D&A Warrior 1000

[TonyV225]

This still has to be one of the most informative posts or threads Ive seen yet.
VERY VERY COOL NOMAD!!!!

 

[night.ranger]

Hey Lonewolf,
To start with, those yellow wires are not used. They lead to a separate winding that will deliver 5 Volts to power the filament in a tube-type rectifier. When that transformer was designed, and sold from a catalog, this was the standard way of rectifying high voltage for tubes. Using tubes as rectifiers.

ALL D&A amplifiers use solid-state rectifier diodes, so those yellow wires were cut off short. D&A started out small, and bought "stock" universal-type transformers from a stock catalog. Once Ed Dulaney was selling enough of his linears to buy transformers in bulk, they began using a transformer that was built without this 5-Volt winding on it. If the transformers have those yellow wires you know that they are old.

One really, really BIG deal with any "Glass-Factory" linear has to do with the Plate Tune controls, and the position at which each one shows a "peak" on the wattmeter. D&A used capacitors that have NO end stop for all three 'Tune' controls on that amplifier. They spin freely 360 degrees, unlike the Final Load control. It will turn only halfway around before it runs into an end stop with a "clunk", and won't turn any farther.

These "360" capacitors can deceive an unwary eye. They can APPEAR to show a "peak" while you tune it, when in fact that circuit never really achieves the resonant peak that you need to get full power.

Here's the rule: As you crank one of these '360'-type Tune controls, you should observe TWO peaks in one whole turn of the knob. Both of these peaks may be right next to each other, or they may be 180 degrees apart from each other.

What matters is that you see TWO peaks in that one, full turn of the knob. I'm gonna skip the long explanation of how this "false peak" phenomenon occurs, or why it matters. I've only been threatening to put it up on a web page for several years, now. Sure would be easier just to post a link to it, once I got a "Round Tuit".

In a nutshell, if you observe ONLY ONE peak in that full turn of the knob, you would observe one of two things if you peeked behind the panel, at the plates on that control.

Either the plates would be as far apart as they go, or they will be meshed as close together as they will go. What happened was that the control ran out of range, before reaching a properly-tuned peak. Since there is no end stop, cranking the knob to either side of this "end" of its range LOOKS like a peak on a wattmeter, even though it isn't. If, in fact, the circuit DID reach a true resonant peak, there would be TWO physical positions of the shaft at which the plates will mesh that close together. One to the left of the 'end' of its travel, one on the right side of that end-of-travel. If your wattmeter peak occurs with the plates meshed exactly halfway, those two peaks will be exactly one-half of a turn apart, with the knob's pointer at 180 degrees one peak from the other peak. If the peak occurs near one "end", those two peaks will be closer together.

The real bottom line here is that there's not a lot you can do about it, if any of the three "Plate Tune" controls fails to achieve a proper "Twin" peak. The control hooked to the knob is only the "fine" tune for that set of tubes. The coil attached to it is the real "Coarse" tune. Changing tubes, from one set to another, will change where the Tune control hooked to them will peak. If someone changed tubes, and threw that peak one-half of a turn BEYOND one end-stop, you'll never see full power from the new tubes. Never mind why changing tubes can throw those controls off of a true peak. They do. And if the coils in that unit were all set with a different set of tubes, they need to be readjusted to suit the tubes that you now have installed in it.

Running a tube-type linear with a Plate Tune control turned away from the peak will stress the tubes. Some folks will attempt to "back down" a linear by deliberately cranking a Tune knob one side of the peak. This reduces the efficiency of the tubes, causing them to overheat inside.

On the other hand, the tube doesn't care whether the Tune control is turned "off" of the peak on purpose, or because it just won't turn "that far".

Here's a pic of the "weak link" that will pop in a 8950 when this happens. The tube's internal connection to the "ground side" pin is a thin strip of metal that comes from the tube's center element leading to pin #2. The excess heat from mistuning will cause that link to melt, like the element in a fuse.

I recommend being cautious with running this box, until it's clear that all three Plate Tune controls are achieving a "True" peak on the meter. Folks who keep tuning, and tuning, and complain that the power just keeps dropping off, will find that they have been blowing the "Fuse" at the bottom of their tubes, one by one. Once the fuse is blown on a tube, there's no way to stitch it back together.

If this fella in Alabama knows his stuff, he's already hip to everything I just told you. But if you keep hammering on this box in its current condition, you could make things worse.

73

Thanks for this post 2600. Very informative. A local CB'er brought me a Palomar 200x he had over driven in to the non-working category. The amp originally came with 8950 tubes, but it had been converted to 6LF6 tubes. The cathode pins show the same melted wire as your picture shows for the 8950. Also the plate choke for the driver tube was burned and the driver tube is on its last leg, so being over driven is the most likely cause for this amp. Unfortunately the 6LF6 tube does not have the secondary connection to the cathode on pin 6 as the 8950, so these 6LF6 tubes are toast. Also the 10 amp fuse had been replaced with a 20 amp fuse with a copper wire wrapped around it to keep it from blowing. Typical CB dumbass. Now he is looking at a repair bill that is worth more than the amp.

Night Ranger

 

[night.ranger]

....
To add insult to injury, the "high-performance" aspect of the Warrior made it necessary to use the "black-cap" 6MJ6 version of the 6LQ6 tube in the final stage. The chrome-cap versions of the tube, with the skinny wire leading to the plate cap, and the thinner glass would have to be 'babied' to keep them from blowing out prematurely.

Trouble is, the "black-cap" 9-pin tube is the rarest and most expensive version. I've seen them listed at 90 bucks each, when you can find them. The price of eight good 6MJ6 tubes would buy a decent new amplifier, all by themeselves.

....

Oh, and BTW there was a little-known 'cheat' for a 8950 that had the cathode link blown. Pretty sure all of the GE 8950 had that right-angle bend in the cathode link to pin 2. That was the weak spot, every time. But there was a SECOND pin connected to the cathode, pin 6. Probably put there to reduce the inductance of the cathode connection. You could put a jumper wire across the socket from pin 6 to pin 2, and if the rest of the tube had survived, VOILA! Returned from the dead, as if by magic.

Did that to our tube tester, but found that most 8950s with a "blown fuse" also had OTHER problems, by the time they had been stressed that far. Filed that trick away under the "nice try" category.

....
/QUOTE]

Once again a very helpful post. I came across a mint condition tan and brown D&A Phantom with the original D&A tubes inside. I wondered why the four 6LQ6/6MJ6 driver tubes marked "D&A Mav250" had chrome caps and the six final 6LQ6/6MJ6 tubes marked "D&A PH500" had dark grey colored caps. Now I know.

Night Ranger