Re: Drake TR-7 - Noisy transmitter
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Hi, Mark.
It has been along time since I looked at the innards of the TR7 so I cannot speak from recent experience.
In particular, look at the coupling capacitors in the TX audio chain. If there are any ceramic or mica capacitors, you might consider changing them to modern polyester types. Ceramic caps can become microphonic and possibly generate noises; mica can generate the crackling noise you hear. Not that it might effect audio, mica have been known to cause intermodulation in RF circuits.
Changing the ceramic caps in the RX 2nd IF and audio board to the polyester caps is also a good idea due to possible microphonics and noise.
73 ES GL,
Bob Loving K9JU Maryville, TN USA
On Saturday, March 30, 2024 at 06:38:40 AM EDT, atlasstuff <g4fph@...> wrote:
Jim,
Just put my later s/n (100xx) TR-7 on the bench, in place of the fixer-upper one, by way of a comparison. About time it saw some power!
Carrier suppression on the later one is -60 dB and no trace of any 1 kHz modulation spurs in the TX noise floor down as far as I can see.
With a normal amount of mic. gain, and replacing the mic. with a 600 R termination, the TX noise floor sits at around -85 dB, looks pretty flat across the SSB bandwidth, and does not sound 'crackly'. Winding the mic. gain flat out, the TX noise comes up to -70dB and again sounds 'smooth'.
So, I think I have answered the question I posed at the start of this thread: My early s/n radio could do a lot better!
Happy Easter to all!
Regards,
Mark, G4FPH.
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