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Heathkit SB-230 Amp

Discussion in 'Amateur Radio Amplifiers' started by WA6MHZ, May 26, 2012.

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  1. WA6MHZ

    WA6MHZ Ham Member QRZ Page

    MEANWHILE, back at the Test Bench.........

    Rewind to Saturday afternoon.

    Here is the Diode board with the nail polish and Sharpie markings ready to etch.

    It etched in a short while and looked great! The parts were transferred from the old board to the new board, except for the new 1N5408 power diodes. Lets see if anyone can spot the GRAVE ERROR before I mounted the board.


    Into the Chassis it was wired and it is time for power up!


    Looks great so far! I button the Chassis side back up


    I plugged it in and turned it on. The BREAKER quickly SNAPPED!!! WTF???

    It was time to plug it into the Variac and bring it up slowly. But as I did, using my 1965 Heathkit VTVM, I noticed that the voltage on half the capacitors was REVERSED!!!! This was quite a hair tearer as I searched for a problem on the cap PCB. NOPE, everything was perfect, so WHY didn't it work???

    Checking the diode board, all the diodes were the correct polarity and each tested good. SO WHY didn't it work???? More Hair tearing!!!! Then I checked the Schematic and found that the RIGHT HALF of the diode string was REVERSED!!!! OH HO!!!!!!!!!!! I turned all those diodes around and Now it worked great!!! That was a 12 hour day for Saturday working on this thing. TIme for BEER!

    Sunday I went to Church and the Church Picnic. But I still didn't feel good. I haven't been HUNG OVER in years and years! I came into work and was going to work on the SB-230, but wound up just going to sleep in the chair. Sunday was SHOT!

    MONDAY MORNING I arrived at work early and tried to make up for Sunday being shot. FIrst effort is to make a meter backlight. Heathkit used a really squirrelly system. They used two 500 ohm resistors in series with a 28VDC Light across the 110VAC. That isn't very safe either. I don't know why they just didn't rob 6.3VAC off the filament transformer to run a silly #47 lamp. I should do the same thing!

    I twisted up some #22 Green wire and attached it to the output of the 6.3VAC green transformer wires BEFORE it goes into the filament choke. I put some Ferrite beads on the wires just to be sure no RF sneaks up it.


    That was routed up through the grommets into transformer area and over to near the lamp. I didn't have the lamp socket for the lamp, so I decided to modernize it slightly with an LED replacement. 3 White LEDs were scored at Radio Shack along with some perfboard, and those were installed back behind the meter.


    The LEDs are narrow point focus devices, but I was able to move them around to give a good uniform lighting of the meter face.


    Once the meter was lit and I could see it, I noticed it read just under 2000V for the High Voltage! Time to investigate the Meter dropping resistors. That consists of Three 1M 2W resistors and a 100K resistor. The 100K read 120K, and the 1Ms all ready about 1.1M. I replaced the 100K with a precision 100K and put a 10M resistor across each of the 1Ms. Now the meter reads 2350V for 110VAC input!


    So this works great now. I still need to build up the SOFT KEY and the SOFT START, but not sure how I can install the soft start as there isn't much chassis space below Unlike the SB-200, the clearance below the chassis is very limited, and also, the 110VAC wires are in the top back near the antenna relay. So the soft Start might be scuttled. But I do need to wire up the Soft key. I will rob the 6.3VAC, run it into a voltage doubler (for the 12V relay and then wire up some transistors to do that. But it is time to work on COMPANY JUNK, so that concludes TODAY's SB-230 Episode.
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    That's a pretty severe "spotlight" effect. LEDs have a "dispersion angle" (or similar verbiage) specification. You want a number as big as you can get and/or you can scuff the lens with sandpaper or a mill file to increase the angle. Be aware that this will make them appear dimmer, since the light is now spread out over a wider area. You would then use more LEDs and/or brighter LEDs. I would've just stuck with an incandescent lamp. 28V lamps aren't hard to find... everyone stocks them. But, the 6.3V lamp idea sounds good. If you want to decrease the running/inrush current (and greatly increase the lamp life), a pair of rectifiers back-to-back in series with the lamp will drop the supply voltage a bit (0.7 to 1V).

