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'51 Deluxe restoration advice solicited


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6/2/2000 12:05 PM
Dr Rico
'51 Deluxe restoration advice solicited
Hi folks...I tried this yesterday, but my message evanesced before dawn. Weird.  
 
I scored an interesting amp last week. Its a transitional model between a 5A3 and a 5B3 with some twists. The preamp tube is a 6SC7 and the PI is a 6SL7. I drew out the schematic and compared it to the closest schematic I could find (a 5B3) and found a few differences. It looks to me like all the parts are original (and wired in by Lupe Lopez 49 years ago) except one electrolytic, one heater wire and the cord was swapped with a 3 prong. Here's how it differs from a 5B3:  
 
1) The PI is a 6SL7 instead of a 6SC7  
 
2) The 6V6 grids are strapped across 250K, 7.5K, 250K instead of 250K, 725K, 250K (the 6V6s have a common 250ohm-5W cathode resistor bypassed by a 25uF-25V cap that ties between the 250K and 7.5K resistors and one of the 6SL7 anodes ties to a point that splits the other 250K from the 7.5K).  
 
3) There is an unmarked ceramic disk cap that ties the anodes together on the 6SL7. On the 5B3 schematic it says .0001 ??-1000V. uF? nF?  
 
4) The inputs have 75K on mine and 50K on the 5B3.  
 
Could any of you all point me to a 5A3 schematic so I can check out what I have? Some of the values are difficult for me to chase down. How close is "close enough"...10% ok? I'm thinking of swapping more modern values for the inputs (68K instead of 75K to the grids, 1Meg instead of 5Meg to earth). And what should I do with that little ceramic cap?  
 
Opinions warmly accepted. Thanks muchly for your time.  
 
Hasta -> Rico
 
6/2/2000 1:20 PM
Dr Rico

Whups, there's a typo:  
 
"2) The 6V6 grids are strapped across 250K, 7.5K, 250K instead of 250K, 725K, 250K"  
 
7K not 725K Sheesh. Where's my coffee... Rico
 
6/7/2000 10:08 PM
pgambon

Nine years ago I found a pathetic looking Fender at a junk shop in Felton CA for $60. I stripped the black tolex off the cab (easy since it was falling off!), and sent it to Sam Hutton. He recovered it beautifully (God rest his soul), it looks like it's been sitting in a shop widow for 50 years!. It turns out to be a 51 Deluxe wired by Lupe. The tubes we're as you described with the tube chart modified in pencil. I changed it to accept two 6SL7's as the 6SC7 blew instantly (NOS is not necessarly better). I think they used the 6SC7's due to the metal case (better shielding?). Anyway this amp distorts on about three. I wonder what junior thought when he plugged his lap steel into these little monsters back in 51! good luck pg
 
6/8/2000 11:11 PM
Dr Rico

Wow! And I thunk I got a good deal on mine!  
 
RE: 6SL7 in the preamp slot. Did you add a jumper to allow you to use the 6SL7? There's one on my PI slot.  
 
RE: The late great Sam Hutton. I have a Hutton cab sitting in my office not two feet to my right. It still smells of freshly sawn pine and has a very nice tweed covering. Its a diagonal 2 x 10 that he cut for side handles, but then tweeded over.  
 
Nice to hear from you. Steve Ahola has a copy of the 5A3 schematic I made by looking through the amp and modifying a 5C3 schematic I have at home.  
 
Hasta -> Rico
 

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