On Fri, Aug 2, 2024 at 06:37 PM, Louis Parascondola wrote:

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.

##? Lou, even if u tweaked the output contacts of the old style clunker 3PDT mech relays such that the output closed before the input+ bias,? it will still hotswitch !? The xcvr puts out RF? NOW.? ?Hence the requirement for the 20 msec delay....so the slow 3PDT TR relay in the amp gets a 20 msec? head start.

##? There is no provision in my fT-1000D for any delay.

##? On my MK-V, there is an adjustable 0-30 msec delay, in 1 msec increments.... BUT that only works on cw mode, using the internal keyer.?

##? My....'fix' for that ( ssb on either xcvr....and CW + SSB on a FT-1000D)? was to RE-use the internal spst mech relay in each xcvr (that was intended to key an amp)..and instead use the internal xcvr spst relay to instead grnd the TX inhibit lead.? ? That tiny spst relay in the MK-V operates in 5 msecs...which is ample for my modified drake amps, since the 3 x sped up vac relays in the drake amps operate in 1 msec.?

##? The oem 3pdt relay in the drake amps operate in 17 msecs.? And 15 msecs in the older ameritron amps.? (The ameritron amps with the newer cube relays operate in 5 msecs. ).? ? ?So the advice of using a 20 msec delay when using the older amps with the slow relays is valid.??

##? here is where I screwed up.? ?You want the 3-20 msec delay when going from RX to TX...... (grnding the TX inhibit lead after 3-20 msecs. )? However, when going from TX back to RX, you want zero delay, or close to zero.?
Here's why. If a say 20 msec delay is used going from RX to TX, fine...... but when going back to RX.....and it takes the same 20 msecs to UN ground the TX inhibit lead.... what happens is..... stop talking on SSB, zero watts out of xcvr on the scope...... and 400 msecs later..... VOX drops out.......(and tiny spst relay in the xcvr starts to drop out, or any external delay)....then? TR relays in the amp also start to drop out. With TR relays in mid air, cough into the mic, and bam, instant RF coming out of the xcvr.....since the TX inhibit lead is STILL grnded.? ?TR relays in mid air = hot switching.

##? It works on my sped up vac relays in the drake amps? since the tiny SPST-NO? relay in the MK-V takes 5 msecs to operate (giving the 1 msec vac relays in the drake amp, ample head start) . Going back to RX, the tiny relay in the MK-V takes 1 msec to open off by .0001"...so the tx inhibit lead is UN grounded asap.... before the vac relays start to rls. ( I slow down the rls of all 3 x vac relays a bit, with a single rvs diode across each coil).?

## On buddy's hb 3x6 amp? (built back in 2007)? it used an external electronic delay...to grnd the TX inhibit lead.? ? Think it was set for 5-10 msecs. What I don't remember is ..what the rls time of it was.?

"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."

Lou, this is the issue with the stupid 7300? xcvr.? ?It keeps putting out RF....AFTER? it opens the key line....and amp switching back to RX.....which then hot switches the TR relays in the amp.??

The alpha amps will not RLS their TR relays, until NO RF appears on the input.? ?The alpha amps have a simple RF sense circuit on their input (which also reads the freq, if it's the 9500 auto tune).
The W7RY? qsk board does the same thing.....( RF sense on input).? ?IF u say run a 1.5 kw cxr on the alpha....and reach over and pull out the key line from the back of the xcvr ( or pull out from the back of the alpha amp)...then amp will still put out 1.5 kw...... until the ptt /footswitch is released..... or if you let go of the hand key.? And if it's a 7300...with it's .....'RF tail', the alpha will not UN key it's TR relay/pin diodes on older alpha amps like the 87A...until the RF tail has finally gone.??

This is also an issue when using high swr shut down circuits, like in the array solutions powermaster wattmeter.? With the high swr threshold exceeded, you have 3 x ways to shut down the amp asap.?

(1)? open off keyline ( doesn't work on alpha amps)

(2) apply a few volts of DC? to the xcvr's ALC input? ( this method works superb)

(3) open off the xcvr's? .....'TX inhibit lead'? ?This method is the fastest if using the array solutions power master wattmeter.

The AS meter uses a SPDT fast relay to achieve any if the 3 x configs above.? ?Takes 4 msecs to get the COM contact to physically move from the NC contact over to the NO contact....(for? #2...applying a few volts to the alc jack of xcvr).??
However, when simply opening of the normally grnded? TX inhibit lead, the COM only has to move .0001" away from the NC contact, in order to open off the TX inhibit lead..... =? < 1 msec.?

Nice drawing, thank you.

You could try something like W1AEX to accomplish some sequencing pattern.

Thank you Alan.

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

?

?

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73,

~Alan

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

On Thu, Aug 1, 2024 at 07:25 PM, Alan - W5ARM wrote:

Howdy Bob,

?

Your second picture provided a better view... I think I figured it out.

?

The "big" 2-pole relay appears to have a micro-switch - or some sort of auxiliary contact -? attached to it (see your pic that I annotated).

?

The micro-switch (or aux contact) (I believe) is actuated by the big relay arm. The "big" relay contacts provide the RF switching (input & output), and the micro-switch/aux contacts provide the bias control via the purple and [barely visible] green wires, which bypass the bias resistor (R-27 on the schematic) located elsewhere.

?

In any case, it appears everything is right there on top, and it should be easy to modify it with a pair of vacuum relays, and a third high-speed relay for bias control.? You'll have to fabricate a little bracket to mount the relays on, and then replace the OEM "big" relay with your new bracket & relays, in the same location.

?

Also, just as an FYI, those Greenstone vacuum relays (from Henry Radio) are pretty compact (see pic below). A pair of them won't take up a whole-lot of room, and should easily fit in the old OEM relay location. I have a pair of them on-hand for a Heathkit HL-2100 project that is on the bench.

?

ON EDIT: FOR SOME REASON, MY TWO SMALL PICS ARE NOT COMING THROUGH... Oh well.

?

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73,

~Alan

?

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73,

~Alan

Hi.

Test Reply with pic pasted in...

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73,

~Alan

Test

Dino - KX6D

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.

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

Guys, I ordered that board from Tom.

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.