Tube subs for D&A Phantom. How not2.

[nomadradio]

The D&A Phantom amplifier remains popular, even though the cost of restoring them continues to climb steadily. The original tube types it used become progressively more scarce decade by decade prompting the use of substitutes that are less popular, and less expensive.

The four driver tubes on the left in this pic are type 31LZ6. The "31" refers to the nominal heater voltage. Four of those heaters wired in series add up to 124 Volts, perfect to simply power from the 120-Volt line current. No transformer needed.

So what's wrong with this picture? For starters, the four driver tubes are rated for 30 Watts each, for a total of 120.

The six smaller final tubes are type 6KM6, rated at 20 Watts each. Six of them add up to 120 Watts.

Hmm. The driver tubes have the same power rating as the finals?

Looks as if the final tubes got hammered a little too hard.

Yes, it's dead Jim. Any time you see white where the shiny spot should be it's because oxygen has turned the thin shiny metal layer to oxide. In fact only two of the final tubes tested bad. The four drivers check just fine.

Gonna have to come up with six tubes, preferably adding up to a larger power rating than the drivers.

Some substitutes work okay in place of the original tubes, others not so much.

73

 

[Enterprise312ok]

6p45s from eastern Europe. I ordered some from Ukraine and received theme in about 2 weeks. around $65 shipped for a set of four.

 

[Shockwave]

Move the 4 big drivers into the final stage, use two of the smaller tubes as drivers, align the tank circuits for resonance again and call it a day.

 

[nomadradio]

$65 shipped for a set of four.

Okay, but it uses six final tubes. The original russki 6P45 is a stout tube, but the pins have a larger diameter. Sometimes the spring contacts in the american tube sockets will spread out and work okay. Sometimes they get stretched past the elastic limit and lose tension. Hard to predict. And replacing six sockets with real "magnoval" 9-pin sockets will be labor item costing well out of reason.

We bought some 6p45s from a ukrainian fleabay seller, but a dud rate of one out of four was routine. Just chalked it up to a 30 percent higher item cost on the inventory records. Learned to buy more than a job would call for.

I like Shockwave's idea. Hadn't thought of that. Might see what the customer thinks about it.

73

 

[linearone]

If you feel like doing a bit of work i can make a tube swap suggestion. You will need forced air cooling like a pressurized cathode cabinet of some sort and a fan or mini blower., and some ingenuity to clamp the grid to a chassis, and some craftiness for chimneys, u could use a sheet of teflon with a clamp or silicone or a tiny silicone tube.

Look at gi21b. I figure they could probably deliver about 200+ watts each. They would run on the phantoms b+ quite happily. The filament would be easy to sort. Plus you'd have a "real" rf tube. They are about 10-12 dollars each on ebay. Sure beats a sweep tube.

 

[nomadradio]

He's not up to a full-bore construction project. Got a 2-by-250R JohnBoy waiting to get stabilized. More than enough "project" for me.

Gonna try Shockwave's switcheroo idea. Talked to the customer and he likes that better than buying six final tubes.

73

 

[Shockwave]

Okay, but it uses six final tubes. The original russki 6P45 is a stout tube, but the pins have a larger diameter. Sometimes the spring contacts in the american tube sockets will spread out and work okay. Sometimes they get stretched past the elastic limit and lose tension. Hard to predict. And replacing six sockets with real "magnoval" 9-pin sockets will be labor item costing well out of reason.

We bought some 6p45s from a ukrainian fleabay seller, but a dud rate of one out of four was routine. Just chalked it up to a 30 percent higher item cost on the inventory records. Learned to buy more than a job would call for.

I like Shockwave's idea. Hadn't thought of that. Might see what the customer thinks about it.

73

When the EL-509 became one of the last easy to access sweep tube replacements, I changed sockets on everything from Yaesu 101's (not easy at all) to Andy Anderson 10 tubers. I even put that ceramic Magnoval socket in D&A amplifiers that already had 9 pin sockets.

One day I got tired of changing those sockets and took a center punch, placed it in my drill and held the file against the tip until I got it down to the perfect diameter where it could be pushed into a 6lq6 socket and open the pins up just enough to still provide a snug fit on the El 509. Several D&A Phantoms are out there with this modification.

I continued this for years until the dud rate on the El 509, got just as bad if not worse, then the Russian tube you are referring to. When RF Parts refused to make good on their defective El 509 sales, I never bought another tube from these creeps again!