Update 5- 2016
This is a precission amplifier that amplifies from DC upto 100kHz with a flat and calibrated gain. The gain is fixed through 3 switches as 10, 100 of 1000x but it has also a variable mode.
HP-463a
I bought this amp in 2010. It worked more or less but at some point in time the magic smoke escaped. I did not have a service manual and so it was stored. I needed an amplifier for a repair job so I decided to fix the 463. The problems were 2 leaking ceramic capacitors, some electrolitic caps,
The power amp
The amplifier is a push pull design with 6 stacked transistors. The dead zeners are top left next to the “27k” resistor.
Input amp
3 dead 60V zeners and a resistor that had drifted to 27k. The colorcode started with brown-black so 27k was wrong. It dissipated to much power because the 3 zeners were short. There was 308V over it and it ‘s temp raised over 100 degrees. After I replaced the zeners (3x60V) I replace the resistor for a 39k version because the zeners I used worked best at 5mA. Now the resistor warms up to 50 degrees.
Top view
I adjusted the powerrails to excactly +210V and -210V. On the preamp/shaper board are two trimpots. One of the two is to null the output with an open input. On the front is a trimpot to zero the output with a shorted input. It took a lot of trial and error to get things good.
Bottom
introductie uit HP journal
specs