Testing Voltage through a resistor

Thread Starter

Squidge75

Joined Feb 12, 2024
25
Hi there,

I am hoping someone can help me. I have just installed some new Trimpots into my circuit for an old B&O Beomaster 1200.

I know that the system works as I have had it working, and I cam changing the trimpots because they are very old and I am getting a crackling scratchy noise through the speakers.

I have attached some images from the manual with regards to adjusting them.

My confusion is when taking the voltage reading across the resistors.

Am I right in thinking that I am to take the Voltage measurement across the corresponding resistors within the images. So in image 1. I adjust the trimpot so that the reading across resistor 456 measures 33volts?

The same goes for image 2 and 3. Adjusting the trimpots so that the resistors 423 and 421 measure 7.5mV?

Image 4 confuses me a little as it asks for an old Tube reading for a maximum VTVM. can I measure this with a multimeter? I presume I am taking the VTVM reading from resistor 190?

I did try to take a reading resistor in image 1, all powered off, but I didnt get any reading at all? Maybe I have my multimeter set up wrong?


Thanks for any help.

All the best
Matt

1.png2.png3.png4.png
 

Alec_t

Joined Sep 17, 2013
14,313
Your manual is not exactly a model of clarity, but my understanding is that you should measure voltage
1) between the right-hand end of R456 and ground (chassis),
2) across R421 and across R423.

A good quality multimeter on a voltage range should have an input impedance of at least 1 megOhm, so would substitute for a VTVM in this application
 

Thread Starter

Squidge75

Joined Feb 12, 2024
25
Your manual is not exactly a model of clarity, but my understanding is that you should measure voltage
1) between the right-hand end of R456 and ground (chassis),
2) across R421 and across R423.

A good quality multimeter on a voltage range should have an input impedance of at least 1 megOhm, so would substitute for a VTVM in this application
Ha yes I totally agree, its from the 1970's and I guess things were a little more 'general' those days. Thanks for the advice with the VTVM reading as well. Ill set it to that.

Thanks again
 
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