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Author Topic: Specs of Taylor 811a vs Taylor 572b  (Read 3185 times)
W6NFL
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« on: January 07, 2007, 10:32:41 AM »

  Hi i see alot of posts talk about how much more durable the 572b is over the 811a in say the al811 amp. I have yet to see actual #s of what the 572b can handle as far as plate current and Grid current vs the 811 tubes. I have a Ameritron 811 3 tube amp and i am real curious to see spec difference in what they can handle. I know that they wont give the AL811 more output because of power supply limitations. Any info would be great.
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WD8PTB
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« Reply #1 on: January 07, 2007, 11:56:27 AM »

I don't remember the exact numbers but 572B's have a plate disipation rating of about 160 watts each, 811's are more like 65 watts each. Don WD8PTB
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W3LK
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« Reply #2 on: January 07, 2007, 12:02:56 PM »

You will NOT get more power out of an unmodified 811 or 811H by switching to 572Bs. What you WILL get is longer tube life if you are trying to drive either of these two amps to their maximim output.

FWIW there are several threads in the Amplifier Forum covering this very topic. Suggest you go over there and do a search and read them.

73,

Lon - W3LK
Baltimore, Maryland
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
N6AJR
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« Reply #3 on: January 07, 2007, 12:40:06 PM »

The biggest problem with the 811/572 tube swap is that is you really don't gain anything.

Everyone quotes the higher plate dissapation, which is true, BUT, no matter what the power is the same, so it really probably does not help.

I have had 3 of the 811 amps and 2 of the 811 H amps. I always ran 811 tubes in them.  the ameritron 811 and 811 H has I think a 1600 volt HV circuit, and in fact the weak point of the amps are the four 400 volt capacitors in the HV string. if one of the HV resistors change value even a little that capicitor draws excess voltage and the cap starts arcing. you change out the 4 caps and the 4 resistors and are back in business. ( about $35 for the set if I remember correctly)

The 572  usually has 2200 volts on the High Voltage circuit, ( I seem to remember this from the Clipperton L's I had) so with 1600 v  max on the HV circuit on the 811 and 811 H, there is no advantage.

Another point is the 811 tubes can be bought from ameritron for $60 for a set of three  811's, or you can buy 1 572 b for $60 from ameritron.  so you could retube 3 times for the price of 1 set of 572's.

I have yet to have a problem in an amp with the tubes. Once you learn how to tune them properly, the tubes last for ever. ( I always tune for max smoke then back the drive down just a tad.) If you run any tube at slightly less than max power out it will last a long time.  

If you constantly overdrive them looking for every last ounce of power, you will eat the tubes quickly, no matter what they are. and you really can not hear the difference on the recieve end with a change from 500 watts to 450 watts. have a frioend with an amp call you and then drop his power 50 watts, no discernable difference.

BTW you can use a 572 as a replacement for an 811, but not the other way aroiund because the 811 tube can not handle the higher voltage in a 572 circuit.

YMMV
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WD8PTB
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« Reply #4 on: January 07, 2007, 12:48:51 PM »

I changed to 572B's because the 811's kept shorting and popping fuses. That got old quick!
   I did get a little more out only because I could drive them harder and still get less grid current. I got 850 watts key down with the 811H. I ran that way for several years, made many contacts, had no complaints, and sold it with the same tubes.
    The only peculiarity I noticed was that the plate tune tuned in a slightly different spot with the 572B's. Don WD8PTB
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W6NFL
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« Reply #5 on: January 07, 2007, 02:19:58 PM »

  The AL811 with the 811 tubes are rated at 150 to a max of 200 grid current. What sort of grid current can the 572b handle in the al811 amp?
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K0BG
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« Reply #6 on: January 07, 2007, 03:03:41 PM »

I'm on Tom's (N6AJR) side on this one. One of the overlooked aspects of changing out 811As with 572Bs, is which ones you choose.

The Svetlana is NOT equal to the Taylor 572B or the Amperex 572B. If you doubt this premise, look here: http://www.rfparts.com/572b.html. What they say is not advertising hype.

While the amplification factor slightly favors the 572Bs, they do in fact have a more plate and inter-electrode capacitance. In some designs, this can (and does) cause loading problems.

The Svetlana tubes are almost the exact size of the 811A, but the Taylor and Amperex 572B are longer, and cannot be used in some amps as a result.

The main reason most folks opt for the 572Bs is because they over drive the 811As, thus drastically shortening their life. The Ameritron 811, and 811H have have maximum drives levels as outlined in their respective manuals (65 watts for the 811H, 50 watts for the 811). I venture to say, 95% of the amateurs who own these amps over drive them. What's more, they take several minutes to tune them up (it shouldn't take longer than 15 seconds), fail to use the ALC as Ameritron instructs, and thus shorten tube life by several magnitudes.

If you just HAVE to HAVE more power, buy a bigger amp! Over driving a small one only produces more splatter and distortion products; all for just a couple of dB increase in signal strength.

Alan, KØBG
www.k0bg.com
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N3JBH
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Posts: 2358




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« Reply #7 on: January 07, 2007, 03:10:02 PM »

http://www.mif.pg.gda.pl/homepages/frank/sheets/049/8/811A.pdf

and

http://www.mif.pg.gda.pl/homepages/frank/sheets/084/5/572B.pdf

i know there not taylor but info should still help some
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WB2WIK
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Posts: 20633




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« Reply #8 on: January 08, 2007, 09:09:31 AM »

811A is rated 60W anode dissipation, 175mA max Ip and 50mA max Ig per tube.

572B is rated 160W anode dissipation, 275mA max Ip and 75mA max Ig per tube.

Reason to replace 811As with 572Bs in an AL-811 is limited purely to "headroom" and tube life, not output power, as repeatedly stated.  However, this isn't a bad reason.  I've seen Tom W8JI, the AL-811's designer, recommend this replacement several times here, just for this reason.

It seems that neither 811As nor 572Bs are "as good as they once were" many years ago, but 572Bs have more margin in the AL-811 design and should last a long time.

WB2WIK/6
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WD8PTB
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Posts: 670




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« Reply #9 on: January 08, 2007, 05:00:11 PM »

I had 2 811a's short the grid out in a 811h amp. Aside from having to take all those screws out I also had to relace the grid resister.(twice). You will probably have to overdrive the 811a's If you want to get the rated power out for 811/811H amps. I did not do this but they blew anyway. I think there were some quality problems with the Chinese tubes at the time I bought my amp.
    The bottom line is when I put 572B's in my tube blowing days were over! I did notice the Plate/Load controls were slightly different but 160m was the only band that was cloase to the end of the tuning range. Don WD8PTB
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