Hi everybody,
I just finished building SE 300b Legacy by Thorsten. Something strange is happening or at list I have never seen anything like this before.
When the amp is first turned on the voltage on the filament of the 300b is 5V. After a few seconds the voltage start to rise up to 68V. That is how it should be. Than it stays at that voltage for about 2-3 seconds and start to fall down to 0V. This fall in the voltage is accomanied by motorboating sound from the speaker.
in meantime the 5V regulator gets very very hot. I measure all the volages in the cct and here is what they are: HT 418V, reference voltage in the HT regulator cct 81V, the voltage at the plate of SV83 it measures 303V and it should be 270V, the voltage at the cathode of the same valve is 5.1V and it should be 5.5V, the voltage at the junction of R1,R2,C1,R4, is 162V and should be 160V. The voltage at the top of C7,C8 just after the rectifiers is lower then it should be at 455V.
The testing of 5V power supply without load show no sign of any problem. As a matter of fact I installed second 5V supply and had the same problem. I also check the HT regulator without load and I was able to ajust HT without problems.
I check all the wiring so meny times and for the life in me I can't find what I did wrong.
Thorsten and everybody else, I would be very thankfull if you can get involved and help me solve this problem. Thank you.
I just finished building SE 300b Legacy by Thorsten. Something strange is happening or at list I have never seen anything like this before.
When the amp is first turned on the voltage on the filament of the 300b is 5V. After a few seconds the voltage start to rise up to 68V. That is how it should be. Than it stays at that voltage for about 2-3 seconds and start to fall down to 0V. This fall in the voltage is accomanied by motorboating sound from the speaker.
in meantime the 5V regulator gets very very hot. I measure all the volages in the cct and here is what they are: HT 418V, reference voltage in the HT regulator cct 81V, the voltage at the plate of SV83 it measures 303V and it should be 270V, the voltage at the cathode of the same valve is 5.1V and it should be 5.5V, the voltage at the junction of R1,R2,C1,R4, is 162V and should be 160V. The voltage at the top of C7,C8 just after the rectifiers is lower then it should be at 455V.
The testing of 5V power supply without load show no sign of any problem. As a matter of fact I installed second 5V supply and had the same problem. I also check the HT regulator without load and I was able to ajust HT without problems.
I check all the wiring so meny times and for the life in me I can't find what I did wrong.
Thorsten and everybody else, I would be very thankfull if you can get involved and help me solve this problem. Thank you.