Heated Chip Servo vs No Servo Test report

[Harry Bissell]

Well the results are in...

I ran a side by side test of the CA3046 Heated chip (a' la Tom G in his
VCO4d) vs
(hey ain't 'side by side' and 'vs.' the same thing....)
The National Semi AN-299 Servo Heater (my version with the substrate
tranny as the sensor.)

In both cases, the tranny tested was the B-E junction of Q1 (pins 1-2
short B-C, and pin 3 Emitter).  The initial (cold ) values are shown in
the graph.

The test chamber was a small 10"x10"x10" cardboard box lined with
styrofoam 1". The circuit boards were side by side in the bottom... with
a type K thermocouple located in free air 1" above them.  2 50 ohm 25W
resistors (parallel) with a 24VDC isolated supply was the heater,
suspended 1" below the box top.  After applying power, the temp was run
up to 75 C and allowed to decay naturally... At 35 C equilibrium was
reached and the box had to be open to run down to 27 C  (ambient was 22
C).  The heaters gave enough heat to keep the temperature from going any
lower in the relatively draft free location.

A Fluke 8050A was used to measure the diode drop. The leads were not
left connected between data points, so no self heating is likely...

The drop from 75 C was rather rapid... so that maybe the chips did not
quite track the temperature change... about 40 C the exponential decay
of temperature really slows things down, so the near room temp. values
are probably most accurate...

The AN 299 wins in my book.  I didn't test the VCO4d type heater vs the
3046 with no heat at all... maybe another test run tomorrow ????

Note: the fact that the ambient in the box never got below 27 C means
that besides the power drain of the heaters, the whole synth is going to
get warm... Maybe the tempco's or the temp compensated oscillators are a
good idea after all...

Hey... maybe we should get some National Lab  (Sandia ??? JPL ???) to
sponsor a
"VCO BAKE_OFF" and may the least drift win !!!

:^)  Harry
-------------- next part --------------
A non-text attachment was scrubbed...
Name: VCO4_HT.gif
Type: image/gif
Size: 6616 bytes
Desc: not available
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/19990908/99e0b6a0/attachment.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 3046_SCH.gif
Type: image/gif
Size: 17763 bytes
Desc: not available
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/19990908/99e0b6a0/attachment-0001.gif>