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Post subject: Need Help Trouble Shooting 79 Pro Reverb
Posted: Thu Apr 05, 2012 6:55 pm
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I recently purchased a 79 Silverface Pro Reverb. Amp seemed to work fine for the first few weeks that I had it. In the last week its developed a rattle that only happens after the amp is well warmed up and only seems to happen on the low E string. Also the main fuse has blown twice in the past few days. It blows as soon as the main power switch is turned on with the standby off. I noticed that the red jewel wasn't on when i flipped the power on. Checked the fuse and found it burnt. I replaced it and the amp worked for a few days. The same problem occured today. Turned on the power switch and no power. Fuse blown again. I know very little about fixing an amp. Just wondering if there are any relatively easy things I could check before bringing the amp in and paying someone who knows what they're doing to look at it. Any info would be appreciated.


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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Thu Apr 05, 2012 7:33 pm
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Sounds like a faulty rectifier tube, as it happens in standby. Maybe time for output tubes and/or filter caps also. If you keep replacing the fuse, you might end up doing more damage, like the OT and more. :idea:

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Thu Apr 05, 2012 7:57 pm
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Jtune, that's a bummer. Obviously something is shorting out. From the rattle symptom, I'm going to suspect a bad power tube. Unless you have spare tubes(including the 5U4GB). It doesn't make much sense, to me, to mess around with the amp. The power supply filter caps would also be suspects. If you want to try something: I'd pull out all of the tubes, except the 5U4GB. Suggestion- mark the small tubes with a sharpie, to serve as a locator, when putting them back in their sockets. If the amp stays on, you could start replacing the pre amp(small) tubes, one at a time. But you'll have to turn the amp off between each replacement. If all the pre amp tubes can be in the amp and it stays on, I'd say the power tubes are at fault. Otherwise, just take it in. Art.....Agree with Shimmy,( he posted while I was slowly typing). The 5U4GB is a prime suspect if the amp doesn't stay on, with all of the other tubes removed. Art

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Sun May 06, 2012 7:58 pm
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Ok so i've had the amp in for this problem twice in the last month. The rattle on the low e ended up being a bad speaker. Had a hole worn through the voice coil. No big deal. But the repair shop cant get the fuse to blow. The first time i brought the amp in he retensioned the output tube sockets and replaced the 6L6 tubes with new JJ's. I had the amp back for about a week and the fuse blew again when I turned the amp on. I brought it back in and its been with them for about 2 1/2 weeks and the fuse hasn't blown for them. The fuse has never blown while playing. Every so often the amp just won't power on and the fuse is blown. I don't wanna ruin anything else by the problem not being fixed. I've heard its better to replace the tube sockets once they've arced out due to leaving a carbon trail. This is the 70 watt model. Is this the ultralinear model and if so does it have a rectifier tube? I don't have the amp back yet or i would just look. Not sure what to do if they can't find a problem with it. Any suggestions? If it has a rectifier tube I will try the diagnosis that was listed previously in this thread.


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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Sun May 06, 2012 9:21 pm
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Not sure which circuit you have but both versions have GZ34 rectifier tubes.

http://ampwares.com/schematics/proreverb_ab668.pdf

http://ampwares.com/schematics/pro_reverb_aa1069.pdf

As others have noted, if the fuse is blowing when the power switch is thrown but BEFORE the standby switch is, the only things in the circuit are the rectifier and the power supply caps. One of those two things may be shorting or leaking.

Just to cover all bases, though, make sure that you are using the proper fuse. Both circuits call for a 2-amp SLO-BLO fuse. When I built a 59 Bassman clone, I had a couple of times where the fuse blew on power up, but not while playing. Turns out I had inadvertantly installed a fast blow fuse instead of the required SLO-BLO. When flipping the standby switch to on, the sudden current in-rush would blow the fuse. With the proper fuse installed now, I have no problems at all.

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Sun May 06, 2012 9:28 pm
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Sorry about that, the 70 watt UL has SS rectifier, not tube.

http://www.studiosoundelectronics.com/schematics/fender_ultralinear_pro_rev.pdf

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Last edited by shimmilou on Sun May 06, 2012 9:45 pm, edited 1 time in total.

