Heathkit SB-303/401 Combo

Discussion in 'General Technical Questions and Answers' started by KD8HMO, Jan 6, 2008.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: Subscribe
ad: K3QNTad-1
ad: L-rfparts
ad: l-gcopper
  1. KD8HMO

    KD8HMO Banned QRZ Page

    Im looking at Heathkit SB-303/401 combo and was wondering if this is a good setup. Anyone have any thoughts or opinions?


  2. K0RGR

    K0RGR Premium Subscriber QRZ Page

    You should read the reviews on eham: SB-303

    I, personally, would not hesitate, because I love the old Heathkit rigs and this would not be my #1 radio. The SB-303 is a 35 year old solid state receiver. 35 years ago, even the top of the line commercial solid state radios had pretty poor dynamic range - that is, they tended to be overloaded easily by strong signals on the bands - particularly on 40 and 80 meters. It looks from the reviews like the SB-303 is not an exception.

    However, it also looks like the addition of a simple attenuator can greatly improve the rig on the lower bands.

    The transmitter is a tube-type rig. Each time you change bands or make a big frequency excursion within a band, you'll need to manually retune it. This is not difficult if you know how, but if you aren't accustomed to it, it can seem tedious. I trust that replacement tubes for it can be found for a decent price.
  3. K7UNZ

    K7UNZ Ham Member QRZ Page

    You might want to check if the '401 has the band crystals installed.

    They were optional on the '401, and are needed should you ever want to use it as a stand-alone unit.

  4. K9STH

    K9STH Ham Member QRZ Page

    The SB-303 is a pretty lousey receiver. It was Heath's first attempt at making a fully solid-state "serious" receiver for amateur radio use. The internal noise is bad (very high without any antenna being connected). Also, the solid-state LMOs used in the SB-102, SB-303, and SB-313 do not "track" that well. They are generally "right on" at the 100 KHz points but vary all over the place inbetween. This is not like the tube type LMOs which are usually accurate to well within 1 KHz across the entire band.

    There is a variable attenuator on the antenna input circuit. Frankly, this is nothing more than a 100 ohm potentiometer between the antenna input and ground. The "wiper" goes to the actual input to the receiver.

    The SB-303 tends to overload and desense very badly when there is any nearby activity. In fact, they overload even on strong signals that come from stations far away.

    The SB-301 (tube type) receiver is MUCH better than the SB-303. I owned an SB-303 for a short while and have worked on a number of them for other operators. The SB-301 compares pretty favorably with the Collins 75S-3 series receivers but the SB-303 is a pretty poor receiver. When I originally got my Collins 75S-3A my primary station consisted of the Heath SB-301, SB-401, and SB-200. I ran the 75S-3A in parallel with the SB-301 for about 6 months before I went looking for a 32S-3 transmitter. About 9 times out of 10 the SB-301 could do everything that the 75S-3A could do. But, it was that 10th time that made me go the the 75S-3A as my primary receiver.

    The SB-301 does not overload even when there are stations operating within a very close proximity. This is due to the tube type "front end".

    You do have to have a "dummy" plug inserted in the LMO output jack of the SB-303 when it is operated separately from the SB-401. Otherwise you get all sorts of "birdies" which makes reception basically impossible.

    All in all, I avoid the SB-303 receiver "like the plague"!

    Glen, K9STH
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I agree with Glen.

    I built the SB-301/SB-401 combo (with the HP-23, SP-600, SB-610, SB-200, etc!) from kits and they were excellent. I also built the SB-303 from a kit and I absolutely loved it at first (all solid state, cool as a cucumber, no warm-up at all -- cool stuff!) but then after a while, comparing it with the older SB-301 it was pretty easy to tell it just wasn't as good.

    My SB-303 almost bit the dust permanently during a nearby brush with lightning. We had a lightning storm nearby and my antennas were all connected, back in about 1977 when I lived in NJ. The only piece of gear I had fail was the SB-303, it went completely dead while everything else worked just fine after the storm.

    I finally debugged it and got it working again, but it took probably ten hours of troubleshooting and component replacements. I wasn't a happy camper during that.

    If you can find a good working pair of SB-301/SB-401 I think you'd be happier with that.

  6. KD8HMO

    KD8HMO Banned QRZ Page

    Is it true that you can control the transmiter frequency with the VFO on the SB 303 instead of having to tune each one manually?
  7. K9STH

    K9STH Ham Member QRZ Page

    The Heath SB-300, SB-301, and SB-303 receivers all will transceive (receiver contols the frequency) when used with the SB-400 and SB-401 transmitters. There is a switch on the transmitters which changes the frequency control from the internal LMO to the receiver LMO.

    This is a feature of the Collins S-Line and Heath definitely copied it when they came out with the "poor man's S-Line".

    By the way, LMO is the abbreviation for "linear master oscillator" which is the VFO in the Heath SB-Line. They do use the conventional variable capacitor tuning whereas the Collins PTO ("permability tuned oscillator) uses variable inductor tuning. In the tube type LMOs (primarily manufactured by TRW) great care was taken to make the unit track very well. As I mentioned above, the tube type LMOs usually track well within 1 KHz across the entire 500 KHz tuning range.

    Unfortunately, TRW did not make the solid-state LMOs (used in the SB-102, SB-303, and SB-313) and the manufacturer who did make them did not take the trouble to get them to track across then entire 500 KHz. They are generally "right on" at the 100 KHz points but vary all over the place in between. I have several of the solid-state LMOs in a box all of which do not track within at least 5 KHz at places between the 100 KHz points.

    There is a fellow in Florida who can make the solid-state LMOs track correctly. However, the average time for him to accomplish this is almost 10 hours of work. Frankly, he does it as a "labor of love" and often doesn't even charge for doing the work. If he were to actually charge the "going rate" for boat anchor repair getting the LMOs to track would run between $500 and $600.

    The LMO is the main reason that I recommend the SB-101 over the SB-102. The difference is basically in the LMO used. With the SB-303 there are way too many differences in performance between it and the SB-301 that I do not recommend even acquiring an SB-303. Now there are a few amateur radio operators who do use the SB-303 on a regular basis and really like them. However, I am definitely not into "S&M", especially the "M" part! [​IMG]

    Glen, K9STH
Thread Status:
Not open for further replies.

Share This Page