Globe Champ

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WD5JKO:


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
Wd5JKO

Steve - K4HX:
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.

WD5JKO:

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
Wd5JKO

K9ACT:
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

w4bfs:
Quote from: K9ACT 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


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  ;D ??? ;D

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