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Author Topic: How to test 572B tubes?  (Read 9744 times)
K7ZRZ
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Posts: 279




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« on: July 16, 2010, 06:14:11 PM »

Another current thread has prompted this inquiry.

At some point I'm going to have to test through 2 sets of Taylor 572b tubes.  I have a Clipperton L in which I have had three sets of these RF Parts tubes (and one set of the original Cetron/Dentron tubes), and all of the Taylors have suffered from low performance, as a set, after a month or two of very judicious use... including specifically setting filament voltage to 6.3V.  The original Dentron tubes seem to still be better than all the rest after all these years.  Go figure!

Does anyone have a suggestion about how to go about testing these tubes - such as some kind or substitution method, or something else?

Thanks.

Brian K7ZRZ
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Brian K7ZRZ
K6AER
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Posts: 3498




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« Reply #1 on: July 16, 2010, 10:33:36 PM »

Quite a few years ago I had a heathkit tube tester made just for 811 and 572 B tubes. You could test conduction against grid drive, gain and frequency responce as well as heater brilliance. I believe it was a model SB-201. You might find a few of these still on the market.

Other that that you could just plug the tubes into your amplifier and see if the performance matcheds what is listed in the manual.

Also if your tubes are failing in short order you might be over driving them or pulling too much dissapation from the tubes.
« Last Edit: July 16, 2010, 10:36:20 PM by Michael S. Higgins » Logged
W8JI
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Posts: 9304


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« Reply #2 on: July 16, 2010, 11:07:14 PM »

Another current thread has prompted this inquiry.

At some point I'm going to have to test through 2 sets of Taylor 572b tubes.  I have a Clipperton L in which I have had three sets of these RF Parts tubes (and one set of the original Cetron/Dentron tubes), and all of the Taylors have suffered from low performance, as a set, after a month or two of very judicious use... including specifically setting filament voltage to 6.3V.  The original Dentron tubes seem to still be better than all the rest after all these years.  Go figure!

Does anyone have a suggestion about how to go about testing these tubes - such as some kind or substitution method, or something else?

Thanks.

Brian K7ZRZ

Oh boy. It looks like 572's are going downhill again. What did RF parts say?

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WB2WIK
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Posts: 20561




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« Reply #3 on: July 17, 2010, 03:53:52 PM »

Quite a few years ago I had a heathkit tube tester made just for 811 and 572 B tubes. You could test conduction against grid drive, gain and frequency responce as well as heater brilliance. I believe it was a model SB-201. You might find a few of these still on the market.


Cruel!
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KA5N
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Posts: 4380




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« Reply #4 on: July 17, 2010, 05:03:21 PM »

Best way to handle 572B tubes is like I did.  I found NOS Cetrons and bought them.  I have two SB-200's and two sets of spares for each.  Average cost was $50 and two weeks search per tube and I figure this is a lifetime supply, either mine or the amps.
Allen
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K7ZRZ
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Posts: 279




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« Reply #5 on: July 17, 2010, 05:51:30 PM »

Thanks fellas for the discussion.  I have been extra-ordinarily careful with this last set, NOT overdriving, NOT operating any mode but SSB, and that with just a few minutes daily on a couple of traffic nets, and a couple of easy qso's each day. The amplifier is well ventilated, filament voltage is at 6.3 volts, and my antenna system is ALWAYS presenting a 50 ohm load with no or very little SWR (using a good tuner for all opeations).

I do like the suggestion of finding NOS Cetrons, but hold little hope of being able to do that, and would expect to pay much more than the $50 a tube for any of those that are actually in good shape. Seems like paying for what is said to be NOS Cetron tubes would be more of a hazzard than purchasing Chinese tubes from RF Parts.  But....

I haven't contacted RF Parts since the last time I communicated with them over these tubes... and was told that they would have to have them back to make any kind of determination. The first time I returned tubes to them, they warranteed them, but insisted that it was my fault and that the amplifier was destroying them. I couldn't argue with them on the first go around because I had no proof that this was NOT the case. My position this time is that the amplifier is fine, and the tubes are crappy.  They're not likely to accept that position easily.

