#1
Skip the first paragraph if you want to go straight into my question...Thanks for reading!

Not just any crate...an 8 year old, USA made 5w tube amp The owner claims the USA made ones come with a tube preamp instead of the SS preamps that come with the now china made ones... But well...i seriously hate myself for getting it when i don't even have an electric guitar..not yet at least...

Anyways, the amp is in great condition...as i said, its 8 years of age...might not be that old to be vintage, but hey, it will one day yeah? Anyways, i've read about mods and improvements which can be done on this amp...and i've found two, but need help..I quote the person

''On the 1st of November 2004 I posted here a mention that after the NOS 12AT7 I'd originally used in this modification gave it's all during a road trip that I was unable to find another 12AT7 that had as high a gain, and that lower gain 12AT7s were giving unsatisfactory results because of the solid state preamp going into clipping before the tube goes into saturation. I have since fixed that with another simple modification. The new change calls for replacing the preamp cathode resistors (R10 and R15) with 560 ohm resistors, or, if you don't feel like pulling the circuit board, wiring a 1k resistor across each of them (the parallel combination of 1.5k and 1k gives 600 ohms, close enough for our purposes.) This change makes the preamp go into saturation earlier. The result is a preamp that works well with either a typical 12AT7 or even with a 12AX7, because this circuit generally won't push even a 12AX7 over into cutoff with such a low resistance on the cathode.''

So if you didn't read that whole thing, it basically means swapping the preamp 12ax7 or a 12at7 tube...

But for the high-lighted part, i'm not too sure what he means...(i have no experience in modding so please bare with me...) He says replace the R10 and R15 resistors, i know that means i locate the 2 and pull them out and implant the new 560 ohm resistors...but i don't want to do that...

But he says i can wire 1k resistors across each of them..what does he really mean by this? solder 1k resistors ONTOP of the 2 existing resistors? Can someone fully explain this?

And when he says 1k resistors for both of them, why does he say ''combination of 1.5k and 1k resistors''?

Is there a large possibility of screw up in this soldering job? These two resistors are directly beside the preamp 12ax7 tube and this mod is supposed to make the amp go into saturation earlier...

The modder claims these two mods would improve the amp a lot...so please help

Sorry for the long thread!
Last edited by NoobOnZone at Sep 11, 2009,
#3
yes, i understand that the two additional resistors will be parallel...but i would like to know how the soldering of the additional 1k resistor to the pre-existing resistor would be done

And series soldering would be out of the picture because i will not want to be removing the entire circuit board...i'll be working with something like this



you will not be able to see the R15, but the R10 is the blue resistor right beside that tube (brown cirlce), under the orange and yellow wires..NOT the one at the bottom...its slightly hidden...thats what i'm going to be working with...so i want to know how to solder on the addition 1k resistor to the blue one
Last edited by NoobOnZone at Sep 11, 2009,
#4
Look, try and see if you can solder it from the other side, I mean flip the board.

It might be easier to take de-atacch it from the amp, flip it, solder your resistors, and attatch it again. I had to do it with a miny amp I moded. I just had to remove the knobs from the pots, unscrew two screws, and unscrew the pots.

Dont know about your amp though
#5
I'd just slide the leads of the new resistor under the leads of the current resistor. Solder it as close to the board as possible and trim the new leads. (Parrallel)

I'm with you, I'd avoid taking the board out. It is a pain that can be avoided.