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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 290 times.)
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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 71 times.)
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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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« 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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« 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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« 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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« Reply #13 on: June 19, 2018, 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: June 19, 2018, 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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« Reply #15 on: June 20, 2018, 08:58:20 PM »

Almost any tube output audio tranny would work to match 8 Ohms to the grids of the 811(A)s. I used 20 watt unit and it was overkill. But it's what I had and it worked FB.


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 #16 on: July 03, 2018, 09:21:57 PM »

My grand plans for an outboard audio chain for the Champ seem to have flopped.

I have: dynamic mic>mic preamp>Behringer 2946>8W speech amp>Hammond 125C transformer>811 grids.

Seems functional but I can't seem, to get more than 50% modulation.

To  minimize the variables for testing, I slimmed it down to a 4V p-p 1Kc sine wave into the speech amp>transformer>grids.

In this config, I can get up to 200V p-p on the grids which is more than the data sheet says is needed but still only 50% modulation.

I was getting something like 80% modulation before I "fixed it".

The audio section in the Champ is turned off and the transformer leads snipped.  I brought out the grid pins and chassis ground to the outboard transformer.

What did I do wrong here?

js
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« Reply #17 on: July 04, 2018, 10:08:36 PM »

My grand plans for an outboard audio chain for the Champ seem to have flopped.

I have: dynamic mic>mic preamp>Behringer 2946>8W speech amp>Hammond 125C transformer>811 grids.

Seems functional but I can't seem, to get more than 50% modulation.

To  minimize the variables for testing, I slimmed it down to a 4V p-p 1Kc sine wave into the speech amp>transformer>grids.

In this config, I can get up to 200V p-p on the grids which is more than the data sheet says is needed but still only 50% modulation.

I was getting something like 80% modulation before I "fixed it".

The audio section in the Champ is turned off and the transformer leads snipped.  I brought out the grid pins and chassis ground to the outboard transformer.

What did I do wrong here?

js

need to see some oscope info .... positive swing vs neg swing at each grid .... exoect pos swing to be rolled off and smaller with neg swing looking like half sine wave (obviously with sine wave excitation) .... also look back at amp output to see if distorted .... measurements please

look at whats going on .... 4V pp drive yielding 200V pp is a voltage transformation ratio of 1:50 and an impedance transformation ratio of 1:2500... this means for a 8 Ohm output Z the the grid load should be 20kOhm ... this is too high of a transform ratio as the minimum grid impedance can be roughly estimated as Z=ExE/P however the positive going peak is much less than the negative going peak .... due to grid current .... guessing 100V peak positive gives Z= 100 x 100 /10 = 1kOhm minimum .... lower the turns ratio and increase drive power and see what happens
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K9ACT
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« Reply #18 on: July 05, 2018, 01:31:09 AM »


>need to see some oscope info .... positive swing vs neg swing at each grid .... exoect pos swing to be rolled off and smaller with neg swing looking like half sine wave (obviously with sine wave excitation) .... also look back at amp output to see if distorted .... measurements please

Seems like I am over my head here. Not sure what or how to measure it.

What I have described is measuring grid to grid as prescribed in the data sheet. I presume this means what it sounds like, not from grid to CT. I see no difference in the size, shape or position relative to 0 voltage no matter which way I measure it.

>look at whats going on .... 4V pp drive yielding 200V pp is a voltage transformation ratio of 1:50 and an impedance transformation ratio of 1:2500... this means for a 8 Ohm output Z the the grid load should be 20kOhm ... this is too high of a transform ratio as the minimum grid impedance can be roughly estimated as Z=ExE/P however the positive going peak is much less than the negative going peak .... due to grid current .... guessing 100V peak positive gives Z= 100 x 100 /10 = 1kOhm minimum .... lower the turns ratio and increase drive power and see what happens

By this you mean increase the speech amp gain?

I don't understand why lowering the turns ratio would increase the voltage at the output.

I have tried a number of different ratios and none get me where I need to go. Here is a link to a hook up table for the tranny...
http://www.hammondmfg.com/125.htm
I have tried 1-2, 4-5, 1-6

Can you suggest an appropriate one?

I think I did something dumb with the basic connection to the grids. I assumed these levels were high enough to be able to get by with the unshielded wire I had on hand but that was probably a bad assumption. Don't know what the wire is called and can't find what I want so I ordered a 10ft XLR cable that I will cut off the connectors and use what I need. The shield would be grounded to the chassis and the other end goes to the CT.

Thanks for your help,

Jack
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« Reply #19 on: July 05, 2018, 07:40:05 PM »

ok Jack .... starting with 811 data sheet .... the required peak to peak grid swing and power required to do it properly will define the minimum grid impedance and therefore the target transformer secondary impedance .... do the calculation

your initial setup with 4Vpp excitation is not the required drive power but just some milliwatts ... so calculate what the 8 Watts available can provide for a voltage swing at its favored load impedance (usually 4 or 8 Ohm)  remembering the rms to Vpp conversion

now you know the voltage ratio primary to secondary so choose the taps that will give you that transformation .... looks like 1-6 offhand
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« Reply #20 on: July 07, 2018, 10:26:04 PM »


I started on a Glub Chumpeon 350... Got part way through. It's still awaiting more attention.

Here's my take.

Remove the Couplates.
Throw in trash.
Remove the bandpass filter (the part with the choke).

Build up a standard speech amp circuit.

To drive the 811a tube, imho, you want to expect to run into AB2.
That means you will draw grid current.

The good thing is that the 811 can be driven quite well with a 6W4, or for more snot
a 6V6. A pair in PP as a driver is more than overkill.

Personally I'd not use an interstage transformer, and would opt for a cathode follower driver.
It's pretty simple. The good part is that the old transformer will work fine as a choke sitting
in the cathode of the driver tube. This assumes that you have something to create the + & -
phase drive.

In reality, one can make a circuit with NO choke in the cathode, and no resistor in the cathode,
the driver cathode goes to the grid directly! Cheesy

Another option is to use the IT to make the phase splitter, and use that to drive the grids of
the cathode followers, then all you need to do is to get the required voltage swing at the
follower that drives the 811 grids.

With about 900volts on the 811, you'll have a zero bias set up - no bias supply required.

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