    Soft start may not be needed if you didn't go crazy with the values of the HV filter capacitors. On my SB-220, I verified the bleeder resistors were very close in value to each other (I had replaced them with higher value 1% tol types). I then measured across part of the stack and extrapolated to get the guesstimated HV number, and verified the SB-220's meter agreed with it. I'm within 50V of the guesstimated number. That's as good as I could do w/o a HV probe. If you want to replace the carbon composition resistors Heath used, you can get by with 1W types such as Vishay VR68-series. Digi-Key has them.
  3. WA6MHZ

    WA6MHZ Ham Member QRZ Page

    I can still yank out the LED board. The reason I didn't go with a 6.3V lamp (#47) is I didn't have a Lamp holder. But now I have the 6.3VAC going up to the board, so it would be easy to change once I score a lamp holder. I will look for one at the Swapmeet Saturday.
  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    Groovy. Hey... there's yet another SB-230 listed on a certain auction site, #110887312031. It's missing the tube and the bidding is up to $290 (11 bids from 7 bidders), with almost 4 days to go. Any bets as to how much the winning bid will be? ;)
  5. WA6MHZ

    WA6MHZ Ham Member QRZ Page

    Today the SB-230 got a real workout. We had KIDS DAY at Santee lakes and I brought the 230 to drive with the Kenwood TS-830S. The 830 put out about 75W and drove the 230 to a good 500 or more watts CW, and alot more PEP on SSB. I was using a garden variety Heathkit HM-102 wattmeter. So that tube is plenty healthy!
    No problems with the 125V 620mA fuse or the Glitch resistor (25 ohms 10W). It was used hard all day, and really overdriven. I didn't hook up the ALC and had several reports of distortion from hitting the mic too hard. When I backed off the mic, they said it sounded fine. There was alot of intense ragchewing at full power and the heatsink got very hot. Not hot enough to set off the overtemp switch, but had I been running RTTY or alotta CW, it might have. So it really needs a serious fan on it to cool it down. I am thinking about putting 2 big muffin fans on it somehow so it won't be a mod that damages anything, but will still cool it down on heavy use. It continued throughout the day and alotta contacts were made. At the end of the day, it still worked great but I could smell the burining in of the 100K bleeder resistors. I will have to take it apart and see if there is any discoloration of any of the new parts. the 100Ks were 2W like the originals, but were metal film instead of carbon. They were mounted up in the air so they would have air around them UNLIKE the Heathkit design where they were trapped under the chassis inside the electrolytic cap compartment. I ran it on 20 and 15. What was disconcerting was when I was away from the rig for awhile and untrained new hams tried to run it on 15 with the 830 and 230 tuned up on 20M. These NEW Hams think all rigs are like modern rigs where you just turn the bandswitch and talk. They have no comprehension of TUNING the plate, load and grids on TUBES!!! Luckily they didn't have any drive to the 230 so it didn't blow up from mistuning.
    I carefully retuned it and all was well. UNAUTHORIZED people should NOT mess with boat anchor radios!!!!

    The well tested Heathkit SB-230 was returned to work for Museum service. I still have to build a Soft key circuit for it (the 830S didn't mind the hard keying) for use with newer solid state rigs. Also, a Tuner should be put in between the newer rigs and the 230 since there is no matching inside the amp or tuned circuits like is on the SB-200.
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    That's good news, Pat. I wonder if the distortion was from the amplifier not being loaded enough. A scope would've told you that.

    I sometimes forget to change bands on my SB-220 but am quickly reminded when it puts no fire into the wire. :eek: An outboard box w/ DPDT relay-switched networks might be a cost-effective way to deal with your concern.

    If you want extra cooling to be automagically engaged, consider using something like the LM35 to sense the temperature. It produces an accurate 1mV/°C and could be compared to a reference voltage to control the fan(s). My experience with controlling cooling fans with a comparator is, you want some hysterisis in the comparator, so the drive to the fan is "snapped" on/off.
  7. KM1H

    KM1H Ham Member QRZ Page

    Dont lose sight of the fact that the 8873 is only a 200W PD tube and 500W CW is really pushing it. Overdriving is the easiest way to destroy it.

    I use my 6M version mostly portable in a contest where its worked hard primarily on SSB and a standard single muffin fan keeps the heatsink temp within reason at around 600W PEP with a bit of exciter RF processing. If the fan is too loud add a 330 Ohm 20W resistor.

  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    Make that 10mV/°C.

    I might add that you can probe the output of temperature sensors such as the LM35 with a millivoltmeter to get precise heatsink temperature (no guessing at the temperature). And since you can get multiple comparators in a package (such as the LM339 quad comparator), you can have multiple output levels... Level 1 = turn fan on/off low ... Level 2 = turn fan on/off high ... Level 3 = inhibit PTT ... etc. With a small power resistor, the LM35 can easily be used to quickly detect loss of cooling air or water flow (for amplifiers using forced-air or water cooling).
  9. WA6MHZ

    WA6MHZ Ham Member QRZ Page

  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    I see that one has 1 bid (so far). It's good to keep track of how much an item sold for. An item LISTED for a million bux doesn't necessarily equal a SALE for that amount. You can search closed auctions as well as current auctions (after logging in).

    For my SB-220, I homebrewed my own relay driver and step-start. I couldn't wait for Harbach Electronics to exist. ;)
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