DX-100

[W2PFY]

Today & yesterday I have been in the process of making one good DX-100 out of two. The tank coil on the one in the best shape was BS so I took the tank coil out of the other one and did the swap. Underneath there are the wires that hook up to the band switch. Does anyone have a clear shot of the arrangement of which tap on the coil goes to what pin on the bans switch waffler pins?

I think I have it right but would like to be sure.

For now it puts out good power on 160,80 & 40 meters. Looks like there could be problems higher so that's why I asked about above?

The other thing I find astounding is the absence of a tune up mode with the transmitter?? How do you guys tune one up without blowing the 6146 tubes?

For a person who is green to the tune up procedure especially on 20 meters and above  could be problematic to say the least! At least with the Apache, there is a tune up feature on the low, high power switch.  

Hit me back please with any thing that come to mind.

[WBear2GCR]

r these imports from moscow?

              _-_-bear

[W3SLK]

Terry said:

How do you guys tune one up without blowing the 6146 tubes?

Funny you mention that because I never gave it any thought. Generally, I tune up everything except the final by placing it in CW mode but not keying the final. This puts power to the VFO, driver, and grids of the 6146's. Once that's done, I'll 'throw' the plate switch and be quick with the plate and tuning controls. I've always found that 6146's are pretty forgiving tubes.
 

[Ed/KB1HYS]

Tunning the Valiant is pretty much the same.  the finals are tuned last but under full power.  It does say in the manual to no take too long to get the plate circuit into resonance.

Put the rig into CW modem then you feed the output into a scope. Usually you can see an output waveform, then tune the whole rig (final as well) for maximum amplitude.  Disconnect scope and key the final.  I find that with the valiant, this gets me either right on or so darn close that retouching is a minor touch of the knob.

[KM1H]

I dumped the DX-100 I built in 57 as I was blowing too many 6146's. Some years later I was edumecated to what happens when screen current goes too high while diddling with the output tuning.

My cure back then was getting a Viking I. Still didnt know better but the 4D32 was indestructible.

6146's are fussier than old wimmin about grid current also, dont exceed 2.5ma per tube.

[W3SLK]

Carl said:

6146's are fussier than old wimmin about grid current also, dont exceed 2.5ma per tube.

I can't say I agree with you Carl. I have yet to replace a 6146 in my DX-100, Valiant I, Apache, Ranger I, HW-101, nor any other rig I've owned with at least one of them in. However, a friend of mine gave me his 32V2 to work on. He didn't know what the problem was. I pulled the 4D32 out and swapped it with the one in my Viking I and lo-behold it came to life. I couldn't believe it myself since it was the first final I've ever had to replace.

[WA3VJB]

Was just talking with a guy in Arkansas Friday night running a homebrew transmitter using pair of 809s modulating a single 4D32.
We remarked at how both of us have had years of good service from a given example of the 4D32; they really seem rugged.
In fact, I had a 30 year old JAN 4D32 example in my 32V2, and it wasn't until I measured the output on 10M that I knew it was getting soft. Full output from 15M lower, despite lots and lots of hours.

[WQ9E]

With rigs like the DX-100, Valiant, etc.  I keep the grid current a bit on the low side and also control plate current through the coupling  control (more capacitance) for initial tuneup.  This helps to limit the off resonance plate current and reduces the possibility of excessive control and screen grid current.  But I also keep a little cheat sheet near most of the rigs so I can preset controls after the initial tuneup. 

I have gotten very good life out of my finals but sweep tubes still make me nervous.  I bought several of the Russian EL-509 type if I have to modify some of my sweep tube rigs in the future.

Carl is right about the 6146 family having fragile control grids and one of the biggest killers of sweep tubes in vintage SSB gear is loading that is too light allowing the screen current to soar.  Improper operation quickly turns a pentode sweep tube into a tetrode with a suppressor which makes a really lousy final.

[KM1H]

I can't say I agree with you Carl. I have yet to replace a 6146 in my DX-100, Valiant I, Apache, Ranger I, HW-101, nor any other rig I've owned with at least one of them in.

And I bet you werent 15-16 either and the 6146 AND DX-100 was still pretty new to most.

I cant think of any tubes Ive blown in almost 50 years since I learned better. Even the 8122's in the 6M NCL-2000 I built in 64 lasted until 2 years ago when the power was down to 600W and I replaced them and gained 3dB.

[W8IXY]

On the two DX100's I have had, I installed a screen voltage switch in a hole on the rear of the chassis.  I used the same circuit the Apache used for its "tune" mode.  When switched, it lowered the 6146's screen voltage enough that you could never draw over about 300ma even with the output completely out of resonance.  "Hiding" that switch on the rear of the chassis allowed me to leave the DX100 front panel intact.


73
Ted   W8IXY

[K1DEU]

Pete, W1VZR said just turn on the 6AQ5 clamp tube with a resistor and switch.