newbie : wrong DC voltage T5 and T6.

[altec604e]

Hi people !


Im posting because Im reading wrong voltage on T5 and T6 in my Stereomour amplifier.

Readings from the Stereomour Manual :
T5 = 0
T6 = 60

My own readings : ( done with my multimeter set to DC Voltage and the black lead set to T8 )
T5 = 58
T6 = 0

I live in Europe so I am running my Stereomour amplifier with a 240V mains transformer.


All help will be appreciated !

PS: All DC voltage readings attached.

[Paul Birkeland]

Hmm, looks like a typo in the manual.  It's sort of amazing that it has been there this long without being noticed!

T5 is tied to the 2A3 filament, and will indeed be around 60V, while T6 is grounded at 0V.

I'll inform our manual guru tomorrow to get this fixed, thanks for the heads up.

-PB

[altec604e]

Hi again,

This was really good news 

Just to be sure : is there any of my other readings in my attachment I should look into more closely ?

Thanks !

_________________________________________________________________________________


I run my Stereomour with a 240V mains transformer.
Will this affect how the DC voltage readings some places are more than 10-15% off ?

_______________________________________


Yesterday when I tried to find an answer to my question about T5 and T6 I found another thread; about tubes.
This raised a question I want to ask :

I have a pair of NOS black plated RCA 2A3 tubes.

When installing these tubes will I need to do any precautions ? 
I read in another thread that you recommend setting the Stereomour amp to 45 tube operation when using for example more expensive NOS 2a3 tubes.

Or did I misunderstand something?

______________________________________________________________________________________________


PS: I did NOT use these 2a3 RCA tubes when reading the DC voltage in my Steremour amp.




Again :  All help / inputs will be appreciated


- altec604e



 

[Paul Birkeland]

The 240V mains/transformer shouldn't move the voltages much.  If anything, they may be a hair low depending on your line voltage.

While you can run a 2A3 with the amp setup for 45's, it won't be optimized for this configuration.  I would use your old stock tubes with the stock circuit. 

[altec604e]

Hi again !

Will leave the 2a3 operation as it is then.


The line voltage in my country is 230 V

I did only read 2V instead of 2.5V on between A1 and A4 and C1 and C4 when measuring the AC voltage.

Any thoughts about why ?

[Doc B.]

If your meter is set to a high scale like 500V it doesn't resolve tenths of a volt. Make sure you use a scale like 20V to read filament voltages.

[altec604e]

Hello !

Thanks for the input 

Did a new AC voltage measurement of A1+A4 and C1+C4 with a second multimeter.

They both measured just under 2.5V AC.

____________________________________

Did not manage to get the hum adjustment under 2.2 mV AC.
Did this adjustment with the volume control set to a minimum.

the best I managed was : ( left = 2.8 mV AC / right = 3.2 mV AC )

_____________________________________

Tried the amplifier with speakers rated around 100dB sensitivity.
It is sound in both channels.

But both channels have a hum  (120 hz ?) that is not affected by the volume control.
The hum is present both with the source plugged in and out.

Is the 120 hz hum usually connected to problems around the power supply? just found another thread talking about this.... but with few solutions ...



Does anyone out there has one or several solutions on what to do ?

[Doc B.]

Is the hum buzzy or a soft hum?

[altec604e]

I would say its a soft hum

[Doc B.]

Do you have the stock tubes on hand, or just the RCAs? If you have other 2A3s try them and see if they can be adjusted to be more quiet.

[altec604e]

I have only used the Sovteks.

I have two pairs of 2a3 tubes.  The Sovteks and the RCAs.

Do you think it only has something to do with the tubes?

I will try the RCAs tomorrow.   

Thanks !


- altec604e

[Paul Birkeland]

For which impedance did you wire the amplifier?

With 100dB sensitive speakers, go for 4 Ohms. 

[altec604e]

YEs!
I read earlier today about another guy on the forum that did this , and after that the speakers were extremely quiet.
But I forgot about it since his speakers were well over 100 dB.

That`s probably it- don

[altec604e]

Hello all,

I have now finished testing my stereomour amp.
The output transformers are both set to 4 ohm operation.

Did the hum balance a second time :
Both channels now are adjusted to a minimum: 2.1 mV

I can still hear hum from my speakers but it is so little...
Still using my svetlana tubes.

I think this is my last question in this thread :

When having the amp set to 4 ohm operation and having speakers set to 16 ohm.
Is it normal that you have to turn up the volume control quite a bit more than usual ?

Best,
altec604e

[Grainger49]

In a word, YES!

The three taps on the output transformer give the same power (voltage times current) at 4, 8 and 16 Ohms.