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Post subject: 1961 Fender Reverb Unit
Posted: Tue Sep 01, 2015 5:13 pm
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Finally have time to start working on the amps I've been accumulating over the last year and a half. First up is a 1961 Fender Reverb Unit. It looks like someone put on a newer logo and a fresh reverb tank in 1966. The last seller installed a 3 prong plug (correctly I believe) and did keep the original (yay!) The large green cap on the pots looks a bit odd as well. Otherwise it appears to be original. Transformers date to 1961 and the one pot I can read seems to be a 1959. Unit works great, but is a touch noisy. Filter caps are definitely due to be replaced, and I think it could use a good cleaning but otherwise not too bad. Replaced reverb tank is a Gibbs so that is a plus. One last bit of trivia, and a reminder that these amps were hand made is that the jack for the foot switch looks to have never been installed. Guess someone just missed that detail!

http://1drv.ms/1L2zs5E


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Post subject: Re: 1961 Fender Reverb Unit
Posted: Tue Sep 01, 2015 6:09 pm
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Odd that the footswitch jack was never installed.

:shock:

Wait for BMW2002ti to show up -- he's our resident expert on the 6G15 and can walk you through the servicing procedure.

Is the Gibbs tank dated?

Arjay

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Post subject: Re: 1961 Fender Reverb Unit
Posted: Tue Sep 01, 2015 6:20 pm
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Not sure you'll need any cleaning on the inside...pretty clean! Nice.

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Post subject: Re: 1961 Fender Reverb Unit
Posted: Tue Sep 01, 2015 6:35 pm
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Gibbs tank is dated 1966 and that would jive with the replaced logo. I have a new reproduction flat brown logo on the unit currently.

I was doing some further exploring and I don't think they did the 3 prong plug quite right. I need to double check on the proper installation of that. Also the one ceramic disc on the tone and mixer pot was changed, so I need to order something for that. I was thinking of adding a modern Switchcraft 1/4" jack so that I can use a foot switch as well.

And there is a good 50+ years of dust in there. :D


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Post subject: Re: 1961 Fender Reverb Unit
Posted: Tue Sep 01, 2015 7:53 pm
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Nice unit! The three-prong wiring seems ok?

Image

BTW... I suggest putting a 1 meg-ohm, 1/2 watt resistor from the 12AX7 (7025) grid-to-ground. Fender didn't put this in the vintage era Reverb Units. But, added it to their SF and reissued units. Helps prevent that 12AX7 from runaway. The added resistor is on lower right of photo. Going from 12AX7 grid (pin #2) to grounding point on jack.

I used a silver mica cap, for the cap you mentioned (on the tone control). This is a great sub. Cleans up the tone a lot.


Image


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Post subject: Re: 1961 Fender Reverb Unit
Posted: Wed Sep 02, 2015 1:44 pm
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All this helpful knowledge! I did some more digging in the amp, and I think there were a couple of small fixes in 1966 or so. So I think the triage list right now is:
1. Clean and dust gently
2. Swap the mystery tone capacitor with a silver mica
3. Disconnect the "death cap"
4. Replace one wonky looking input jack and check on wiring of input/output jacks
5. Add foot switch jack
6. Add runaway capacitor (does this affect tone at all, or could I use a generic electronics project cap?)
7. Recap with F & T's

And speaking of reverb tanks, here is a rare beast (although the seller has the date all mixed up)

https://reverb.com/item/1008373-fender- ... 1967-black


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Post subject: Re: 1961 Fender Reverb Unit
Posted: Wed Sep 02, 2015 1:52 pm
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Hokusai22 wrote:
And speaking of reverb tanks, here is a rare beast (although the seller has the date all mixed up)

https://reverb.com/item/1008373-fender- ... 1967-black


Likely a typo and the seller meant '76 since that's the grill-cloth color then extant from 1974 through late 1977.

