K4000 R36..R39 burned out

Kits Audio Hi Fi Projects
1

After using the amplifier K4000 for several years it just began to burn out resistors R36…R39 (They no longer show correct Ohm-Values), and up to now I replaced them 3 times.
When they have been replaced the amplifier works again correctly. But just replacing the resistors does probably not solve the cause of the failure. What could possibly be the couse of this?
Any hints are welcome.

Franz

2

Difficult to say.
Has your amp been set to 230VAC instead of 220VAC?
Have the EL34 tubes been replaced yet?
Did you perform a monthly check of the bias current for each tube?