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Globe Champ




 
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K9ACT
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« on: May 28, 2018, 12:49:46 AM »

My new station since the fire is a Globe Champ, generously donated by K9WEK.  Works like a champ but some folks are just never satisfied.

The manual specifies an audio bandwidth of 3.5 kc and I presume there would be some mods out there to broaden it a bit but can't find any searching this site.

I have seen suggestions of replacing the Coupleats with caps but nothing very specific.

Anyone have any experience on this?

Thanks,

Jack
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« Reply #1 on: May 28, 2018, 02:59:19 AM »

no experience on that unit but if following the articles and stuff that others have done is not satisfactory then you can tune it up into a dummy load and give it a constant amplitude swept frequency audio signal and find the restrictions part by part and stage by stage. Then you will know for certain what to change.

3.5KC is pretty good. Maybe a so called '75us pre-emphasis' filter would get good results with it as-is. -if what you want is extra intelligibility in bad receiving conditions.
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« Reply #2 on: May 28, 2018, 11:16:56 AM »


Jack,

   I once brought back from the dead a Champ. The Ax9909 finals were gassy, and the 809 modulators were flat. In the pre internet days, finding tubes like that was a lot harder, so I went to the junk box. Had a nice pair of Eimac 4-65's, and some 808's. The conversion was a long story, but worked out quite well. I recall the audio driver, a 6AQ5 was the bottleneck in modulation capability. Switching to an Octal socket gives more choices (like an el-34). Perhaps para-feed the driver transformer, and add some negative feedback.

Jim
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Jim, W5JO
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« Reply #3 on: May 28, 2018, 03:37:29 PM »

See if this works for you


* audio.JPG (444.23 KB, 2550x3300 - viewed 158 times.)
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nq5t
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« Reply #4 on: June 06, 2018, 03:10:17 PM »

Getting rid of the couplets is a must.

My affinity for the Globe Champion goes back to my mis-spent teenage years when I had a 350 and used it throughout high school.  Bought a 300 in the mid-90's, restored it,  and ran it off and on until a couple of years ago, when I parted with it prior to a cross country move.

If I can ever find my audio mods (lab books are somewhere, still in some box .. somewhere) I'll send them to you.  I did install some negative feedback.  All in all, it played well, and according to reports sounded good.  I usually drove it from an audio chain through the phone patch input. 

Don't know if you have a 300, 300A, or 350.  In any case, the 300 did NOT have cooling fans on the AX9909s.  That proved to be deadly to the tube seals at the base, which shortened their lives considerably.  The 300A did have cooling, and that is likely the only substantive change from the 300.  So if you have a 300, you need to add cooling.  I installed two DC fans in the final shield, blowing at the tube bases, and never had a tube failure.  When I finally sold it, it still had the original tubes (plus 2-3 sets of new AX9909/6083 tubes I'd acquired over the years just in case). 

It's a nice radio

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Tim WA1HnyLR
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« Reply #5 on: June 07, 2018, 06:32:16 AM »

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
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« Reply #6 on: June 07, 2018, 01:13:26 PM »

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

* Globe Champ Audio.pdf (54.03 KB - downloaded 42 times.)
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Steve - K4HX
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« Reply #7 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.
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« Reply #8 on: June 08, 2018, 11:55:44 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
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K9ACT
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« Reply #9 on: June 09, 2018, 01:38:32 AM »

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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WD5JKO
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« Reply #10 on: June 09, 2018, 04:40:12 PM »



Jack,

  I link an old AMFONE thread about this topic here:

http://amfone.net/Amforum/index.php?action=printpage;topic=18430.0

In that thread, it is mentioned that the OS-51 has low efficiency. Other finals such as the 6083 and 8643 are mentioned.

One more thing, look at the audio driver transformer carefully. The Globe King 400/500 uses one with a primary centertap wire that is tucked into the transformer bell. This is a push pull CT to push pull CT transformer, but only used with a single ended audio driver. If the Glum Chump uses a similar driver transformer, then some options might come to mind such as push pull 6AQ5 audio drive.

