Globe Champ

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Tim WA1HnyLR:
Hi Jack,
The Globe Chump can be made to sound good. BUT like all Globe transmitters. many corners were cut. If time is taken to study what's there one can formulate their game plan. Yes, replace the couplates with discrete components that will give good frequency response. The 809s can easily be upgraded to a pair of 811 s. The stock mod iron is lack luster. I have a chump that I mounted up a mod transformer from a Globe King 500. As suggested replacing the 6AQ5 driver with a octal based tube like a 6L6 would help, but the audio driver transformer would need to be upgraded as well. The power supplies are woefully under filtered and should be solid stated. The plate supply components are on the edge as far as current ratings are concerned. Running at the claimed power places things at the edge. Filter capacitor values in ALL of the power supplies need to be fattened up. Use the space left by the 866s for something else. The stock tank components are underrated as well . They are basically DX 100 type 100 watt components. It may think in terms of de-powering the transmitter by thinking with a 100 watt mentality  There are many choices of tubes that may be used instead of the AX 9909 s. The pair of 4-65 s is a good one. A single 813 will work. A single 4D32 will work quite well. The 4D32 becomes a real performer with 1000 volts on the plate. BUT one has to be real careful when tuning up. A pair of 4D32s may be used but the tank circuit may complain. I started the project about 30 years ago and never finished it. I had the transmitter in storage at the time of my fire in 1992. I pulled it out. I would like to get back to it soon. The previous owner mounted up a pair of 807s for the PA stage. A little piss weak though . An external Variac was connected to the plate transformer. I may replace the 807s with a single 4-125. At 1000 volts the 4-125 should easily be able to load up to 175 Ma. Its' high frequency performance is much better than the 813 on 10 & 15 meters. The 4-125 should be quite bullet proof with 1Kv on it. So what if the outpoot is in the order of 100 watts or so. Actually if you are not going to upgrade the iron and the modulator tubes down size-ing the RF end to the 100 watt class will allow what's there to work well . It is better to have a well modulated lower power transmitter than higher powered one that strains to make full modulation. It is also better to have a reliable transmitter at lower power than one that is crapped out for trying to get too much out of whats there. Good luck with which ever route you choose Jack. I hope to get mine going soon when time permits.
Tim WA1HnyLR

DMOD:
If you are looking for a schematic to replace those Couplates and some extraneous circuitry, here is a modification I would use.

If you still want the Phone Patch, you must use an isolated RCA jack.



Phil

Steve - K4HX:
I used a single 7094 in the final. It was an easy mod (15-30 minutes) and worked FB.

WD5JKO:
Quote from: Steve - K4HX on June 08, 2018, 12:12:33 AM

I used a single 7094 in the final. It was an easy mod (15-30 minutes) and worked FB.


   Yes, this is a good choice. The 7094 is a good tube, but not easily found these days. I recall that Hoisy Hoisington, W4CJL SK (Chairman of SPAM) used a 7094 in his Champ.

It is worth noting that the AX9909 finals had 12v filaments. Many of the tube replacement ideas would require a new filament transformer.

I remember Jim W5JO was using VHF RF tubes in his Champ. I forget the tube number, but I thing there is a 12V tube from the VHF FM era that works well in the Champ.

Jim
Wd5JKO

K9ACT:
Thanks for all the comments.. lots of food for thought.

Now that I have had some experience using it and studying it visually and digesting the comments, I think I will probably leave well enough alone.

The finals are OS51s and the modulators are 811s and the HV supply has been solid stated.  The VFO is disabled and I am using an external DDS VFO..

I spent some quality time with my new function generator and my RTL dongal receiver and find the audio response is flat from 400 to 4000 Hz and near zero at 300 and 5000.  As near as I can tell the modulation percentage is about 80%.

My first look inside was pretty much in line with Tim's comments and think it best not to push it too hard.

This brings up a question I have about a warning in the manual about not running it  below 275 ma plate current.  It does not explain why but seems like loading it lighter would not only prolong it's lifetime but lighten the burden of the modulator allowing full modulation.

Am I missing something?

BTW, a $30 RTL dongal with no antenna makes a great spectrum analyzer for modulation testing.

Jack

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