I just went through this with my 4 x Drake L4B's.?

I used 3 x new Gigavac GH1's.? ?You can buy em with either a 12 vdc coil or a 26.5 vdc coil.? ?Jennings version is called an RJ1A. The kilovac version is called a HC-1.....and the coils in all 3 x brands are field swappable to either a 12 / 26.5 / 115 vdc coil.? ?The Gigavac uses metric threads on the big lockdown nut.

I used em for input / output / bias.? ?In my case, I used the 12 vdc coil version.....and wired all 3 x coils in series.? The oem drake fil xfmr also has a 22 vac winding on it to run the oem 3PDT clunker TR relay.? Drake used a 1/2 wave rectifier, so the output was 31 vdc no load.? ?In my case, I changed that to a FWD ( full wave doubler) to obtain 63 vdc no load.? ?A 175 ohm @ 25 watt metal finned dropping resistor is used in series with the 3 x series coils. 36 vdc used to operate the 3 x series 12 vdc coils.? 27 vdc is dropped across the 175 ohm series drop resistor. Drop resistor dissipates 3.9 watts on TX....and 0 watts on RX.?

IE: when T=0, the relay coils get hit with an initial over voltage. (63/3 or 21 vdc per coil)....which will? speed em up.? To speed em up even more, a 50uf @ 150 vdc lytic is wired in parallel with the 175 ohm drop resistor.? This is called a ...'RC hotshot' circuit. Jennings, Kilovac, Gigavac all mention it's use.? ( Alpha used it on their older amps, that used a vac relay.? Alpha used 36 vdc applied to the 26.5 vdc coil, and also a small lytic across the series drop resistor).? With the small cap in parallel with the drop resistor, it sustains the over voltage a hair longer.? The concept works superb.? ?All 3 x vac relays in each drake amp operate in slightly under 1 msec.?

80% of the total operate time is spent just building up the magnetic field in the coil. (The XL of the coil impedes DC current flow).? The over voltage? makes the current flow faster.

The ONLY thing that needs to be sequenced is the RF output from the xcvr itself.? You want to key the amp NOW,? but delay RF from the xcvr by 1-2 msecs.? This gives the sped up vac relays in the amp a head start.?
Modern xcvr's have an adjustable TX RF output delay...which works on both CW + SSB.? ?My yaseu MK-V has an adjustable 0-30 msec delay, ( in 1 msec increments) to prevent hot switching? the slow 3PDT mech relay in the older tube amps. The drake 3PDT operates in 17 msecs.? ?The 3PDT in the ameritron amps operates in 15 msecs.? ? The delay in the MK-V was set at 20 msecs to ensure the oem drake relay got a head start.? BUT the adjustable delay in the MK-V only works on CW.? ?For SSB use, plan B.... which is to re-use the spst tiny relay in the MK-V? (was used to key an amp)? to instead GRND the TX inhibit lead in the MK-V.? ?UNTIL u grnd the TX inhibit lead, you can key the amp, but zero RF coming out of the xcvr.? ?To actually key the relays in the amp, I use an opto isolator. The input of the opto is keyed? via the 'electronic TX grnd'? from the MK-V.? Input of opto only draws a few ma.? ?You can get em with a 5-15-24 vdc input ( and each of those has a super wide operating range)..and the output side is rated for either? 60 vdc @ 3 amps CCS...or 250 vdc @ 1 amp CCS.? 5 kv? isolation between input side and output side.?

You can also use a 2nd opto to do the bias in the amp, which works good.?

Ok, back to the henry 2K-3.? ?The small relay? xfmr in the 2K-3 is 8.5 vac on either side of the CT.? ?It's a FWCT config.? Output is 8.5 vac x 1.414 = 12 vdc.? ?I would reconfigure the small relay xfmr to a FWB..and use the entire sec winding ( CT not used).? ?Then it becomes 17 vac x 1.414 = 24 vdc no load.? ?Ok, then? wire the 3 x 12 vdc vac relay coils in parallel.? ?Each 12 vdc coil is 80 ohms.? ?12 vdc / 26.67 ohms, ( 80/3 = 26.67 ohms)? ?= .450 amps.
The series drop resistor will be 26.67 ohms.? Diss in the resistor will be (.45 x .45) x 26.67 ohms = 5.4 watts.? ?Each relay coil will diss? 1.8 watts.? Each coil has 150 ma flowing through it.? Wire a 50 uf @? 100-150 vdc (axial lead) lytic across the drop resistor.?

