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Post by tubefan on Jul 30, 2019 22:04:13 GMT -5
I purchased a couple of crystals above 23 for the mk3 ssb transmitter. I have been using the ch38 crystal in a mk3 transmitter and all I did was pull the ch9 and swap it with the ch38. A touch of the plate control on the rear of the tx and power is where it should be.
I got another setup recently that was serviced by Barkett. I pulled the 38 crystal from the mk3 I was using it in and put it into this new transmitter. Power drops from 5 watts down to about 1 watt. I adjust the plate and can only get it to come up a touch.
So all the other channels put out full power but when I go to ch9 on the selector which is now the 38 crystal power just drops off. But the crystal works perfect in my other mk3 so I know its a good crystal. Anything I can adjust in the tx to get it to put out like it should?
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Post by 2600 on Jul 31, 2019 22:12:04 GMT -5
Yep.
Dern shame it's not just one thing. Somebody (else) needs to put up a YT vid showing a step-by-step alignment for that transmitter.
Oddly enough, the original Mark 3 SSB transmitter has one less tuneable coil than the later one, the transmitter that has a control to set the SSB ALC (limiter).
The late (ALC) transmitter has one more tuned circuit in line with the signal path, and can make that transmitter less wide-banded than the older version.
There are two single-slug adjustments that are not affected by the channel frequency. They peak the at the very same spot no matter the channel selected. T2 and T6 each has a fairly-sharp peak when the slug is adjusted. If any of these is adjusted off its peak, that can hurt the drive level above 23 or below channel 1.
You need a proper non-metal hex adjusting tool. A metal "Allen" wrench will disrupt the adjustment, and might crack the coil slug. They're really brittle.
T3, T4 and T5 are each a double-tuned transformer, with an upper and a lower tuning slug. If you peak them all on channel 12 or 13, this is correct to cover 23 channels, but may cause it to drop off above 23 and below channel 1.
The technique for those is a little different. The top slug gets peaked near the low end of the coverage range, like channel 5. The bottom slug gets peaked at the high end, like channel 30. The two slugs in one transformer will interact, so if one of them turns very far to reach a peak, the other slug should get rechecked at the other end of the range. Eventually you find the upper slug already at the peak position on channel 5, and the lower slug already peaked at channel 30.
Naturally, this is a bit tedious, but does the job so long as nothing in the transmitter is performing below par.
There are three separate frequency sources being mixed together in this transmitter. If any one of them is weak, that tends to make it seem narrowbanded, no matter how the rest of the transmitter is performing.
And if this radio is the late version that has the ALC adjust sticking up out of the chassis next to the final tube, you'll find that the single-slug coil located just inboard and to the front from the marking "V6" on the chassis. This one will also affect broadbanding if it's peaked at the low or high end of the coverage.
A weak tube in any of the three frequencies that get mixed together can do this even if every adjustment is where it should be.
Troubleshooting a radio that's just "dead" is more straightforward than troubleshooting one that's just "weak".
One thing to consider is that peaking these adjustments on carrier alone may not do the job. Modulating the transmitter, peaking the internal adjustments for max peak power tends to make the peak setting more distinct.
73
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Post by tubefan on Aug 1, 2019 15:51:17 GMT -5
 Here is the transmitter. I assume it is the early one? |
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Post by 2600 on Aug 1, 2019 22:42:14 GMT -5
It's the 'later' version, with the ALC trimmer pot at the lower (in the pic) edge of the chassis, near the driver tube. The single slug-tuned coil I was talking about is just alongside the printed "V6" legend on the chassis deck.
73
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