My hope is that not all of the 8 tubes are actually bad, and that I can put together one set of good ones out of the lot.  Maybe I'm dreaming.

Thanks again.

Brian K7ZRZ
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Brian K7ZRZ
PA7WWO
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Posts: 14




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« Reply #6 on: July 20, 2010, 10:20:11 AM »

hi to all

I use a AL572 with 4 572B's (chinese ones they came with the amp.) .
I needed a fresh reserve set of spare tubes.
As the Chinese 572B are for sale in the Netherlands for 75 Euro's a piece (more then US 100 dollars) , I tried my luck with a factory in China.
They delivered me 18 572B's for 24 US a piece, with taxes and transport the tubes came to 45 US a piece.

There was one bad tube in the 18 ones I bought ( I bought 4 sets of 4 and 2 reserve tubes for me and some friends here)
The anoe of this one tube rattled when I shook it and tapped it with my finger.

The rest of the tubes were tested in my 572B and after a warm up period of 3 hours without High Voltage they were tried.
All 17 worked just fine.
I found out that the origenal 572's of my amp. were warn out after 3 yrs of use and abuse, and I now use a new set of chinese tubes for abt 3 month now.
They do a FB job in the AL572 amp.

I found the manufacturer at AliBaba.com and the name was High Hope International located in Jiangsu.
E-mail contacts with Ms Wendy Lu were frequent and well replied every time I had a question.

Delivery and packaging was Quick and eccelent.
I think you must have a bit of luck with these tubes from China.
Production date of the tubes was early 2009.
It saved me and my friends over 200 dollars for every set of 4 x 572B tubes
« Last Edit: July 20, 2010, 10:22:05 AM by jos van den helm » Logged
K7ZRZ
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Posts: 279




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« Reply #7 on: July 23, 2010, 07:03:41 AM »

To the last fellow,

That's an interesting story. I looked all up the Alibaba thing, and they don't actually give a price for their tubes. You have to contact them for that information. I'm not sure why that is the case, but I might try something like that if I'm stymied otherwise.

SO....  does anyone have any suggestions as to how to test the (about 16) RF Parts tubes I already have?  (as I originally asked)

I have a Yaesu amp that uses two of them, and the Clipperton that uses 4.  Is it worth the time to try to cycle one tube at a time through one of the amps and then record some of the readings (output, plate current, idle current) at a set condition of drive and all other transmitting conditions?

Thanks again.

Brian K7ZRZ
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Brian K7ZRZ
KX5JT
Member

Posts: 217




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« Reply #8 on: July 23, 2010, 08:41:43 PM »

Quite a few years ago I had a heathkit tube tester made just for 811 and 572 B tubes. You could test conduction against grid drive, gain and frequency responce as well as heater brilliance. I believe it was a model SB-201. You might find a few of these still on the market.

Other that that you could just plug the tubes into your amplifier and see if the performance matcheds what is listed in the manual.

Also if your tubes are failing in short order you might be over driving them or pulling too much dissapation from the tubes.

I doubt you could use an SB-201 to test an 811 tube.
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K7ZRZ
Member

Posts: 279




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« Reply #9 on: July 26, 2010, 05:50:51 PM »

So I guess that's a no.
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Brian K7ZRZ
K0ZN
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Posts: 1543




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« Reply #10 on: July 26, 2010, 08:27:07 PM »

Hi, Brian...

