Are 3CX800A7 a good tube for longevity/SSB?

Discussion in 'Amateur Radio Amplifiers' started by KK4YDR, Feb 1, 2016.

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  1. KK4YDR

    KK4YDR Ham Member QRZ Page


    Are these tubes pretty good for many years of operating? My usage scenarios are SSB/SSB/and SSB. I am not a digi or CW type person. I like to get on after work, late at night, and rag chew on the low bands.

    I use an AL-811 (3 tube) and it works good. Was looking to separate my shack into two halves. A high power low band side and a lower power high band side using different radios and tuners and stuff I have acquired.

    I know the tubes are somewhat spendy but two of these tubes on RF parts right now are about as much or the same as 1 8877 and definitely less than a 1200a7 tube.

    Do you anticipate the longeivity and availability for years to come or is this a tube worth full avoidance?

    They look like they are high gain valves with low drive power required and appear to be fully ceramic commercial ones. How good are they will idiot operator moments? I know the 3cx1200a7 is a proverbial titanium battle robot but I have no idea about the 3CX800A7 .

  2. W8JX

    W8JX Ham Member QRZ Page

    Properly used a 3cx800 will give long life but they are not forgiving tubes and easily damaged by operator error. If you want rugged try a pair of 3-500z's.

    BTW, the 3cx800 and 8877 on RF parts is made in China while 3cx1200 is still US made.
    KA2FIR likes this.
  3. KK4YDR

    KK4YDR Ham Member QRZ Page

    Thanks. When you say not forgiving would a good comparison be the 811a? Or are the 811 stronger as far as error resistant. I typically no longer make tuning mistakes as I have two 811 based amplifiers now and am able to do tune ups in mere seconds compared to when I first started.
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    If you run to much grid current they may never forgive you.

    No problem if you keep a eye on what the amps grid current is doing. Using ALC is a good idea.

    Good Luck.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    They are good tubes but not instant-on like 811As. Usually 3-minute warmup time; most commercial amps using them have a timer in the circuit so you can't transmit with them until about 3 minutes has passed from "power on."

    Grid current is the only important thing to watch, so just tune up using that and a wattmeter.
  6. KK4YDR

    KK4YDR Ham Member QRZ Page

    Yeah I never run my 811s past 100mils grid current. Typically I try to keep them 80 or less.

    From the sound of it, like most tubes, if your careful they will perform admirably. I use a tuning pulser also so load is lower during tuneup. I found carrier tuning can be dangerous.
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Well a single 3CX800A7 can run more power than four 811As on their very best day.:)

    But its grid current max is 60 mA, and it's best to stay way below that and maybe limit it to 60 mA for a pair of them. With proper LOADing, it's not difficult to keep the Ig way down.
  8. KM1H

    KM1H Ham Member QRZ Page

    An amp with the proper protection circuitry will allow a 3CX800 to run for decades of casual use. Very few commercial amps do not have that circuitry. If in a dirty-dusty, (not beer cans :rolleyes:) environment the tubes need to be pulled and the fins vacuumed on a regular schedule.

    Since the tubes in question are made in China with Eimac supplied tooling and training I think it is time to end the racist crap as you repeatedly spread on a couple of forums.

    With good tubes and heavy loading, 10 ma Ig per tube is fine. A pair at the original 800 ma Ia spec will run 2200-2400W so there is good overhead at 1500W As the tubes age more drive is necessary but even 20 ma/tube is well in the safe zone.

    Last edited: Feb 2, 2016
  9. W8JX

    W8JX Ham Member QRZ Page

    That is rich and very insecure of you indeed. So sad. Only one talking racist is you. I said they were made in china to explain why they are cheaper duh... You need to grow up and stop acting like a child. BTW a 3cx800 is indeed a easy tube to toast if you are not careful and amp does not have bullet proof grid current protection US or China made.

    The OP was about rugged tubes and while a 8877 or a pair of 3cx800's are good tubes when used properly they are far less forgiving to tuning errors than a 3-500 or 3cx1200 amp. It has nothing to do with where a 3cx800 is made as it has a fragile grid. More than one ham has found out how expensive a tune up mistake with a 8877 or 3cx800 can be.
    Last edited: Feb 2, 2016
    N9DOK and AI3V like this.
  10. KK4YDR

    KK4YDR Ham Member QRZ Page

    So the 3-500z's are rugged. I have heard that from way more than just a few people. I could always do an AL-82 type amp/Alpha ... you know, whatever is best for my budget.

    I just really liked the idea of having a truly low drive high gain tube that can do an excessive amount of power and would last years. I probably will never get into digital and if I do it will be @ barefoot power levels. And for CW I definitely love QRP, not QRO. CW is no fun @ QRO because for me it defeats the purpose and the challenge and the spirit of Morse code.

    While I am not hell bent on a particular amplifier, I do admit, I am still a bit giddy at the prospect of an 3cx800a7 powered shack. I am a careful operator and have made my costly mistakes already, enough so that I am extremely cautious before flipping any switches. In fact I popped 2 of 3 tubes in one of my amps, blew my ICOM up, and other things. I have paid some mistake fees for sure.

    Does anyone here think that the 800's are just "Stay away from them" tubes? They do not seem to be particularly popular and maybe it is due to their apparent fragility as I now perceive from this thread.

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