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Post subject: 1973 twin reverb question about channel 1&2.....
Posted: Mon Nov 04, 2019 1:42 pm
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Location: In a house....unless I'm at work....then I'm in a shop.
Hi all.
This maybe a newby question, I have played mostly through Peavey amps over the years. I came across a 1973 (So they tell me by the serial number) Fender Twin Reverb amp with the master volume and pull boost at an estate sale, it had been sitting for 20 some years in a garage. The owners son said his Dad gigged with it for a while, then once he stopped playing out he got a Vibrolux that he would play in the house and didn't play it as it was too much for just playing in the house.
He said he tested the amp,, and put some new tubes in it, and that the reverb was working but weak and the tremolo did not work.
I inspected it, it had some mold issues, as it was in an unheated garage, but the speakers (Utah speakers) were in perfect shape with no rot or tears and the original footswitch.
We came to a price of 375.00 for so I took the risk and took it home.
I removed the chassis and used electrical cleaner to wash out the dirt and mold and cleaned the amp case put. I found that the tube he had replaced for the reverb/Tremolo drive and a bent over pin. I pulled out a spare 12AX7 and put it in.
The footswitch leads were dry rotted and going open, so I got a new replacement one from Fender (It is the RCA jack style) and now it all works great.
I have it currently set with the pull off (It seems to kill the reverb when on) and I set it at 10 to basically take it out of the circuit and just use the channel volume and the volume on the guitar to control it.

So here is my question, on either the normal or Vibrato inputs, channel 1 seems to have more of a brighter fuller sound the channel 2, with seems a more midrangy. On my Peavey amp, the two inputs are usually marked high and low gain, so it's normal on a Peavey but is is normal for a Fender?

I understand old amps have electrostatics that can dry out and need to be replaced from time to time, is this a sign of that?

When I found that bent pin (That, and these were no name Chinese tubes) I replaced them with a set of tubes I had on hand (Peavey branded one all 12ax7's or ECC83's). I know it has a couple that are meant to be 12at7's (ECC81's) is this the possible issue?

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Fender Play November 2019
Post subject: Re: 1973 twin reverb question about channel 1&2.....
Posted: Mon Nov 04, 2019 2:51 pm
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Each of the #1 inputs (regardless of which channel) has a higher gain than the #2 inputs, by design.

For proper operation you should install 12AT7's in the V3 and V6 sockets as soon as you can. V3 is the reverb driver while V6 is the phase inverter.

Arjay

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Post subject: Re: 1973 twin reverb question about channel 1&2.....
Posted: Mon Nov 04, 2019 4:09 pm
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Other than replacing the tubes, do you plan to fix the issues yourself or are you more inclined to find a repair tech in your area to fix it?
The electrolytics having sat 20+ years in a basement are likely bad/leaking and could cause major issues. There are PSU power supply electrolytic capacitors and several smaller electrolytic capacitors that deviate each of the circuits that make up the amplifier. For optimal performance in the future those should probably all be replaced.
Pictures will help everyone here help you, so if you have the time, take some pictures and upload them to a web based site such as imgur or flickr or google. By uploading them somewhere on the internet they will receive an http:// .jpg file name. Copy that filename one at a time and post it here using the IMG button above this text box when replying to a post in this thread. You can preview your post to ensure the photo shows up as expected. There is a specific format thats required and by holding your mouse cursor over the IMG button that format is listed in the tip box. "Image_url" is the code for the actual filename you save-whatever that may be.

The image in your signature doesn't show up because it is not hosted on an active internet server.
Thus it won't help us if you try to post photos on that server. Use one of the suggested photo hosting sites mentioned or choose one of your own that works.


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Post subject: Re: 1973 twin reverb question about channel 1&2.....
Posted: Mon Nov 04, 2019 5:10 pm
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The Sarge is correct, jeffy. ALL of the amp's electrolytics should be replaced as soon as possible -- the filter array beneath the doghouse, those in the cathode-bypass circuits, and the bias supply (note the polarity is reversed on the latter). While you're at it take a look at the power-rail resistors (co-located with the filter caps) and the 470Ω/1W resistors on each of the power-tube sockets. Replace any that look wonky (metal-oxide types are fine for this application). If the power cable is not grounded, replace it with a new one that is. You should also remove or disconnect the "death cap". Clean all jacks -- input, speakers, reverb tank, and footswitch -- either with De-Oxit spray cleaner or emery cloth. And take it easy on that cabinet -- it's not Fender's traditional finger-joined construction. IOW you can't toss it around like the older blackface furniture. The corners are rabbet-style and held fast by forty-six year old glue.

Arjay

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Post subject: Re: 1973 twin reverb question about channel 1&2.....
Posted: Mon Nov 04, 2019 8:49 pm
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Thank you for the advice, while I am able to do the work, I think I will take it to a amp tech and have her looked over.

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Post subject: Re: 1973 twin reverb question about channel 1&2.....
Posted: Mon Nov 04, 2019 10:21 pm
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You should be able to get everything serviced for $125 to $175 unless some other issue is discovered.

Arjay

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