[Amps] re: EBS at soft or quiet moments

[rm1]

>rm1 wrote:
>>
>>
>>>
>>>> In the 2 meter amplifier after a 3 minute CW transmission at about 20
>>>>wpm
>>>>into a dummy load, the average anode exhaust temperature went from 205
>>>>degrees F
>>>>to just under 100 degrees F when using the EBS.
>>>
>>>This is the aim.
>>>
>>>EBS seems to have a poor reputation because of either:
>>>
>>>1. Being the only means of keying the amplifier, which is guaranteed to
>>>cause hot-switching. Competent EBS works along with the hard-wired PTT
>>>line - it cannot replace it.
>>>
>>>2. Being RF-actuated at too high a level (ON4UN suggests around 0.5W in
>>>a kW amplifier, related to the dynamic range of he speech processing for
>>>SSB).
>>>
>>>3. Being too slow to turn on.
>>>
>>>Any or all of the above can cause a poor signal, and then of course
>>>there's:
>>>
>>>4. Being unreliable and easily damaged.
>>>
>>>... but it doesn't have to be that way.
>>>
>>>Like many other features in amplifiers, EBS can be very useful if it's
>>>competently done - or a disaster if not.
>>>
>>’Ǩ  Good points, Ian.  The solution is to allow the transceiver to control
>>the EBS with its +DC-V on Tx signal.  This gives the RF relay contacts in
>>the amplifier at least a 5mS headstart so they can be closed  Before  RF
>>arrives.  When the EBS is controlled by RF arriving from the transceiver,
>>this is not the case.  In other words, when the transceiver DC-controls
>>the T/R switching in the amplifier, all will be well
>
>The logic would be to kick the EBS on immediately the PTT line goes low 
>(TX). 

***  What about those who do not use PTT -- i.e., folks like yours truly 
who use VOX?  In this case, the (+DC-V on Tx) signal switches between 
+12V or so on Tx and 0V on Rx.  This signal is ideal for controlling the 
amplifier's bias and RF switching because it is always in sync with the 
transceiver.

>When the PTT goes high, release the EBS after a short delay 
>(because transceivers typically output RF for a few ms after the PTT 
>goes high). While the PTT remains low, it can be left to the RF detector 
>to control the breaks during the transmission.
>
***  Nevertheless, when the amplifier bias is RF-determined, the bias 
will switch in and out of linear operation during soft-syllables even 
though the PTT line remains low.

>That would work, but also requires that the EBS operates very quickly... 
>so no relay!
>
>
>>-- provided that the
>>amplifier T/R switches faster than the transceiver.
>>
>The PTT needs to switch to TX *before* the RF appears. Most modern 
>transceivers do this for CW... but not if you use the relay-switched PTT 
>option. The timing for SSB VOX is anybody's guess.

***  By using an o'scope to measure what's what, there is zero guessing.  
For example, an FT-1000 begins to produce RF 5mS after the VOX trips -- 
and it produces no RF after the VOX switches to Rx mode.  I have heard of 
no transceiver that produces RF after the VOX drops.
>
>Ideally the PTT should also hang low for a few ms *after* the end of a 
>transmission (or end of each dot /dash in full QSK). I don't believe any 
>transceiver does this - more typically the PTT goes high and then 
>there's a 'tail' of RF for a few more milliseconds.
>
***  I have not seen what you describe on an o'scope.

>...