Noise floor questions...

[Paul Birkeland]

I'd triple check the voltages.  The Stereomour shouldn't vibrate unless the iron is being drastically overstressed, which would show up in the voltage checks.

[altec604e]

Will do!

can't do it until tomorrow though- it´s late in the evening here over the pond...

[Doc B.]

Do you mean microphonics?

[altec604e]

hi,

what do you mean by microphonics?

when tapping the stereomour the sound is reinforced through the left speaker - I´ll guess like a microphone....

[Grainger49]

That is microphonics.  Many tubes are microphonic, some more than others.

[altec604e]

Hi,

I still got issues with noise from my left speaker.

Today I did the checklist of AC and DC measurements described as in the Stereomour manual.


I`m attaching two files in this replay:

Checklist 2 Voltages is from before I got the issues with noise from my Stereomour in the left channel.
Checklist 3 Voltages is from today.

Can anyone read anything strange / different / off - "THE PROBLEM" - from these two lists?

All help will be appreciated.

[Paul Birkeland]

I think you have a loose heater wire on your 12AT7 (pins 4/5), or back where those wires connect to the power transformer.

Your first test reveals a 12AT7 that is just gasping for breath in terms of operation.  Your second test reveals a 12AT7 that is working very well.

Since both halves exhibit the same issue, it is most likely a loose heater wire. 

-PB

[altec604e]

Hi !

I´ve just sat down to rearrange some of the wires in my Stereomour after reading your answer to my previous post replay.

I was wondering what you mean by "loose":

My interpretations of the term...
1.  The wire is not connected at all in one of its ends.
2.  The wire is not well enough soldered ( bad soldering ) at one of the two points connected.
3.  The wire is not well enough twisted around other wires going the same way ...

Thank you for your answer !
Really do appreciate it!

[Paul Birkeland]

1.  The wire is not connected at all in one of its ends.
2.  The wire is not well enough soldered ( bad soldering ) at one of the two points connected.

It's really #1 and #2.  I would revise #1 to be that the wire passes through the terminal, but may not be soldered at all.

For #2, it would just be a solder joint that isn't shiny, and maybe has a lot of excess solder lumped up onto it.

-PB

[altec604e]

Hi !

So I´ve gone through my Stereomour amplifier and resoldered all joints that where not shiny.
 
The red wire from IA soldered to HV+ in my Stereomour was loose at the PCB board.
When doing the fourth measurement of the DC measurements ( not attached this time ) I also saw that I had red light shining on the little circuit board - something I can not remember I saw last time I did these measurements.

The microphonic reinforcement is still there, but it is now in two channels instead of one.  (for example when turning the volume knob the sound is reinforced through the speakers )  - as you guys previously told me this often depends on the tubes used I guess.

The other strange vibration sound through my left channel is gone.

There is a little hum from both channels when not playing music - this sound I`m familiar with ...  it´s all good!

Thanks for the help!

[Paul Birkeland]

I'm glad you got it all nailed down.  No doubt the amp will sound a bit better too!

-PB

[pin_punk_13]

Hello,

I bought a Stereomour second hand a year and a half ago and I realized that the hiss was a little too loud but I thought that is the way it is suppose to work. Reading this post I realized that I needed to check the LM431s which I did and they are indeed the WS ones. Is thre any chance you might have a good set lying around? I was planning on ordering 2 bottlehead badges so if you still have a pair of LM431s can you please through them in as well. I can pay for them there is no issue there.

[Doc B.]

replacementparts at bottlehead dot com is the best contact address for replacement parts.