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Post subject: Fender Super reverb 1978
Posted: Wed Jan 11, 2017 3:02 pm
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Hi Guys!
First of all,my wishes for a healthy peaceful new year!
Now to the point.
I recently owned a 78' super reverb and i believe that the PT and OT transformer have been replaced.I wonder if someone can help me to indentify the trans for the correct dating but specialy the decade.

Power Transformer
013917
EIA606-144

Output Transformer (also has the fender mark in one side of the trans)
013897
EIA606-909

From the search i ve done i think that the PT is 71 or 81? (44 week)?
And the OT is 79 or 69? (09 week)?
How can i be sure for the decade?
Any help will be apreciated!


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Post subject: Re: Fender Super reverb 1978
Posted: Wed Jan 11, 2017 5:06 pm
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mikeva wrote:

Output Transformer (also has the fender mark in one side of the trans)
013897
EIA606-909

From the search i ve done i think that the PT is 71 or 81? (44 week)?
And the OT is 79 or 69? (09 week)?
How can i be sure for the decade?
Any help will be apreciated!


Year are right we can say more , pictures will help


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Post subject: Re: Fender Super reverb 1978
Posted: Wed Jan 11, 2017 6:20 pm
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The power tranny for a Super Reverb made in 1971 would carry Fender P/N 022798 so yours likely dates to 1981.

Arjay

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Post subject: Re: Fender Super reverb 1978
Posted: Thu Jan 12, 2017 3:06 am
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Retroverbial wrote:
The power tranny for a Super Reverb made in 1971 would carry Fender P/N 022798 so yours likely dates to 1981.

Arjay


So I have to guess that the OT is propably a 79' matching the era.
I hoped that it was an earlier model :(
Thanks for your help!


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Post subject: Re: Fender Super reverb 1978
Posted: Thu Jan 12, 2017 10:52 am
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mikeva wrote:
So I have to guess that the OT is propably a 79' matching the era.
I hoped that it was an earlier model


It can't be and here's why. In the late '70s the Super Reverb was totally redesigned, becoming a 70-watt ultra-linear platform. That metamorphosis cost the amp its tube rectifier and required a beefier P/T to generate the 500 volts required to coax that much power from a pair of 6L6GC's. Likewise, the O/T was upgraded to withstand that increased power. The pre-amp sections were revised as well, becoming for all intents and purposes identical to those of a Twin Reverb. So there's really not much commonality between an original Super Reverb and the ultra-linear version.

Arjay

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Post subject: Re: Fender Super reverb 1978
Posted: Fri Jan 13, 2017 4:27 am
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I understand what you mean.Thanks.
Now.. i found some time to work with the amp and i have to say that strange things happens there!
First o all i noticed that all the cables from the OT were black.Someone did his tricks there!
Then, when i pulled the chasis out i saw 4 big caps parralel from stanbye switch to the ground.I thought it was something wrong with the filter caps as they were old and one was missing.
I replaced all the filter caps with Tad and removed those from stby switch.Also i noticed that the red/yellow wire from the PT was in the air but according to the schematic it suppose to be connected to the 220 uf filter caps.I reconected the wire.Found the two powering filtering resistors drifting and change them too.Checked all the components and everything seemed ok.
I hooked the amp to the balb tester and took some measurements.After seeing that everything seems to work,i bypassed the bulb tester to get full power.
Here the measurements.
fillament: 6.3
V1 V2
plate voltage : 486 488
grid voltage : -54.3 -54.4
Bias(1ohm res) 0.052 0.054 (could't reduse that from the maching pot)

oscilloscope showed output.

Now the real problem.
When i switched back on the stby WITHOUT the bulb tester, it kicked off the rooms braker.Tried again couple times...same thing happen. I quess that's the reason fot the 4 caps placed there?But what is the cause for that?
Here a photo with the caps.

Image

Any thoughts?


Last edited by mikeva on Sat Jan 14, 2017 1:57 am, edited 1 time in total.

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Post subject: Re: Fender Super reverb 1978
Posted: Fri Jan 13, 2017 7:13 am
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Can't say for sure from the photo but that's definitely a non-standard (ie: not original) wiring job). I'm wondering if the choke took a dump at some point in the past and those large electrolytics were installed in lieu of a proper replacement tranny......?

Arjay

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Post subject: Re: Fender Super reverb 1978
Posted: Fri Jan 13, 2017 7:14 am
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Ok after searching more carefully the circuit,i noticed that one of the power tube socket has signs of arcing.
Is this a cause to blow the breaker?The amp's fuse is not affected by the way.
Image


Last edited by mikeva on Sat Jan 14, 2017 1:58 am, edited 1 time in total.

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Post subject: Re: Fender Super reverb 1978
Posted: Fri Jan 13, 2017 7:17 am
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It could very well be. Definitely time for replacement (do them both for peace of mind).

Arjay

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Post subject: Re: Fender Super reverb 1978
Posted: Fri Jan 13, 2017 7:29 am
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Retroverbial wrote:
It could very well be. Definitely time for replacement (do them both for peace of mind).

Arjay

Yes i will replace the socket and see what the results are.
Thanks for your reply.


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Post subject: Re: Fender Super reverb 1978
Posted: Fri Jan 13, 2017 7:38 am
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While you're at it, take a look at the screen-grid resistors. If they look "crispy", change them out as well.

Arjay

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Post subject: Re: Fender Super reverb 1978
Posted: Fri Jan 13, 2017 11:42 am
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I wouldn't re-use those output tubes either, they may be damaged as well.

That's a scary looking set of caps, what voltages are they seeing.


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Post subject: Re: Fender Super reverb 1978
Posted: Sat Jan 14, 2017 2:23 am
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sfceric64 wrote:
I wouldn't re-use those output tubes either, they may be damaged as well.

That's a scary looking set of caps, what voltages are they seeing.


Those tubes that came with the amp were already gone!One was broken too.
The capacitors rating were 350 v. Four of them laying around not even tighten.Go figure.
Anyway i changed the socket and seems that the problem is gone!
Now i'm struggling with the bias.I converted the tube mutching pot to a bias pot but i cannot bring down the bias less than 46mA.I will check a few things but maybe i will need your help!Be prepaired! :D


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Post subject: Re: Fender Super reverb 1978
Posted: Sat Jan 14, 2017 2:37 am
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You may need to install a fixed-value resistor in series with the bias pot to bring the current range down to a usable level. That 46 mA is far too high for any conventional 6L6GC. Incidentally, the power-tube plate voltage for the ultra-linear version of the Super Reverb is in the neighborhood of 500 VDC -- only the stoutest of bottles should be used. Tung-Sol's re-issue STR would be a worthy candidate.

Arjay

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Post subject: Re: Fender Super reverb 1978
Posted: Sat Jan 14, 2017 8:33 am
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For the bias pot i used this wiring which i found here in an older post.
https://docs.google.com/drawings/d/1gcFNxnLbSU3piK7in7RV3rFqBBuMe1LEk9N869IJVyI/edit
With the pot fully turned clockwise i get 46 mA.Adding a resistor in series from the wiper to the 220k's junction is that what you mean?I did that, and although the pot's resistance increased,still i get the same mA.
I tried 2,2k-4,7k-10k.
So maybe i need to try swapping the two 220k with larger ones?


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