SB-220 HV and line voltage Concern

Discussion in 'Amateur Radio Amplifiers' started by N8PWM, Aug 19, 2016.

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  1. AF6LJ

    AF6LJ Ham Member QRZ Page

    Nice station... Nice Icom....
    Nice FT-101...



    I have a Cantana some dip-tard soldered the lid closed, and the resistor reads 85 ohms....
    So it looks like I will be using my home brew paint can load with the motor oil in it for some time to come.
     
  2. N8PWM

    N8PWM XML Subscriber QRZ Page

    Whoops my error. Not prime. $63.35
     
  3. N8PWM

    N8PWM XML Subscriber QRZ Page

    Thanks Sue! The XYL deserves some of the credit for the layout. I would have an old workbench in the house if it were just me lol.
     
  4. N2EY

    N2EY Premium Subscriber QRZ Page

    Which can be fun at the checkout. If you know what I mean.
     
  5. N8PWM

    N8PWM XML Subscriber QRZ Page

    Lol yes I do!
     
    N2EY likes this.
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I just took a peek at the ICOM manual and that radio has an RF power level control so you can dial in how much drive you want. The FT-101 doesn't have that built in for voice communication. That radio wants to be tuned up for full power in order to get the best audio and clean RF. To throttle a hybrid down, you want to connect an adjustable negative DC voltage to the ALC pin on the accessory jack. This can be as simple as a 9v battery, a 50k pot and a few pieces of wire. I looked through the FT service manual and operations manual and didn't see a pin-out of that jack (I must have missed it but I have to get back to work). Maybe you have that or someone else here has a handy picture of the pinout. You tune the hybrid as normal, switch the amp on and tune the amp as Lou W1QJ suggests, and then dial the power back to where you want it.

    mics.jpg

    To give another perspective, for my system (Kenwood TS-820/SB-200) I've built a T/R sequencer so the radio and amp get staged contact closures. Into Transmit, their respective T/R relays are thrown and then the ALC (used as cutoff and power control on the 820) and amp cutoff are released (the T/R and cutoff are separated in my amp). Out of transmit does the reverse order... cutoff the amp and pull the alc line low, then let go of the T/R relays, in about 30ms. It's a bunch of stuff to do that's not really necessary, but I don't like hot-switching. I have an unloaded board and box files if you get bored and want to make one. A 9v battery is a lot less work! :p

    P1000362.JPG
    P1000361.JPG
    "Coffee break's over, everyone back on their heads!"

    edit:
    That's a great looking Shack-O-Radios, Craig!
     
    Last edited: Aug 26, 2016
  7. N8PWM

    N8PWM XML Subscriber QRZ Page

    Thank you Chris. I wish I could keep it looking that clean lol. My FT-101E has the carrier control. I usually turn that down to about 50 Watts sometimes 100 Watts but would that not serve the same purpose as the RF control on the ICOM? Its reducing the output of the transmitter. I retune it when I lower the power. So if I am understanding right, the ALC on the SB220 will only work at full power. Would this be a correct statement?
    So the FT-101E uses pins 8 and 9 on the accessory jack for the amplifier ALC. I like the 9V circuit to supply the negative 9 volts. So if my statement about the carrier control is not correct then I need to use the ALC to lower the power. Right? I might be totally out in left field.
     
  8. KJ4NOO

    KJ4NOO Ham Member QRZ Page

    I use mineral oil from TS in it and I can tell if it is heating up !
     
  9. W2VW

    W2VW Ham Member QRZ Page

    Decent audio compression is cheap these days and will allow effective reduced power transmission from older equipment.
     
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    That would be this derating curve chart on my HN31 (link):
    [​IMG]
    Note that there's a significant difference between transformer oil and mineral oil. Also, consider that removal of the heat is only via the tin can. After being heated, it takes time to cool down. That time would be improved if there was some form of radiator + fan attached to the can to remove the heat faster. As it is, I've found it takes a long time to cool down.


    For a DL that can't take high power for very long (especially when using mineral oil), and considering you intend to hit it with MUCH more than the 90W rating of the resistor, I highly recommend you use the best oil you can. For me, after I repaired & reconditioned my HN31, I was left with a gallon of very old unknown oil. I sought out a local source. It turned out my local power company's transformer shop was only 2 miles away, and the supervisor was happy to give me a gallon of oil. Their gnarly fill pump made it a bit tricky to get ONLY one gallon. After I repaired/refurbished my HN31, I use it only for barefoot/100W rigs.

    For high power, I use a homebrew air-cooled dummy load (link) that can take 1500W all day:
    [​IMG][​IMG]
    It uses four 50Ω/400W flange-mount RF resistors in series-parallel on two heatsinks, with air moved by a 100cfm fan. The DL uses scrapped (free) parts from my then employer. However, suitable RF power resistors are available from sources such as Henry Radio on ebay (
    link).

    Jim W7RY (seller 'radioamplifiers' on ebay) is in the process of moving and isn't currently shipping. For the SB-220, he sells a bare PCB. When you purchase, he emails complete documentation and a link to a Bill Of Materials on Mouser's website. He doesn't supply the vacuum relay (output switch) but recommends a source (Max Gain Systems) and can supply the reed relay (input switch). The worst-case measured switching time is about 1ms (most rigs take at least 5ms to produce RF). The FAST relays eliminate Rube Goldberg-ish sequencing/delays. This QRZ thread (link) has more info and links.

    Bryan WA7PRC
     
    AF6LJ likes this.

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