Pro Audio Design Forum

I finally got the Vbe Matcher off of a Protoboard by moving it to Vectorboard.

It's been awhile since I did point-to-point Vectorboard.

The connections across the top are Power, 'Scope Monitor Out (filtered), Output to A/D, 1.5 mV P-P Calibration signal, 15V Trigger output.



The two jumpers and shunts switch the test socket from NPN to PNP.

There are two rows in the test socket.
The right-hand row is for CBE pinout transistors.
The left-hand row is for BCE pinouts.



The clip is to thermally equalize the test transistors.

A pair of BD139 BCE pinout transistors:



A 2SB737 pair:



One more project I can check off the list...
It's been a productive few weeks.

JR. wrote: ↑Sun Dec 22, 2019 8:38 am If you add a 50k or so resistor from the junction of the two emitters to ground that would prevent potential reversed junctions from zenering when switched for the wrong polarity.

JR

I added D1-D4 to clamp Ve.
Not only for the reason JR gives but also to reduce recovery time for when both devices are removed from the test socket.
Without D1-D4 Ve goes to the rail when Q1 and Q2 are removed.

I had used up my stock of matched ZTX-851 transistors for the flat MC preamp and the time had come to match some more up.

The ZTX851 for this run was from a different lot.

Out of 30 devices I had no problem getting 12 pairs matched to <1 mV which is adequate for the MC preamp.

This lot had higher gain, the average HFE was 185. The highest was 230.

Of the 6 transistors that wouldn't match 1 was bad (B-E short) so the yield is 24/29 or about 82%.

FWIW (knock on wood) I haven't found a noisy one yet out of about 120 devices.