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On Tue, Jan 14, 2025 at 07:05 AM, Jim VE7RF wrote:

I used an opto-22? ?opto isolator.? You can get em in 5 vdc.....15 vdc...and 24 vdc? on the input side....... (and each of those 3 x different input vdc's is nominal...... IE:? u can go a LOT higher / lower).? ? And they only draw 10 ma on the input side.? ?Output side on any of them is either 60 vdc @ 3 amps? CCS...... or 250 vdc @ 1 amp CCS.? ? Switching time is 100 Usecs for operate, to turn em on.... and 750 Usecs to turn em off, for rls.? ?5 kv isolation between the input and output side.? Input and output sides are isolated via the laser between em...hence the term, opto isolator.??

That's as dead simple as it gets.? ?And NO mech, slow relays involved anywhere. We use em to key the coils of sped up vac relays.? The last thing we want is a 5-15 msec slow relay that in turn keys the coil of a sped up vac relay...which would defeat the initial purpose of the sped up vac relays.? ? Same opto isolator can also be used for cut off biasing on a triode amp. Our friends in VK land have that concept down to a fine artform.? ?The secondary of the opto just shunts the bias cut off resistor.? Again, dead simple.

The Opto-22 has been my go-to method for key-line buffering as well. You can find 'em on eBay (usually brand new) for around $10-$12, although sometimes more. Or, buy them brand-new from Mouser, Newark, etc.

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I've installed them on my three Henry amps (3K-Classic, 3-KA, 2-KD Classic), as well as in a "rebuild" I did on a 2KD-5 for another ham. Worked great.? Drops the key-line current from >200ma, down to about 13mA.? And as Jim said, they are VERY fast... no relay delay, nearly instantaneous (100 micro-seconds on-time is FAST!).

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The Opto-22's are tough-as-nails, and in a fairly small package.

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If all you need is key-line isolation, they're a very easy way to go.

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I documented the install of one on my Henry 3-KA (in 2021), HERE: /g/Henry-Radio-Legacy-Amps/topic/updated_mod_s_to_3k_a/87885687

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73,

~Alan