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Yet another AL 811H Question...

Discussion in 'Amateur Radio Amplifiers' started by WO4K, Jun 26, 2017.

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  1. WO4K

    WO4K XML Subscriber QRZ Page

    Amp Gurus...
    I have inherited my SK father-in-law's first generation AL 811H. It has sat unused in an un-airconditioned shed in Southwest Florida since 2003, according to his logbook. Read as: it sat unused in high heat and humidity for 14 years. Remarkably, it is in good cosmetic condition with very little rust/ corrosion. Out of an abundance of caution it is going back to Ameritron for a check up before I use it. New tubes, perhaps more. So I have three questions for this group:
    1) Given that this is an early version of the 811H, are there any significant or worthwhile upgrades I should ask Ameritron to do?
    2) I have read W8JI's website and info on AL-811s. I am curious about his TOF mod. I understand that it will help prevent damage to the amp from improper tuning. While his site has excellent detail on how to install the mod, I could not find how it works. Can anyone please school me on the TOF (start with what TOF is an abbreviation for, anyway?) or direct me to a website that has a TOF tutorial? I have Google searched and searched this forum, with little info returned on the TOF.
    3) And is it a worthwhile mod for someone who is into boat anchors, has a DX-100B and a DX-40, and some pretty good experience in the arcane vagaries of tuning up vacuum tube transmitters? Having said that, I've never owned a vacuum tube linear amp...my modern rig is a K-line with a KPA-500 amp. My BAs have, until now, gone barefoot.
    Thanks in advance for your advice and opinions.
    Bud WO4K
     
  2. W1QJ

    W1QJ Ham Member QRZ Page

    TOF was only offered by Tom, not Ameritron. It is no longer offered by him. So that is moot. Have Ameritron suggest upgrades.
     
  3. WO4K

    WO4K XML Subscriber QRZ Page

    Yes, I knew it was a W8JI mod. So, even though it is no longer available I would still like to learn about TOF was and how it worked. And, yes, I had planned to ask they folks at Ameritron. I'd still like to hear from the ham community what upgrades they think are worthwhile.
     
  4. G3YRO

    G3YRO Ham Member QRZ Page

    Just Googled it . . .

    No idea what TOF is meant to stand for ! But Tom's TOF Board basically feeds the Grid Current Meter with a circuit that detects the proper Peak Reading . . .

    He says Grid Current is the most important thing to monitor on a valve amp . . . and that on SSB you have no real idea what the real peak grid current is. (as the needle is dancing around, and never reaches the true peak reading)

    Actually, if you have a Processor that isn't true ! I tune my Amp on CW with a continuous carrier (in short bursts) . . . then adjust the output of the Processor so the peak power level is the same on SSB.

    So even though I can't READ the peak Grid Current on SSB, I know it's not going any higher.

    Roger G3YRO
     
    K9AXN and WO4K like this.
  5. W1QJ

    W1QJ Ham Member QRZ Page

    TOF means "Tune on the fly". Basically it is a peak grid current detector circuit that works with an LED. The LED flickers when voice peaks on SSB reach a certain pre-determined value. That flickering of the LED tells the operator that the peak grid current is a bit high so as the operator speaks he can slightly advance the loading control until the LED does not flicker any longer. Hence the name "tune on the fly". SO that is what the TOF circuit does. As far as mods. Well like everything else, everyone has opinions. The real question is who should you listen to if you obtain a laundry list of mods? Have you read the section on Tom's webpage dealing with the Al-811 amplifier? I think he deals with the amp in depth and makes recommendations. I am more inclined to think he would have the best sense on what needs to be done. If you believe what some say about this amplifier, they will tell you it is a piece of junk and to get rid of it and but a different amp. If more suggestions were of that nature, would you take their advice and get rid of it or would you not? I'm surprised that they haven't already swarmed in here with that advice. Maybe just a matter of time.
     
  6. WO4K

    WO4K XML Subscriber QRZ Page

    Thank you for the info on TOF. Yes, I did read the W8JI pages on the AL-811. As far as the "piece of junk" comments that may or may not happen, my usual go-to sources for equipment reviews are QST and eHam. But thanks for the warning.
     
  7. AA7QQ

    AA7QQ Ham Member QRZ Page

    I picked up an older 811H. Got new matched tubes from RFParts.com. Did the grounded grid & arc protection, as per Tom's page. Replaced the HV blocking capacitors. Wroked well, but intermittently. Swapped out the relay & added a much smaller relay for the "Bias" (Or whatever) & no problems since.I run it at 600W regularly on all bands. Just tune it into a dummy load & make a chart to refer to. If using a tuner, tune the antenna with the amp bypassed, then put the amp settings to the chart & turn it on. Slightly tweak, then up the loading a tad.
    When removing the cover of these amps, always replace D-16. I also replaced all of the diodes on the PS board, just because I had them.
    I also had a bad sensing resistor for the meter. Ordered it direct from MFJ/Ameritron, as it was cheaper.

    Ed
     
  8. WO4K

    WO4K XML Subscriber QRZ Page

    Thanks, Ed.
     
  9. K7MH

    K7MH Ham Member QRZ Page

    I used to have an early version AL-811 amp. I had it for several years and the only problem with it was it needed some more padding capacitance on 80 meters. Only real complaint I had was that the fan was rather noisy but it is an economy amp.

    Ameritron does have a grid protection board for about $30 you might want to look into but if you are reasonably careful with the amp it should work well for a long time.
     
  10. G3YRO

    G3YRO Ham Member QRZ Page

    A much better Modification would be proper ALC control circuitry . . .that senses the Amp's Grid Current, and generates an ALC voltage when it goes too high (to be fed back to the rig's ALC control)

    This would stop the Amp being overdriven (and splattering) . . . as well as protecting the Valves.

    All Amps should really have this built in . . .

    To me, this is what ALC was always SUPPOSED to be - Automatic LINEARITY Control..

    Roger G3YRO
     
    WD4IGX likes this.

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