Is your Super Reverb still louder?


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