HP-463A DC to 100kHz calibration-grade amplifier

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

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 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

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

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

Bottom

introductie uit HP journal

specs

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