[R-390] R390A help, RT301 current regulator tube

[Jim Whartenby]

Sam
It seems that Collins thought that the ballast tube was not necessary, according to the following passage.

>From page 15 of the R-390 Engineering Report, September 15, 1953

"The ballasttube (3TF7) operates on a current of 290 to 330 mils and holds this current within ±10 mils for input voltage variations of ±15%. This reducedthe 15% variation to approximately 3%. There is some question if afilament regulator is necessary in these receivers since the oscillatorsare very good even without regulation. However, since the stability wasa big factor in this design and since the factor of tube aging was notknown, the regulator was included."

Present day line voltages are quite steady when compared to what was available back in the 1950's or earlier.  When my 3TF7 fails, and it will, I plan to use either method 3 or 4 since I tend to be a bit "thrifty!" <grin>

HNY, Jim

Too much agreement kills a chat.  E. Cleaver

-----Original Message-----
From: Renee K6FSB <k6fsb.1 at gmail.com>
To: Studiumtelecom S.Rocha <battcharger at gmail.com>; R-390 Forum <r-390 at mailman.qth.net>
Sent: Sat, Dec 25, 2021 3:59 pm
Subject: Re: [R-390] R390A help, RT301 current regulator tube

I believe you are working on an R390A, to my knowledge amelco did not 
make the R390
there are several methods
1. use 47 Ohm 5W (Sand) Resistor IIRC in the pins of RT301
2. build a current limiter using LM317 set at 300ma
3. use a 12BY7 (or similar) that still has functioning filaments...plug 
and play
4. use 12BA6 in both V505 and 707 and jumper the pins in RT301 solid 
wire jumper
5. there was someone making a SS replacemet
6. obtain a new/used ballast tube 3TF7
7. I am certain I left off a couple

personally I used #2 all that was needed was a ground wire, i built it 
in/on a 9 pin tube base

I think the Y2k manual may have this ...or is it Y3k by now?
If you follow the schematics I am certain you will see what is needed.
Merry Christmas
Renée


On 12/25/21 1:28 PM, Studiumtelecom S.Rocha wrote:
> Dear members,
>
> I am restoring an  R-390 /URR Amelco serial 1596 and the V505 and  V701
> 6BA6 do not have the filament voltage, so I would like to know how to
> replace the RT301 current regulator tube.  Any other suggestion will be
> greatly appreciated !
>
> Merry Christmas  and a much better New Year for all  !
>
> Regards,
> Sam Rocha
> Py1dkw
>
> Em sáb, 25 de dez de 2021 04:53, Larry H <larry41gm at gmail.com> escreveu:
>
>> I have updated our website's (r-390a.net) 'references' page.  I added a
>> link to the Navy's R-390As tech ref of Apr, 1970 on  Nick England's
>> website.  The link is at the bottom of the 'US Navy Manuals' section in
>> our 'references' page.
>>
>> I have also added meter face files, a TIF file for the VU meter face and a
>> Visio file containing 'white' faces for the VU and C/L meters.  All
>> these can be found on the 'references' page on our website in the
>> 'drawings' section.  They also have matching PDF files for viewing as the
>> Visio and TIF files are only downloadable (oooops, I forgot the PDF file
>> for the TIF file - I'll add it in soon).
>>
>> Happy Holidays.
>>
>> Regards, Larry
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