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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 11:54 am
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Jerry, you know looking more carefully at the photos of the guts... this amp has been semi-modded back to AB763. I see two 220k-ohm grid-to-ground resistors (replacing the later SR circuit 100k-ohm). And the sand-box resistors are 5 watt, 1k-ohm grid stoppers.

And the MV is between the tone/gain stage and the PI. Of all the Fender amps of this era, the SR, TR, and PR seem to have undergone the most post OEM alterations. IME.

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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 1:16 pm
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BMW2002Ti wrote:
Jerry, you know looking more carefully at the photos of the guts... this amp has been semi-modded back to AB763. I see two 220k-ohm grid-to-ground resistors (replacing the later SR circuit 100k-ohm). And the sand-box resistors are 5 watt, 1k-ohm grid stoppers.

And the MV is between the tone/gain stage and the PI. Of all the Fender amps of this era, the SR, TR, and PR seem to have undergone the most post OEM alterations. IME.


Steve,

Being semi-modded back to AB763 is a good thing right ?

Jerry


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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 1:28 pm
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BMW2002Ti wrote:
And the MV is between the tone/gain stage and the PI.


+1

Similar to the configuration used in the later ultra-linear SR models.

Arjay

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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 2:14 pm
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Jerry, the AB763 is prolly a better choice for those seeking the classic early to mid 1960's Fender tone. The higher value grid-to-ground resistor (220K-ohm versus 100K-ohm), plus the higher plate voltages (due to use of the GZ34 vs the 5U4GB rectifier) on the AB763 compared to a AA270 = a hotter output stage.

You need a good set of 6L6GCs in the AB763. As the silverface AC568 and later circuits have several components added to help stabilize this stage. I believe that this may have been due to the rumors of RCA stopping production of 6L6GC, in the late 1960s.


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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 2:37 pm
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As you guys already know. I don't know the significance in the different end results of any of the specific wiring schematics on the SFSR or any other Fender amp for that matter. There is always a lot of talk about folks preferring the AB763 wiring.

As far as you checking/servicing my amp, I'd just as soon you make the decision on what would be the best by making it easy on yourself (amount of work involved). (if that makes any sense).

The amp sounds great to me as it is but I can't hear worth a crap anymore :lol:

I appreciate the way you and Arjay weigh in on all this stuff with the incredible knowledge ya'll possess.

Jerry


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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 4:02 pm
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BMW2002Ti wrote:
Jerry, the AB763 is prolly a better choice for those seeking the classic early to mid 1960's Fender tone. The higher value grid-to-ground resistor (220K-ohm versus 100K-ohm), plus the higher plate voltages (due to use of the GZ34 vs the 5U4GB rectifier) on the AB763 compared to a AA270 = a hotter output stage.

You need a good set of 6L6GCs in the AB763. As the silverface AC568 and later circuits have several components added to help stabilize this stage. I believe that this may have been due to the rumors of RCA stopping production of 6L6GC, in the late 1960s.


+1

Plate voltages on the AA1069 and subsequent revisions actually ran lower than the earlier circuits (437VDC) but once that CBS mess is unfucked and the final drive (and the biasing system) restored to AB763 specs, I don't the EHX bottles will have any issues performing at their optimum design parameters.

Arjay

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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 5:41 pm
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I forgot to add.

My new faceplate arrived last Friday from Germany, so I thought I'd post a photo.

They sure packaged it well :D The box was 7"x6"x24" and had several of those plastic things with air pockets for cushioning.
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It sure does look purdy !! Can hardly wait to get it installed !!
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Gonna have to wait until I get the switchcraft beauty rings I ordered and the knobs from Arjay.

I already ordered the period correct (thanks Arjay) grill cloth from Mojotone:
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Jerry


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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 6:07 pm
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Jerry, this is going to look as good as it sounds when it is all done! I can't wait till it's done and to see the pics!

T2

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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 6:20 pm
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T2Stratman wrote:
Jerry, this is going to look as good as it sounds when it is all done! I can't wait till it's done and to see the pics!

T2


Thanks Tony,

Yes, the waiting until I get all the parts together and installed is driving me crazy. Still, after that, I have to let it go for Steve to work his magic on anything that needs replacing.

You can be sure I'll post up photos of the finished product because I'm sure I'm gonna be proud of it :mrgreen:

Jerry

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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 6:49 pm
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Jerry, yeah when I did both my Bantam refurbs, the waiting on parts was the worst part. But in some ways it made me take my time and left time to get as many of the details as good as I could get them. So in a way it works out...but am here sending you some patience mojo!

T2

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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 6:58 pm
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"Plate voltages on the AA1069 and subsequent revisions actually ran lower. "

Arjay, correct! this is true with most Fender amps that had GZ34 rectifiers initially. Then, replaced them with more ubiquitous (with good RCA-made available) 5U4GB.

5U4GB = lower plate voltage and more "sag."

GZ34/5AR4 = higher plate voltages and tighter bass.

For the SR, VLR, PR, and DR... I like the tone of the GZ34 over the 5U4GB. Plus, less current draw of the GZ34 makes life easier on the PT. Slow warm-up is a nice feature of the IDH GZ34.


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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 7:03 pm
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T2Stratman wrote:
Jerry, yeah when I did both my Bantam refurbs, the waiting on parts was the worst part. But in some ways it made me take my time and left time to get as many of the details as good as I could get them. So in a way it works out...but am here sending you some patience mojo!

T2


Tony,

Thanks for sending the "patience mojo". But you are right, it works out well in the end because of the advice from Arjay and Steve.

Jerry


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Post subject: Re: NAD - 1969 Super Reverb
Posted: Sun Jul 14, 2013 7:05 pm
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BMW2002Ti wrote:
For the SR, VLR, PR, and DR... I like the tone of the GZ34 over the 5U4GB. Plus, less current draw of the GZ34 makes life easier on the PT. Slow warm-up is a nice feature of the IDH GZ34.


+1

I just wish NOS GZ34's were as plentiful now as original 5U4GB's seem to be.

:(

Arjay

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Post subject: Re: NAD - 1969 Super Reverb
Posted: Mon Jul 15, 2013 6:46 pm
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Retroverbial wrote:
BMW2002Ti wrote:
For the SR, VLR, PR, and DR... I like the tone of the GZ34 over the 5U4GB. Plus, less current draw of the GZ34 makes life easier on the PT. Slow warm-up is a nice feature of the IDH GZ34.


+1

I just wish NOS GZ34's were as plentiful now as original 5U4GB's seem to be.

:(

Arjay


+10K! If you can find those NOS GZ34's they want your first born for a nice pair of em! I am down to my last Bugle Boy spare...but I have a couple NOS 5U4GBs!

T2

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Post subject: Re: NAD - 1969 Super Reverb
Posted: Mon Jul 15, 2013 10:33 pm
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T2Stratman wrote:
Jerry, yeah when I did both my Bantam refurbs, the waiting on parts was the worst part. But in some ways it made me take my time and left time to get as many of the details as good as I could get them. So in a way it works out...but am here sending you some patience mojo!


A full set of replacement parts (some vintage, some repro) are now on their way......I expect that by the end of the week the amp will have assumed a completely restored cosmetic persona.

Arjay

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