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d&a Phantom 12 tube

nmewarlok

Member
Aug 4, 2011
2
0
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Ok I have read and poked around, then read some more, and poked some more and read and looked over schematics and poked, and you get the point, and at this point realize im in over my head a little when it comes to sweep tube gear.

I was freely given one very old d and a phantom amp. It is the 12 tube 6lq6 version, with 3 relays, and the 12aq5 keying tube. I know the high / low relay part of it has been blown apart, but it is stuck in high mode. Not a huge deal to fix. and since it is working, except for the meter on the front, is not a huge concern atm.

I am really wanting this to work on SSB, and it will as long as you keep making noise, but let the carrier drop, and the relay never seems to want to re engage. It works fine on AM and works fine with CW, and works fine on SSB as long as you keep the modulation going. All the tubes test OK, and I am getting around 600 on 10m so I tend to believe the tester as this seems in line with what others are getting.

What I am wanting to do is to give it an acceptable SSB delay, OR replace the keying tube with a tip type transistor, such as the 10 tube versions carry. OR replace all the relays with 12 volt versions, which would still involve getting rid of that pesky keying tube. Has anyone thought about this or done this in the past? I have a perfectly good 12v transformer, and a rectifer circuit to provide for the relay keying.

Another thought, there is a RCA jack on the back that i "thought" would be hooked to an external relay for keying , such is commonly found on other amplifiers. However this one does nothing. According to the schematic, and poking around, it is connected to the standby switch, and then to ground.


Any help from anyone with more experience with these amps than I do? If I left out anything, I will be happy to supply additional information.
 

watching this thread, I have a 10 tube, with the keying tube, I though about replacing with a transistor too.
 
there was a 14 tube D&A on eBay not too long ago.
i could only imagine what it costs in ($$$) to run such a large tube amp even @ 12 tubes.
 
transistor keying will work easy to build tip121 125 etc. or 2n2222 or npn/pnp transistor couple of detector diodes,1000mfd 25vdc cap and two resistors input resistor determines drive limit. check web for rf keying cicuits. change all my tube amps this way. you will need a diode across the relay coil to avoid transient voltage.
 
You would need to make a 12vdc keying voltage from the filament voltage as the old D&A I believe use 110vdc relays.

the schematic of the keying circuit is not my work so I am not taking credit for it but they are basically all the same except some use NPN and others use PNP transistors
 

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Nice! Thank you for posting that!

As a side note, today I received my ceramic el509 sockets, and 10 el509 Russian tubes. One tube is broke:mad:and on of the sockets had the pins smashed down. But, i can steal pins from the other sockets to make it work. Though now I have to wait another 2 weeks for more tubes, I did want spares anyway, should have known better and ordered more.

But at least now i can work on the amp and get it ready, I have a few caps I am going to replace. But first i have to lower the deck where the tubes are, they are a little close to the top of the cover, too close IMO. Besides, that way i wanna drop the tubes, it will allow the sockets to get some airflow too.

I do have a question though, there is a variable tuning capacitor right under the driver tubes I believe, what is that one for and how would I know if it is adjusted right?
 
I would like to change all those z5u 1kv disc caps under the tube sockets also, is there a newer style replacement for those? I see some nos stuff, but it is just as old as whats in there.
 
I have a D&A PDX-400 and the SWR trimmer (small tuner knob) in the back had went bad and I replaced it with a new trimmer but it still didn't fix the problem. The SWR between the radio and the linear is sky high. Before the stock one went bad it was always good. Any ideas of what's going on with it or how to fix or bypass this completly and get a good SWR between the radio and linear?? It worked Excelent befor the trimmer went bad. Output was 800-850 watts. Any help would be very much appreciated.
 

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