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Author Topic: 572B upgrade for twin 811A amp  (Read 3253 times)
VE3LYX
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Posts: 160




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« Reply #15 on: November 18, 2014, 07:45:59 PM »

Back to the problem at hand. The input cap checked out fine. It would appear I smoked the tubes on the mismatch. So I will double check a couple of things but I think I will be buying new tubes and they will be 572Bs. I have power B+, I have heaters. I have a good input circuit. I have a good output circuit. Not much else it can be unless I have missed something. I had a 211A runaway on me last Christmas. It was gone in an augenblick.  Found a source for the 572Bs that I trust. Now to break into my piggy bank.
don
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WB6BYU
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« Reply #16 on: November 18, 2014, 08:39:30 PM »

Did you blow out your current indicator lamp?
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W4FID
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Posts: 138




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« Reply #17 on: November 19, 2014, 04:31:28 AM »

A key to consider is the power supply. Many Collins 30L-1 guys swapped the 811As for 572s expecting to run a little more power but found out the power supply wasn't stiff enough to handle extra power. The 572s were more rugged -- good ones may last longer -- but without enough horse power in the power supply you'll still be at the same RF.
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W8JX
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« Reply #18 on: November 19, 2014, 04:38:44 AM »

A key to consider is the power supply. Many Collins 30L-1 guys swapped the 811As for 572s expecting to run a little more power but found out the power supply wasn't stiff enough to handle extra power. The 572s were more rugged -- good ones may last longer -- but without enough horse power in the power supply you'll still be at the same RF.

If proper cooling can be maintained you would not need 4 of them as even 2  572's have greater dissipation than 4  811's
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You can embrace new computer/tablet technology and change with it or cling to old fall far behind....
VE3LYX
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Posts: 160




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« Reply #19 on: November 19, 2014, 05:13:25 AM »

Did you blow out your current indicator lamp?
I  didn't check that but will this morning. I had blown the bulb I usually run sometime ago so had a much heavier (hi MA) in the hole just to keep my fingers out of it. There is a good shunt behind it so the Amp runs fine with no bulb anyway. The Source, our radio shack stopped selling the bulbs last fall. I wish I had bought a dozen of so as I find them very handy.
The PS is very stout. Does even get warm even after a long transmission.
don
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KM1H
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Posts: 73




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« Reply #20 on: November 19, 2014, 09:59:00 AM »

Quote
If proper cooling can be maintained you would not need 4 of them as even 2  572's have greater dissipation than 4  811's

Not necessarily as the Chinese rate them at 125W Pd and RFP and others claim 160. The Shuguang with the thicker anodes Ive mentioned may be uprated andthe actual tubes RFP is now importing. I wont know until I get a pair side by each, as they say up north, to compare under magnification.

Carl
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VE3LYX
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Posts: 160




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« Reply #21 on: November 19, 2014, 05:07:56 PM »

Found a couple of blown resistors in cathode circuit. Unfortunately I don't have any low value resistors. I will have to order a bunch.  Indicator bulb is still good BTW.
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VE3LYX
Member

Posts: 160




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« Reply #22 on: November 20, 2014, 06:11:35 PM »

I found some heavy duty 10W 10ohm resistors in my supply of weird stuff. It took a bit of rework but I got them installed. Wow. Fired it up and warmed up the DX60B. Put it on the dummy load and got just over 100W resting carrier. Never had that much before. Rechecked tuning and got a wee bit more. I wonder if this has been a weak spot for a long time and finally blew with the mismatch. Anyway, I am back in business and out of pocket 0$. The things you can fix with patience and a meter! I will keep the 811As for now. maybe next time.
don
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KH6DC
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Posts: 666




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« Reply #23 on: November 21, 2014, 03:16:07 PM »

I replaced chinese 811As in my 16 year old Ameritron AL-811 with Svetlana 572Bs several years ago and it ran for a couple more years until I sold the amp.  I believe it's still working as of today.
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73 and Aloha,
de Delwyn, KH6DC
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