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

Dave and Sharon Maples dsmaples at comcast.net
Sun Dec 26 19:10:39 EST 2021 

Jim: The Harris land-mobile radio gear generally uses TNC connectors now.  Their MIL gear uses either N or BNC.  I don't think anyone is still using UHF connectors besides the amateur and CB communities, but I could be wrong.

Thanks,
Dave WB4FUR

-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On Behalf Of Jim Whartenby via R-390
Sent: Sunday, December 26, 2021 15:26
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Amelco R390A help, RT301 current regulator tube

SamIf I put on my engineer's hat and look for which method produces the least amount of waste heat, then #4 is the way to go.  Eliminating the current regulator reduces the current draw from 300 mA to 150 mA at 25 or so volts from the power transformer so there is also less stress on the power transformer.  Power goes down from 7.5 watts to 3.75 watts for that particular heater string.
In my 4 1/2 years in the Air Force back in the early 1970's, the only equipment I ever saw that used the UHF type RF connector was the WW2 designed AN/ARC-3.  It was used as the VHF comm gear in the MPN-13 RAPCON van when I was stationed in the Philippines.  Mactan AB was also used by both the Philippine Air Force and commercial aviation so VHF was needed.  There are adaptors available to convert from UHF to N or BNC so no surgery is needed. I am not sure but I think that  American Hams are the only group still using the UHF style of connector?  New equipment sold everywhere else has either N or BNC connectors.  True?
Regards,Jim
Too much agreement kills a chat.  E. Cleaver

-----Original Message-----
From: Studiumtelecom S.Rocha <battcharger at gmail.com>
To: Jim Whartenby <old_radio at aol.com>
Cc: R-390 List <r-390 at mailman.qth.net>
Sent: Sun, Dec 26, 2021 12:50 pm
Subject: Re: Amelco R390A help, RT301 current regulator tube

Thanks to all ! I used method number 4, with a solid jumper and a pair of 12BA6, I found a regulator tube for usd$28.00 here in Rio, so I think it worths buying it also in the future. The interesting point is that I have all spares tubes for this radio, except the only which was defective!
Another question: should I replace the antenna connector for a SO-239 UHF type?Regards and a Happy New Year to all!Sam Rocha Em dom, 26 de dez de 2021 00:26, Jim Whartenby via R-390 <r-390 at mailman.qth.net> escreveu:

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
>> ______________________________________________________________
>> R-390 mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:R-390 at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net Please help support this 
>> email list: http://www.qsl.net/donate.html
>>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net Please help support this email 
> list: http://www.qsl.net/donate.html

______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

More information about the R-390 mailing list