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Sun May 06, 2012 9:42 pm
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shimmilou wrote:
Sorry about that, the 70 watt UL has SS rectifier, not tube.


Ampwares site says this:

"Rectifier: 5U4GB, Some ’78 and ’79 models had a solid state rectifier."

"Some of the PRO RVB AA1069 Circuits (Silverface with the Mid control)came with a solid state rectifier."

"Watts: 40 or 70 (late models) Watts"

The amp was produced until 1982. The OP's amp is from 79. Is that considered "late model"? Does the OP's amp have a miderange control? The OP asked if his amp is ultralinear, so he does not know. I think more info on the amp model is required.

http://ampwares.com/amplifiers/fender-s ... ro-reverb/

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Sun May 06, 2012 9:53 pm
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:oops: I misread that.

I put a link in my previous post in case it is the UL. I would think that the tech would know the model and whether or not there is a rectifier tube.

Maybe a pic of the amp front and back would help identify. :idea:

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Sun May 06, 2012 11:19 pm
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JT, did you replace the speaker? Don't see the tube sockets, as a concern, unless the tech found a shorted power tube, that was arcing. Is the rattle gone, as the amp is now? Art

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Sun May 06, 2012 11:27 pm
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bluesky636 wrote:
Ampwares site says this:


Ampwares has screwed the pooch with a number of Fender listings.

The '79 Pro Reverb is indeed an ultra-linear amp......solid-state rectifier, 70-watt output with multi-tapped secondaries on the output tranny, tone stacks in both channels configured as with the Twin Reverb. This chassis and circuitry was shared by the equivalent-year Super Reverb and Bandmaster Reverb.

Ampwares will tell you that the non-verb Princeton was discontinued in 1979. Yet I own one that clearly dates to 1980 by the EIA codes on the pots, trannies, and cap can.

Caveat Emptor

Arjay

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Sun May 06, 2012 11:54 pm
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Arjay, that speaker would seem to be a prime suspect, right? Art

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Mon May 07, 2012 12:27 am
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I'm doubtful, Art.

A bad speaker generally does not cause an amp to blow its fuse.

It's got more serious issues, I'm afraid......I'd start with the power supply and work forward from there.

Arjay

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Mon May 07, 2012 12:37 am
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Right, Arjay! Just wasn't sure. Art

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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Mon May 07, 2012 12:01 pm
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Im gonna pick the amp up today. He couldn't get the fuse to blow. He said they went over the amp with a fine tooth comb and found no problems with tube sockets or caps or anything. He did say the pilot light was incorrect and they changed it. The first time they worked on it they replaced the output tubes and retensioned the sockets. I got it back and about a week later I tried turning it on and the pilot jewel wasn't lit up. I never tried actually playing any notes to see if it was working. I just assumed the same problem was occuring and checked the fuse. It didn't look blown but i stuck a new one in and the light came on. Maybe they fixed the fuse problem the first time and the pilot lamp just wasn't lighting up on power up? He said its also possible that with the bad speaker the amp might not be seeing the proper ohms and blowing the fuse. Either way they cant find a problem there. Im gonna pick the amp up and replace the bad speaker and see how it does i guess. Thanks for the input.


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Post subject: Re: Need Help Trouble Shooting 79 Pro Reverb
Posted: Mon May 07, 2012 1:01 pm
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Retroverbial wrote:
bluesky636 wrote:
Ampwares site says this:


Ampwares has screwed the pooch with a number of Fender listings.

The '79 Pro Reverb is indeed an ultra-linear amp......solid-state rectifier, 70-watt output with multi-tapped secondaries on the output tranny, tone stacks in both channels configured as with the Twin Reverb. This chassis and circuitry was shared by the equivalent-year Super Reverb and Bandmaster Reverb.

Ampwares will tell you that the non-verb Princeton was discontinued in 1979. Yet I own one that clearly dates to 1980 by the EIA codes on the pots, trannies, and cap can.

Caveat Emptor

Arjay


I didn't say that Ampwares was correct, I only quoted what they did say and asked for more information about the amp to narrow down what the OP actually has.

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