[R-390] R390/URR for Sale

joldenburg2 at new.rr.com joldenburg2 at new.rr.com
Tue Feb 24 17:47:55 EST 2026 

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 to
the 12 volt versions of the two oscillator tubes and jumper pins 2&7
of the ballast tube socket. The only need for the 3TF7 was due to the
very large line voltage requirement by the Signal Corps in the
original contract. The intent was to prevent excessive oscillator
drift due to line voltage changes. Modern line voltage is held to a
+/-5% variation, not the +/-15% of the original R-390/URR contract.
See page 14 of the final R-390/URR engineering report.
 Tube heaters are a non-linear resistance. Changing the heater voltage
by 10% does not change the heater current by the same percentage, it
is more like a 5% change in heater current. The final R-390/URR
engineering report on page 15 indicates that the ballast was not
needed since the oscillator performance was quite good without the
ballast tube. It is my feeling that the ballast tube was a Signal
Corps requirement, not an engineering requirement.Jim
 Logic: Method used to arrive at the wrong conclusion, with
confidence. Murphy

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

 Those 3TF7 seem to always be missing. I have 2--R390 and 3--R390A,
 awaiting work. Two of them are missing the 3TF7. one of the R-390/URR
 was restored by David Medley, probably the last one he did. I have
 that one up soon, it buries the Smemeteer when turning it on with no
 antenna or output.
 Found and games.....

 Jon AB9AH
 "I have always preferred diversions to duties; this strange taste has
 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 a A.

 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/power cord)
 > I took this radio in a trade 10+ years ago from a list member and
 set it on the
 > shelf. The person who I traded with just happened not to remember
 that the 2-
 > 6082’s as well as the 3TF7 were missing. (Radio was represented
 as complete.)
 >
 > So after a 2,500 mile move and still no “roundtoit” it’s time
 to sell.
 > The radio front and rear panel are fair and it does have the 7 and
 9 pin tube
 > straighteners.
 >
 > I’ve added the correct size 30 NOS IREC tube shields for all the
 7 and 9 pin
 > tubes, as well as 1 Corcom 3EEA1 input filter, 1 CL 90 input surge
 limiter, 1
 > 130VAC MOV surge limiter, 1 NOS Nichicon 390uF/450 capacitor to
 replace the
 > C101 10uF filter, 1 NOS 2 pin connector for the balanced antenna, 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 to be
 shipped in two
 > boxes. The receiver in one and the power supply and the audio
 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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