[Amps] Best source for Gigavac GH-1 ?

[Paul Christensen]

> Can you tell me why sequencing is a requirement? I have found that the RF 
> never flows (6 ms after the tranciever control circuts energise)until way 
> after the relays and cathode bias has switched which as you have pointed 
> out is  3-4 ms.

Sequencing is mostly a non-issue when using recently manufactured 
transceivers.  Almost all of them will delay RF by at least 8 ms. after the 
transceiver's PTT line goes low.  They will also allow enough time for RF to 
decay before reversing the sequence.  Apart from any changes in delay by 
mode, the time from PTT activation to RF shouldn't change.  As both of you 
point out, there's generally ample time for bias de/activation and for the 
waveform to ramp up/down in CW mode.

I think sequencing is more of an important issue with some older 
transceivers - like a KWM-380 I once owned, or where classic separates are 
used into an amp.  In addition to sequencing, I think it's a good idea to 
include RF sensing at the amplifier input.  In the presence of any input RF, 
the amplifier's T/R should be inhibited from R=>T or back from T=>R until 
the RF envelope decays to near zero.  Even without sequencing, that one 
feature alone will prevent relay hot-switching accidents.

Consider a case where a multi-transceiver station controller is used and a 
transmitter is keyed at 100W while maybe adjusting a tuner.  Then, you 
accidentally go to the transceiver controller while the rig is still in 
transmit and select the hot transceiver into the amp and the amp immediately 
keys with RF.  Since the transceiver is already generating RF and the rig's 
key line is low, the amp will hot-switch when the PTT line is quickly routed 
to the amp from the controller accessory.  RF input sensing at the amp would 
prevent this accidental form of hot-switching and save the amp's relays.

Paul, W9AC