Rewiring fail...Help please!

B

balancedtriode

New member
The other day I was rewiring my stereomour by upgrading the 3.3uf caps and instead of wiring them to teminal 1 and 5 of their respective strips I wired the to 2 and 4(i think maybe 1 and 4 or 2 and 5) and turned the amp on (big mistake). then I noticed my mistake and rewired it. now only one side of the board lights up and one half of the 12at7 glows bright and no sound ( unless at max lvl then it just plays music that crackels ) and when I turn it off It crackels for a sec then sounds fine then shuts down any Idea's on what I need to fix? please help I love this amp!
thanks,
Coltrane
 
coltrane --get your manual out and do your resistance cks for starters--notate the differences-what they are and what they should be-double ck your wiring and soldering--then get back to the forum with this info if you are unable to figure it out
 
The 'AT7 heater is wired in series, for 12v power, so if only one half is glowing there is likely to be something wrong with the tube. Resistances and voltages are always a good precaution; also inspect the heater wiring (pins 4, 5, and 9).
 
Resistance checks out fine. I think I blew some thing. I should clarify bothe sides of the 12at7 glow one is just a lot brighter. Only one side of the board with the LED's light up
 
1=
2=
3=0
4=249.1k
5=1.39k
6=0.3ohm
7=OL
8=0
9=OL
10=0.2ohm
11=1.39k
12=249.1k
13=0
14=
15=
16=1.17k
17=
18=0
19=
20=1.175k
a4=1.1.187k
a3=249k
a2=
a1=1.187k
c4=1.184k
c3=249k
c2=
c1=1.188k
so the resistances are off I should mention I eliminated the potentiometer and the selector switch
any Ideas? I know 7 and 9 should not be OL. any Ideas on how to fix it would be greatly appreciated!

 
coltrane notate for the forum what the resistance readings are --which you have done but also give us what it should be-in the meantime--ck for a broken wire from the c4s board --anywhere the resistance does not match the manual follow that wire/trace both physically and on the schematic-if the resistance is off-why is it off-bad joint --broken wire-or part malfunction--i myself am not sure exactly what problems your wiring mistake may have caused-
 
Coltrane,

I can be only minimal help, I have a schematic only for Stereomour.  As Howard suggests, post only those resistances that are 15% out of spec (plus or minus).  Also, as Howard says it is good to give the expected.  That way it keeps the helpers from flipping back and forth in the manual.  

I'm assuming that everything worked well till the cap swap and getting them on the wrong terminals.  

This ought to be a big hint, but I don't know what it means.  "when I turn it off It crackels for a sec then sounds fine then shuts down"

I'll think on it.  Do both channels sound fine?
 
i have seemed to narrow it down to a board issue,
how ever I have no idea how to test the transistors on the L.E.D Board.
maybe I should just replace everything on that board? transistors are my weakest point of knowledge.
Grainger-Neither channel sounds fine, until I turn the amp off then is sounds great as the tubes shut down I think then its off
unless someone can help me troubleshoot the board, I may just need to buy replacement parts.
any suggestions will be greatly appreciated!
 
Pulling all the components off of a C4S board and keeping the holes open is darn near impossible.  I have tried and failed.  So let's not go there yet.

The problem wasn't swapping caps, per se.  There must be a clue in it playing well as it shuts off.  All the tubes glow, right?
 
all the tubes glow, 1/2 of the 12at7 turns compleatly orange, kinda scary bright.
i checked all the wiring, and i keep coming back to the board. but there may be other issues i just dont know I have tried a couple of different 12at7`s with the same result.
 
The 12AT7 is 12.6V AC from pins 4 to 5 with a ground on 9 which is the "Center tap."  Try measuring from pin 4 to 5 then from 4 to 9 and 5 to 9.  Remember it is AC volts.
 
coltrane-your resistance readings seem fine-now go to page 75 in the manual-give us what you have for voltage readings and what it is supposed to be-not knowing exactly what you did but you may have attached one end of the parallel cap to the coupling cap-soo!!! guessing that may be so-give us your voltage readings-and ck the coupling cap to see if you get a reading should be .1 uf-ck those little 249k resistors from 4 to 6-and ck the resistor going from 4 to a3- according to your initial post i think that you either connected the output transformer to the grid or the plate and choke to the grid-which in turn through the coupling cap connects to the 12at7 plate and the c4s board
 
Coltrane,

In my opinion the voltage is fairly well split between the two halves of the heater.  Maybe try another tube?  That is always easiest and fastest way to check things.
 
I am sure now that it is the board... all the voltages checked out,maybe its a amperage issue) I tried different tube sets, same issue.
I know I need to redo the board but I dont know how to get my hands on a blank one. are the avail from bottlehead? I love my scott 299-b but it is no stereomour.
-coltrane
 
I received and installed the board today, the 12at7 no longer looks like it is going to ignite!!!!! :D but the volume in the system is almost inaudible :( going to do a full resistance and voltage check tomorrow, any ideas? is it possible I also blew my 2a3's an if so how would I know? they appear to light up fine, but I don't know how to test tubes, since i have no tube tester. any ideas?
 
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