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Author Topic: Anyone convert a Dentron GLA-1000 to 50mhz  (Read 1645 times)
N1MT
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Posts: 5




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« on: October 24, 2003, 10:25:38 AM »

I've got an older Dentron GLA-1000B that has been collecting dust as my back-up amp. Has anyone ever converted on of these to 50mhz operation ??  Any info or experiences on what's involved in the conversion would be great.

N1MT@yahoo.com

Thanks, Mark
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WB2WIK
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Posts: 20540




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« Reply #1 on: October 24, 2003, 01:33:05 PM »

Didn't this use four sweep tubes?  If so, it could probably run about 200W PEP output power on 50 MHz after conversion.  If you have a 100W exciter, that obviously wouldn't be worth the effort (a lot of work for 3dB power gain).

(BTW, I make this assumption based on the fact that the only succesfully marketed 6m rig that used sweep tubes was the Drake TR-6, which used three of them, and ran the "heck" out of them, to produce 150W PEP output power.  So, if three sweep tubes can produce 150W, four should produce 200W.)

Although, maybe I don't remember this amp that well.  What tube/tubes does it use?

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N1MT
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Posts: 5




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« Reply #2 on: October 24, 2003, 02:27:39 PM »

Thanks Steve for the reply. Yes, it does use sweep tubes. Don't remember exactly which ones (not at home now). I didn't realize that sweep tubes became that inefficient at 50 megs. As you stated, its not worth the conversion effort. Thanks

Mark

ps. I saw your info about converting the SB-220 to 50mhz. Maybe I'll sell the gla-1000b and pick a sb-220 up and give it try. Do you have a good source for the Jennings vacuum variables, that won't kill me financially ??
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KO4NR
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Posts: 117




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« Reply #3 on: October 24, 2003, 03:53:02 PM »

Vacuum relay source on my web site as well as a lot of Dentron GLA-1000 series of amps information.

Maxi-Gain sells the Jennings RJ1A (as removed from equipment) for a little of $30.00 each.  I bought two from him and they have worked flawlessly.  His web site is on mine as a link.

If you want to convert the amp to 6 meters I would convert it using a Russian Metal Ceramic GI7B tube.  They are plentiful and inexpensive.  One on HF puts out as much power as four 6LQ6 tubes as orginially supplied in the amps.  The GI7B is much better suited to 50mhz.  GI7B tube conversion info on my web site as well.
73,
Bill
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K9FE
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Posts: 8




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« Reply #4 on: October 25, 2003, 08:16:34 PM »

The GLA-1000 series, with its 6lq6/6je6a tubes is pushing the limits of the tubes normally.  You would be lucky to get 250 watts on 6m and if you lose the tubes, they are getting hard to find unless you put out a good amount of cash for them.  I have a GLA that is now in the history rack.  The tubes are over $125 per set if you can find them.  The tubes are only rated for 30 watts each normally, so what do we do?  PUSH THEM TILL THEY LIGHT THE ROOM!

73 de K9FE Mike
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WB2WIK
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« Reply #5 on: October 27, 2003, 11:47:33 AM »

Re the SB220 conversion requiring a vaccum capacitor (and *not* a vacuum relay!), the Jennings vacuum variables, either glass or ceramic, in the 2-30 pF range, rated 5000V or 7500V, all work perfectly for this application.  So, you don't need one specific model of capacitor -- any of about a dozen models will do.  What you need is a rating of 5kV or higher, and a tuning range down to 2 or 3 pF.

I'll tell you how easy these are to come by, inexpensively: Last time I needed one for an NCL2000 conversion for my friend Mike, W6YLZ, I asked him to post a "want" on the internet, on some of the free ham radio websites.  He did, and two days later, he had the capacitor.  I think it cost him $30.

Good luck!

WB2WIK/6
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KA2LIM
Member

Posts: 13




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« Reply #6 on: October 27, 2003, 01:32:06 PM »

You need to look at a tube chart and check what the frequency range a paticular tube is good for when you are looking to convert a amp for 6 meters. The reason that a SB-220 works so well is that it uses 3-500Z's. Check the spec's for a 3-500Z tube aginst the tubes that are used in the GLA-1000 and you will understand why.
Ken KA2LIM
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W9GB
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Posts: 2581




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« Reply #7 on: November 03, 2003, 04:46:43 PM »

Bill does have a very nice site for everything you wanted to know about the GLA-1000 !!
http://www.geocities.com/ko4nrbs/

Lawson Summerrow / W4EMF also has great conversions of older sweep tube amplifiers to the the surplus Russian tubes (which are alot more capable and cheaper than 1970's TV sweep tubes).

w9gb
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