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bassman 5F6 vs. 5F6-A


 :
8/5/1998 11:57 AM
jason
bassman 5F6 vs. 5F6-A
I was comparing these two schematics and noticed that the 5F6 has a cathode bypass cap on the first tube of the direct coupled pair. I know this causes an increase in gain but how does that translate to overdrive/tone.  
(my bassman is the re-issue with the pc board. I would just try it and see what it does but it's such a pain in the *%@ to remove the pcb that I thought I would see if anyone thought it was even worth the time.)  
thanks for any input  
jason
 
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8/5/1998 1:19 PM
Doc

Which side of the board is visible? How about tack soldering the cap across the resistor location on the side of the board facing you? If it's good, then go in for the permanent surgery. If no good, just remove the unwanted appendage.  
 
I don't have any experience with it, but if you didn't get any direct answers, the above suggestion might encourage you to slide the chassis out anyway.  
 
Doc
 
8/6/1998 12:44 AM
Steve A.

jason:  
 
    I think that a 22uF cap would boost the low frequencies too much at this point in the circuit; I just added in a 2.2uF cap in this position for a similiar circuit and was very impressed by the results (nice gain, not muddy at all). Turns out that Sunn used the same cap in their Model T so I guess I got lucky.  
 
    The 5F6 has a very different presence control and feedback circuit than the 5F6A (it's added in at the bottom of the mid control in the tone stack!)  
 
    I bet that they didn't make the 5F6 amps for very long... Has anybody run across one?  
 
Steve Ahola  
 
P.S. The killer mods I've heard about involved replacing the gawdawful 0.1uF bass cap in the tone stack with a .022uF. Probably wouldn't hurt to replace the 100k slope resistor with something like a 56k for more mids and bass.  
 
    Replacing the 27k feedback resistor with a 56k to 100k resistor might open up the response of the amp a bit, too.  
 
    Anybody out there have any ideas about the 47 ohm grid resistors used on the Bassman RI? A lot of amps use 1k5 resistors- or no grid resistors at all. Why 47 ohms?
 
8/6/1998 7:19 AM
Ron Orlando

Hey RI fans....I have replaced the .1 uf with the .022uf and changed the 100k slope resistor to 56K. The amp sounds great..big improvement.. I think the slope resistor change has the biggest effect. I have also wondered about the 22uf bypass cap??? The other mods that I have performed .... adding a bias pot and shellacing the tweed. I retubed with Svetlana's and rebiased..Fender ships these things way cold and biasing them to 34ma really wakes them up. The 'relicing' of the tweed makes it look like an ol' 59.
 
8/7/1998 3:06 AM
Steve A.

Ron:  
 
...shellacing  
the tweed
 
 
    So what type of shellac did you use?  
 
Steve Ahola
 
8/7/1998 7:17 AM
Ron Orlando

Hey Steve, I used Bullseye AMBER shellac. I cut the shellac with denatured alcohol.Make a 50/50 mix. I removed the baffleboard with the speakers, removed the chassis, removed all the hradware (feet, handle) carefully removed the front and rear name plates, and removed the back panels. Apply 3 or 4 coats, with a brush, of the 50/ 50 mix (Depending how dark you want it) let each coat dry for 5 or 6 hours..over night is better.As the alcohol evaporates it darkens a little more..so be sure to let it dry before adding the next coat. Seal the final coat with light coat of clear lacquer to protect it. You need to seal it because alcohol will disolve the shellac..and you know what they serve in bars! Be careful with the back panels..don't get the stain on the grille. The name plates are held on with small brads..I was able to slide a blade under the plates near the nails and slowly work the nails loose. To re-attach, put a drop of wood glue on the end of a toothpick and insert the toothpick into the nail holes..snap them off flush with the tweed. Once they are dry about an hour or so you can re-attach the name plates with the nails. The amp looks like the real deal....I think it helps the sound..really!
 
8/10/1998 1:15 PM
Mike D.

>Anybody out there have any ideas about the 47 ohm grid resistors used on the Bassman RI? A lot of amps use 1k5 resistors- or no grid resistors at all. Why 47 ohms?  
 
Hi Steve,  
I believe I remember reading in The Ultimate Tone Vol 2 that these 47 ohm resistors are basically "jumpers". O'Connor recommended changing them to 1k5. I don't have the book in front of me now, I'll check it this evening. Maybe Fender was embarassed to put actual jumpers on the PCB!  
I heard a guy playing a Bassman RI in a music store and it did seem to be very bright sounding to me.  
I dig your webpages, by the way.  
 
Regards,  
Mike D.
 

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