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| WARNING ! If you are going to work on one of these it's assumed that you are experienced in working on valve / tube equipment and are aware of the dangers involved and the safe working practices required for high voltages (these amplifiers have around 2300 Volts HT) and high RF power levels. If you are not then I suggest that you ask someone suitably experienced to advise and assist you |
I bought this old Heathkit Linear Amplifier from an online auction, intending to give it an overhaul before using it on the station here. All valve (tube) equipment of this age would need some attention to return it to full working operation. I've restored a number of valve audio amplifiers over the years. I didn't however realise what a poor condition this HF linear amplifier arrive in !
This was going to be a long project !
As the photo above shows, from the facia it didn't look too bad.
The horrid surprises were discovered when opening the case up and finding...
...a bent and damaged screening cover and no 572-B TX Output valves (tubes) !! There should have been two of these Hi-Mu triodes here. I'd also have to make a new anode 'top cap' as one was missing.
Going over to the power supply section...
...revealed some corroded and mouldy main reservoir capacitors and wiring. These would all have to be replaced together with the rectifiers. An excellent article I found on "The Mules Ham Radio Page" explains how to do this.
Further inspection revealed problems like this bad joint (above) from the SWR bridge to the RX/TX relay that caused the wire insulation to melt. Another burn-up due to a bad joint was found where the bifilar heater (filament) choke joins onto the output valve (tube) holder heater connection. This joint had turned to powder and the connection was almost open-circuit. These tubes have a high heater current so the repair needed to be good. I repaired it by cleaning the wires and tags with a fibre-glass pen, then wrapping a couple of wire loops around the joint to make it mechanically tight before re-soldering it. A similar problem was found where the stiff wire 'bus bar' output connection from the 'loading' variable capacitor (C28a/b) joins L7 at the band switch (wafer B tag 1). Tapping this wire caused it to immediately spring away for the joint ! It was repaired in a similar way.
Once these 'minor' problems were out of the way, the real repair work could start. See this on the Next Page
