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Many amplifiers have a watch dog circuit that avoids the amp relays from being hot switched. Many amps will delay the closing of the relays until the PTT signal is present and no RF is at the input.? This is mostly prevalent when using CW.? The amp will clip the first bit of RF until there is none and then the relays close.? A 7300 or just about ANY solid state radio without RF delay control will hot switch an SB200,SB220,TL922, Drake etc etc unless the modern radio has an RF delay, the? amp will hot ?switch.? In?the case of the old open frame relay amps, the TR relay can be mechanically sequenced so that the contacts won’t hot switch by insuring that the output contacts switch?before the amplifier is biased on with the bias switching contact of the relay. The 7300 isn’t necessarily singled out on this regard.? Use a 20ms RF delay when using old amps with new radios.

On Friday, August 2, 2024, 11:42 AM, Alan - W5ARM <W5ARM.mail@...> wrote:

On Fri, Aug 2, 2024 at 08:23 AM, Bill K3HZP wrote:

Sequencing is required for some rigs. The classic example is the ICOM 7300 which releases the amplifier key line before the RF goes to zero.? See QST review for IC7300.? In this case, sequencing is required on the release transition.??

? .... Bill K3HZP

I find that really hard to believe. That means that using a 7300 with ANY amplifier - even a modern tube or solid state amp - would allow the 7300 to hot-key (or hot "un-key") the amp? This would mean that, in reality, ALL amplifiers are effectively unusable (or subject to damage) if using a 7300, unless "sequencing" were employed.

?

I had (abut sold) a 7300. Never heard of such a thing...

?

I was unable to access the referenced QST article ("members only"), so please provide a quote or screen-shot of the appropriate article section to validate this claim.

?

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73,

~Alan