[R-390] RE: Ovens

[Bob Camp]

Hi

Well if we are going to get into the "pick one up while they are still 
available" thread .....

Back when I was in school surplus stuff was a lot more common than it 
is today. This was just after the invention of dirt. R-390's sold for 
$150 to maybe $200. Any way ...

I wandered into a surplus house in Indianapolis Indiana of all places 
and here in front of me is a General Radio frequency standard. The 
thing was based on a double oven enclosure around a bar (not a piece a 
bar) of quartz. The chunk probably weighed half a pound. The whole 
thing fit nicely into a relay rack and had more than a couple of tubes. 
I suspect it was an orphan from the Crane Navy Depot.

Talk about the perfect item to calibrate your R-390 with. Great big X 
cut bar standard. Here's the standard that was the standard for most of 
the 1940's and early 1950's. I wish I had picked the darn thing up. As 
it was I bought a model 15 teletype and checked it as luggage on the 
filght back home. It came out ok ...

	Take Care!

		Bob Camp
		KB8TQ


On Aug 9, 2004, at 9:54 PM, Michael Murphy wrote:

> I think the calibrator in the ART-13 uses an old FT-243 pin spaced 200 
> kHz
> crystal. No oven there! Plus they definitely are aged. My guess is 
> that Fair
> Radio should have some. That ought to get you within a couple of kc 
> after
> zero beating WWV!
>
> Bob was starting to talk about SL-cut crystals which are normally 
> required
> to hit frequencies much below 1 MHz and are somewhat less stable than
> AT-cuts, hence the requirement for ovens etc..
>
> Mike Murphy WB2UID
>
>
> ----- Original Message -----
> From: "Bob Camp" <ham at cq.nu>
> To: "Laird Tom N" <LairdThomasN at JohnDeere.com>; "R-390 HF Receiver 
> List"
> <r-390 at mailman.qth.net>
> Cc: <Llgpt at aol.com>
> Sent: Monday, August 09, 2004 8:54 PM
> Subject: Re: [R-390] RE: Ovens
>
>
>> Hi
>>
>> The calibrator crystal would be a bit tough to do as a "stable at room
>> temperature part". The 200 KHz  frequency is low enough that you can
>> not do it as an AT cut in that holder. The HR202 oven is actually a
>> pretty good little unit. It will hold a couple degrees during fairly
>> major external changes. Since it's a plug in it's easy to replace if 
>> it
>> runs away. It's not all that different than the units you wold see in
>> the older two way radio sets.
>>
>> One interesting thing you could do would be to replace the first LO
>> crystal with a room temperature unit and then replace the calibrator
>> crystal with a cell phone TCXO and a digital divider. You would have a
>> more accurate calibrator. What ever you did would fall into the
>> category of easily reversible modification if it was all in a
>> replacement oven plugin. Next step up would be to phase lock the first
>> LO to the TCXO.....
>>
>> As you pointed out "why spend the extra money".
>>
>> Take Care!
>>
>> Bob Camp
>> KB8TQ
>>
>>
>>
>> On Aug 9, 2004, at 11:26 AM, Laird Tom N wrote:
>>
>>>> From all that I have read over the years, I agree; don't use the 
>>>> oven.
>>> For the semi-purest. You can buy crystals for HR202 from 
>>> mhelectronics
>>> that are designed for room temp. Although, the consensus is "why 
>>> spend
>>> the extra money".....
>>>
>>> Tom Laird WC9M
>>> Moline, IL.
>>>
>>> -----Original Message-----
>>>
>>> My 3 cents
>>> Don't use the ovens period!
>>>
>>> Les  Locklear
>>>
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