Discussion in 'Amateur Radio Amplifiers' started by AC2MM, Dec 30, 2018.
I get 1KW PEP out and plate dips to 1450 volts. About 1500 volts plate with 800 watts PEP out
Out of curiosity, what's the grid and plate current under those conditions?
Also, are you measuring power going into a dummy load?
Grid was I believe was about 15-20ma- very low with Cetron 572B. RCA 811A had much higher grid current. I do not remember peak plate current, but I think around .75 amp- went to top of scale on peaks. Ham station is not set up at the moment due to recent move. I tune for max watts out.
Sometimes I will upgrade for reasons other than higher power output, like longevity.
In the case of the 811, the increase of longevity would be from the 527 tube being able to sink higher power in the plate which allows less hurried tune up cycles. Without modifying the power supply and bias, you won't see higher power output.
Just like the output transistors in some transmitters, I upgrade some for higher SWR handling capability because the originals had the nasty habbit of burning out when the SWR went too high, again, just because the transistors had higher power capability, the output power remained the same without modifying the power supply and bias circuits.
Once in a while, the output power went down and retuning brings it up, but not to the same level, but the benefit of not having the transmitter quit when needed is worth the change.
While you can continue to use equipment in original form without any problems, with minor modifications, they can handle accidental overloads without stress or failing. I consider this type of mod as important as those that increase power output or receiver performance improvements.
I reported safe PEP power out from an Ameritron AL-811H at 650 watts PEP. This expert states maximum of 550 watts PEP out from four 811A tubes for long life- specifically the Chinese tubes that are not rated 65 watts dissipation like the older finned plate older RCA 811A. See below.
The 3 and 4 tube Ameritron amps that use 811A tubes are very popular. A large number of users experience short tube life and wonder why? Lets examine that question.
RCA made the 811A in the late '30's, about '38 or '39. RCA made the originals and made them under high quality production standards. Anyone else who manufactured them did so under license and were making copies. RCA wrote the book on the 811A and no one presumably knew more about the tube than they did.
There are 2 ratings applied to power amplifier tubes, CCS and ICAS. CCS stands for Continuous Commercial Service and ICAS stands for Intermittant Commercial/Amateur Service. The RCA rating of the 811A was 45 watts plate dissipation in CCS and 65 watts plate dissipation in ICAS.
Examining what this means, an 811A in CCS can run about 128 watts input and at 65% efficiency, will produce about 83 watts of rf out while dissipating 45 watts as heat in its plate structure. Additionally, it will do so for what is considered a long life in commercial service. An amplifier with three (3) of these tubes could produce 250 watts output and four (4) tubes could produce 334 watts, all enjoying the same long life in CCS.
RCA rated the tubes higher in ICAS, recognizing that amateurs did not generally use tubes in the same manner and would accept shorter life in absolute terms. Even then, the life was considered adaquate as it was spread out over several years of activity and inactivity. Thus, in ICAS the tube could be run at 65 watts plate dissipation, running 187 watts input and about 122 watts output. A three (3) tube amplifier could run 366 watts output and a four (4) tube amplifier could run 488 watts output, assuming 65% plate efficiency in both cases.
As I remember, the Collins 30L-1 amplifier had four (4) 811A's in it and was rated at 500 watts, a pretty honest rating. Word was, if you saw orange coloration in the plates while operating, you were driving them too hard. Dull red was considered proper and that was with RCA's.
From these ICAS ratings, folks took liberties. CW is a 50% duty cycle mode, therefore we should be able to raise the power input/output some to compensate for the fact that the tubes will not be at work full time while transmitting. SSB is an even lower duty cycle mode, perhaps 20-25%,therefore we should be able to drive them even harder and still not cause anymore heating. With speech processing, the duty cycle climbs towards 50% and higher.
RCA 811A tubes are gone, practically speaking. Sure there are some NOS tubes, but how many? Most users are using Chinese tubes. These are not thought to be high quality tubes. Is it honest to even believe these are as good as RCA's were? I think not. RCA's had small horizontal fins attached to the vertical plates or perhaps they were merely punched from the vertical plates and bent horizontally. In any event those horizontal fins distinguished the 65 watt ICAS tubes from the 60 watters. In all likelihood, the Chinese tubes are no more than 55-60 watts in rating, no matter what.
How about the cooling? Does the cooling in these amps meet the standards RCA called for to cool the glass envelopes and plate seals? I don't know but I do know that some have reported that the failures among their tubes always seem to be a particular one. It reminds one of the days when Volkswagon engines ran hot on number 3 cylinder!
All of the modes of thinking that suggest we can drive these tubes well beyond the ICAS rating are pushing inferior (inferior in the sense that they don't measure up to the RCA's) tubes to the ragged edge. Its no wonder that holes appear in the plates, glass envelopes melt, elements short, etc.
Even though you bought tubes that were matched or thought they were matched, can you really be sure that they were/are matched over the entire conduction curve from cutoff to saturation? For that matter, can you be certain that they remain matched after some use? W8JI says not!
Even Heathkit never claimed an output rating of 800 watts PEP for the Warrior HA-10. For Ameritron to do it is entirely bogus. In fact, the only reason an amplifier can produce more power output on ssb than on cw is because the filter capacitors don't discharge to quite as low a value of plate voltage during low duty cycle voice peaks. For the 811A's to produce 800 watts pep output, they would have to produce 1200 watts input. Its pure baloney.
