ZL1RS - Amplifiers
A Compact 6m 8877 Amplifier
A "carry-on" sized 6M 8877 1KW Amplifier.
A home made all aluminium chassis contains the amplifier RF deck, HT power supply, blower and RF changeover relays.
It is completely self contained and measures just 320 x 300 x 160 mm.
The placement of the anode coil and loading capacitor are not 100% ideal but this came about because the amplifier
was originally intended for 2m and the Load control veriner drive was already mounted when I changed to 6m. While it
does not look so "nice" it works OK. The HT supply is an ANTEK toroid 650+650 secondary in a voltage doubler circuit.
The amplifier provides an easy 1KW output in SSB/CW and 1kW continuous carrier in JT65b/FT8 without any sign of excessive heat. It's first outing was to E51EME (pic above) followed a few months later by a dxpedtion to
VK9N/ZL1RS where it worked well. Since returning home I sold the Acom1000 I was using on 6m and now use this amplifier at the home station.
Update: January 2013.
The amplifier's relays have been changed to a vacuum relay at the output (VHC-1 with a 12V coil) and small 'general purpose' relays at the amplifier input and for the bias/cutoff relay. Suitable relays are JQX-115F or Schrack RT314012. These relays have a switching time of 6 or 7mS ... this is the specified time, so likely they will actually switch even faster (measurements by others indicate 2-3mS is typical).
To ensure the relays do change over faster than the switching time of my radio, a 'relay speed-up' circuit by K6XX is used to reduce their switching time. Now the amplifier switching is fast enough to allow full break-in CW. In addition, the IC-7600 settings include a 20mS TX delay to prevent 'hot switching' the change-over relays.
Update: November 2020.
The VHC-1 vacuum relay at the output developed an intermittent 'RX' contact, so it was replaced with another of the 16A 'general purpose' relays mentioned above. These relays are used successfully in various RF applications at higher power levels than this amplifier will produce ... as shown
Update: December 2020.
After thousands of 6m QSOs, this amplifier finally 'blew up' with a mighty bang in the middle of a JA pile up on FT8. From the symptoms, I suspect that the HT transformer has an internal short.
Update: 17 July 2021.
Repaired ... replaced the blower (earth leakage fault) and the internal PSU transformer (filament to HT winding leakage). Now there is a separate filament transformer and an external HT power supply, so the amplifier is no longer "carry-on" sized! ... but it will run comfortably for extended periods in digi-modes at 1kW RF output.
Update: 05 Dec 2021.
Tubes have 'had their day' here. The 8877 PA has been 'retired' and replaced by a solid state LDMOS 6m kW amplifier.