W8Jx seams to pick my post apart, but the facts are the facts.
If an 811 and a 575 are kept within there operating parameters the useful life is the same. They go soft due to a loss of electron emission. I in no way said the 2 tubes are created equal in dissipation.
The flaw here is that in typical usage in a AL 811 the proper operating parameter on a 811 is exceeded a good bit so all bets are off on same life of tube. very few if any 811's live long enough to get to end of emissions life.
In note 2, I was not misleading in any way.
Yes you can drive a 572 harder. This will stress the rest of the amp as expected. The difference in an amp designed for an 811 verses a 572 is primarily plate voltage. I had stated a 3 tube 811 is only a reasonable >500 watt amp with 400 to 450 watt much more realistic.
No argument there but few do this and follow Ameritrons ratings and put pedal to the metal. By far there is more complaints of AL 811 amp problems and tube failures than all other amps rolled up.
In note 3 I said a 572 was no more or less dependable.
“Not true” I beg to differ. Again I said running in a conservative manor in SSB. This statement is true and as long as the tubes are ran within manufacturers specification the tube life will be approximately the same. As for 572s being more strain on an amplifier. I should have qualified this statement by saying the 572 can be driven harder causing more strain and yes 3,572 can be driven hard causing more strain than 4, 811 in either case this will cause a greater B+ drop causing problems not only mechanical but in a much more distorted output. But then again that is a case of abusing the amplifier.
By design the tubes in a AL 811 are not running in the "zone" unless you greatly reduce power but even then you can still easily greatly exceed tubes rating during a tuneup especially with many modern hams that have little understanding of how to tune and use a amp. A proper amp does not have tubes that are so easily damaged from plate current. As far as straining power supply you can run three 572's at same level as 4 811's and with far much less stress on 572's. If you run 4ea 811's at 700ma too you will greatly exceed tubes rating and shorten life. With 3ea 572's they are just getting warmed up. As far as abusing a amp, by design a AL811 as rated by Ameritron, you are abusing the 811 tubes in amp if you follow their guide lines. Swap to 572's you will have a hard time hurting tubes.
As for holding its value. Just look at the price they are getting for a used 811, In my opinion quite high for such a marginal amp. Yes the SB200 holds its value due to quality and nostalgia. I did not say sell it and find something like a SB200.To trade a modern 3, 811 designed for 811 for an amp designed for 2, 572 is a marginal improvement. I mentioned replacement with a sb220 or similar.This is a considerable different amp with 2, 3-500z.
Lets see a AL811 "rated" at 600 watts with 135 watts total "continuous" rated dissipation and a 1600 volt power supply vs a SB 200 with 320 watts continuous dissipation and a 2400 volt power supply is a marginal upgrade? Get real.
In my early days as a ham and when tubes were a lot cheaper. I built several 811/ 572 amps with tube counts ranging from 1 to 6 tubes. I also set up a test stand just to play with the 811/572 tube as several were damaged over the years. In all test the 811/572 could take a lot of abuse but this is not about how to melt a tube is it? Just a side note. I recently donated a 2, 811 tube amp that I built in the early 80s. It was only used at or just over 200 watt and still had one original US made 811 and 1 Russian 811.
Once again you are depending on tube being run within design ratings which a AL811 does not at factory ratings.
I stand by all my earlier statements as to the dependability of the 811 verses the 572. The 3 or 4 tube Ameritron 811/572 foundation is designed for the most bang for the buck. Not for longevity. They sell well for this reason. Most who start with a beginner amp such as an Ameritron 811 will eventually go with a better amp or due without an amp all together.The RF deck nor the power supply will take a lot of abuse.
AL811 amps provide the least bang for buck because they experience the highest failure rate of any amp of tubes in them which raises true price of amp a good bit. It is best to avoid AL811 completely and buy a real amp.
John while I have a great respect for you, your electronic and technical skills. I must disagree on your evaluation of this amp and the choice of tubes. Replace 811s with 572s and raise the plate voltage in an amplifier that can handle the strain. Use it as such and enjoy it. Do that in am Ameritron 811and be prepared to spend some money. If anyone has done this. I am interested in a Ametitron burn out. To use the case and meters on another project.
You could install a higher voltage power supply you could make a nice solid 800 watt amp with 3ea 572's and need less plate current and less drive to get there too. At no time did I suggest turning it into a kilowatt+ box.
This is not to say that it would not improve the dependability of this amplifier to change to 3, 572s. It will help with operator error in tuning and help with a bit more duty cycle as far as plate dissipation. It will not produce more wattage out for the same drive as with 811s. It will give the impression as putting out more because the average amateur will see the 572s with no appreciable plate color and drive the amp harder.
A bit more duty cycle? With proper cooling the power supply is limit of duty cycle not the 3ea 572's in a AL811. Also, you keep detouring that a AL811 needs same drive for same power with 572's but you skip that if you follow Ameritrons rating using 811's you better have a drawer full of spare tubes. With a good trio of 572's you need no spares. In 25 years of using amps with 572's I have never had one fail on me. Tubes in my Dentron are dated 1985 and still going strong.
