[time-nuts] About HP10544A

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Mar 7 22:02:54 UTC 2009

Esa Heikkinen wrote:
>> Please provide a circuit schematic for your emitter follower buffer.
>> Include transistor types and component values as well as power supply
>> voltages.
> 10nF DC-blocks at input and output, 4k7 pullup and 10k pulldown at the 
> base, 180 ohms pulldown from the emitter, 12V input voltage having some 
> 100n coupling capacitors. BC547 as transistor (should do 250 MHz?).
> I built that from schematic of 10 MHz distribution amplifier but with 
> dirrefent transistor (there was BC849C in the schematic) and without 
> LC-filters at output.

The emitter follower current is too low to drive 1Vrms into 50 ohms

Its probably better to increase the emitter current to 40mA or so and
place 47 ohms between the emitter and the output coupling capacitor and
accept the resultant +7dBm output.
The transistor dissipation will increase and it may be better to
substitute something like a 2N5943, 2N3866, 2N 5109, BFW16A or similar.
You will also need to reduce the values of resitors in the resistive
divider at the base or use collector current sensing via a small signal
pnp a LED and a few resistors to ensure a predictable emitter current.


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