Bottlehead Forum

Bottlehead Kits => Kaiju Stereo 300B amp => Topic started by: pfontana on March 15, 2020, 09:00:30 PM

Title: blown resister [resolved]
Post by: pfontana on March 15, 2020, 09:00:30 PM

I built both the A and D socket boards for the 5670 tubes driver testing.  During testing the A board's voltages were incorrect.  The D board was perfect, but during the final testing, I accidently touched the positive mm probe to the 5731A transistor to OA.  See pictures for all the damage caused by this error!
Do I need to build another board?  Or just replace the blown resistor, leds, and transistor?
I may need to buy both boards/components too because the other one wasn't testing correctly.

Please let me know what I may need.  Thanks,
Philip

Title: Re: blown resister
Post by: Paul Birkeland on March 16, 2020, 05:54:58 AM

I would start with a fresh board.

Title: Re: blown resister
Post by: pfontana on March 17, 2020, 08:58:58 AM

Hi,
I'll start with a fresh board on the D side.

The A side, the board tests within range, except for the oA.
That reads 350V instead of 300V.
Any ideas offhand?
thanks,
Philip

Title: Re: blown resister
Post by: Paul Birkeland on March 17, 2020, 10:00:50 AM

How are the Kreg voltages?  That 350V indicates that the regulator is not functioning.

Title: Re: blown resister
Post by: pfontana on March 17, 2020, 10:48:54 AM

The kreg was 13.59DC.
Any ideas?
Philip

Title: Re: blown resister
Post by: Paul Birkeland on March 17, 2020, 02:40:06 PM

Can you post some photos of that board?  Is the little red jumper installed on the top side of the board?

Title: Re: blown resister
Post by: pfontana on March 17, 2020, 06:29:01 PM

Problem fixed....
I reversed the 330K 3W and 147K 1/2W resistors on the board.  I corrected the two resistors and it tests great!
Thanks,
Philip

Title: Re: blown resistor
Post by: pfontana on March 23, 2020, 07:29:54 PM

Hi,
I built a new D board and attached it.
The measurements are:
IA 518V
OA 0V
46U 0V

Any ideas?
thanks,
Philip

Title: Re: blown resister
Post by: pfontana on March 23, 2020, 10:23:27 PM

I reviewed my work and went to check in my voltages again.

This time the D board 90R9F blew up.

Any ideas what I did this time?
I checked my work three times for the board and for wiring it up to D.

See pics...
 :(

Title: Re: blown resister
Post by: Paul Birkeland on March 24, 2020, 04:50:35 AM

Problems with the tube socket wiring can cause these boards to blow, as can installing any of the zener diodes backwards.

Title: Re: blown resister
Post by: Doc B. on March 24, 2020, 07:54:57 AM

Yup, usually a bad zener string.

Title: Re: blown resister
Post by: pfontana on April 07, 2020, 07:36:51 PM

Hi,
I built the replacement board with the new Zeners.  The D board tests within ranges, except the OA is 296V.
Should I be concerned I'm slightly outside the 300V +/- 1%?
thanks again!
Philip

Title: Re: blown resister
Post by: Paul Birkeland on April 08, 2020, 05:06:28 AM

That is just showing the tolerances of the resistors to set the OA voltage.  As long as your Kreg voltage is above 3V and below 32V on the side without the blue trim pot, there's nothing to worry about there.