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Author Topic: AL-811H vacuum relay  (Read 1402 times)

Posts: 5


« on: June 16, 2003, 11:31:07 AM »

Has anyone converted an AL-811H to a vacuum relay, if so could you give me the details.

73, Jim

Posts: 21764

« Reply #1 on: June 16, 2003, 01:09:53 PM »

You could do exactly what AG6K proposes on his website

He has a vacuum relay and relay speed-up circuit published there, intended for use with the SB-220 or TL-922, but actually it's appropriate for *any* HF amplifier regardless of model.

I wouldn't go to the bother and expense with an AL811H; however, Ameritron sells their QSK-5 PIN diode T-R switch for less money than vacuum relays and the PIN switch is even faster.


« Reply #2 on: June 16, 2003, 01:52:49 PM »

Vacuum relays are easy to use as replacements internally or externally.  Just sub them where the current relays are located.  Using a relay like HC-3 Kilovac will relieve you of using some sort of timing circuits since these relays have tungsten coatings on the contacts that allow power switching without burning the contacts if the relays should get a little out of sync.  These or similiar relays are almost always on eBay.

Posts: 124

« Reply #3 on: June 17, 2003, 09:33:41 AM »

At this power level I would consider to use NAIM/Matsushita S2 or ST type relays. They are available in 5 volts, 12 volts or 24 volts versions.
Typical switching time is around 7 milli-seconds.
Should be a minimum conversion effort with your AL-811H. I've converted various amps to these relays. Works great.

73, Klaus, DK3QN

Posts: 124

« Reply #4 on: June 19, 2003, 07:32:07 AM »

update to my earlier post:

the company name is NAIS (sorry for the typo).

There web site is:
Click 'mechanical relays' or go directly to the URL

I've used the ST type relay in several amps. Their DE type also looks quite fine (from the specs) and is somewhat faster than ST (5mS). (No experience with this type so far).

You will most likely need 3 relays as ST type 1 has one make and one break contact only (allowing for one switch-over contact) and you will need 3 make/brake contacts: input, output and bias switching.

Cost per relay in DL-land is about 8 Euro.

I did not mount the relays onto a PCB. Instead I took a piece of foam and carved out 3 rectangular holes a little more than half-way down the foam so that the 3 relays fit into the holes with their connecting pins facing upwards and outside the foam. Then I glued the relays upside down securely into the foam holes.
The foam itself was securely glued to the amp's chassis.
The wiring is done with appropriate stranded wire 'cause this takes away mechanical stress from the relay solder pins (opposite to solid copper wire).

This mounting method minimises the noise during switching. Now there is only a slight clicking when the amp is switched over instead of a loud 'bump'.

The relays are available in a large variety of coil voltages. So it's quite easy to select the one that best fits the given amp switching voltage environment.
By selecting relays with lower coil voltages you could even implement a speed resistor arrangement which speeds up switching time even more (not tried).

The switching current capability of you transceiver (relay contacts or transistor driver) should be at a minimum of 12 volts at 100mA. Three ST1 type of relays in parallel will consume about 60 mA at 12 volts.

Finally, don't forget to mount a diode across the relay coils and make sure to mount the diode in the right orientation. One diode for the 3 relays is good enough as the relays are driven in parallel.

73, Klaus, DK3QN

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