Arjay

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Post subject: Re: 1961 Fender Reverb Unit
Posted: Wed Sep 02, 2015 3:20 pm
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Yes, I believe that is a 1976 model. It has 3 X 12AX7 and one 6V6GTA. Not the one 12AT7, one 12AX7, and the 6K6GT of the vintage early to mid 1960s units.

http://ampwares.com/wp-content/uploads/ ... b-Unit.pdf

Here a photo of the power rail I replaced on my 1965 unit. I used a supply of older US made Sprague ATOM caps. Before all the issue with whether new ATOMS were made in Taiwan and relabled. Increased failure of the Sprague started to be reported in the mid 2000s. Supposedly, QA/QC has improved since then.

OEM:

Image

New:

Image


Last edited by BMW2002Ti on Wed Sep 02, 2015 3:36 pm, edited 1 time in total.

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Post subject: Re: 1961 Fender Reverb Unit
Posted: Wed Sep 02, 2015 3:30 pm
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" 6. Add runaway capacitor (does this affect tone at all, or could I use a generic electronics project cap? "

It's a grid-to-ground resistor. 1 meg-ohm. It will not effect the tone. It helps to set the idle bias. If there is excessive current swing is present on the grid --- like when a unit has temporary parasitic oscillation issues --- some of the current is sent to ground.

You can see it in the current reissued Reverb units.

Original:

http://ampwares.com/wp-content/uploads/ ... ematic.pdf


'63 Reissued Reverb Unit (see R13 on schematic):

http://bmamps.com/Schematics/fender/63_ ... manual.pdf


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Post subject: Re: 1961 Fender Reverb Unit
Posted: Wed Sep 02, 2015 3:46 pm
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Cool stuff. I think I'm on the right track over here. It looks like one input jack was swapped out, the input/output wires replaced and the mystery cap added to replace one of the ceramic discs originally in there. The 3 prong plug is good but they forgot to remove the dreaded death cap so that can go. My local version of radio shack has a giant mixed bag of resistors for about $5 including 2 or 3 1 meg ohm so that is the cheap way to go. Now its just a waiting game till some parts appear. :D

I double checked and I have 47 uf 500v F & T caps for the unit. Should be perfect. There at least half the size of the old Mallories, though!

And, I found out today that one of the small Swiffer hand held dusters is perfect for getting into all the nooks and crannies of an old cabinet, while being gentle enough not to damage a tube chart! I could see it pulling out 50 years woth of dust. Who knew?


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Post subject: Re: 1961 Fender Reverb Unit
Posted: Thu Sep 03, 2015 7:24 am
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47mfd/500VDC F&T will work perfectly. I went to a wire-wound 10k-ohm, 5-watt resistor in the power rail. A 2-watt metal oxide resistor will work fine, too. Helps reduce some background hiss, that can be a problem with old carbon comp resistors in the PSU.

If you are interested, here is where I bought the 250 pico-farad tone cap. For the Reverb Unit, I highly recommend this mod. As the unit deals primarily with altering mid-to-high frequency tones. And this disc cap is the primary coupling to the output stage.

Black plate Tungsol, RCA, or Sylvania 6K6GT are the way to go. The 6K6GT has a very clean midrange-highs. Much better than a 6V6GT, in this app.


http://www.partsconnexion.com/cgi-bin/s ... direct=yes


http://www.ebay.com/sch/i.html?_from=R4 ... T&_sacat=0


Good luck! These units are the greatest thing, since sliced bread. :lol: :mrgreen: :lol:


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Post subject: Re: 1961 Fender Reverb Unit
Posted: Thu Sep 03, 2015 9:29 am
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Ok, so I've got the caps covered and I ordered some bits and pieces. I actually needed to replace one of the springs suspending the tank. Boy was that hard to track down. To keep costs down, I tacked on a Fender Pure Vintage Silver Mica 250 cap to my parts order so I will try that first. I can get the giant bag of resistors for cheap when everything else arrives. I noticed you had swapped in that white cap in your photos, but didn't realize it wasn't just maintenance. Since the only issue with the unit is a bit of noise, I might have to try that.
For now I have a black plate RCA 6KGT, a Jan Phillips AT7 and probably an old Tung Sol 12AX7. That should work.
Thanks again for the insights guys!


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Post subject: Re: 1961 Fender Reverb Unit
Posted: Thu Sep 03, 2015 9:36 am
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That's a primo selection of tubes......you should be good to go once the remaining issues are addressed.

Arjay

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