# Old Silverface Pro Reverb



## JeremyP (Jan 10, 2012)

Hoping I have this in the right forum, if it's in the wrong place maybe someone could point me in the right direction. 

I am hoping the Fender fans on here can help me out a bit with this. I am getting ready to retube/recap/clean up etc, am old Silverface pro reverb for a friend. When I went to see what model it was there are some contradicting factors. According to this page Superior Music - Fender Amp, Amplifier Serial Numbers. 
All the pro reverbs that are AA165 with the an A07 serial number are black faces , but this one is has Aaa165 circuit with an A07 serial number and the blackface GZ34 rectifier. Here are some pictures so you guys can see what I mean. It is a one owner amp , the exact same way he bought it from showroom in early 70 as a floor model. 
If anyone has any insights on it, or suggestions , tips etc for the recap and stuff I am all ears. Really want this to be bad ass for him.


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## davetcan (Feb 27, 2006)

I can't help but damn that's clean!


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## cboutilier (Jan 12, 2016)

Going by the drip edge moulding I'm going to say that is a 1968 with the blackface circuit. And a pristine one at that, a players dream.


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## sammyr (May 7, 2013)

cboutilier is likely right. The drip edge would date it to the transition era. You can't really trust the tube charts on those old fenders the only way to tell is to get under the hood and compare it to the schematic/layout. I have a 68 drip edge bassman that has an ab165 tube chart but when you check the actual circuit under the hood its a later aa371 circuit. Some of the earlier silverfaces have blackface circuits with silverface cosmetics whereas some are just silverfaces lol. 

In terms of tips for cleaning up and recapping. Don't forget the bias cap as its typically hiding near the pilot and not in the filter cap dog house.


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## WCGill (Mar 27, 2009)

The serial # suggests 1967 (late), drip edge 1968, black lines 1967 or later, some as late as '71. There was a lot of "bleed" between years. Check the date codes on the transformers and pots.
As far as "rehab" for this beauty, lose the 2 pronger, change the caps only if they're bulging or the amp buzzes (hums), check that none of the coupling caps leak dc, pretty much about it, clean the pots.


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## JeremyP (Jan 10, 2012)

Thanks for the tips guys , gonna get started on the weekend. Will take all kinds of pics for u guys to see.


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## nonreverb (Sep 19, 2006)

As WCGill states, it could be a '67 as well which would be more desirable. (I've actually had Blackline Twin Reverb in for service that still had an ink date code stamp on the tag.) They are identical circuit-wise to the Blackface amps.
The early blackline '68's circuit design was messed with by the CBS engineers although easily converted to BF spec.
Just to be clear, there are no "blackline" amps after early '68. It's a very accurate way to date an early silverface amp.


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## JeremyP (Jan 10, 2012)

So because it has the black line Dividers on the faceplate and the drip edge around the cab it would have to be either late 67, or 68... I will get pictures of all the guts and transformers so hopefully can narrow it right down.


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## nonreverb (Sep 19, 2006)

There are ink stamped date codes on the speakers. Since you're speakers appear original, it's a good place to start as speakers, along with tubes, where usually the last thing to be installed in the amp. The code is a 6 digit number. In the case of your amp, it looks like they're Oxford's or Utah's so the first three digits will be 465 or 328 followed by another 3 digits which is the date code.


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## JeremyP (Jan 10, 2012)

The code on spkrs is 081828


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## nonreverb (Sep 19, 2006)

There will be another. That's not it. It might be hidden under the tag. Check the rim where the bolts are as well.


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## JeremyP (Jan 10, 2012)

Right u are , right under the label. You can see it in the pic 328701


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## nonreverb (Sep 19, 2006)

1st week of '67. That pretty much confirms the amp is a '67....unless of course the speakers were changed but in this case, I think not.


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## JeremyP (Jan 10, 2012)

Wow that's awesome ! Thanks for the info and help. When I pull the chassis out I will double check the transformer numbers.


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## nonreverb (Sep 19, 2006)

Transformer numbers could be later....or earlier. I've seen transformer date codes on those Blacklines from '66.
Code for the transformer will start with 606


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## keithb7 (Dec 28, 2006)

That right there my friend is a killer Pro Reverb amp from late '67/early '68. 
I have serviced many SF amps from the same era. Every single electrolytic cap needs to be changed no matter if they are bulging or not. No matter if the caps are original or not. Caps are stupid cheap. No point in wondering what/if/when they were last done. I recommend F&T b+ caps. Sprage/Atom cathode caps. Go for 25uf/50V upgrade. Change bias caps with F&T as well. Update cord to 3 prong. Lube all pots. Replace 6L6 plate resistors as well as all in the B+ circuit. Set bias. Test tubes. Be ready to be amazed how well it sounds again. Save old parts.

