I'd say that they are pre-production or engineering samples, tubes that are 
produced either for in house development or samples sent to presumptive 
buyers/customers who are interested in designing with them to release 
products as they become available in production volumes.

/Martin

On Wednesday, 27 October 2021 at 22:29:18 UTC+2 Bartek Ogryz wrote:

> Thank you Martin!
> What does it mean in practice? Are those just an old names of the same 
> tubes, nowadays named DR22xx?
> Sorry for banal question. I understand the words, but not the whole phrase.
>
> Mark, those are beautifull, I won't be able to sleep now ;)
>
> Bartek.
>
> środa, 27 października 2021 o 20:02:53 UTC+2 Pramanicin napisał(a):
>
>> Er, you're not the only one with a stash of these.... :)
>>
>> They are nice looking tubes...
>>
>> On Wed, Oct 27, 2021 at 10:50 AM Mark Moulding <[email protected]> wrote:
>>
>>> I have a pretty good sized collection of RCA DTF-104B Numitrons, which I 
>>> think are especially attractive - they're large digits, in a flat-topped 
>>> end-view tube.  They're quite rare now, and in fact I think I have most of 
>>> the remaining world stock of these things (around 150 or so).  Although 
>>> I've successfully used them in a couple of projects, I've never been able 
>>> to locate a data sheet for them - does anyone have any pointers for this 
>>> specific tube?
>>>
>>> Thanks!
>>> ~~
>>> Mark Moulding
>>>
>>> [image: WoodClock (Small).JPG]
>>>
>>> On Tuesday, October 26, 2021 at 2:21:21 PM UTC-7 Dekatron42 wrote:
>>>
>>>> I knew I'd seen the number, and found them just now: 
>>>> http://www.tube-tester.com/sites/nixie/dat_arch/Numitron_RCA_01.pdf at 
>>>> the bottom of the page, they are development numbers for the DR2200 series.
>>>>
>>>> /Martin
>>>>
>>>> On Tuesday, 26 October 2021 at 22:21:47 UTC+2 Dekatron42 wrote:
>>>>
>>>>> Tubes designated DTF are development numbers used by Apollo/RCA - it 
>>>>> says so at the bottom of their datasheets.
>>>>>
>>>>> /Martin
>>>>>
>>>>> On Tuesday, 26 October 2021 at 21:43:52 UTC+2 Bartek Ogryz wrote:
>>>>>
>>>>>> Hi!
>>>>>> They appeared on eBay last days: DTF137, DTF138, DTF140 (or maybe 
>>>>>> DTF/37, DTF/38, DTF/40). What are theese? Anyone has some more knowledge 
>>>>>> about them?
>>>>>>
>>>>>> Bartek.
>>>>>>
>>>>>> BTW: If someone is interested in numitrons, quite rare Apollo DA-2500 
>>>>>> are hiding on eBay: item no 254866404573. Unfortunatelly, as the seller 
>>>>>> told me, all that have left, are without markings...
>>>>>>
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