One 3TF7 is used in the R-390A. It is a current regulator or "ballast" tube.
The Amperite part number for the ballast tube is 3TF7. Amperite also carries an equivalent, the TJ311M01.
- RT510 is located on the IF subassembly, where it provides a regulated 6 volt filament voltage to V505 and V701, which are wired in series. RT510 is fed from the 26.5 volt filament supply. RT510 appears in figure 77 of TM-11-856 and in figure 85 of TM-11-5820-358-35.
Of all of the tubes in the R-390A, the ballast tube has garnered the most controversy, discussion and creativity regarding a replacement. Replacement tubes cost between $15 and $25, generally.
Some replacement suggestions that have been tried:
Nolan Lee provided some additional background on the 3TF7:
- Jumper pins 2 and 7 of RT510 with a piece of wire, Replace V505 (The BFO oscillator tube) and V701 (the PTO oscillator tube) with 12BA6 tubes.
- Jumper RT510 with a resistor of 40-50 ohms rated at 5-10 watts.
- Install a 3-terminal Solid state voltage regulator to provide 12.6 volts.
- Rewire the sockets of V505 and V701 to use the 6 volt filament string available to other tubes.
- Rewire the RT510 socket so that a worn out 12BY7 or 12BH7 or other tube can be used to provide the 12 VAC drop required. Add a jumper on the socket from pin 2 to pin 4 and pin 7 to pin 5.
"OK, after listening to all of the hype and BS about the ballast
tubes in the R390A, I figured I'd research it a bit an post my
findings. Put your boots on bubba, it's gonna get deep...
If one of you guys is saving stuff for an R390A FAQ, the info below
would go well in it.
Digging thru a 1982 Amperite AM-82 application guide, I found a few
interesting things that I'll pass on to you guys. If you deal with
a distributor that handles Amperite, get them to get you a copy,
it's an interesting book.
The resistance wire is usually iron, and the glass envelope is
filled with either hydrogen or helium gas for heat conductivity.
The glass envelope runs about 160 degrees. Since I'm one of those
people that refuses to use the metric system, you know WHICH
160 degrees I'm talking about. It ain't Kelvin either.
One of the posts I read today mentioned a shelf
life with ballast tubes. I suspect that it's related to ballast
tubes that use helium as the filler gas. Helium is famous for
it's ability to pass thru the wall of sealed steel high pressure
cylinders. I ain't no engineer or chemist but have had some
experience with high pressure gases and have see firsthand that
helium will "disappear" from sealed bottles. If I'm not mistaken,
the 3TF7 ballast tube is filled with hydrogen rather than helium.
OK, back to my original post...
Current regulation is usually within plus or minus 1%.
They work with either AC, DC, or pulsating current.
When the current in the circuit is increased to a high enough
level for the regulating function to start working, only a
small portion of the filament will glow. As the voltage across
the ballast increases, more and more of the filament will glow.
When the entire filament is glowing, you're at "max" and any
additional increase will overheat the tube and shorten it's life.
The rated life expectancy when operated as recommended within it's
ratings is 2000 hours. Run it at "max" all of the time and it's
only 1000 hours. Run it at 80% of max and it's 5000 hours.
Here's a direct quote from Amperite AM-82 that you'll really
DUTY CYCLE DEPENDANT
If a steady voltage of a value in the middle of the operating range is
applied to the tube continuously, it's life will be tens of thousands
of hours. Opening and closing the circuit with the resulting expanding
and contracting of the filament greatly reduces the life of the tube.
Also, as in incandescent lamps, turning the unit on and off many times
will reduce it's life especially if the unit if operated near it's
maximum voltage. If full voltage is applied to the tube, the circuit
may be opened and closed only a few hundred times before the current
is outside of the limits or the filament is burned out. Thus the life
of the tube will be determined entirely by it's duty cycle.
I figure that over the last 23+ years that I've had the old Collins,
it's been on for "24 and 7" for at least 15 of those years. 15 years
is 131,400 hours. That original 3TF7 is still going just fine. I'm
not saying that it won't puke when I finish the overhaul of the
receiver and power it up, but even if it did, it gave pretty damn
I finished my OH of my 67 EAC back in the middle
of October of 1998. It's been running 24 hours a day and seven days
a week since then. That's about 18 and a half months or more than
13,300 hours on the very same ballast tube that was installed in
it when it was assembled back in 1968. If the gas hasn't leaked out
yet, I suspect that it won't. Back to my original post...