Rinse and repeat as needed.


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## WCGill (Mar 27, 2009)

I've never changed a 6L6 plate resistor-ever. Once upon a time I used to change everything out as well, don't find it necessary anymore. If it ain't broke..... The more an amp is used, the better shape the e-caps are. The pristine ones, not so much.


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## Sneaky (Feb 14, 2006)

Speakers don't look original to me. Amp is probably 67 or 68.


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## nonreverb (Sep 19, 2006)

They are indeed original. Utah and in rare cases by this time Jensen. I've worked on many...and the amp is a '67 100%. As for B+ caps, they should be replaced more often than not. The caveat is replacing all the other components you mention. There is no need to start replacing components if they're not showing signs of excessive wear. It can also change the sound of the amp in ways the customer does NOT like. I had an old BF amp in once and went nuts replacing all the cathode caps and several resistors. His reply was: It's lost some of it's sound I like. In this case, component drift had contributed to the overall tone.


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## greco (Jul 15, 2007)

nonreverb said:


> In this case, component drift had contributed to the overall tone.


@nonreverb
Does this drift apply mainly to carbon comp resistors or does it include capacitors?
Can the "drift" of capacitor be measured ?
Is drift in a capacitor the same as "leakage"? (i.e., electronic .... not material from the inside of the cap)

Thanks in advance.

Cheers

Dave


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## nonreverb (Sep 19, 2006)

Drift applies to both Dave. Where cathode caps are concerned, they most often drift up increasing the low frequency in the stage they're in. This can have what some consider, a desirable effect on the overall tone of the amp. Of course it is dependent on how much and where in the circuit it takes place. There is a point where the bypass is so large the circuit becomes unstable and can motorboat. Obviously, replacement is the only option at that point.
Low voltage caps like cathode bypass caps are not under nearly the same stresses as B+ caps are and consequently, don't fail as readily. A visual inspection is always necessary though. Any sign of leakage or significant change in the cathode dc voltage and they're gone.
As for resistors, it's always a good rule of thumb to first visually inspect the ones handling high voltage, then do a meter reading to be sure they haven't gone too far out. All BF and early SF Fenders used 1/4 watt carbon comp. resistors for the preamp tube plates. They can be troublesome as they were not really designed to handle those kinds of voltages and have a propensity to fail. Sometime around 1970 they switched to 1/2 watt which is one of the changes the CBS engineers did that was good.


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## jb welder (Sep 14, 2010)

keithb7 said:


> Replace 6L6 plate resistors





WCGill said:


> I've never changed a 6L6 plate resistor-ever.


I would guess that is a typo and Keith meant screen resistors. It is extremely rare to find plate resistors on power tubes, I don't think any Fender ever used them.
The "change all caps no matter what" debate is something that will go on forever, I don't like any blanket absolute rules and often disagree with replacing old caps that are good. However, these vintage Fenders are getting quite old, so I can understand Keith's point when dealing with really old stuff.
That being said, in over 30 years of working on thousands of amps, many of this vintage or older, I have yet to see an old amp that was damaged by a cap that went bad. Usually they just dry up, go open, and cause hum. Just to speculate, newer era caps seem to be where you see the occasional shorted cap that can damage an amp.


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## WCGill (Mar 27, 2009)

Yes of course, screen resistors. I had a '66 Deluxe Reverb here last week. The two primary filter caps had been replaced and were bad, causing coupling through the power supply resulting in a reverb whistle. All other caps factory-original, no bulges or hums. I just re-replaced the two and left the others. It's indeed a judgement call on this and I tend to rely on my ears and eyes and only do what I deem necessary, taking a minimalist approach.


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## keithb7 (Dec 28, 2006)

Sorry. Yes typo. Screen resistors. 

OP do you have any gut shots? B+ cap shots?


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## greco (Jul 15, 2007)

nonreverb said:


> Drift applies to both Dave. .........


Thank you for taking the time to write such a detailed response. Very much appreciated.


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