> > 2. A "T" voltage is brought out to the accessory connector on the rear
> > panel. Can this be used with a relay to drive an amp correctly -- i.e.,
> > with enough lead time before RF appears to avoid hot-switching?
Yes. In many of my Ten Tec's, I have bypassed the internal "Ext. T/R" relay
with a 2N5551 NPN transistor for fast, completely solid-state amplifier
switching with non-Ten Tec amps. It's important to only use the "T" voltage
as a reference rather than "TD" or other such keying voltage references. I
have found that any point other than Ten-Tec's "T" voltage point results in
hot-switching the amplifier. After any such keying mod, it is always a good
idea to observe the keyed waveform on a scope.
I like the 2N5551 because it is Vceo rated at 160 VDC, is Ic rated at 600 mA
and is available in a small-signal transistor package. I have found
isolation to be fine although someone who wants more circuit isolation could
cascade two of these into a Darlington transistor. For me, a single 2N5551
has worked well with my high key line voltage Alpha Seventy amplifier.
I just take one side of a 10K resistor to the "T" voltage point. The other
end of the resistor connects to the transistor's BASE. The EMITTER is
grounded. The COLLECTOR is then brought out to form the amplifier key line.
You can build the circuit into the 515 or build it externally. Whether you
use a 2N5551 or not, it's important to select a NPN transistor with a Vceo
rating that is greater than the amplifier's key line voltage. For modern,
logic-controlled amplifiers with 12V or less on the key line, the transistor
can be a 2N3904 or 2N2222.
In the event you desire a relay instead of solid-state amp switching, the
above description is changed to the extent that the Collector now connects
to one side of the relay's coil...the other side of the relay's coil is
connected to it's rated voltage source (e.g., +12V either through the 515 or
externally). Then, the N.O. relay contacts connect to the amplifier key
line.
-Paul, W9AC
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