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Re: super reverb silver vs black vs current production


 :
12/29/1998 12:18 PM
Paul West
Re: super reverb silver vs black vs current production
OK, OK, I got up the nerve to that a sticker off, and you guys are right. The part number IS 064121 and the speaker is "137". What are the characteristics of the various speakers? What does CTS mean?  
 
Charles, you are right about the Rectifier plug-in (again). There is a recto in the socket, and it is filled with epoxy. There is a date code on the recto "7-18-83". Whats the deal about the epoxy? Is this a true tube recto? Also, I'm concerned about the possibility of the tech. guy taking the original '68 Fender Recto. tube for himself and replacing it with this epoxy thing. If there is a epoxy thing vs. tube difference, can I just replace the epoxy thing with a real tube?  
 
Thanks in advance for all your help!  
 
Paul
 
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12/29/1998 8:33 PM
Bruce

Paul, if there was no other changes made, as a matter of course, I would think you could pull the SS rectifier out and insert a 5AR4.  
But, since it has the SS rectifier in it now, there is a good chance that the bias voltage has been adjusted more negative to allow the higher plate voltage caused by the SS rectifier.  
That probably means the 5AR4 will cause the amp to actually sound a little colder, because the rectifier has no effect on the bias voltage but the plate voltage is effected by what kind of rectifier is used.  
IOW.. the bias supply might be set to a more negative bias voltage value to hold the idle current down at the higher plate voltage with the SS rectifier.  
When using the 5AR4 there will be much more voltage drop in the power supply and the result is lower plate voltage.  
With the bias voltage now set more negative then needed, the tubes will be biased coldish.  
I guess you should have someone check it.  
I know that was wordy but did it make sense?  
 
BTW, some folks think those 10" CTS speakers sound pretty good.  
 
Bruce  
Mission Amps
 
12/29/1998 10:50 PM
Charles

Bruce is right in that the bias really should be reset when changing rectifiers.  
 
The rectifier you have gives the highest voltage and most "punch" to the amp. If the caps are in good shape, you should have no real problems with the SS rectifier. The epoxy is there as a sealant/insulator for the diodes inside the "tube base".  
 
The 5AR4 (or GZ34) will result in a little lower voltage, and introduce some "sag" at higher volumes. Sag is a sort of compression that happens when the voltage drop is a bit higher thru the rectifier at higher currents.  
 
The 5U4GB will give even lower voltage and have just a little more sag or compression.  
I like the sound of the 5AR4 better - to me the 5U4GB makes the amp lose some of it's punch - but it's really a taste sort of thing.  
While not all Fender amps can/should use alternate rectifiers, the Super Reverb can use those three with only a bias reset.
 

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