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crate vc5112 schematic

1/10/2000 7:12 PM
mike Santangelo
crate vc5112 schematic
does anyone have a schematic for the Crate  
vc5112. It is a 50 watt combo with a 12" spkr  
and has 4 12ax7, 4 el84's. I m trying to find how to mod this amp with a variable resistor for a bias adjustment. presently, the amp has no adjustment. I think it is a fixed bias amp. Can anyone help me oput or direct me.  
thanks, Happy new year.
1/10/2000 7:57 PM
Rob W.

The design of the Vintage Club (i am assuming that this is the fixed bias version) does not allow for the bias voltage to be varied. You would have to derive bias voltage in a different manner in order to vary it. i.e. create a new bias circuit off of the B+...  
I worked on one of these for a friend about a month ago, and i was desperately trying to get the bias adjusted differently, but to no luck. Fianally fellow ampagers set me straight as to how this circuit functions.  
Unless you want to spend a lot of time messing around with things... I would leave the baby stock and get a fan and blow it into the back of this baby... (the power tubes are being run at about 110%-115% of their rating, i think that my friends ran the EL84's at 375V on the plate, and about 38mA per tube...This cooks them pretty well...(Inspiration to keep this baby stocked with fresh power tubes..))  
*end of rant*  
Have Fun!  
Rob W.  
Ps.. I think i still have the posts around from my discussion about this amp... Lemme know by email if you would like me to look for them...
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1/10/2000 9:14 PM
mike Santangelo

Thanks Rob. I did not know that this amp was difficult to mod. You saved me probably big $$$ and lots of hours or months.  
Anyway, I would love any other info or files you have about the 5112 crate. Thanks again for your expeditious  
return email!  
1/10/2000 9:22 PM

....i am looking for all of the info i can find about these amps as well, please send any info you have regarding these amps to me please. as it is VERY HARD to find any info at all about these amps, also if you have a schematic that would be cool too (look at my post below for crate VC5115)  
1/10/2000 10:24 PM
Rob W.

Here are some schematics that I was able to find...  
*all thanks to Steve Ahola!!!!! ;-)*  
These are for the cathode-biased version... All of these amps are built on the same board except for the biasing circuit/configuration which changes with model...  
Plus this is something that Ken Gilbert (who normally posts on ampage)suggested doing for a variable bias circuit.  
Here is what he said:  
"I would say your best bet here is to capacitively couple to the B+winding, and derive a bias voltage from that. Just use a cap toattach to the raw secondary for the high voltage winding, and be sure it can withstand the peak - bias voltage plus the peak +secondary swing.  
There are other amp schems out there that cap couple to the hv winding--Marshalls, which usually use FWDB recs, have them, as well as some Ampegs. This will get you all the - voltage you need. -KG "  
I would suggest looking at some of these circuits, marshall, ampeg, etc.. to find a way of doing this off of the high voltage winding..  
Hope this helps!  
Rob W. :-)  
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