If you want your tubes to last don't look for more than 500 watts cw output or perhaps 550 watts pep on ssb out of a four (4) tube 811A amplifier. Don't look for more than about 375 watts cw or 425 watts pep out of a three (3) tube model. And on RTTY, which is a 100% duty cycle mode, don't look for more than 350 watts or 275 watts respectively.
The ratings I've suggested are approximately 1 db down from claims for cw output and only about 1.5 db down for ssb output. To put a db in perspective, it is the smallest change in power that is barely discernable, and then not by everyone.
Another possibility to consider is to change the tubes to 572B's. These used to be known as 572B/T160L's. Their rating is 160 watt plate dissipation each. Some have suggested that the Chinese versions may only have a proper rating of 130 watts each. Even then, they sound like a perfect replacement for the 811A's. I haven't checked the specs. for the plate-grid capacitance and don't know if they can be neutralized without modification in the AL-811/AL-811H. That might be inportant up around 15/12/10 meters.
One more thing-If the manufacturers produced the 3-500Z amplifiers with the same specsmanship applied to 811A amps, we'd see single 3-500Z's rated for 1600 watts pep out on ssb and 1150 watts out on cw. 2 tube models would be rated at 3200 watts pep ssb and 2300 watts cw. Seems they're much more conservative when the tubes get a lot more expensive. I guess they just expect that you'll be willings to buy 811A's more often.
BTW- The Russian 811a called G811 on ebay are very good tubes and thought superior to Chinese tubes. The G811 is about $11 each plus $22 shipping for four tubes from Ukraine as listed on ebay here- https://www.ebay.com/itm/G-811-G811...a19:g:j8cAAOSwdZdbjYfE:rk:1:pf:0&shqty=4#shId
eham review below:
Chinese Killers Time owned: 0 to 3 months
The Russian 811A called G811 are far superior to Chinese 811A tubes. Although the plate structure us rated by size 65 watts, like Chinese tubes the rating is closer to 55 watts. A true 65 watt plate 811A is made by GE or RCA with the plate fins.
These Russian tubes are properly made with high vacuum and a carbon coated thorium tungsten filament.
The Chinese 811A tubes that are reported to last 1500 hours by some may be missing the carbon coated filament that greatly reduces filament life.
The carbonization process is a more costly and adds another step and longer evacuation time. The Chinese have a bad habit at times and will do anything to save a dollar and unfortunately 'toss you under the bus'.
So, buy the Russian 811A for your ham radio amplifiers. You do not have to suffer with an inferior product. These are available on ebay.
Note- some state vintage RCA 811A will last 50K hours.
What is it in the AL811H design that allows unmatched tubes to be used? The RCA data sheet suggests that when using 2 or more tubes, they should be matched. Also, in the RCA 811A tube data sheet notes 2, 3, 4, and 5 section of characteristics range of design values, they clearly demonstrate why matched 811A's are necessary.
You will find the notes highlighted in yellow. http://k9axn.com/attachments/811A_463_AB2_FOR_WEB_ALTERED_1.pdf
If after reading the notes you continue to believe that matching is unnecessary please state your position for clarity noting the extraordinarily wide grid current range and what design has been used to equalize the grid current.
I will take a shot at matched 811A triodes. I would buy matched same brand tubes. I am not so sure triode tubes easily test as matched vs pentode or tetrode tubes on a tube tester from what I read. If one tube plate glows red vs others not, a problem does exist.
I finally got my 811H going last night after having it a while. I've just been busy.
The very most power output I can manage, with 80 watts drive, is right at 500W key down output. At that (and yes I kept key down times short and allowed twice the key down times at minimum for cool down) output level I was seeing 1475 volts and 575ma for a DC input of 848 watts and efficiency of just short of 60%. Note though that the 500W output is the reading on the meter in my MFJ tuner so that is suspect. The input figures should be more accurate. Grid current was right at 150ma at that drive level.
I'd think it would be capable of somewhat more even though best run at about that level, and that it shouldn't have to be driven that hard to get there. I did buy it used. Tubes nearing of their days?
When I had sticker shock above from 572Bs that was for NOS Cetrons from RF Parts. At $200 that's a no-way. I'd sell the 811H and add the money for the 572Bs and buy an AL-80B. But the Chinese ubes are affordable enough that I have pretty well decided to get a set of four, though once I have them I may keep using the 811As in the amp until one dies - might as well flog 'em like a rented mule when you have better replacements waiting on the shelf.
The question becomes whether to get the matched set of four Chinese tubes off eBay or pay a $20/tube premium from RF Parts for extra peace of mind of possible return, not having to ship from China etc.
I could have sworn I saw some Russian Svetlana 572Bs the last time I looked at RF Parts but I don't know. Either I'm "misremembering" that (thanks GWB for that cool word ) or they've sold out I guess. If they turn up again are they sufficiently better than the Chinese to warrant a price premium?
I found new Svetlana 572Bs, NOS with the US, matched set of four for $65 or so more (when shipping is included) than the set of four Chinese ones from China. Worth it? Any problems in particular with Svetlana 572Bs?