Just running through the TX right now, looking for problems and sorting them out. A big 'thank you' to the folk on the KW_Radios Yahoo group for helping me out with circuit diagrams and advice as I work through this lot!
|29-Jul-2004: KW with the cover off - no big investigation
at this stage, just testing the valves. 14 out of the 21 valves are
below serviceable emission levels and an order has been placed with Triode Electronics
in Chicago to replace them.
The preselector and AF gain knobs have been swapped round at some stage, and there is a cracked mica capacitor in the PA stage - not much to write home about... The RX works OK even with the ageing valves, TX won't be attempted until the new valves arrive and the capacitor has been replaced.
|06-Aug-2004: The new valves have now arrived - 14 out of the 21 valves in the set have been replaced. One of the 6BA6 valves had a 6AM6 in that place (crystal oscillator for band switching). The 6AM6 has a different pinout, so putting the new 'correct' 6BA6 in there stopped the set working altogether... It's possible that the underside wiring may have been modified for the 6AM6 in the distant past, I'll come back to this one later.|
|Something is wrong with the IF filtering - it appears to allowing both sidebands through, flipping the tuning dial around while holding the 'cal' button down gets you an equally strong signal either side of the IF beat frequency. The carrier crystals appear to be generating sensible frequencies; LSB=453.52kHz, USB=456.57kHz.|
|17-Aug-2004: The Kokusai mechanical filter has been removed and tested. The response is poor with no defined 'peak', and the losses vary from around 50dB to 60dB. Time to take the hacksaw to it...|
|The foam inside has completely deteriorated. Not visible in the picture, with no foam to retain the mechanical element, one of the wires has become detached from each end. It's a real surprise the filter let anything through at all.|
|All but one of the remaining wires have been de-soldered from the piezo transducers so the element can be removed. Some partial cleanup has been carried out on the inside of the can and the resonator elements although I'll give it a proper clean at the weekend with solvents etc.|
|10-Jan-2005: The attempt to fix up the old filter met with failure - here is the solution, a replacement Collins 455KHz mechanical filter which is compact enough to fit in the existing can. This is available from Inrad, and is reasonably priced although the impedance is a little low for the KW2000. Pictured behind the filter is the first of the toroidal transformers to match the 2K ohm impedance of the filter to the c. 8K impedance of the KW.|
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