I had originally intended to publish a more extensive article, but havemoved on to other projects. I am sharing here some tips that you mayfind useful. I always coveted the Heathkit Twins, but could neverafford them. A friend was cleaning out his basement and passed thesealong at a reasonable price. I now had the opportunity to enjoy adream from the past.
These are the early filter type sideband rigs from the sixties, so be awareof their limitations. The spurious output performance is better thanthe Heathkit Marauder, the previous SSB rig. Unless the trap wasadjusted carefully, the spur on 20 meters was a problem. Drift wasgreatly improved by the new LMO in the twins. The Marauder occupieda monster Apache cabinet and was similar in appearance to the Apache. The SB401 and SB301 are significant improvements over the earlyversions. In particular, the transmitter is much easier to switchfrom split to transceive. A small reed relay to switch the VFOaround would correct this in the early 400. The 300 is an excellentreceiver, especially if it has the accessory AM and CW filters. The301 was friendlier to the 6 and 2 meter converters, but no othersignificant changes.
SB-303 Amateur-R Heathkit Brand, Heath Co.; Benton Harbor MI, build 1970–1976, 13 pictures, 4 schematics, 27 semiconductors, United States of America. How do I obtain a replacement manual for a modern Heathkit product? If you need a replacement manual for a modern Heathkit, please contact customer support, as this may entail custom printing of your replacement manual, deactivation and replacement of the old serial number, reprogramming of your custom MPU or other kit changes, and changes in your accounts at Heathkit.com. SB-303; Heath Company SB-303. Below you will found our manuals on the Heath Company SB-303. The service manual functions as a repair guide for troubleshooting and sometimes contains tips for refurbishing and modifications. The schematic is a technical drawing or diagram of your system, a perfect supplement to the Service Manual.
The SB303 was an all solid state receiver, the last in the series. Iplan to do a write up on this project later, as this is part of mypermanent collection.
Heathkit Sb 301 Manual
Compactron tubes are used extensively in the transmitter. These are gettingscarce. Stock up on them while you still can. The receiver has onlyone compactron. It can be replaced with a 12AU7 and 6AU6, if you areclever.
The transmitter was improved by inserting 10 Ohm resistors at various B+points. It did give the kit builder a “second chance” ifthere were shorts. The resistors smoked to alert the owner oferrors. Perhaps you could recover from them if you killed the powerquickly. More significantly, the 82K resistor on the terminal boardunderneath in the front was changed to 2 Watt. You should check thisbefore power up. As a minimum, the CW & Tune Drive adjust willnot work right if the value goes up. If it goes down in value, thebalanced modulator diodes will fail and other ugly things will occur.
The antenna relay (not the main control relay) also develops a permanentmagnetism that causes it to hang up in transmit mode. I have seenpeople put thin pieces of plastic on the pole piece to fight this. The easiest way to correct this is to use a powerful tape headdemagnetizer to reduce the residual magnetism. Then swap the wiresto the coil of the relay; it will probably magnetize again, but itwill take quite a while. If it happens again, just swap them back.
Follow the manual during alignment. Be sure to perform the neutralizationcarefully. Power output will be 100 Watts, but lower on 15 and 10meters for sure. If you get 75 Watts on 10 Meters, call it good. Use the grid drive meter to determine if the power is not up tosnuff. If you are not getting enough grid drive, changing the finalswill not correct it. Low B+ on the low voltage or resistors thathave drifted in value can cause the exciter to not deliver enoughdrive to the finals to operate properly.
Operating the Heath Twins as a complete station requires the constructionof three cables each exactly 24' long from RG-62/U coaxial cable (90 Ohms)exactly as described in the SB300/301/303 receiver manual. Yes, thetransmitter connection is described in the receiver manual. The cable partscame with the receiver, not the transmitter. Go figure. Anyway, theimpedance is not relevant. The shunt capacitance per foot is very critical,since it can detune the circuits which are used to link the receiver to thetransmitter. The crystal HF oscillator in the receiver is used to drive thetransmitter. The USB and LSB BFO crystals in the receiver are used tooperate the transmitter. In the SB400, you may find it advantageous toremove the BFO crystals EXCEPT THE CW crystal, to prevent a beat note onreceive. The CW crystal is required to operate CW and Tune modes. I do notknow if the 401 requires this, but try it if you have problems. The LMO(VFO) is linked between the two rigs for transceive, and is the ONLYoscillator switched to go to split frequency operation. In a pinch, I haveheard that some people will disassemble a junked AM car radio antenna,which often uses a similar coax cable. I have a quantity of the correctcoax on hand, which I have often mailed to those who need this item.
The LMO sometimes develops a jump or warble as you tune in a station that is annoying in CW or SSB modes. This is a link to fix that problem: http://nebula.wsimg.com/d6a8106142d2492dec285d95be47aaf6?AccessKeyId=D1250C433DB440D6B60D
NOTE: The SB400/401 often comes WITHOUT the crystal pack. You do not needANY crystals (except the CW crystal) installed to operate the transmitter,if you are using it with a Heath SB300/301/303. For troubleshootingpurposes, to operate the SB400/401 as a stand alone unit, simply 'borrow'one or more crystals from the SB300 until you can get the SB400 running.Then connect them as described above. Note also that you have to re-alignthe HF oscillator coils as described in the manual as well as some otheradjustments. Since the crystals for 29.0 to 29.5 and 29.5 to 30 MHz coveredterritory for AM and FM, many did not install the crystals in a SSB/CW onlyrig. Again, the receiver came with the whole set; use the cables describedabove and you have no problem.
UPDATE -I have heard one report for VFO changing frequency when switching to transmit. I have never encountered this myself. I found the voltage regulation built in OK. The person told me he added another VR tube. I am not sure that the power supply capacitors, resistor values drifted, or something else may have been off. But this is added as a cautionary note, in case you have problems.
Good luck with your restoration. These have nice audio on transmit. TheALC circuitry works better than the transceiver SB100.
Heathkit Sb 303 Manual Download
GUEST UPDATE 4/19/2014 -I was studying the schematic for the SB-300 and found an error on theheterodyne crystal oscillator switch wafer labeled BS1R. The commonconnection for crystals Y6, Y5,Y2 and lastly Y1 should be grounded. Rightnow without any connection, one side of all of these crystals are floating.They do have it correct for Y3, Y4,Y7 and lastly Y8. This is just aschematic drawing mistake and obviously the wiring of the receiver iscorrect since the receiver works!
73,
Joe, W3GMS
UPDATE 7/12/2016 -One more Heathkit Twins glitch is addressed at:http://www.boatanchor.com/heath/SB300-SB301%20Voltage%20Regulation%20.pdf.I have not personally tried this modification myself, but it appears to be carefully researched and implemented. Please keep in mind that the SSB equipment of this day was not very stable; people were using SB-10 adapters driven by DX-100 VFOs that were barely stable enough for AM, marginal for CW, and totally unacceptable for SSB. Comparing first or second generation SSB gear to modern rigs is just not reasonable.