Twins

[NQ6U]

Okay, the XYL is out of town so I have had some time to play with my radios for a few days. Last night I practiced the tune-up procedure on the T-4X until I had it down. Kind of fun and certainly more satisfying than just switching on the Icom and dialing it to the desired frequency but there's a little problem with the rig. While I can tune it up to 100 watts output on 80 meters, I can only get about 50 watts on 40 meters and correspondingly less power out as I go up in frequency until I hit 10 meters, where maybe 5 watts is the best I can get.

What do you experts think on this? Bad final tubes or is it something in the drive section?

[N8YX]

Driver is easiest to replace. Try it first. Then verify that no one has tried "adjusting" the rack assembly which moves the pre-driver/driver tuning slugs in and out of their respective coil cores.

[NQ6U]

Driver is easiest to replace. Try it first. Then verify that no one has tried "adjusting" the rack assembly which moves the pre-driver/driver tuning slugs in and out of their respective coil cores.

Roger, thanks. I know the tuning slugs are okay (checked them out during the restoration process) so I'll try replacing the 12BY7A driver tube first.

[N8YX]

Roger, thanks. I know the tuning slugs are okay (checked them out during the restoration process) so I'll try replacing the 12BY7A driver tube first.

If that fails, suspect the final tubes.

[K7SGJ]

You might might want to try to neutralize the finals. That could tell you a lot. I'm assuming power dropped as you increased frequency while on a dummy load? How does the drive and plate current act when it's tuned up on the different bands? It's been a very long time since I worked on one of those, so I'm just shooting from the hip. (Maybe I need a hip replacement) Most of the older gear will have a little lower output on 10 then 80 but your Drake seems to have a huge change. Even if the outputs, or driver, tubes were flaky, I wouldn't think there would be such a large difference between 80 and 40, although it's certainly possible. I'd also be curious to see if the drive drops by 50% from 80 to 40. It almost sounds, no offense, that you may not be tuning it up right. I know on some of my older stuff, I can get it to tune in several places with varying degrees of RF output, but there is an optimum sweet spot. The other thing I might be suspicious of, is a fubar cap in the tuning circuit, or maybe a coil that has some debris between a turn or two. That would account for the major output difference vs frequency. Then again, you might just have a bad knob.

[NQ6U]

No offense taken, but there is really only one tuning that even comes close to working on any given band so I think I got that part right. And yeah, I was turning into a dummy load. The drive control (called Gain on the Drake) needs to be turned progressively farther clockwise to advance the plate current above idle as you move up in frequency; by the time it gets to 10m, it runs up against the stop. Plate current when properly tuned is about what the manual says it should be—between 2800 and 3200 mA.

[K7SGJ]

Well, if you are getting enough drive to get the plate current in the right neighborhood, that does tend to point to the outputs. Needing to jack the drive way up kinda says "soft tube". Did you try to neutralize them?

[NQ6U]

Well, if you are getting enough drive to get the plate current in the right neighborhood, that does tend to point to the outputs. Needing to jack the drive way up kinda says "soft tube". Did you try to neutralize them?

No, I haven't. They are the original tubes so I didn't think it necessary but I will look into doing it.

[K7SGJ]

Keep us posted on the fix. Personally, I always enjoy a success story as I have so few, personally.

[NQ6U]

I ordered a new set of tubes—a pair of 6JB6 finals and a 12BY7A driver but I'll play with neutralizing the existing tubes before I install them just so I know how to do it.