Re: {Collins} R388 Readings



If the BFO is set to 500 kHz, bands 2 and 3 (e.g 2.0 MHz and 3.0 MHz) should zero at the same mark on the dial.  In any case, you can just set the BFO frequency using the front panel control to make that happen, and then check the other bands relative to that mark.

I pulled power from the filament line for the muting relay, but used a voltage doubler.  Under load I get about 10-11 volts at the relay which works fine.  Look at the schematic for the SB-51 from Treetop Circuits.

I haven't ordered the crystals yet --- if they fit the "standard" price model that ICM has on their website, they should be around $25 each.  I'm tempted to buy a couple more, but the affected bands are only 1Khz out, and I can live with that :). My worst bands are 25 and 26 which are both 6Khz out.  They use the second harmonic of the 14MHz crystal --- and of course bands 11 and 12 are 3KHz out as would be expected also.

Grant NQ5T

Sent from my iPad

On Jul 20, 2013, at 12:17 PM, Philip <ka4koe@xxxxxxxxxxx> wrote:

> Set BFO per manual, ie plates half meshed, then zero'd with alignment tool with known calibrated WWV.
> 
> Another question.
> 
> One mod I've seen takes 6.3 volts off the filament line to energize the mute relay. Tried this and it doesn't work. Moved contacts on the relay and the mute function is working. So, I assume the relay needs more than 6.3VAC to work. The mod is dated 3-16-75.
> 
> I'll recheck the calibration of the BFO.  BTW, how much did the crystals cost you from ICM???
> 
> Philip
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