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Author Topic: So I was given a Dentron GLA-1000  (Read 1938 times)
AE5JU
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« on: December 02, 2009, 09:00:21 PM »

... from Bob, a good friend and Elmer.  This was the guy that when I asked about what to put up for SWL'ing said, "Don't buy nuthin'... the ham club is going to fix you up."  He showed up the next day with a roll of RG-8/U over his shoulder and a big box of parts.  Next thing I know, I'm a ham.  It was all kind of a blur, but Bob was an instigator in this.

Now he's had to move into an assisted living place due to his wife's health.  He called me up, "I can't take this stuff with me.  I want you to have my amp.  I've got it disconnected, come over and pick it up."  I talked him into keeping his Icom HF rig and Kenwood 2m, to not give that stuff away just yet.

Really, I really appreciate this amp, but I'd rather have Bob around.

Anyway, it's a Dentron GLA-1000.  It has Raytheon 6LQ6's in it.  He says he used it earlier this year.  I found the manual online.  It says on page 2, Introduction, "...1000 watts DC CW input and 1200 watts input PEP SSB."

I've been warned to be cautious with the sweep tubes, not to push them too hard, and that they were expensive (they are) and the amp not worth the cost of new tubes.  So, what is "1000 watts DC CW input and 1200 watts input PEP SSB" in terms of real output?

What is the suggest maximum output?  The manual says 1.25 Amps on CW.  What do guys that have these amps actually suggest as a max, looking toward not damaging an old amp.

Also, it says max drive 125 watts.  My radio is 100 watts, so that should not be a problem.

Care and feeding instructions, and guidance to a tubey newbie appreciated.

Paul
AE5JU
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K0BG
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« Reply #1 on: December 03, 2009, 07:12:24 AM »

If I just had to use it, I wouldn't push it to more than 450 to 500 watts PEP out, and I'd keep the tune up times as short as possible. That is, a few seconds at most. Remember, for all practical purposes, the finals are nonobtainium.

Alan, KØBG
www.k0bg.com
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K5END
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« Reply #2 on: December 03, 2009, 08:27:32 AM »

Caution...I believe you will need a couple of things to "isolate" your 100W HF radio if it is solid state.

There is a bypass switch, ARB 704 (?) and you may need to match the output impedance of the solid state radio to the input of the Dentron tube amp. 

This is my understanding anyway. Check into it.

 
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K3JVB
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« Reply #3 on: December 03, 2009, 09:59:45 AM »

The rigs internal tuner should handle the match on input. But be careful keying it. A buffer relay may be the best insurance. Check the amps relay for voltage, and draw.

And as was stated prior, keep the full power tune up times to short, blips. Sweep tubes at full voltage can get soft quick.

Good luck-73
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AE5JU
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« Reply #4 on: December 03, 2009, 02:31:20 PM »

I'm already using the ARB-704 with a new Ameritron AL-811H.  The ARB-704 buffer came very highly recommended by a number of guys on a net I frequently check in.

Yeah, I was thinking 400 w or so might be more realistic.  I certainly didn't want to abuse it.  I was able to find a pair of Sylvania 6LQ6 NOS tubes.

Thanks, guys!

73
Paul
AE5JU
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ZL4IV
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« Reply #5 on: December 04, 2009, 12:37:51 AM »

email me, details on qrz.com and I will give you the info for the mod that makes the tubes last and solves a lot of problems. Don't listen to those that never owned one with the mod done. I cost me $4.00 to do it plus a little time. GLA is 'great little amp'!
73's Rex
ZL4IV
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AE5JU
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« Reply #6 on: December 04, 2009, 05:43:05 AM »

Email, sent... thanks!
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K5END
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« Reply #7 on: December 04, 2009, 01:40:49 PM »

The rigs internal tuner should handle the match on input.

Which rig's tuner, the radio or does the GLA-1000 have an input matching network?

Reason I ask is I have a GLA-1000 on the bench.

I've never used it for a QSO.

Just checked the power output when I bought it off a tail gate. I think it has a ripple on key down and therefore suspect the power supply electrolytic caps.

I plan to go through it thoroughly before getting on the air, so thanks in advance.

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K5END
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« Reply #8 on: December 04, 2009, 01:42:24 PM »

email me, details on qrz.com and I will give you the info for the mod that makes the tubes last and solves a lot of problems.

Hmm. You mind if I send an email asking for the same thing?

As I just confessed in the last post, I have a GLA-1000 I probably need to work on a bit.
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K3JVB
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« Reply #9 on: December 04, 2009, 08:59:45 PM »

I do not think the amp has a tuned input. I meant the transciever's tuner.

John
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W8JI
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« Reply #10 on: December 05, 2009, 03:25:22 AM »

I do not think the amp has a tuned input. I meant the transciever's tuner.

John

Some of them had tuned input.

The biggest problem with the GLA was the owner listened to Bill Orr. Orr somehow got the odd idea that the tubes would last longer if they always has cathode current, even when at idle, and if idle current was as high as possible.

Most GLA1000's ran at or past the rated dissipation of the sweep tubes while the amp was just sitting there in the operate position. This would eat tubes up.

Another Orr tactic was to tie the control grid to the cathode. While this did lower the effective mu of the tubes and allow higher drive, it also allowed enough feedback to be unstable on upper HF in some amps. This isn't an issue if you keep the loading control open far enough, but if you close the loading control up at higher frequencies you can sometimes make the amp oscillate.

The tubes are sweep tubes. They need evey bit of help running as cool as possible, especially short tuning times.

Tom
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