You are in the exact same situation I am with 811A's.  Here is what I did; this crude but a little better than nothing.  First, after reading all the "stories" about current tubes and failure rates and after having one go gaseous and catastrophically short and take some components out in my AL-811, I decided to build a simple test fixture to at least run some basic tests on new tubes. I didn't like the idea of using the amp to test or "cook in" tubes. So, I simply bought an 811 socket and a 6.3 V filament transformer from RF Parts (prices were really pretty cheap, I thought), then mounted them on a small aluminum box with a 4 ohm power resistor in series with the transformer primary to provide a tiny bit of extra R in the primary circuit. It took about 20 minutes to build it once I collected all the necessary parts. Now, I plug new tubes in the socket and "cook" them for 12+ hours or so and cycle them on and off a several times. The hope here is that this low level "heat cycling" will cause any really severe defects in the tube to show up and fail in the test fixture and not in the amplifier. I also use a ohm meter to check for internal shorts between the tube elements. Admittedly, this a crude test but at least it finds bad filaments and obvious shorts and the 12 hour run with only the filaments on hopefully find any tubes where the vacuum had failed. I need to "up grade" this tester by building a small HV supply to get a better idea of lower gas level or internal shorts, etc.

Bottomline: Personally, I would rather build a homebrew project than REPAIR an amplifier that had been zapped by a bad tube.  Very obviously, this "testing" doesn't guarantee anything, but it seems a little better than doing nothing.     "Your results may vary...."

73,   K0ZN
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K7ZRZ
Member

Posts: 279




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« Reply #11 on: July 27, 2010, 10:06:28 AM »

KOZN,

Thanks for the details.  My situation is just a little different from yours, in that my problems (thankfully not shorts that have wiped out components) are related to performance reduction issues. I think I understand that this is caused by filament composition changes and/or depletion of certain materials manufactured into the filament wires - which is causing electrons to not conduct at the same level as they do when brand new, after a short period of use.

I'd like to be able to test THAT property of these tubes.  Someone brought up the subject of a tube tester, and if there was such a thing (older gear) that would test 572B tubes for that kind of performance, I'd be on the lookout for it.  So far, no one has gotten around to actually suggesting any particular tester, or other method for trying to sort out good tubes from bad ones, if there are such good/bad tubes in the bunch that I have - and not just ALL BAD tubes.

I did like your thinking about your little device, but I also do think that you need to go further with it to make it a really useful tool. Or at least, that's what some of the discussions I have read here and there are leading me to believe.

Thanks again.

Brian K7ZRZ
« Last Edit: July 27, 2010, 10:09:33 AM by Brian J. Ingoldsby » Logged

Brian K7ZRZ
K0ZN
Member

Posts: 1543




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« Reply #12 on: July 27, 2010, 10:06:15 PM »

 Hi, again....

Man.... these threads sound like something that hams would have been writing in the 1920's or '30's !!   "How can we accurately test tubes?!"

  Who would have thought?!!



73,  K0ZN
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VR2AX
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Posts: 586




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« Reply #13 on: July 28, 2010, 05:37:38 AM »

Why not test every tube individually by putting a single tube alone, one at a time, in your amp and measuring the standing or idle curent in your existing amp. You can then 'match' tubes according to the idle current that they draw. After that, it is a gamble what happens when you plug tubes that you have matched in the amp as a set and load up. Some are chosen, some are not. I can't see that it makes much sense to build a tube tester as the test will be what works, and what goes pop.
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K7ZRZ
Member

Posts: 279




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« Reply #14 on: July 28, 2010, 11:08:50 AM »

Why not test every tube individually by putting a single tube alone, one at a time, in your amp and measuring the standing or idle curent in your existing amp.

If you're asking me, I don't know why not... that's why I'm asking about this in the first place.\

The typical Clipperton L amplifier has the Idle current for 4 tubes set very low - about 40 mils seems to be common. One tube would barely move the plate current meter. I however, have made a modification to the bias circuit to bring that idle current up to about 120 mils (meter reading for 4 brand new tubes), and perhaps that reading for one tube would be enough to determine something...  but for me, I don't exactly know what.

Anyone else think this is a valid test?  And, how would I interpret the results?  If some read higher than the others, I suppose I could group those together and try them in the amp to see what the max plate current and output power would be at typical drive level. Perhaps that is the point of this suggestion. (thinking at the keyboard here, I guess).

Thanks.

Brian
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Brian K7ZRZ
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