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Author Topic: CHINESE HF-2013  (Read 3214 times)
K1ZJH
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Posts: 1934




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« Reply #15 on: April 06, 2015, 12:32:42 PM »

Was he tuning the amp when that arc over occurred?  Correct antenna selected?

I'd wonder if that voltage surge you are seeing is simply the blocking capacitor charging?  There should be an RFC across the Pi-Net output, regardless, for safety reasons to shunt DC to ground in case of failures.

Pete
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W1QJ
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Posts: 1768




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« Reply #16 on: April 06, 2015, 12:51:55 PM »

OK, I could not get the friggin coax cables on the SO-239's.  The first few threads were stripped.  No way would they go.  I have no idea how the last tech ever used the amp???  So he claimed he could only get 800 watts out on 40 meters.  Anyway, I borrowed a 5/8-24 die from buddy down the road.  I cleaned up the first few threads and the PL-259's went on a little better but then stopped again.  I had to chase the threads all the way to the end.  Once I did that the PL-259's went on perfectly and jiggling the connector it was solid and the ground was tight.  NO WAY THE LAST TECH HAD A GROUND.  So  now that I got the coax cables tightly in place I selected a band that had nothing to do with the burned contacts or the secondary blocking cap.  That was 10mhz.  It has a separate 10mhz tap on the band switch.  Well, the amp works beautifully.  38 watts drive an 2200 watts out no pain no strain.  I'll try some other bands but my guess is the last tech had no ground on the feed line.  The band switch needs to be changed now anyhow but I think this looks like operator error or something.  Too bad.  More info as I gather it.  BTW.... it appears as though the SO-239's were metric but they are not anymore.  Hi hi   Lou
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G3RZP
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Posts: 5920




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« Reply #17 on: April 06, 2015, 02:39:53 PM »

Lou,

Just a thought.......Some years back, we had a load of N type connectors appear here, all very cheap. The threads on them were NOT 5/8-24 but were cut on a metric lathe without a 127/128 change wheel and so came out as a non-standard but metric dimensioned thread. Could this be what happened on that amp?

Hard experience tells me that if the workshops find something 'too difficult' or 'too expensive', they go their own way. One that got me is where the drawing called up a Teflon insulator: after I had a problem with wrong results and got on to them, I was told "we haven't got Teflon but it's a white plastic and we have some of that, so that's what we used". At 400MHz, and the hot end of a quarter wave resonator, there is a BIG difference! Another one was an RF Choke calling up SRBF (Synthetic Resin Bonded Fibre) or Tufnol: they used some weird stuff that softened at 45 deg C and the equipment had to operate to a +55 deg C ambient close to a pair of glass tubes dissipating 125 watts each. They do get very pi**ed off when you refuse to authorise payment until they produce exactly what they quoted for.....
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N7EKU
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Posts: 262




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« Reply #18 on: April 06, 2015, 05:20:35 PM »

Yep,

Those are not standard UHF connectors, but metric ones.  I had one of these on a Youkits transceiver.  You can read about them here:  www.w6ze.org/btt/BTT008.pdf  That document is from 2010, so the problem has been around for awhile.  For sure replace them with the standard types unless your die work went OK.

That would cause a big probem as the is no secure ground unless the plug base is tight up against the socket.  The push on adapters work OK on these -- they don't go on all the way either and depend on just the threads touching but work OK for qrp.

The manufacturer should be told about this problem if they plan to sell these over here!

73,



Mark/n7eku



« Last Edit: April 07, 2015, 12:57:53 PM by N7EKU » Logged
W1QJ
Member

Posts: 1768




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« Reply #19 on: April 06, 2015, 09:26:47 PM »

Well, there is no doubt that those So 239's were metric.  I borrowed a 5/8-24 die from my ham buddy down the road.  He has a nice little machine shop and had the die.  I ran the die all the way down the 239 and it worked like a charm.  SO that problem is solved.  Once I did that I hooked up my cables to the amp and I selected to try 10mhz, The amp has a separate tank coil tap for 10mhz.  On that band there is no association with any part of that rear wafer that was all burned up.  Just as I thought, the amp worked great.  When I switched to 20 meters where half of the plate choke is shorted out I saw the switch arcing badly.  Speaking with another ham about the tank circuit design we concluded that we did not like something we saw.  He pulled an Alpha 99 schematic he had and low and behold this amp and the OM 2500 is pretty much the same design.  But on the Alpha they did what we would have done when we discussed the design we did not like.  SO there was a difference there.  Tomorrow I will be changing the circuit a little bit to make it like Alpha.  We think that perhaps this flaw could be causing the problem.  We will see.  It si amazing how all these companies copy each other.  This amp is looking for a DC ground for the 3 one meg resistors in the tank circuit.  instead of getting a DC ground directly to the chassis like Alpha does, they ground the resistors through the 3 tank coils and then it finally finds it way through the safety choke to ground.  HUH??? Huh
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G3RZP
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Posts: 5920




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« Reply #20 on: April 07, 2015, 12:35:54 PM »

Lou,

the only really sensible (in my opinion) comment about going metric was the USAF in the 1970s:

"We'll do it if it doesn't cost us anything".....

Metric coarse is too fine to be really useful: UNC or BSW is far better. For small sizes (under 0.25 inch), British Association (BA) is stronger (because it is a 47.5 degree pitch angle), is the only rational thread (0BA is 1mm pitch, 1 BA is 0.9 mm pitch, 2BA is 0.81 mm pitch etc) and BA is metric anyway, being originally the Swiss horological Thrury thread.

Change for the sake of change........
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W9GB
Member

Posts: 2807




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« Reply #21 on: April 07, 2015, 01:17:54 PM »

Lou -

Of course, there is also the metric dimensioned coaxial cables,
 that have appeared via some Asian radios.
I see that Belden now has 2 spec sheets for their
coax cables (English, metric) to educate the Asians, OR translate for USA..


greg
w9gb
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KM1H
Member

Posts: 508




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« Reply #22 on: April 07, 2015, 02:07:41 PM »

Metric PL-259/SO-239's have been around since the 70's when Jap equipment started arriving enmasse; some had the proper SAE threads. Even in the 80's some Kenwood gear used metric including the TL-922 amp which also had a metric RG-8 type cable available.

Carl
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W1QJ
Member

Posts: 1768




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« Reply #23 on: April 08, 2015, 03:42:07 AM »

Metric PL-259/SO-239's have been around since the 70's when Jap equipment started arriving enmasse; some had the proper SAE threads. Even in the 80's some Kenwood gear used metric including the TL-922 amp which also had a metric RG-8 type cable available.

Carl

Maybe so but even the Jap version of the 922 I got hold of via the Philippines had regular SO-239s.  This Chinese amp had metric until I chased the threads with an SAE die.  This amp is a knock off of the OM-2500 and the OM-2500 is a close knock off of the Alpha 99.  Alpha started with a weird type of split plate choke which required a series of resistors apparently to load down a hanging capacitor when not used.  Don't know why they did not use an Ameritrion type choke instead.  But I think the later 8410 did use one.
A lot of copy cat goes on in EH and China.  One board in this Chinese amp actually has OM Power on it.
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