Step up Xformer Question - Amp

Discussion in 'Amateur Radio Amplifiers' started by KK4YDR, Dec 19, 2015.

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  1. AC8AC

    AC8AC Ham Member QRZ Page

    i think that will be my next build if i ever do it again . i really like the 1500 just dont care for the alc or die part of there ownership .. although i have found they are a bit more rugged than people think . but 100 watts with overdisipate them quite easily if the tuned input is right

    i just worry about knocking the alc line off . but legal limit at 700ma with 15 grid at 3.8kv is nice for a medical pull

    now to find 2 more for $125 would be nice i guess i got lucky
     
  2. VK3BL

    VK3BL Ham Member QRZ Page

    And whats the IMD specs on that 2 decade old amp Reaston?
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The 8877 is pretty robust.

    Also has a lot of gain (>15 dB) at 4kV so to protect it, it's pretty easy to just add a 50 Ohm attenuator between the rig and the input of the amp to prevent overdriving it. My 6m 8877 produces ~1500W output power with about 45W drive. If it's LOADed properly it's impossible to drive the grid current to anything near a destructive level.

    The only PITA is the 2-minute warmup time.
     
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    But it is worth the wait.
     
  5. N7WR

    N7WR Premium Subscriber QRZ Page

    The signal strength difference between 1 KW and 1.5 KW on the receiving end is generally not worth the added expense of a legal limit amp vs a 1 KW amp. I have never been unable to work what I wanted to work when running an AL80B. Probably the best bang for the buck in the amplifier world and it is made to run on 120vac
     
    WA7PRC likes this.
  6. AC8AC

    AC8AC Ham Member QRZ Page

    yeah the wait time can be a pain but i rarely use that amplifier on resonant antennas so i have to tune them up first hardly notice the wait 40 in usually gets me to legal limit except on 10 take about 50 thought of building a 3db attenuation when i built it i think the tube has seen better days i was using junk box band switches when i built it!! that didn't work out well ended up having a 86 series switch made for me im sure that didnt help the tube much .. it had 6000 hours on it when i got it so it has seen some life

    N7WR i have the al-80a with the transformer upgrade on my test bench and yes its a great amplifier i like it alot more than i like my al82 i think its built better for the power level

    i use a Russian gs31b on 6 meters one day im going to replace the plate iron in it . i used a rewound sb220 transformer for it but it sags horribly after 600ma drives the grid up but i only use it to 7-800 ive never needed more to make the contact so no rush on better plate iron i suppose
     
  7. KK4YDR

    KK4YDR Ham Member QRZ Page

    I agree generally and I have never owned a HAM amp but my observations lead me to have witnessed the extra 500 watts over 1000 is useful for breaking into pileups and especially for low bands during summer. Hows that 1kw perform during 80m summer operations? Im curious as Im wanting a used AL1500 for 2200 from someone I know but an AL80b is a thousand less.

    Ive considered that tye extra 1000 used or 2000 new for the AL1500 has alot more value than just 500 extra watts. In my research I see A 15-20 year life span commercial tube, commercial everything in the amp, extra protection circuits, very easy to tune, extremely robust and strong tube that can take a beating when you dont do the best tune. I know the tubes in that can run in excess of 1kw AM broadcast for a long time 24/7 duty cycle and a number of other reasons. I was just thinking for an extra 1000(used) and at the way I would probably run 500 watts most of the time I can leave the amplifier to my son in 20 years and it will run fine. But I am not opposed to an AL 80b if a light duty cycle 50% of peak power capability avg usage unless conditions need full QRO would work for many years. I dont wanna buy a 500z tube every year because they are not tough for casual isage but then again I have never owned an tube amp except a fully blown junk al811 I got for free and will not use because its total junk. Was in a flood and underwater for like 2 weeks.
     
  8. N7WR

    N7WR Premium Subscriber QRZ Page

    Ask WB2WIK about his experience with the AL80B. I had one for about 5 years, didn't baby it but was careful to tune it properly. 5 years and lots of Q's and it was still rated output on the original tube.
     
  9. N8MSA

    N8MSA Ham Member QRZ Page

    You should be concerned. It is easy, in favorable conditions, to receive a significant number of greater-than -73 dBm ('S9') signals and up-to -40 dBm ('S9+30') signals along a given path. Transmitting a signal over a path that produces a -40 dBm desired signal in a given receiver means that transmitting a signal with -30 dBm 3rd-order IMD imparts a greater-than 'S9' signal across roughly 9 KHz of bandwidth. This is, by any reasonable standard, poor operating practice and can be avoided - even with solid-state amps - in a number of ways.
     
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    If you can not make contacts using a Desktop amp running 500 watts, You do not need a bigger amp, You need a better antenna.

    ERP is more important than power out, Unless you are using a dummy load for test.
     

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