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Discussion in 'Amplifiers' started by airplane1, Mar 8, 2009.
Is that what I look for??
I did use the amp on am but the instructions dont say any thing about it. will this hurt it?
Can I still use the tubes for a while or should I chuck them and get new tubes?
There is a reason for that,that amp is NOT a good candidate for use on AM.The 811A's will take a real beating if you run the carrier over 75-100 watts. Remember that the pep rating of an AM signal is four times the carrier so 100 watt carrier equals 400 watts pep for AM.The amp is rated for 600 watts flat out but you MUST leave some headroom when running AM.The 811A's will take a beating but it is very common to actually blow holes in the plates by running them too hard in high duty cycle modes like SSTV or AM.
I am getting one of the Mr pecker tuners, if you do a search you can find it on the net. the thing got all 100% good reports on eham reviews and it makes it hard to blow up the tubes.
I did want to use it on AM though, if I run it with low exciter power will it work or is it not a good idea to uae it on am?
And please advise as to can I run the tubes with the little blisters till they go totally bad or do I need to replace them right away?
Ain't that the truth! I have seen the glass soften and suck inwards until the point of failure but on an 833A tube instead. Some guys will replece the 811A's in those amps with 572B's. They are basically an 811A on steroids and are a simple drop in replacement. This gives about two and a ahlf times the plate dissipation rating and if graphite plates are used should last forever in that amp. You will NOT gain any more power output due to the supply voltage and current capability but the tubes will be worked far less harder.
Are you talking drive levels INTO the amp?
You can run the damaged tubes but you must realize that there is now a weak point in the plates and meltdown will be easier to obtain.See my suggestion above about 572B replacements. They cost more but are worth it for high duty cycle use.The plates of the 572B's should not even show ANY color at max output in that amp.
Tune the amp up properly and then run whatever drive level you need to see about 100 watts carrier out of the amp and cross your fingers until you replace the tubes.
When you say they have more plate dissipation rating what does this mean?
Will I tune the same way as with the 811 tubes?
Then will I be able to use them on AM because of the higher duty cycle?
I know, so many questions. Please bear with me I just want to learn some thing here.
The output of a tube depends on certain things. The voltage on the plate being one of them. 811's use less voltage than 572's, which means that the 811's voltage on the 572's plate won't give you full output, or even as much as you can get from an 811. So, running those 572's with 811 voltages will always mean less output than the 572's are capable of. It also means that they are just sort of loafing along, and will last longer than an 811 under the same conditions.
Sound like a really good idea? It ain't bad, but there are some 'catches'. Using 572's in those conditions also means that the resulting signal will be a little bit 'wider' than if the 572's were run correctly. Nothing really noteworthy, but still there.
An Ameritron AL-811 can be 'modded' to run 572's at their normal levels (voltages,etc.), but there are definitely 'catches' with that! The simplest 'mod' is to change the primary voltage on the transformer to produce more secondary voltages. The 'catch' there is that it also raises the filament voltage and that ain't good at all. It will also result in more heat production than the stock fan can handle, and push several other components at -least- close to their ratings if not over. There's more to it than appears on the surface, sort of. Best advice is to don't do that, just get a 572 amplifier. Or a 3-500 amplifier, more better. Or a 3CX1200 which is probably the biggest 'forgiving' tube that's common.
Why do I think I know a little about 811's? Cuz I've got AL-811, serial number '13' sitting on the desk over there. I've cussed that thing since the day I got it. But it worked, and still works after what, 20 years? The later ones are not exactly the same, my wrecking this one so many times is probably one of the causes for that. It's also been replaced by an AL-80A, and now an AL-80B. (That AL-80A was used by a friend to drive a really 'big' amplifier, believe it or not. Don't ask, I have no idea what tube was used in that thing.) None of that's bragging by the way. Well, maybe the #13 thingy, somebody has to be one'a the first idiots to buy something. Right?
It ain't easy being an idiot!
If I want am power I will get a solid state amp for that mode.
The filament structure is functionally identical. Same for the grid
811A Mu = 160 572B Mu = 170. Numbers vary a little depending on the source.
You can certainly pop a 572B into a circuit which uses an 811A without modification. If the 811As in your final are melting, switch by all means.
The 572B can take a lot more voltage than an 811A but it does not need it to work properly.
Some offshore and even onshore manufacturers change the specifications slightly. IMHO the Asian 572B might have a higher Mu than 170. This means it needs a lower bias voltage to achieve rated idling current, will drive easier and will also take marginal parasitic stabilization components over the edge. Read FL-2100.
BTW Doc,sorry to hear that you were the "lucky" owner of serial # 13. Man, I would have returned it as soon as I saw the serial number and bought another one. By then it would have likely been serial # 666.
I think A search is at hand tonight to find a good price on the net. What is matching sets??
Ameritron shows them on there site but they are more expensive.
Modern manufacturing should be able to hold tubes of similar type and vintage to a match without any further manipulation.