[R-390] R-390 PTO Warmup Time

[Barry]

That makes sense.  It probably takes longer to stabilize out of the radio than in.  The tube by itself isn't exactly poised to be the best heat source for the inside components.

Thanks!
Barry - N4BUQ

> Hi
> 
> The tube has relatively little impact on the warmup process (other than
> supplying heat, just like the rest of the radio ….). The big deal is typically
> the coil. That comes both from the coil core and from the coil form / windings.
> 
> I’ve run R-390’s for weeks / months at a time. It was the only way to keep them
> stable enough to make me happy :)
> 
> Bob
> 
>> On Jul 30, 2026, at 12:59 PM, SCOTT Barry <n4buq at knology.net> wrote:
>> 
>> 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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