Suddenly on one channel the tubes light much brighter(or may be the other channel less brighter). The four tubes on a specific channel light evenly. No noticible change in sound. Suggestions?
Tubes don’t have an eternal life and they go when they go, apparantly for no reason.
Replace the tube and the cathode resistors of that tube.
Make sure to re-adjust bas afterwards.
I think I am misunderstood. With one channel I mean the four tubes on the same side. So, all four tubes have the same difference towards the opposite channel. The tubes of the oppossite channel are also equal to each other. So 4 tubes on the left side versus 4 tubes on the right side.
Can you measure left and right heater voltage?
Please be extremely careful when performing this action, the voltages in the amp can kill!
Reference 6.3VAC
J2 left; green 4.40 violet 1.32
J2 right; blue 2.61 grey 2.57
Print left; V5 between 5-9 6.13
Print right; V5 between 5-9 5.62
Print left; V1 till V4 between 2-7 6.11
Print right; V1 till V4 between 2-7 5,62
Do you all ready have any sugggestions after the information given above?
Not really, it confuses us.
Did you measure the heater voltage with respect to GND?
Anyway, is it correct that one side measures 6.13V and the other side 5.62V
All measured towards ground. Print or powerboard, no difference.
Other measurements;
+V1=+V3= 450V which should be incorrect?
-V= -48.5V
Indeed, there seems to be a difference between the two windings.
You say it happened suddenly, that is quite strange.
Are all tubes of the same brand (i.e. do they draw the same current)?
Anyway, if the sound is not affected, I would not worry about it.
The +450V is a littleon the high side, since the caps are rated for 450V.
Did you configure the amp for 235VAC? Most likely, it is configured for 220VAC.
Very early amps do not have a 235VAC winding, since 220VAC was still the norm in those days.
Some people use a hefty adjustable transformer to drop the input voltage.
All tubes the same and low hours
Indeed 220V, pink wiring
The one channel which I think the tubes are glowing dim seems not working proberly
The one channel is really bright compared to the other side
The K4000 manual talks about +V1 430V but +V3 350V?