Jim
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Steve - K4HX
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« Reply #11 on: June 10, 2018, 05:29:59 PM »

Jim, I was told that 7094s were rare. But I easily found 3 within months and that wasn't even using eBay.

The 7094 has a 6.3V filament. This is easily found by using the 809 fil tap. I installed a standalone 6.3v transformer for the 811As I installed in the modulator. One could just as easily install a similar transformer for the 7094. There is plenty of room under the chassis.

The key to getting the 7094 to perform is to raise the screen voltage by changing the screen dropping resistor (IIRC). The screen voltage used with the AX9909s is too low for the 7094, especially with only 1 kV on the plates. Once this was done, the 7094 would easily put out 250 watts. I only ran it at about 200 watts out though and would recommend this to save the original mod and HV transformers.
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WD5JKO
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« Reply #12 on: June 10, 2018, 11:35:58 PM »


Steve,

     I remember some of what your mentioning from Hoisy W4CJL SK who also used a 7084 in his Champ.

I got the Champ from Dr. Jim W5YDO SK, and converted it for Dr. John in Alabama. This was about 35 years ago. I don't recall his call, but I talked to him a few years ago on 75m. He ran a 4-1 modulated by a pair. He told me someone flew a private just in from the east coast to pick up that Champ!

I used a pair of 4-65's. It was a bit of a bugger to convert, and I made a big error. I used the 12v for the ax9909 filaments, and wired the 4-65 filaments in series. This resulted in low level 60hz cathode modulation. The signal had hum that peaked with QSB signal dips. The cool thing with the 4-65's was the tubes ran the same from 80m to 10m. Very efficient.

The HV transformer was the weak link. I once made the HV filter a c-l-c and that raised the B+ to around 1400v. That woke things up, and over 300 watts RF output with good modulation from the 808's I added.  Boy that transformer got HOT fast!!

I think I have a 7094 in my stash.

Jim
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K9ACT
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« Reply #13 on: Yesterday at 02:01:07 AM »

I am thinking that all those serious mods to the audio are sort of like making a silk purse out of a sow's ear.  It's probably not fair to the Champ to call it a sow's ear as it is pretty nice as is.  Making all those mods to it seems like a lot of work when there may be a much simpler way to upgrade the audio.

Both my 810 and 2 X 8000 transmitter modulators were driven by an inexpensive audio amp board using a TDQ2030 and some kind of transformer driving the 811s or 813's.

The audio chain could be switched to either transmitter as desired and it all worked very well.

Problem is, all my files were lost in the fire and I don't remember what the transformer was.  I think it was a Hammond but I don't see anything in their list that would match  8 ohms to whatever the 811 grids would be.

Can anyone suggest a readily available transformer?

Thanks,

js
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« Reply #14 on: Yesterday at 05:07:19 AM »

I am thinking that all those serious mods to the audio are sort of like making a silk purse out of a sow's ear.  It's probably not fair to the Champ to call it a sow's ear as it is pretty nice as is.  Making all those mods to it seems like a lot of work when there may be a much simpler way to upgrade the audio.

Both my 810 and 2 X 8000 transmitter modulators were driven by an inexpensive audio amp board using a TDQ2030 and some kind of transformer driving the 811s or 813's.

The audio chain could be switched to either transmitter as desired and it all worked very well.

Problem is, all my files were lost in the fire and I don't remember what the transformer was.  I think it was a Hammond but I don't see anything in their list that would match  8 ohms to whatever the 811 grids would be.

Can anyone suggest a readily available transformer?

Thanks,

js

awhile back I looked at using some Antec power inexpensive toroids as interstage/driver xfmrs with promising results .... high efficiency and bandwidth and low cost ....IIRC a 12VA xfmr say 12V to 120V driven by a 10W ss power opamp such as a TDAxxxx gives a very high damping factor (read low source impedance) which works well in class B driver applications .... very smooth freq response to 30 kHz if resistor loaded to 10x load impedance.... I never got around to building it up so I am still like Yoric considering the skull  Grin Huh Grin
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