572b Tubes - hard to find quality & supply

[BoxHillBoy]

Hello all, I have Ameritron AL-811h amplifier (Quad tube) that I picked up. The tubes installed are 811a which are down on power, well used for many years.
I would like to change to the 572b tubes but finding a good tube at a fair price seems to be difficult. Most major Ham supply shops seem to be out of stock and there are many reports of Chinese tubes performing well for a very short time and dropping off a cliff with power not long down the track.

Then some brands seem to arc and carry on a lot more than others.

Can anyone recommend a 572b tube that is still available, performs like it should and not cost my first born?

 

[AudioShockwav]

https://www.ctrengineeringinc.com

The most reliable source I know of at this time.


73
Jeff

 

[Shockwave]

All of these glass tubes are made by one of two low end Chinese manufacturers and are simply rebranded to the distributors name. While they have a decent 3-500Z, the 572B has proven problematic with these manufacturers.

Because the dud rate on the 572B is so high, as Jeff points out, it matters who you buy from and what they consider acceptable voltage breakdown and cathode emissions to be, prior to resale.

Places like RF Parts are under enough pressure to move stock that they will sell you tubes that just barely meet usable breakdown voltages with no headroom to account for a poor match or overdrive condition.

If the vacuum is just strong enough to prevent arcing, it's not meeting the standards required to provide extended tube life and internal contaminants will quickly degrade cathode emissions.

KB1SEL who operates an amplifier repair business and replaces many of these tubes every week for customers, no longer uses RF Parts for the above reasons and the fact they are resistant to ligitimate returns. He now buys from Penta Labs with much better results and service.

 

[BoxHillBoy]

So after reading forums and suppliers product descriptions Ameritron dont disclose where they get their 811a and 572b tubes from and its a lottery on what you are going to get supplied in your new amp. There is no stocks of many of their tube amps and delivery seems to be slated sometime between July - September and im tipping it might be tube supply as they cant supply replacement tubes if needed. I dont know if its true but after doing reading it sounds like the 572b tube compared to a 811a is a little easier to manufacture? So it seems my search goes on

 

[BoxHillBoy]

All of these glass tubes are made by one of two low end Chinese manufacturers and are simply rebranded to the distributors name. While they have a decent 3-500Z, the 572B has proven problematic with these manufacturers.

Because the dud rate on the 572B is so high, as Jeff points out, it matters who you buy from and what they consider acceptable voltage breakdown and cathode emissions to be, prior to resale.

Places like RF Parts are under enough pressure to move stock that they will sell you tubes that just barely meet usable breakdown voltages with no headroom to account for a poor match or overdrive condition.

If the vacuum is just strong enough to prevent arcing, it's not meeting the standards required to provide extended tube life and internal contaminants will quickly degrade cathode emissions.

KB1SEL who operates an amplifier repair business and replaces many of these tubes every week for customers, no longer uses RF Parts for the above reasons and the fact they are resistant to ligitimate returns. He now buys from Penta Labs with much better results and service.

I have sent Penta Labs an email, to make things a little more difficult im in Australia so I need to make sure they will send to me, thanks for the lead

 

[BoxHillBoy]

https://www.ctrengineeringinc.com

The most reliable source I know of at this time.


73
Jeff

thanks for the link I have sent them an email, im in Australia so checking if they will ship to me

 

[Shockwave]

I dont know if its true but after doing reading it sounds like the 572b tube compared to a 811a is a little easier to manufacture? So it seems my search goes on

The two tubes are both constructed exactly the same. The only difference is the material the anodes are made from. The trouble with the 811A, is a real one hasn't been made since the 1970's.

Everything after that date, skipped the six pieces of metal, bent to form horizontal radiators on the anode while also preventing them from deforming.

Companies are hesitant to disclose the tube source because they're all coming from the same garbage manufacturer in China. The only difference is the resellers testing standards and their willingness to reject anything marginal.

