[ARC5] Audio power output and BFO fixed - 10 meter BC-454

[brianclarke01 at optusnet.com.au]

	Hello Ken, 

	Interestinger and interestinger. 

	If the output impedance of the 12A6 is 7000 Ohm (RCA design value)
and the secondary of the OPT is exactly matched to 500 Ohm, the turns
ratio of the OPT is sq rt (7000 / 500) = 3.74. (This, of course, is
researchable hypothesis, as I am unaware of the design specs of the
OPT. All I have seen are wire gauge and resistance specs - probably
for trouble-shooting.) 

	3.74 x 72 Vp-p = 269 V. This is more than the rated output of the
dynamotor, and doesn't allow for the loss of swing because of cathode
bias. It is also much higher than the ignition Voltage of the neon
across the OPT primary. I reckon your output must be highly distorted.
So, it probably sounds loud because of that distortion. I suspect
there is something odd here. The likelihood of running the 12A6 plate
from rail to 0V is negligible, especially if the screen is still at
rail. 

	In some of my Command receivers, the wiring in the chassis is glued
down with glyptal. The use of single-core wire throughout was another
piece of Drake's genius - to remove possible sources of
vibration-induced capacitance change. 

	73 de Brian, VK2GCE.

----- Original Message -----
 From:"Ken Gordon" 
To:"Arc5 mail list" 
Cc:
Sent:Tue, 19 Feb 2013 01:33:12 -0000
Subject:[ARC5] Audio power output and BFO fixed - 10 meter BC-454

I rechecked the audio power output here and tried to be a bit more
accurate this time.

Peak-to-peak voltage at 400 Hz into 500 ohms on my HP o'scilloscope is
72 V.

Peak voltage is thus 36 V

Erms=36/sqrt2=~25.5 V

P=E^2/R=1.296 watts.

Even on the cheap Radio Shack CB speaker with the 8:500 ohm
transformer I installed in it, 
it will literally rattle the windows.

Secondly, I removed all the broken bits of ferrite from the BFO
transformer can, then liberally 
brushed Mike's coil dope over every thing that I thought could use it.

I let the stuff harden, then thoroughly cleaned, and then reassembled
and reinstalled the BFO 
transformer.

Result: no more ringing or frequency jumping from that source, and the
BFO is much more 
stable. Furthermore, the tone no longer has what appeared to be some
sort of modulation on 
it.

I have one more thing to do to this thing to stablize it, then I think
I can button it up and do a 
more thorough testing of it.

Ken W7EKB
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