On Sat, Aug 3, 2024 at 05:21 AM, Bob wrote:

Dave, That link takes me to the 7300 group IO home page but cannot find the RF tail fix.

I do not own a 7300 but have a few friends that do which each of them seem to get things confused so I end up helping them, if you know what I mean.

Bob W4JFA

Hey Bob,

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I downloaded and attached the 7300 "RF Tail" document... (See attached PDF).

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73,

~Alan

Icom IC-7300 Hot-

switch Mitigation

The Issue

The Icom IC-7300 was released with a flaw in its external amplifier keying circuit apparently caused by an incorrect timing parameter

programmed into the SEND relay logic. The SEND jack on the rear of the transceiver is used to key an external linear amplifier on and

off in synchrony with the IC-7300 RF output as mitigated by the Menu/Set/Function TX Delay parameter. That parameter sets the time

the RF output is delayed from the time the transmitter is keyed on until RF output begins. (The TX Delay parameter sets the time the

RF output is delayed from the time the transmitter is keyed on, which is not what is addressed in this article; the TX Delay functions

nominally as expected. This article is concerned with the RF output continuing beyond the time the transmitter is keyed off, termed an

RF-tail, causing hot-switching of external linear amplifier.)

Unfortunately, there is no similar user adjustable menu setting for controlling the delay time from when the transmitter ceases RF output

and the SEND jack commands an external amplifier off. Because the IC-7300 continues to output RF energy while an external amplifier

is in the process of switching off, the amplifier's TR/RX relay is subject to hot-switching and the concomitant possibility of arcing at the

relay contact points, or worse yet, welding together of those points resulting in the amplifier taken out of service.

This RF-tail issue has been extensively addressed for years by Amateur operators on both the IC-7300 discussion group, and

Forum. Below is finally a possible hardware solution to the hot-switching issue originally suggested by Frank Johnson

(G0GSR)

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Complete description of the fix in in the ic7300 forum files.

/g/ic-7300/files/ic7300_rf_tail_fix.pdf

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73,

Dave, w6de

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From: [email protected] <[email protected]> On Behalf Of Alan - W5ARM via
Sent: 2 August, 2024 19:00
To: [email protected]
Subject: Re: [ham-amplifiers] Henry 2K-3 TR switching

?

On Fri, Aug 2, 2024 at 01:40 PM, Bob wrote:

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As far as the 7300 goes, I thought all that was adjustable in the menu???

Bob W4JFA

It is...

In: MENU --> SET --> FUNCTION --> TX DELAY HF

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73,

~Alan

Please reply to this message and include an attachment. I don't want to have a discussion here or for this thread to get out of control so please just say hi, attach a picture, and that's it.

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.

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

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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

Robin,

Here is a problem that may be similar to yours:



I had the shorted Q2 problem as well in my Centurion.

73 Bill N4LG

PS: Another problem is a wonky mode switch. I had to make a
modification to my Centurion logic to fix a "state" problem. See
attached.