bass 400 +

[fredouille]

Hi all

any expert on the bass 400 + here ?

I'm checking my own 400 +, some noises.. discovered 1 tube dead and some 680 ohm resistors out of specs and some far away

I discovered that I don't have the zener 15V to drop the B+ .. strange even that it is on the schematic as bassmans for example running on 6L6 don't have any drops and even small resistors. 470 against 680 here.

amp worked fine since 1 years, no red plating and so one, so i was wondering adding or not this zener..

didn't check the bias yet, as I need to replace a pair of tubes first.

thanks for your ideas here

[sluckey]

I would do it. Easy enough to add to the schematic. Could be a bit more challenging to actually install it in the amp.

[fredouille]

I would do it. Easy enough to add to the schematic. Could be a bit more challenging to actually install it in the amp.

yes but at the same time I saw that a resistor was added in bias section, might it compensate on this side.. at the end this voltage drop is to control the power on the tube , can be done by increasing negative value on the bias

I will wait new power tubes to check the bias, i guess there is a reason if this diode was not put there

[Olomert Brever]

Just curious but could the 1N5362 diode be a failsafe? The spec sheet I see rates it for 170mA.