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Author Topic: Dentron GLA-1000 Plate Voltage Drop - HV caps?  (Read 12660 times)
KH6AQ
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Posts: 7718




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« Reply #15 on: July 07, 2012, 11:36:15 PM »

Mouser stocks a suitable replacement for the Dentron GLA-1000 HV caps. 500 volt caps, as used in the Dentron, are not common but these 450 volt caps should work.

Nichicon
   
TVX2W101MDD

In stock and $7.86 each.


   
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K4DPK
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« Reply #16 on: July 08, 2012, 03:57:11 AM »

K4POZ has electrolytic filter caps for just $2-$3 each.  Best deal around.  I use them all the time, and they're high-grade caps.

Phil C. Sr.
k4dpk
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W3DBB
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Posts: 116




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« Reply #17 on: July 08, 2012, 05:49:30 AM »

Been running an original GLA-1000 with an Icom 737 in the basement station and it has been reliable.

RF Parts says do not exceed 70 Watts p.e.p. output per sweep tube in SSB service which is 280 Watts p.e.p. output for 4 tubes. My gut feeling is this is good advice. However the driving power is 100 Watts on peaks. IIRC the driving power of a linear amplifier appears on the output as pass-through power. 380 Watts output from the system is a good number to shoot for. This power level is achieved without a whole lot of fuss.

I am concerned about the original high voltage electrolytic filter capacitors and bleeder resistors as they are more than 30 years old. The high voltage reads 1125 VDC no load but it's replacement time for those aged components.

The bearings in the original fan were shot. It was replaced in the early going. The replacement is whisper quiet. I am willing to accept a bit more fan noise so I acquired another fan from the same vendor with ball bearings and greater airflow.

I shopped the Mouser store for:
647-LGN2H101MELB25
Nichicon aluminum electrolytic capacitors (3)
100 mFd, 500V, 20%, 105 degrees C
$3.82 ea.
I had to wait on a backorder for these.

Also:
756-W24-100KJI
Welwyn wirewound bleeder resistors (3)
14 Watt, 100 kilOhm, 5%
$2.25 ea.

The new replacement higher flow ball bearing fan came from All Electronics Corp., item number CF-282 ($18). They also stock the #382 incandescent lamps that slide into the rear of the GLA-1000 plate meter for 50 cents apiece.

 
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KD0PCJ
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Posts: 20




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« Reply #18 on: July 14, 2012, 03:49:38 PM »

Many thanks to all for their guidance as I worked to restore functionality on this Dentron amp.  Problem solved!  It was the filter caps...plate voltage is back up to 1100v from 800v, and RF output is back to normal.  Special thanks to W1QJ, K4DPK and especially K4POZ for the excellent deal on the caps and resistors. This was amateur radio at its best. 
73, and thanks again!
Mike
K0IVY
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KB4QAA
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Posts: 3306




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« Reply #19 on: July 14, 2012, 04:30:08 PM »

....Tubes are nearing unobtainium status and if found will be expensive. 
This is not true, of course.  A recent check of Ebay found dozens of 6LQ6 tubes.  Without any bargain hunting many were offered at "Buy it now' prices of around $40.  6JE6 tubes have typically been lower in price, in my experience.
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KD0PCJ
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Posts: 20




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« Reply #20 on: July 14, 2012, 10:45:00 PM »

Quite right, 6LQ6s are not at the unattainable point at all. My Swan 270 takes them too.  I've put together 11 spares over the past few months between eBay and local fests, three of which are 6MJ6 (the more robust version).  I didn't pay more than $24 for a single tube, and most between $15-20, a few for less, all pre-tested except for two and I lucked out on those.  Only paid $250 for the amp including shipping, considerably less than these often-defamed sweep tube amps are going for lately. Cheap power, for as little as I need/want.       
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QRP4U2
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Posts: 262




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« Reply #21 on: July 15, 2012, 02:12:31 PM »

I looked up the schematic on BAMA and it is a full-wave bridge PS.

I would also replace each rectifier diode with 2 1N5408''s and the 0.01 uFd 1kV ceramic caps while you are rebuilding the PS.
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AC0OB - A Place Where Thermionic Emitters Rule!
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Besides, when you're a Ham, you experiment with and improve boat anchors - that's what you do!. Smiley
KD0PCJ
Member

Posts: 20




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« Reply #22 on: July 17, 2012, 01:10:29 PM »

I looked up the schematic on BAMA and it is a full-wave bridge PS.

I would also replace each rectifier diode with 2 1N5408''s and the 0.01 uFd 1kV ceramic caps while you are rebuilding the PS.
Thanks for the suggestion.  Would you classify this additional work as being "thorough/for good measure", or, a "critical preventative" to avoid a potentially catestrophic failure? I'm assuming the two 1N5408s would be in series given the 1500v 3A original equipment?  
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K4DPK
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« Reply #23 on: July 17, 2012, 01:35:19 PM »

I looked up the schematic on BAMA and it is a full-wave bridge PS.

I would also replace each rectifier diode with 2 1N5408''s and the 0.01 uFd 1kV ceramic caps while you are rebuilding the PS.

Just curious....Why replace the diodes and disc ceramics?

Phil C. Sr.
k4dpk
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