At 04:52 PM 12/27/03 -0500, David A. Pruett wrote:
However, if you put vacuum relays in, I'll bet the 4PDT will become the
next level of annoyance.
Most vacuum relays used by hams are 26 VDC. All of these relays have 12
VDC coils, so the relay supply in the MLA-2500 is 12 VDC. My friend N8CC
ran an HC1 vacuum relay in his MLA-2500 by changing the relay supply
rectifier circuit to a voltage doubler.
Vacuum relays are to be preferred from the speed and voltage handling
standpoint, but many amps get by with open frame T/R relays. The SB-220,
for example, while not totally quiet is a lot less annoying than the
MLA-2500. It uses essentially the same relay, but mounts it to the amp
chassis through a rubber grommet. This might be a viable approach to get
quieter without requiring extensive re-design.
I can testify that, even when isolated with a strip of silicon rubber
around its circumference, the HC-1 vacuum relay in my modified SB-220 is
noisier than the original open-frame relay. Before you do radical surgery,
try Dave's suggestion, and maybe substitute some short flexible braid for
any rigid wire connections to the relay, all in an effort to isolate
contact vibration from the chassis, which acts as a sounding board.
73, Pete N4ZR
Happy Holidays
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