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eHam Forums => Amplifiers => Topic started by: W4CDI on August 08, 2010, 04:19:44 AM



Title: Retubing Ameritron 811
Post by: W4CDI on August 08, 2010, 04:19:44 AM
 :o
OK I'm going to re-tube my ameritron 811 and plan to re-tube using the 572b tubes. After reading all types of post on the many Brands of 572b's on the market, question now is which brand to use.
Open for all comments on which brand.
tnx's
w4cdi
Doug


Title: RE: Retubing Ameritron 811
Post by: KA5N on August 08, 2010, 06:44:28 AM
All new manufacture 572B's are made in China.  There are a few NOS (new, old stock) 572B's that can be found from time to time, most are 30 or more years old.   The Chinese tubes are labeled with various "brand names" which don't mean much since the tubes may have come from anywhere.  RF parts gives a warranty and Ameritron is probably a fairly good source.  Ebay has dozens of Chinese
branded tubes and some people swear by them, while others swear at them.
First off you will get no more power output by swapping to 572B's.  They have more plate dissapation
160 watts per tube, so you don't have to be quite so careful with them.  Otherwise there will be scarce
difference between  811's and 572's.
You pays your money and you makes your choice.
Allen


Title: RE: Retubing Ameritron 811
Post by: W4KVW on August 08, 2010, 08:25:43 AM
There is ONE BIG DIFFERENCE other than the price that I found.The amount of HEAT is MUCH "LESS" it appears coming from the 572Bs compared to the 811s.The 572Bs will LAST a VERY long time in an 811 amplifier for sure.I have NOT measured the temp difference but it's VERY noticable in my shack when running the amp hard for a while! :o

God bless,
Clayton
W4KVW


Title: RE: Retubing Ameritron 811
Post by: K6AER on August 08, 2010, 08:53:14 AM
In the amplifiers I repair, I have used 572B's from RF Parts and found them to very reliable.


Title: RE: Retubing Ameritron 811
Post by: W4CDI on August 08, 2010, 05:30:52 PM
 :D
Tnx's, think I'll go with RFparts
w4cdi
Doug


Title: RE: Retubing Ameritron 811
Post by: WB2WIK on August 08, 2010, 05:43:04 PM
New 572Bs from RF Parts have a warranty, so even though they're all Chinese stuff, if one fails you're covered under the warranty and most failures usually occur pretty soon.

I'd prefer NOS RCA-811As made in the 1970s.  They're really good tubes, if you can find them.


Title: RE: Retubing Ameritron 811
Post by: PA1ZP on August 08, 2010, 09:40:54 PM
Hi All

I have replaced the stock 572B in my al572XCE wich came with the amp, with new Chinese ones.
I bought 18 pces 572B in China.
One of them had a ratling anode, when sturdy but not to hard shaking the tubes anode hit against the glass.
1 of the tubes that came with the amp from Ameritron had the same defect but, so I finally found out what was wrong with my 572 because it had a nasty habit of making noise now and then in use.

12 of the 17 FB tubes went to some friends to use them both in AL811(H) or in AL572.
They worked FB
I didn't pay a lot for the Chinese tubes in compare to prices in PA (Netherlands) I saved over 50% on each tube.

In your case I wouldn't buy tubes straight from China but I would go for RF parts.
RF part prices are not bad at all, and cost for importing Chines and Post+Pack. and taxes will be enough to destroy your profit.
I wouldn't go fer NOS , prices are extreem high and falure rate due to gassing in time will be as high or higher as with brand new Chinese tubes.
And I really would advise you to use 572B's.
They do not give you more power but the tubes will last very much longer.
My first set of 572B's lasted 3 yrs and I gave them a very hard time in use, I never knew that one of the factory tubes was defective as delivered.
When replaced the original set would still give 800 watts key down in CW at 65 watt input to the AL572, but they wouldn't go any higher even when I would increase power input to 100W.

