[R-390] R-390 PTO Warmup Time

[SCOTT Barry]

Since I'm doing this with the PTO removed from the radio and the ovens 
off, I presume this is a product of just the 5749 warming up. Is that 
correct?  If so, could a solid-state replacement for that tube work 
here?  I know it's a remote cut-off, etc., but in an oscillator circuit, 
would that matter that much?

I'd be hesitant to leave the radio on unattended so having an extended 
warmup like that is pretty much out of the question for me.

Just thinking out loud...

Thanks,
Barry - N4BUQ
> Hi
>
> Best to simply let the radio warm up for a while. The ovens will heat things in a way that is not “same / same” as normal warmup. Unless things are really cold, you probably will not save a lot of time.
>
> How long does it take for a radio to stabilize? That depends a lot on how picky you are and the exact radio you happen to have. Picky folks just might turn it on a few hours before they need to use it. Very picky folks might turn it on the day before :) :)
>
> If the radio has been in storage, humidity will have had an impact. It will drift longer than a radio that is used on a regular basis. Store it in a damp barn for years and who knows how long you should run it to get it dried out. On some stuff the answer is measured in weeks. I have gear here that the answer is measured in months.
>
> Bob
>
>> On Jul 30, 2026, at 12:30 PM, SCOTT Barry via R-390 <r-390 at mailman.qth.net> wrote:
>>
>> While I know the manual states that the receiver should be allowed to warm up (30 minutes?), I wonder how long it should take for the PTO to stabilize.  I have the PTO out and monitoring the frequency from cold and it takes quite a while to stabilize - maybe 15 or 20 minutes.
>>
>> It climbs until it reaches a certain frequency and then starts very slowly up and down a few hundred Hz before settling down to a reasonably stable frequency.  Before I took it out, I was seeing end-to-end about 1,000,001.5 kc so I thought it may need a touch-up on that; however, I don't think I had let it warm up sufficiently because if I let it warm up a good while, it is much closer to 1,000,000kc end-to-end (approximately 1,000,000.300kc), hence my wondering about warmup time.
>>
>> Any thoughts on this?  Would running the oven for about 10 minutes and then turning it off help stabilize it faster?
>>
>> Thanks,
>> Barry - N4BUQ
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