The folks at Amperite that I've dealt with have been a hell of a
nice bunch. I needed some information on some odd "non standard"
numbered ballast tubes. They transferred me to an engineer and I
received all of the answers that I needed. Very sharp and friendly
bunch of people.
For what it's worth, there's another part number for the 3TF7
that was used for tubes that had different testing requirements
than the standard mil-spec and was for a Govt contract in 1978,
and not for civilian or commercial sales. After I corner the market
on them I'll post the number. Just joking...a friend of
mine found a stash of them and sent me three of them last week or
so to research and experiment with. After talking to the engineer
at Amperite a few hours ago, there's no need to experiment. I now
know exactly what they are.
The end flap of the boxes is labeled as follows:
The side panel is labeled as follows:
Resistor Current Regulating
The tubes themselves are labeled as follows:
(circled Amperite "A" with lightening bolt)
So, if you spot any of these TJ311M01 marked ballast tubes, grab
a few, they'll work just fine in your R390A."
Two 26Z5W tubes are used in the R-390A. The 26Z5W is a high voltage rectifier tube.
Solid state replacements were installed in some R-390A receivers by the military. Often, The shield bases on the tube sockets were bent inward and flat with the chassis to prevent tubes from being inserted into the sockets. This modification can usually be reversed by removing the solid state diodes from under the tube socket, carefully bending the tube shield bases back into position, and inserting tubes into the sockets. When the solid state modification is in place, a somewhat higher B+ voltage is present in the receiver. A dropping resistor must be added to reduce the higher voltage or premature damage will occur to the 2 audio output 6AK6s.
- V801 is located in the Power Supply subassembly, where it forms one half of a full-wave rectifier. V801 appears in figures 47 and 80 of TM-11-856 and in figure 28 of TM-11-5820-358-35.
- V802 is located in the Power Supply subassembly, where it forms one half of a full-wave rectifier. V802 appears in figures 47 and 80 of TM-11-856 and in figure 28 of TM-11-5820-358-35.
Seven 5814A tubes are used in the R-390A. The 5814A designation is for the Mil-Spec version of the 12AU7, a dual section medium-mu dual triode.
- V205 is located in the RF subassembly where one half, V205A, is used as the oscillator tube for the crystal calibrator and the other half, V205B, is used as the 100 kc oscillator cathode follower. V205 appears in figures 46 and 75 of TM-11-856 and in figures 27 and 58 of TM-11-5820-358-35.
- V206 is located in the RF subassembly where the two halves form a multivibrator. V206 appears in figures 46 and 75 of TM-11-856 and in figures 27 and 58 of TM-11-5820-358-35.
- V506 is located in the IF subassembly where one half, V506A, is used as the AGC time constant generator and the other half, V506B, is used as the detector. V506 appears in figures 34, 38, and 77 of TM-11-856 and in figure 17 of TM-11-5820-358-35.
- V507 is located in the IF subassembly where the two halves form a limiter. V507 appears in figure 77 of TM-11-856 and in figure 17 of TM-11-5820-358-35.
- V509 is located in the IF subassembly where one half, V509A, is used as the AGC rectifier and the other half, V509B, is used as the IF cathode follower. V509 appears in figures 37 and 77 of TM-11-856 and in figures 20 and 21 of TM-11-5820-358-35.
- V601 is located in the Audio subassembly where one half, V601A, is used as the 1st AF amplifier and the other half, V601B, is used as the AF cathode follower. V506 appears in figures 42 and 45 of TM-11-856 and in figure2 23 and 26 of TM-11-5820-358-35.
- V602 is located in the Audio subassembly where one half, V602A, is used as the local AF amplifier and the other half, V602B, is used as the Line AF amplifier. V602 appears in figure 43 of TM-11-856 and in figures 25 and 62 of TM-11-5820-358-35.
Six 5749/6BA6W tubes are used in the R-390A. The 5749 designation is for the Mil-Spec version of the 6BA6W, a remote-cutoff pentode.
- V501 is located in the IF subassembly, where it is used as the 1st IF Amplifier. V501 appears in figures 33 and 77 of TM-11-856 and in figures 16 and 60 of TM-11-5820-358-35.
