[R-390] R390/URR for Sale

Tue Feb 24 18:00:11 EST 2026

Yes, but that just adds more heat to an already hot chassis.
Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Tuesday, February 24, 2026 at 04:47:57 PM CST, joldenburg2 at new.rr.com <joldenburg2 at new.rr.com> wrote:   

 There's an alternative of putting a resistor across pins 2&7. I'd to look up the value used or look at a 3TF7 spec sheet. 

Jon  AB9AH
"I have always preferred diversions to duties; this strange taste has clung to me all through my life." Clarence Darrow
-----------------------------------------
From: "Jim Whartenby via R-390" 
To: 
Cc: "R390 qth list"
Sent: Tuesday February 24 2026 1:26:47PM
Subject: Re: [R-390] R390/URR for Sale

One can easily eliminate the need for the ballast tube by going tothe 12 volt versions of the two oscillator tubes and jumper pins2&7 of the ballast tube socket.  The only need for the3TF7 was due to the very large line voltage requirement by theSignal Corps in the original contract.  The intent was toprevent excessive oscillator drift due to line voltagechanges.  Modern line voltage is held to a +/-5% variation,not the +/-15% of the original R-390/URR contract.  See page14 of the final R-390/URR engineering report.
Tube heaters are a non-linear resistance.  Changing the heatervoltage by 10% does not change the heater current by the samepercentage, it is more like a 5% change in heater current. The final R-390/URR engineering report on page 15 indicates thatthe ballast was not needed since the oscillator performance wasquite good without the ballast tube.  It is my feeling thatthe ballast tube was a Signal Corps requirement, not an engineeringrequirement.Jim
Logic: Method used to arrive at the wrong conclusion, withconfidence.  Murphy

On Tuesday, February 24, 2026 at 11:50:38 AM CST,joldenburg2 at new.rr.com <joldenburg2 at new.rr.com> wrote:

Those 3TF7 seem to always be missing. I have 2--R390 and3--R390A,
awaiting work. Two of them are missing the 3TF7. one of theR-390/URR
was restored by David Medley, probably the last one he did. Ihave
that one up soon, it buries the Smemeteer when turning it on withno
antenna or output.
Found and games.....

Jon AB9AH
"I have always preferred diversions to duties; this strange tastehas
clung to me all through my life." Clarence Darrow

    -----------------------------------------From:"Les Locklear"
To: "Perry Sandeen"
Cc: "R390 qth list"
Sent: Tuesday February 24 2026 7:39:52AM
Subject: Re: [R-390] R390/URR for Sale

Chuckling...

Yeah, you got it right. Undoubtedly someone will ask you if it's aA.

Les

----- Original Message -----
From: Perry Sandeen via R-390
Reply-To: Perry Sandeen
To: r-390 at mailman
Sent: 2/23/2026 9:16:10 PM
Subject: [R-390] R390/URR for Sale
________________________________________________________________________________

> List
> I have a Collins R390/URR (right Les?) for sale. (W/powercord)
> I took this radio in a trade 10+ years ago from a list memberand
set it on the
> shelf. The person who I traded with just happened not toremember
that the 2-
> 6082’s as well as the 3TF7 were missing. (Radio wasrepresented
as complete.)
>
> So after a 2,500 mile move and still no “roundtoit” it’stime
to sell.
> The radio front and rear panel are fair and it does have the 7and
9 pin tube
> straighteners.
>
> I’ve added the correct size 30 NOS IREC tube shields for allthe
7 and 9 pin
> tubes, as well as 1 Corcom 3EEA1 input filter, 1 CL 90 inputsurge
limiter, 1
> 130VAC MOV surge limiter, 1 NOS Nichicon 390uF/450 capacitorto
replace the
> C101 10uF filter, 1 NOS 2 pin connector for the balancedantenna, 1
NOS 6BJ6
> tube and a 4 3/4 x 4 3/4 metal boxer cooling fan.
> The radio needs a bath. I have never attempted to turn on.Other
tubes
> condition is unknown
> Because of the FedEx weight requirements, the radio need tobe
shipped in two
> boxes. The receiver in one and the power supply and theaudio
amplifier in
> another.
> Asking $500 plus shipping from Clinton, SC 29325
> Please reply with and ORIGINAL email if interested.
> 73,
> Perry KM6FQV
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
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