 

[AudioShockwav]

Here is a vid about the 811/572 tubes from Tom.
It's got a lot of good info about how the tubes are constructed.



( Tom is the guy who designed the 811 and 811H amps)

The last 811 tubes I bought years ago from RF Parts were new old stock RCA JAN tubes..
Problem was that when I got the them, one tube, out of the box had a blob of solder floating around in the bottom of the tube.
Literally you could shake the tube and see this bouncing around inside the glass.
RF parts gave me grief about a replacement tube.
I got a little bent with them on the phone and they did not respond well when I asked them how the tube got past there Inspection and testing process.
I did finally get a replacement tube, but that was the last tubes I ever bought from RF parts.
Tom may charge a little more than others but I feel confident that he tests each tube completely before it leaves the shop.

73
Jeff

 

[Shockwave]

With RF Parts, the customer is NEVER right. Even when the defect in the tube, is an obvious manufacturing issue. They beat me once on defective tubes and worked hard enough to avoid responsibility, that I won't even trust them to buy a tube socket, let alone any tubes.

 

[BoxHillBoy]

Has anyone heard or know of the quality of Machlett tubes, their website says they are owned by Penta labs so I would imagine they are from the same manufacturer? http://machlett.com/history.html

 

[W4KVW]

Hello all, I have Ameritron AL-811h amplifier (Quad tube) that I picked up. The tubes installed are 811a which are down on power, well used for many years.
I would like to change to the 572b tubes but finding a good tube at a fair price seems to be difficult. Most major Ham supply shops seem to be out of stock and there are many reports of Chinese tubes performing well for a very short time and dropping off a cliff with power not long down the track.

Then some brands seem to arc and carry on a lot more than others.

Can anyone recommend a 572b tube that is still available, performs like it should and not cost my first born?

RF Parts is not CHEAP but they come with a Warranty unlike most places.I had an 811H for about 12 years or more & I tried a New set of 572B's in it & I was really disappointed that they did not last very long compared to the 811A's that were in it. They ran a bit cooler but for my money I went back to the 811A's from Ameritron & they were very dependable & fairly priced as well.

SIX-SHOOTER
aka:W4KVW
aka:WRMX520

 

[Robalo]

811A's from Ameritron & they were very dependable & fairly priced as well.

yes me too !!

 

[BoxHillBoy]

I just ordered some 572b tubes for the Ameritron AL-811h amplifier through Penta labs. What a great company to deal with and even offered fair pricing to ship them to me.

I also found out that Penta labs now own Machlett tubes now and they are in their words...very similar tubes to the Penta branded tubes.

Thanks Shockwave for pointing me to Penta labs.

I also ordered some Russian made 811 tubes that are suppose to be very old stock, 1970's, they were very cheap, $105.00 for a set of 4 including shipping.

After reading many post lots of people have bought these Russian made tubes and are happy with their performance and longevity.... guess I will be finding out

 

[Mr Fix it]

All I use is for my customers amplifiers are penta labs 3-500z and 572b tubes

Yet to have an issue with one of their tubes , they also have fantastic customer service

You can take that to the bank as I work on a LOT of amps that use these tubes

YouTube Amprepairguy

 

[Mr Fix it]

Besides China 572b tubes not having the same cathode emission life as a cetron. They aren’t a bad tube

Believe it or not , most of the issues people have aren’t due to them being made in China . They are due to issues with the amplifier for example grid loading resistors out of tolerance or open, parasitic suppressors out of tolerance or open , grid pin clip on socket for tube spread and not making a good connection to the pin.

Other failure causes I see, on almost a daily basis are, abuse, putting the amplifiers output into a open or into a crazy impedance mis match .

Then band switches , air variables, tubes etc etc start flashing.

I have installed hundreds of 572b China tubes over the years. I have yet to hear a customer say they had one fail out of the blue.

But installed only after I completely went through the customers amplifier .