Ameritron AL811 / AL811H

[YardDog]

Well I'm about to show my ignorance so bear with me for a few questions.
#1 Ameritron advertised their 811 tubes as fully neutralized and ready to rock. Many other manufacturers never mention this. Do the tubes have to be neutralized for my 811H?

#2 I've read that using 572b instead of 811 tubes is preferred in an 811h. They won't give more power, but are more robust. But I've also read that using 572b puts more strain on the rest of the amp. Is this true?

#3 My SB-200 has the original 572b RCA tubes that are fine, but I want a spare set on the shelf. I've never read anything about them being neutralized, but should they be?

#4 If I had tubes that were neutralized and put them in an amp that didn't require it, are bad things going to happen?

I don't work on amps and have no desire to know all the intricacies. I just buy them and use them. I'll pay someone else to handle the rest.

 

[nomadradio]

To get old school 811A performance today, you need to upgrade to 572B.

Been my advice for decades. Yeah, 811A tubes are cheap, and good 572B tubes are getting tougher to obtain.

Doesn't change the physics of the problem.

73

 

[nomadradio]

using 572b puts more strain on the rest of the amp. Is this true?

No. When operating at the lower voltage limit of the 811A it behaves exactly like one in all respects other than thermal robustness.

Neutralization sounded like a good idea, but all the 60s, 70s and 80s designs leave it out. Wish I could explain the difference, but the Yaesu, Heathkit and Dentron amplifiers are reasonably stable without it.

I'm sure Tom knew what he was doing including neutralization in the Ameritron designs, but I'm at a loss to explain why the older products got away without it.

73

 

[Shockwave]

Well I'm about to show my ignorance so bear with me for a few questions.
#1 Ameritron advertised their 811 tubes as fully neutralized and ready to rock. Many other manufacturers never mention this. Do the tubes have to be neutralized for my 811H?

#2 I've read that using 572b instead of 811 tubes is preferred in an 811h. They won't give more power, but are more robust. But I've also read that using 572b puts more strain on the rest of the amp. Is this true?

#3 My SB-200 has the original 572b RCA tubes that are fine, but I want a spare set on the shelf. I've never read anything about them being neutralized, but should they be?

#4 If I had tubes that were neutralized and put them in an amp that didn't require it, are bad things going to happen?

I don't work on amps and have no desire to know all the intricacies. I just buy them and use them. I'll pay someone else to handle the rest.

1) Neutralization takes place through a separate circuit in the amplifier. It is not a function of the tube. In others words, there is no such thing as buying a neutralized tube.

2) This is entirely up to the operator. The tube can handle more abuse and drive. The amplifier cannot. If the tube is the only thing that changes, the amplifier will never know the difference. All specifications are identical except for plate dissipation which is larger.

3) Spare tubes are always a good idea. I have a set for my FL-2100, however, the new ones will never last as long or be as robust as the original set of Cetron's, still in the amplifier since the 1970s.

4) You can't buy a "neutralized" tube. You can buy a neutralized amplifier. The neutralized Ameritron will have a metal plate that you can bend, located near the tubes. It is the bending of this metal, closer or further from the tubes, that adjusts the neutralization. This adjustment is very critical for a tetrode tube however, it's not very critical on a triode like the 811A. Although, slight variations in the manufacturing of the tube, can cause the adjustment of the neutralization to require realignment. The reason ameritron is saying their tubes are ready to go, is because staying with the same manufacturer, typically removes the need to readjust the neutralization.

Today, I'm pretty sure all of the 811 tubes are made by one Chinese Factory and the quality of the tube the consumer can purchase, is totally dependent on the third party tube distributor. That's because, they decide which specifications are acceptable to them. For example Penta Laboratories has a higher high pot test voltage then RF Parts.

Therefore when you buy the same tube from penta labs, it's typically more reliable. Also, getting RF Parts to take a tube back that hand grenades on you on the first try, is like pulling teeth! They want you to fill out a tube failure chart that looks like the tube data sheet. As though anyone is going to have all of this information recorded at the time of unexpected failure. So, I just put all the information for the tube data sheet, on their failure chart and then started buying from Penta. LOL! As if any of the other operating conditions matter, when the tube arcs the second you apply plate voltage!

 

[snippits75]

Regarding question #2 and the 811H.

The designer of the amp says to use three 572B tubes in the 811H. I forget which hole he said to leave empty. Tom was involved in a thread on Contesting.com, but I can't find the thread right now, and that's where I read about using three 572B tubes in the 811H.

 

[YardDog]

Thanks guys. I guess the claims of selling "Fully Neutralized" tubes is what had me baffled the most. And the info I'd read a few times saying that swapping 811A for 572B wasn't good for the amp didn't seem right, but figured I'd better ask the experts here to be sure. Looks like six matched 572B's should cover me for quite a while.

 

[AudioShockwav]

Also, getting RF Parts to take a tube back that hand grenades on you on the first try, is like pulling teeth! They want you to fill out a tube failure chart that looks like the tube data sheet.

My experience also, I had to push hard to get them to replace some 811's that had obvious faults.
And yes as far as I am aware only one manufacturing place left and quality requires that every tube be tested.
If I buy 811/572 tubes now they come from CTR engineering.
Tom has the equipment to properly test these tubes under operating conditions.


73
Jefg

 

[AudioShockwav]

Regarding question #2 and the 811H.

The designer of the amp says to use three 572B tubes in the 811H. I forget which hole he said to leave empty. Tom was involved in a thread on Contesting.com, but I can't find the thread right now, and that's where I read about using three 572B tubes in the 811H.

Tom has links to his stuff on his web site.

811A 572B 3-500Z Vacuum Tubes For Sale – CTR Engineering, Inc

73
Jeff