- V502 is located in the IF subassembly, where it is used as the 2nd IF Amplifier. V502 appears in figures 33 and 77 of TM-11-856 and in figures 16 and 60 of TM-11-5820-358-35.
- V503 is located in the IF subassembly, where it is used as the 3rd IF Amplifier. V503 appears in figures 33 and 77 of TM-11-856 and in figures 16 and 60 of TM-11-5820-358-35.
- V505 is located in the IF subassembly, where it is used as the BFO oscillator. V505 appears in figures 36 and 77 of TM-11-856 and in figure 19 of TM-11-5820-358-35.
- V508 is located in the IF subassembly, where it is used as the AGC IF Amplifier. V508 appears in figure 77 of TM-11-856 and in figures 21 and 60 of TM-11-5820-358-35.
- V701 is located in the VFO subassembly, where it is used as the VFO oscillator. V701 appears in figures 28 and 78 of TM-11-856 and in figures 10 and 61 of TM-11-5820-358-35. Nolan Lee reports that 'used" tubes that have aged for a while seem to work better than new tubes when making replacements of the VFO oscillator tube. "New" tubes appear to cause oscillator drift with age, moving the tuning range as much as 1 KC.
Three 6C4WA tubes are used in the R-390A. The 6C4WA designation is for the ruggedized version of the 6C4, a medium-mu triode. The numeric equivalents are types 6100 and 6135.
The 6C4 and 6C4W will work as replacements, but may not work quite as well as the 6C4WA.
- V202 is located in the RF subassembly, where it is used as the 1st mixer. V202 appears in figures 22 and 75 of TM-11-856 and in figure 4 of TM-11-5820-358-35.
- V203 is located in the RF subassembly, where it is used as the 2nd mixer. V203 appears in figures 24 and 75 of TM-11-856 and in figure 6 of TM-11-5820-358-35.
- V204 is located in the RF subassembly, where it is used as the 3rd mixer. V204 appears in figures 27 and 75 of TM-11-856 and in figure 9 of TM-11-5820-358-35.
One 6DC6 tube is used in the R-390A. The 6DC6 is a sharp-cutoff pentode according to the most recent tube manuals. Some earlier tube manuals refer to it as a semi-remote-cutoff pentode.
- V201 is located in the RF subassembly, where it is used as the RF amplifier. V201 appears in figure 75 of TM-11-856 and in figure 3 of TM-11-5820-358-35.
Two 5654/6AK5W tubes are used in the R-390A. The 5654/6AK5W designation is for the ruggedized version of the 6AK5W, a sharp-cutoff pentode.
- V207 is located in the RF subassembly, where it is used as the 1st crystal ocsillator. V207 appears in figures 23 and 75 of TM-11-856 and in figures 5 and 58 of TM-11-5820-358-35.
- V401 is located in the Crystal Oscillator subassembly, where it is used as the 2nd crystal oscillator. V401 appears in figures 25, 26 and 76 of TM-11-856 and in figures 7 and 59 of TM-11-5820-358-35.
Three 6AK6 tubes are used in the R-390A. The 6AK6 is a pentode power amplifier .
- V504 is located in the IF subassembly, where it is used as the 4th IF amplifier. V504 appears in figures 33, 40, and 77 of TM-11-856 and in figures 16 and 22 of TM-11-5820-358-35.
- V603 is located in the Audio subassembly, where it is used as the local audio output amplifier. V603 appears in figure 43 of TM-11-856 and in figures 24 and 62 of TM-11-5820-358-35.
- V604 is located in the Audio subassembly, where it is used as the line audio output amplifier. V604 appears in figure 44 of TM-11-856 and in figure 62 of TM-11-5820-358-35.
One OA2 tube is used in the R-390A. The OA2 is a 150-volt voltage regulator.
The OA2WA or the 6626 is a better replacement for the OA2, according to Nolan Lee, because they give longer service
WARNING: The OA2 family of tubes has a small amount of radioactive isotope inserted into them during manufacture to enable them to 'fire' consistently at whatever voltage they are designed to regulate. Handle broken tubes with care!
- V605 is located in the Audio subassembly, where it is used as a voltage regulator. V605 appears in figure 79 of TM-11-856 and in figure 28 of TM-11-5820-358-35.