The new set goes to 1100 watts agn key down with 90 watts input power.


A few friends of me use 572B's in their AL811 and they get abused in contest and hard and long work, but they last for over 4 yrs now.

73 Jos  


Title: RE: Retubing Ameritron 811
Post by: KH6DC on August 11, 2010, 02:00:55 PM
Svetlana 572Bs from RF Parts.  These are premium Russian-made and you can get a matched trio for your AL811.  I replaced mine 9 months ago and they work fine.  heavier duty than Taylor Selects since Taylors are made in china.  Svetlanas has a white porcelain base, slimmer profile, thicker glass envelop and the insides looks heavy duty bomb-proof.  cost about $150 for 3.


Title: RE: Retubing Ameritron 811
Post by: K9RLB on August 16, 2010, 12:17:27 AM
With a 572B - it will always be mistuned in an AL-811(lack of plate voltage for a 572b. Also, there are circuit differences in the amps constructed to run 572B's and the amps constructed to run 811's.
All the 572B amps have a grid leak resistor in the control grid circuit to provide "self bias' for the tube.
The 811 circuit has the control grid grounded, so if a 572B tube is put in that circuit without the proper modifications done for the grid leak resistors then that tube (the 572B) Is gonna draw more current than it should and it's gonna draw current when it shouldn't.
I'd get a new set of 811a's, and take the money I saved and buy a 3898 tuning aid! That will make the tubes last longer.
Otherwise, plan on new 572b's at least every year or so.



Title: RE: Retubing Ameritron 811
Post by: K4RVN on August 16, 2010, 11:39:21 AM
K9RLB
Thanks for your informative post on the 572 replacements for 811A tubes. There are no free lunches in life so replacing a tube in an amp with a different tube requires some investigation. Looking at the 572 specs, I found nothing to disagree with what you said.
The Ameritron amp designed for the four 572 tubes provides 2500 volts for them while the 3 tube and 4 tube 811A amps only have 1500 under load. Also The rf bias is cut off on the 572 amp which documents to me what you said about bias differences required. The big difference in cost of the two amp designs should reveal a clue to many.
I had already ruled out putting 572B tubes in my AL811 three tube and have had good service with the 811As because I operate them below their maximum ratings. I'll spend my bucks on 811a tubes, a good peak reading watt meter, and good antennas and not look for a free lunch. To properly tune an Ameritron AL811 amp, you need a watt meter in my opinion.

73s

Frank


Title: RE: Retubing Ameritron 811
Post by: N3OQD on August 23, 2010, 06:17:07 PM
K9RLB states, "All the 572B amps have a grid leak resistor in the control grid circuit to provide "self bias' for the tube.
The 811 circuit has the control grid grounded, so if a 572B tube is put in that circuit without the proper modifications done for the grid leak resistors then that tube (the 572B) Is gonna draw more current than it should and it's gonna draw current when it shouldn't."   I beg to differ.  Not "all" but some are designed this way.  The Dentron Clipperton L and Dentron Clipperton QRO have directly grounded grids on their 572B's just like the AL-811.  Its just the QRO version (later version) has a tuned input circuit stock.  No one to my knowledge has had any real problems with those over their many years of use in relation to this particular subject matter of "self grid" bias.


Title: RE: Retubing Ameritron 811
Post by: AE5JU on August 25, 2010, 10:45:25 PM
I have two sets of 572B's, both Svetlana.  One set is from RF Parts, the other set from Frank K5SVC.  Both sets of tubes work well.


Title: RE: Retubing Ameritron 811
Post by: W6GF on August 27, 2010, 10:35:23 PM
Although 572s have a higher plate dissipation rating, the real benefit is their much high grid dissipation, so if you accidentally overdrive the amp, the 572s will probably survive.  You may cook the 811s.

Also, if an amp's  input is 1000 watts and the output is 700 watts, you are going to generate 300 watts of heat, no matter what tubes are used.

George, W6GF