Stereomour Voltage readings

[Filthymidget]

Ok, so i've been keeping my amp turned on figuring it would burn in.  I haven't finished building my speakers yet but they should be done this weekend.  I was noticing that one tube glows less than the other.  I switched them around and the weaker tube remained weak and the strong glowing tube remained strong glowing in the different four pin socket.  So does this mean i have a bad tube?

My DC voltage readings are incorrect in a couple places.  First across the 3.3 uF film capacitor at terminals 1 and 5.  Term. 1 is correct with a 419mv reading but Term. 5 is reading 0 where it should be 60.
Next, my .1 uF 630V film cap. is reading 51.5 mv at term. 1 where that should be 0 and correct at term. 14.
Terminal 16 should read 60 and i'm getting .4mV and down to 0.

My four pin sockets:
A1- .3 should be 60 A4- 0 should be 60; C3- 49.4 should be 0
Everything else checked out fine!

[Paul Joppa]

"... across the 3.3 uF film capacitor at terminals 1 and 5.  Term. 1 is correct with a 419mv reading but Term. 5 is reading 0 where it should be 60."

Terminal 1 should read 350 volts DC. It is connected to the 2A3 plate (A2) which is connected through the plate choke to the power supply high voltage (380v). If that tube is not getting high voltage power, then the cathode at T16 will also be zero volts, and it is connected through the output transformer primary to T5.


"Next, my .1 uF 630V film cap. is reading 51.5 mv at term. 1 where that should be 0 and correct at term. 14."

The 0.1uF capacitor is connected to T2, not T1. T2 should read 230v (well, something around 200-250v anyhow) - but if the high voltage power is not functioning on that side, then it will be at ground potential.


"Terminal 16 should read 60 and i'm getting .4mV and down to 0."

See the first note.

"My four pin sockets:
A1- .3 should be 60 A4- 0 should be 60; C3- 49.4 should be 0
Everything else checked out fine!"

C3 should be grounded through the 249K resistor (T12 to T10) and the 220 ohm CC resistor (T12 to C3). You should have confirmed this by measuring 249K ohms from C3 to ground in the resistance measurements. The 220 ohm CC resistor is a little fragile, so that's the likliest place for a failure - do the resistance check again, and wiggle that resistor a bit to see if it's intermittent.

[Filthymidget]

"the 0.1uF capacitor is connected to T2, not T1. T2 should read 230v (well, something around 200-250v anyhow) - but if the high voltage power is not functioning on that side, then it will be at ground potential."

That should have read T12, T12 is reading 51.5 and T14 is reading 215.

"C3 should be grounded through the 249K resistor (T12 to T10) and the 220 ohm CC resistor (T12 to C3). You should have confirmed this by measuring 249K ohms from C3 to ground in the resistance measurements. The 220 ohm CC resistor is a little fragile, so that's the likliest place for a failure - do the resistance check again, and wiggle that resistor a bit to see if it's intermittent."

I remeasured and got 248K ohms C3 to ground.

"Terminal 1 should read 350 volts DC. It is connected to the 2A3 plate (A2) which is connected through the plate choke to the power supply high voltage (380v). If that tube is not getting high voltage power, then the cathode at T16 will also be zero volts, and it is connected through the output transformer primary to T5."

I guess that is quite a bit more than 15% isn't it?  :-)

 
 
 
 

[Filthymidget]

2:30 in the morning!  All the voltages checked out perfect after wiggling that resistor and rechecking the resistance at C3 and ground.  It wasn't intermittent though it was steady.

[Grainger49]

2:30 in the morning!  All the voltages checked out perfect after wiggling that resistor and rechecking the resistance at C3 and ground.  It wasn't intermittent though it was steady.

Wiggling and getting a different reading says you need to rewet the solder on both ends of the resistor.  Just start with a tiny bit of solder melted on the soldering iron and touch it to the joint.  Count to three after the joint melts and remove the iron.  Put another dab of solder on the tip and do the other solder joint.

[Filthymidget]

Namaste!  I will rewet those two joints tonite!  Thank you for all the help gentlemen!  I'm ready to start another kit!