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Post subject: Vibrato doesnt work
Posted: Wed Dec 15, 2010 1:08 pm
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The vibrato on my 68 Pro Reverb doesnt work. I just got this amp and it was dead when I got it so I replaced the e-caps and replace the rectifier tube and the 2 power tubes. I also replaced the plug with a 3 prong. And with yalls help I found a wire on the heater circuit that needed resoldering. After that I thought it all sounded good but I hadnt messed wtih the vibrato until this morning and it doesnt work. I have the original foot switch.
Also it make a bad pop sound when I reached back and turn the standby switch off that I didnt like. Where should I start?


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Posted: Wed Dec 15, 2010 6:13 pm
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Hi OG, guess I'd check the foot switch first. A continuity check will let you know if the switch is working. V5 must be a good working tube( you can swap it with V1 for a test). If the tube and switch are OK, check to see if there is any light emitted from the component on the circuit board directly across the board from V5, looking from the rear towards the controls( if the amp is in the cab, then look through the ext. speaker jack). Art

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Post subject: Re: Vibrato doesnt work
Posted: Mon Dec 20, 2010 11:05 am
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Thanks Art,

I checked the continuity of the foot switch and it checked out ok.

I think I may have got the tubes out of order. They seem to be original 1968 tubes and most of the lettering is worn off so I guessed. To make things worst the tube layout chart in the cab is mostly peeled off. Whats left of the tube chart shows a GZ34 rectifier and then two 6L6GCs but the pre amp tubes section is mostly scratched off. The top of the chart that would show which circuit is missing too. So I went over to the fender amp guide to check to see the pre amp tube arrangement but the two circuits listed (AB668, AA1069) for the silverface Pro Reverb don't have a GZ34 rectifier. So I thought maybe its an early 68 model and has the blackface circuit AA165 but it shows it was only in models up to 1967. I searched the web and read there is another circuit named AA1265 but couldn't find it on the Fender amp guide and cant find the tube layout for that circuit. Any guess as to what the correct tube layout should be. Could the wrong tube be my problem?

OG

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Post subject: Re: Vibrato doesnt work
Posted: Mon Dec 20, 2010 11:16 am
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Also, How can I find out for sure which circuit I have. All the component date codes show the 11th and 12th week of 1968.

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Post subject: Re: Vibrato doesnt work
Posted: Mon Dec 20, 2010 11:17 am
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Disregarding the rectifier tube (GZ34 or 5U4GC) the remainder of the tube layout remained constant to the original AB165 circuit.

HTH

Arjay

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Post subject: Re: Vibrato doesnt work
Posted: Mon Dec 20, 2010 11:19 am
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I should of thought to look at that. Thanks!

OG

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Post subject: Re: Vibrato doesnt work
Posted: Mon Dec 20, 2010 11:32 am
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Judging from your components dating to the 12th week of '68, your amp is likely an AB165 -- especially if the wiring is all of the cotton-insulated variety. The follow-on circuit revision did not occur until June.

HTH

Arjay

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Post subject: Re: Vibrato doesnt work
Posted: Wed Dec 22, 2010 10:42 pm
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Hey OG, did you have a chance to check out that light(LDR) ? If that V-5(12ax7) is a weak tube, the circuit function will be in trouble. Some new production tubes can't even do the job. If a known good tube doesn't help, then the LDR component would be the next likely suspect. Art

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Post subject: Re: Vibrato doesnt work
Posted: Thu Jan 06, 2011 1:59 pm
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I decided to just order all new preamp tubes and see if that works. You said some of the new production tubes aren't even powerful enough so I asked a few friends and they said JJ tubes are suppose to be some of the more powerful ones so I ordered those. Is that right? Most of my friends are musicians and not amp techs.
Also while Im waiting for the tubes I started poking around and I found another wire that was loose. It wasn't even soldered at all. It barely had a mechanical connection. I checked the schematic first just to make sure it was in the right place and then soldered it on right. It was a brown wire on pin 3 on the power tube next to the rectifier. Does that have anything to do with vibrato? I almost want to power it up right now to see what the wire did but I think I will just wait for the tubes. They should be here tomorrow.

OG


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Post subject: Re: Vibrato doesnt work
Posted: Thu Jan 06, 2011 2:06 pm
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OracleGreen wrote:
Also while Im waiting for the tubes I started poking around and I found another wire that was loose. It wasn't even soldered at all. It barely had a mechanical connection. I checked the schematic first just to make sure it was in the right place and then soldered it on right. It was a brown wire on pin 3 on the power tube next to the rectifier.


Whatever is soldered to pin 3 of the V8 tube socket should be duplicated on the V7 tube socket.

Is there a brown wire on pin 3 of V7?

Arjay

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Post subject: Re: Vibrato doesnt work
Posted: Thu Jan 06, 2011 2:17 pm
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No, the wire on pin 3 of V7 is a blue wire. The brown wire on pin 3, V8 and the blue wire on pin 3, V7 are twisted together and go through the chassis to the small transformer in-between the other two transformers.
http://www.ampwares.com/schematics/pro_reverb_aa165.pdf

OG


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Post subject: Re: Vibrato doesnt work
Posted: Thu Jan 06, 2011 2:34 pm
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That's correct then. The wires on pin 3 are the output signal feeds from the 6L6's to the primary of the OT.

Best to check all the other solder joints on each tube socket as well. The '68 models are notorious for shoddy wiring and assembly problems.

Arjay

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Post subject: Re: Vibrato doesnt work
Posted: Sun Jan 09, 2011 10:58 am
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Did you follow Art's suggestion about check the optocoupler roach? Also, double check the wiring to the pots off this part of the circuit. May have been mis-wired, bad solder, shorted, whatever. Here's a link that may help:

http://music-electronics-forum.com/t21202/


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Post subject: Re: Vibrato doesnt work
Posted: Tue Jan 11, 2011 12:20 pm
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Tried to check it out today but it blew the fuse. All I did was resolder the brown wire on pin 3 v8 and put in new preamp tubes. It was working except for the vibrato. Now it blows fuses about 10 seconds after I switch it on. I had the speakers plugged in and all knobs on 3 1/2. I don't know what it could be.


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Post subject: Re: Vibrato doesnt work
Posted: Thu Jan 13, 2011 10:47 am
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Hi OG, blowin' fuses ? Maybe you got a bad tube. I'd start by removing all the tubes except the rectifier. Then testing at each step: first the rectifier alone; add the power tubes; add the phase inverter; add V5; add V1; add V2& V4; add V3. When the fuse blows that tube should be swapped for another to check whether it's the tube or a short in that circuit. Good Luck, Art

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