Here is a method for providing a quick and easy crowbar.Place a Diodes
Incorporated 1.5KE15A (NTE4920) across the power output AFTER the fuses
ans before the rig. Band goes to +. It will clamp 1.5kW, about 100
amps@15 volts and blow the fuse.
I found this in "73 Amateur Radio Today", May 2002, page 38. Title "An
I have installed this on my rigs, but it has never been needed to
prevent a problem.
Mike Hyder -N4NT- wrote:
> When that has happened to me, it has been due to bad diodes in the ALC
> circuitry. Those diodes are to generate the ALC voltage without which the
> power amplifier can oscillate and almost instantly draw excessive current.
> Be really careful with that 252 power supply. As originally made, they have
> no crowbar circuitry. Thus if the pass transistor shorts, the supply will
> put 25 volts into the rig -- somewhat shortening the rig's life. Ten-Tec,
> realizing the oversight, later sold an "Over Voltage Protection" circuit
> board, an OVP they called. It was a small board, perhaps one by two inches
> and had an SCR, a zener diode and a fuse. It mounted inside the rear panel
> of the supply. I suggest you check there and see if it is present. When
> installed, the large red wire to the supply's output comes from that small
> circuit board. The OVP is no longer available from Ten-Tec but someone can
> surely send you the schematic.
> Good luck with your Omni-D
> 73, Mike N4NT
> ----- Original Message -----
> From: "Ken Johnsson" <firstname.lastname@example.org>
> To: <email@example.com>
> Sent: Monday, February 20, 2006 9:00 PM
> Subject: [TenTec] Help
> I am a new owner of a Omni D and when turn up the drive, it kicks the P/S
> off, all help would be appricated
> Ken N4ALP P/s the Ps is a 252 m
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