New Stereomour, left channel bzzzzzz... (SOLVED !!!)

[zs1962]

Dears,

I've just built the Stereomour and tests were OK except of 14 and OB that were 193v (very close to the range).
Left channel has a strong Bzzzzzzzzzs strong .
he area of the problem. Once the input to the cap 0.1MF is disconnected, the bzzzzzz is gone; and when I used the output of the volume pot from the right changel into the left change;, the bzzzzzz was there.
I therefor assume that the bzzzzzz adds between these two points, i.e. on the 12at7.

Any experience with this ?

PS the right ch is perfect

Ze'ev

[Grainger49]

Give Dan's post a read.  As he suggests, list only those measurements that are out of spec greater than +/- 15%.

[InfernoSTi]

Ze'ev,

Per Grainger's question, are all the measurements within tolerance on all the test points?  Resistance and voltage?  My impression was that they are but perhaps post affirming that.

Secondly, is it a mechanical "buzz" or a amplified "hum" please?  Does it change with volume or remain a constant level?

Best,
John

[Paul Birkeland]

Your deduction seems about right.  I would double check the little carbon composition grid stoppers on both channels to be sure one isn't broken or cracked. 

If not, try another AT7? (there are some other variants that will run temporarily if you don't have extra AT7's)

-PB

[zs1962]

There is a chance that I've got it... after switching OA and OB without change, I disconnected the 220ohm resistor from AT7 socket and there was silence on the left side ! OK, the problem must be at the area of the socket or the ground (assuming the 431 os OK)...
I started digging into the area and noticed two bad things on pin B9. First, the pin is loose but even worser than this, B9 is connected to Terminal 9 ! BAD !!! It is my fault and grounding the input is not something I should have done... I guess that the fact that within the bzzzzz noise there was a weak music signal has something to do with the fact that B9 in the socket was broken...

Well, remembering I had few mistakes and correction when mounting the terminal I went back to the manual... Yes, I probably did the mistake when getting to page 62. I thought that the wire is wrongly connected (see page 45) and probably got confused... I guess that my mistake was a result of the conflicting photos on page 45 & 62 and not understanding what is being connected (ground). Then, while doing the changes I probably damaged the socket (B9).

However, the good thing is that I really get to know the Amp and hope that after getting a new socket and connecting everything back (and this time right) all will be OK ....

Thank you guys for the attention and I will update when connecting everything back...

Ze'ev

[Grainger49]

A7 is the input to the driver tube.  Removing the resistor and not reconnecting it means the buzz is coming from either the input RCA jack(s), the selector switch or the volume control.  This also says that the circuit downstream is OK.

If you have buzz on all inputs then it is more likely the volume control connections.  If it is only one input you need to check the RCA jacks and the selector switch.

[zs1962]

YYYYYYYYEEEEEEEEEEESSSSSSSSSSS !!!!!!!!!!!!!!!

The problem solved and the joy is beyond borders sound is terrific and the Hawthorne SSI seem to love this 3.5w AMP. Thank you for the fast and open heart responses.
Knowing that there are people somewhere there, that care, at any time of the day (or night), is not something to be taken for granted !!!

The problem was a wrong wiring that connected ground to B9; this made the bzzzzzzz. However, the broken pin (B9) added ticks that made me think of capacitors... Now I really 'stopped being afraid and learned to love the amp'. it is so easy to get inside, disconnect points of test and find the problems... Real FUN !

BIG THANKS FROM TEL AVIV,

Ze'ev

[InfernoSTi]

Congratulations, Ze'ev!!!  Well done!!!

Now enjoy those Hawthorne Audio SSIs and your wonderful Bottlehead Stereomour 2A3: what a match if you love music!!!  Nothing makes you feel connected to the amplified sound more than building and troubleshooting your amp...your sweat, tears, and love are in that Bottlehead 2A3 amp and you will feel that connection each time you switch it on! 

Many heartfelt congratulations!

Best,
John

[zs1962]

...your sweat, tears, and love are in that Bottlehead 2A3 amp and you will feel that connection each time you switch it on! 

Many heartfelt congratulations!

Best,
John

Thanks John for the warm and very right words; and your support from the very start!
Now I will rest a bit, enjoy the music and continue to the Duets with 15"SSI and 10"Augies... yes, the other way around 
Ze'ev