Hello Joe:
I replaced the open frame t/r relay in a 2500E, with Gigavac Relays, GH-1,
the equivalent to Kilovac HC-1. I found the Chinese relays to work well,
and to be equal in performance to the HC-1.
There are issues with the keying circuits for the existing t/r relay, in
terms of speed and timing with regards to the separate relay keying for the
bias voltage. These issues exist in the earlier models, produced during the
mid 90s. I installed separate keying for the vacuum relays, rather than
having them keyed by the existing bias relay switching. I also use a
separate 12 volt supply to power the new relays, due to current limitations
with the existing on board 12 VDC supply.
The amp no longer hot switches while running VOX, and is a very quiet
switcher now. I mounted the two relays on the removable back panel of the
amplifier, and there were a few issues regarding the strain relief of the
stiff coaxial cables used by the factory. You have to be careful not to
place any strain upon the vacuum relay terminals, either during
installation, or in subsequent removals of the back panel.
This is not a modification for the novice builder, and takes a little
patience to get exactly right. One day, I will go back and change out the
rest of the control board to improve the protection circuits in this older
amp. In the meantime, the amp switches quietly, with no more hotswitching
and occasional arcing on VOX.
I would be careful about changing the blower, those triodes are expensive.
Perhaps adding two speed capability would be better, with thermostatic
switching for high speed blower activation. That would be fairly
interesting to design and install if the blower noise is too great for your
installation. In the past, I have used noise gating to avoid transmitting
the blower noise. Today, I use a compressor/limiter and a downward expander
with my Mark V to keep the transmissions blower noise free .
Regards,
Mike Schatzberg
WB2AJI
----- Original Message -----
From: <n4jbk@bellsouth.net>
To: <amps@contesting.com>
Sent: Wednesday, September 28, 2005 9:55 PM
Subject: [Amps] commander hf2500hp
> 2 questions regarding the commander hf2500hp, 1- has anyone changed out
the t/r relay to a jennings or kilovac vacum relay, if so what model relay
was used and how difficult and 2- are there any blowers that are easily to
replace the stock one with that moves comparable air and is less noisy?
thank you, Joe Barnes N4JBK
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