Depending on xcvr used, it has to handle? 24 vdc OCV (open circuit voltage)? @ 450 ma under load.? You do NOT want to use a slow mech relay in the xcvr to key the sped up vac relays!? ?Hence the use of either an opto isolator or a fast switch transistor.?

Ok, the 3 x relays will operate / rls in just a hair < 1 msec.? No hot switching.

I found a sidewall on the L4B, that would take all 3 x vac relays.? ? A 9/16" hole is required.? ( A 5/8" will also work).? ?The greenlee 1/2" -? 9/16"? - 5/8"? punches all use a 1/4" draw stud....and hence require a 1/4" pilot hole.? I used my roper whitney hand punch to punch the 3 x 1/4"? pilot holes....bam, done.? Then the greenlee 9/16" punch (die and cup, just tighten the wrench).?

You could use just 2 x vac relays...for input / output.....and an opto for the cut off bias.? That would save one vac relay.? ?You could maybe, use a super fast SPDT tiny mech relay for the input side.? I wanted vac relay on both the input and output, so the amp will handle 2 kw on bypass mode.? ?I do that, since I string several drake amps in series, one per band, or one at each end of 80m etc, or any other combo.? A simple rotary switch in the key line of the xcvr ensures only one amp can ever be keyed at one time.? ? ?On the drake L4B, the only way to calibrate the internal wattmeter is to take it apart to get to the underside of chassis....and apply 1 kw cxr from a 2nd amplifier ( with a bird 43)? to the drake amp...which of course is powered down, and on bypass.? IE: it has to handle a kw on bypass mode anyway.?

You could mount one vac relay near the input coax connector, and a 2nd vac relay near the output side....or near the load cap.? Then a short length of RG-400 between the NC contacts of the input + output relay. ( aka..the 'bypass leg' ).? ?

All 3 of my vac relays are dead quiet.? ?The gigavac GH1 hi -pot tests to 7.5 kv.?

The idea of using a 12 vdc coil came from the eng dept at Kilovac, during a phone call I had with em years ago.? "IF u are voltage limited, use the 12 vdc coil".?

There is also another method to obtain 28 vdc in ur henry amp.? It uses a 10 vac fil xfmr ( with fils in series).? ?Tap off the 10 vac sec...and use a FWD ( doubler)? to obtain 28.28 vdc.?

Without the speedup circuit, the vac relays typ operate in 2-3 msecs.? ?In the past, folks would use a semi complicated sequencing mess...so the output relay would operate 1st.....like say 3 msec.? ?Then the input relay next, say 5 msecs...then the bias relay last....say 7 msecs.? When going back to RX, the rls sequence was reversed, with bias relay releasing 1st, then input relay, the output relay last.?

Simplify it....just operate all 3 of em at once ( even if u don't speed em up....and all 3 operate in 3 msecs) .? The only thing that has to be sequenced is to delay grnding the handy dandy? TX inhibit lead in the xcvr.?

?

Sri? for the diatribe.?

Jim? VE7RF

?Without the speed up, they will operate in 2-3 msecs.? The 3PDT clunker u have in there now will be 18-20 msecs at least.?
You could even leave the oem FWCT? 12 vdc supply in there.? ? Just toss the oem? clunker....and replace it with? 3 x vac relays, each with a 12 vdc coil...and wire all 3 x coils in parallel.? ? Then no drop resistor required.? ?Each coil will draw 1.8 watts? (5.4 watts in total)? ?on TX...and zero watts on RX.?

You will have to get creative on locating them,? but it's doable.? ? I still have the 2K-3 PDF manual saved.? ?I didn't realize this was an antique.?

?

The actual pickup / drop out voltage is a helluva lot less than the rated coil voltage.? The 6 msec they quote is for the actual pick up voltage.? When run at rated voltage, the actual operate time is 2 msecs on a GH1.?

If u need any help with this, lemme know.?

On the 2K-3 schematic,? RY3 is a 3PDT..... with input / output / and cutoff bias.?

If urs only is only a DPDT....there must be another relay in there for cut off bias.? And it only needs to be a SPST-NO relay.?

On the schematic, the NC contact is not used on the cut off bias.? It just shorts out the 10K @ 25 watt resistor on TX....leaving the CR7 bias diode in the circuit.?
The COM on any relay is the contact that actually physically moves.??

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.

?

--

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)

?

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

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

?

73,

Dave, w6de

?

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:

?

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

--

73,

~Alan