Noise floor questions...

Again, thanks for the replies!

Will definitely check out the Sylvania tubes from tubedepot.
Will never ever buy tubes from a not trusted or really well known seller again.
Will not buy myself a tube tester.

Cool that you also used to have thorens td124 with a SME tonearm Grainger49 ;)

Paul Joppa said:
Your voltage measurements indicate that you have a weak tube (the plate voltage is higher than ideal). It is within an acceptable range for performance, but a fresh tube may make an audible difference. (If it does not, then at least you will have a spare on hand!)

Paul Joppa; are you talking about the sheet with DC measurements I attached earlier in one of my posts?

Info:
These DC measurements are from the first time I fired up my Stereomour.  I had the stock 2A3 Svetlanas tubes installed when measuring these checkpoints.

Should I do a second round with these DC measurements?

Do you think the bad 431's had a great effect on these DC measurements?



 
Ooohhh - good catch!

Yes, re-do the measurements, specifically the OA and OB voltage of the C4S board, which go to the plates of the driver.

It is not uncommon for a fresh tube to have a high plate voltage, and then drift down to a lower, stable value as the cathode finishes forming - usually in 50 to 200 hours, depending on the particular tube. Your original measurements showed a slightly high voltage. If you have run the amp for 50 to 200 hours and that voltage has come down, then the tube is fine.

The 431 will not affect that measurement.
 
Hi,

I have redone the checklist.

You`ll find the checklist attached.

Checkpoint 4 is really off from the manual.
I was to replace the resistor that goes from A3 to T4. I have a already a spare on hand.

First time installing this resistor it a little bit of the resistor fell off from the body- used a tweezer too hard I guess...  Do you think this is causing the off measurement?

Anything else I should look into further based on the numbers attached?

PS:  Just ordered the Sylvania tubes from tubedepot !

 
I'm not sure where in the circuit checkpoint 4 is.  It is likely a grounded terminal.  If so 14mV indicates that it needs the screw tightened. 

Give that a try and see what happens.
 
Hi again ,

So I tightened the screws on all three terminal strips ( each with 5 terminals) in the front of my Stereomour.

It is Terminal 4 and Terminal 12 that do not have a 0 V DC reading. These two terminals mirror each other-  Both are connected to same terminal to the 2a3 sockets on each side with a resistor - A3 and C3.

I also resoldered all four of the points without any new/good results with my multimeter.

Any idea on what to do next?






 
altec604e said:
Checkpoint 4 is really off from the manual.

0.014V is not really off from 0V.  Terminal 4 is not an issue. 

A3 can't be 24V with the rest of those conditions, I'm guessing 24mV?

Your 12AT7 is reading a bit high, and may not be the quietest of tubes.  Trying a spare isn't a bad idea. 

Wiring the output transformers for 4 Ohms will yield the lowest noise floor, highest damping, least distortion, and least power into 16 Ohm speakers.  If you have ~100dB efficient speakers, this is the way to go.

-PB
 
oh man...  ;)

my fault...  got a bit carried away there.

24mV is correct.

I just ordered a new 12AT7 tube when I ordered new 2a3 tubes ... 

Thanks!
 
hi,

I´m having trouble with my stereomour...

so the issue is that one channel ( the left channel ) in my stereomour is making a mechanical noise- it vibrates.
in addition: when adjusting the volume knob the noise I´m making when moving the dial is reinforced in the left speaker.

the mechanical background noise that is always present has a much lower noise than when turning the volume knob or touching the chassis of my stereomour amp...

anyone got a clue what`s causing this background noise?

 
How are your voltages?

What do you mean that the left channel vibrates?  A vibration would suggest that the amplifier itself is vibrating, and this would generally be tough to localize to just one side.

-PB
 
I checket the hum balance last week - they were almost the same.  low.

I have not done any voltage checks since last time I posted my second voltage list.

As far as I see it my left speaker is reinforcing a vibration sound from my stereomour.

I cannot feel that my stereomour is vibrating, but for example when turning the volume knob the sound from turning the volume knob is reinforced through my left speaker....


HOLD ON !  - I may have not put back the lock washer on one of the two screws ( holding the left output transformer in place ) - is this causing the issue?

If it is ... I´m so sorry for bugging you... 

 
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.
 
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....



 
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.

 

Attachments

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
 
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!





 
altec604e said:
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
 
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!




 
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