Re: Fender DRRI questions

On Mon, 12 Mar 2007 00:19:06 -0600, "Elvis Kabong"
<ampscience@xxxxxxxxxxxx> wrote:


"J.P." <jpasano@xxxxxxxxxxx> wrote in message
news:ef13v2pqm85t5t3f6vh7rj26jqsal5aept@xxxxxxxxxx
Okay, next project...my nephew's DRRI started making crap noise and so
he sent it to me. I opened it up and noticed several things. \
The circuit board where R62 and R63 used to go was burned and
several components around there had smoke on them. After looking under
the board, I noticed several resoldered joints in that area but no
burning or lifted traces.( Cap C36 tested in circuit was 180mfd
instead of 100mfd). R62 and R63 had been clipped / removed leaving the
ends in the board. An added wire now goes from the old R62 pin (end
next to C36) to V7, Pin6 (orange wire).
There are resistors soldered from pin 4 to pin 6 on both V7 and
V8 (6V6's). The one on V8 is burnt and no connection.The one on V7
measures about 470 and is a 1 watt.
So my questions: Is there some tech update to remove these
resistors and put them on the tubes?What does the orange wire
accomplish? Are these screen resistors? How do I check bias on this
amp? If I wanted to put a bias checking plugin for my meter to test
this from outside the chassis, where would it be connected? Would I
need 1 Ohm resistors installed? Exactly where and what wattage...
Oh yes, this is a 2001 amp and all of these changes were done when
he got the amp. I suspect the Ruby tube in V7 went north. Does this
assessment add up?

Sorry podnah, but it all adds up to you needing a tech or becoming an
experienced enough tech to the point you will already know the answers
to all of your questions as well as know what else to look for when repairing
any of those series of amps.
I am in no hurry. I will be gutting this chassis and redoing it with
p2p and super rvb guts when the guy gets the cash. The boards and
other removed components are mine after the job and will either go on
the shelf for a later need on DRRI or maybe a project when I get the
xtra cash. I would like to repair the board before I shelve it though.
No profit in this upgrade either...just the learning experience. He
offered me an upgraded Squier for it but I do not want another damn
Squier, American pups or not! Yeah, I'm a cheap date right now..lol

here's LV's sign " Will Work for Amp Parts"...lol


But I will tell you this. Filter caps need to be discharged then measured
out of the circuit unless you are using an ESR meter and even with an
ESR meter, they still need to be discharged.
Okay..I don't have an ESR meter right now but that is a targeted tool
in the near future. I have a discharge device - 5 amp resistor
soldered into the middle of a jumper...
my Fluke 189 can check discharged cap values.. not sure how accurate
it is in or out of circuit

You need to replace both output tubes. The burnt screen resistor of V8 indicates
V8 is defective and V7 should be replaced since it was doing the work of 2 tubes
for some time. BTW, did you check the main fuse? Is it what is required or some
15-20 amp automotive fuse.
let me go look.... AGC 2A half inch fuse...

Where are R62 and R63? Where are they supposed to go to?
Use a tube pin or any major component as referrence.
They are supposed to be on the main pc board next to C36,R60,ect. They
have been removed and apparently soldered across the V7 and V8
terminals from pin 3 to pin 5 on both tubes.

I hope to go to the Austin Guitar Show Saturday after 4 p.m. See ya
there...J.P.
.

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