Henry Radio 5K Classic Amplifier
|Before modification photo of the original TR relays which are located on the underside of the RF deck (cover removed) The Jennings RJ2B 'RF Output' relay is the bright white object at the far left. The 'RF Input' and 'Bias' switching relay is the white object slightly above and to the right of the Jennings. Both relays were hard mounted (not sound isolated) to angle brackets.|
|Close-up of the Jennings RJ2B vacuum relay. CLICK HERE for a spec sheet on this relay.|
|Close-up of the DPDT Guardian relay originally used for 'RF Input' and 'Bias' switching. It's a 12-volt relay that was being sped up by applying 30 vdc through a current limiting resistor.|
Kilovac HC-1 relays as
installed by WD7S.
This modification required four (4) of the HC-1s. I purchased them from MaxGain Systems. CLICK HERE to go directly to the vacuum relay page. The relays Allen sells are pulls from new equipment and have been hi-pot tested.
|Close-up of the two HC-1s in parallel -- 'RF Output'. WD7S used the existing relay control wiring and coax. He fabricated the mounting brackets and mounted the relays in grommets to sound isolate them from the chassis.|
|Close-up of the rear of the paralleled 'RF Output' relays. Mounting the relays in large rubber grommets does a great job of acoustically isolating them from the chassis. The four new relays are much quieter than the two originals.|
|Close-up of the new HC-1 'RF Input' and 'Bias' switching relays. Although I could have opted for a solid state switch for the 'Bias', I instead went with a HC-1 to simplify the installation. In then end, spending and additional $32 for another HC-1 for the 'Bias' relay was a much more cost effective bulletproof approach over the solid state alternative.|
|WD7S tested the relays for contact closure and opening times using 26.5 vdc coil voltage. According to his tests, there's no reason to go to all of the trouble of building a "Speed-up" system when the HC-1s are used. The times Paul measured were all less than 2.5ms. CLICK HERE to read more about the measurements he made.|
|Close-up of the new low current MOSFET relay keying circuit components (center left) located right behind the 'RF Input' and 'Bias' relays. This mod makes it possible to control the amps relays with any modern transceiver. Now the radio is only required to sink 5 vdc at a few milliamps rather than 30 vdc at 400 milliamps!|
|Here's the schematic for the QSK relay modification and low current keying system. Drawn by WD7S.|