More Keyall HV comments
The Keyall HV was mentioned yesterday:
https://wb9kzy.blogspot.com/2024/10/kit-re-assurance.html
Here are a few more comments on the Keyall HV kit and keying. I received email today asking about the Keyall - unfortunately it was from a DX ham so I wasn't able to try to sell him a Keyall HV. But I did try to mention commercial alternatives to the Keyall designs. Also I presented a little information about Solid State Relays (SSR).
In general for ham radio applications a relay is used to switch DC voltages/currents. A mechanical relay will handle either DC or AC - I've never seen a mechanical relay with polarity indicated on the output contacts. However SSRs often DO have restrictions on what can be switched. AC voltage/current is usually switched using a Triac, a 4 layer device. But a Triac isn't useful for switching DC because once a 4 layer device goes on it stays on until the current goes to zero. There may be ways to get around this (commutation) but in general a Triac based relay relies on the AC current transitioning through zero to turn off (assuming the control voltage was turned off).
A MOSFET based SSR like the Keyall HV can switch either AC or DC. Since the Keyall HV has two MOSFETs in series it can switch either AC or DC of either polarity, just like a mechanical relay.
In this case the DX ham had a Heathkit SB-200 amplifier which he wanted to use with an Icom 7300. I looked at the offerings that he might be able to purchase commercially. First on the high end:
https://www.digikey.com/en/products/detail/sensata-crydom/D5D07/751983
A Crydom D5D07 SSR, rated at 500 volts DC, 7 amps - over $100 but a quality brand from an authorized seller. Note that it does have a polarized output so a single MOSFET design. This high pricing and need to consider polarity was the reason for developing the Keyall kit in the first place: the Keyall HV has a lower price, it is a repairable, simple circuit with no output polarity - The Keyall HV is a relay !
For a less expensive alternative here is an Ebay item:
https://www.ebay.com/itm/196195482431
This Berm MGR-10DD SSR, rated at 200 volts DC, 10 amps - but priced at roughly one tenth of the Crydom relay. Since the SB-200 has a higher keying voltage and higher current than the Yaesu FL-2100B amp mentioned yesterday, this cheaper relay might be right on the edge as far as specs go.
But hopefully I was able to give the DX ham some choices - there are a myriad of other models but I think the hockey puck package style with screw terminals would be easy for a ham to try. Alas my Keyall HV would have been in the middle in price but potentially better in performance.
BTW here is an SSR I purchased from Ebay a few years ago with similar specs to the Berm mentioned above:
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| comes with a nice plastic insulating cover |
I did try it but never put it to use on a tube rig or amp, at the time it was less than $10 delivered.
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
