Heathkit SB401

Discussion in '"Boat Anchor" & Classic Equipment' started by KB1FGC, Jan 11, 2021.

ad: L-HROutlet
ad: l-rl
ad: L-MFJ
ad: Subscribe
ad: QSOToday-1
ad: abrind-2
ad: Left-3
ad: Left-2
  1. KB1FGC

    KB1FGC Ham Member QRZ Page

    Hi,I am cleaning up a SB401 and have most of it done,But the 2 Tubes V10 and V11 don't seem to unplug and am afraid of damaging them.Does anyone know if they just pull out like most tubes?It looks like it. have the Manuel and so far haven't found the step where it would show that.I do see the pictorial diagram and it shows the sockets,so maybe they are corroded.
    Rich
     
  2. KB1FGC

    KB1FGC Ham Member QRZ Page

    Never mind.I took off the back panel and shot some electronic cleaner in it and it came out.I'm sure I'll have more questions-lol
    Rich
     
  3. KI4ZNV

    KI4ZNV Ham Member QRZ Page

    While you're doing that, cramolin ALL the sockets and don't forget the rotary switch wafers and pots either.
    --scott
     
  4. KB4MNG

    KB4MNG Ham Member QRZ Page

    Very nice unit. hope you have the crystal pack
     
  5. KB1FGC

    KB1FGC Ham Member QRZ Page

    I'm set up for the 301/401 combo.I'm still leaning a lot about it,I know some crystals are not there but assume that is for use when using another brand for receive.
    Thanks Scott,yea I sprayed all the contacts,now I need to fix the dial and am putting in a new power cable.Hope it works after that.
     
  6. W5RKL

    W5RKL Ham Member QRZ Page

    [QUOTE="KB1FGC, post: 5733663, member: 912824"I know some crystals are not there but assume that is for use when using another brand for receive.
    [/QUOTE]

    I don't know what you mean by "another brand for receive". Maybe that's a typo. If, however, you are referring to the missing crystals that control
    another "receiver brand", then that's no true. The missing "crystals" have nothing to do with receive nor "another brand for receive".

    There are 8 crystal sockets on the top of the chassis. The transmitter operates on 80 thru 10, no WARC bands. The crystal pack includes the
    crystals as follows:

    80 - 12.395Mhz
    40 - 15-895Mhz
    20 - 22.895Mhz
    15 - 29.895Mhz
    10 (28.0) - 36.895Mhz
    10 (28.5) - 37.395Mhz
    10 (29.0) - 37.895Mhz
    10 (29.5) - 38.395Mhz

    Using any other crystal frequencies inserted into any of the SB401's 8 crystal sockets, will not work.

    The 8 individual crystals are required when the SB-401 transmitter FUNCTION and FREQ CONTROL switches are set for
    option #1 listed below:

    Option #1
    FUNCTION switch set to TRANS (Transmit)
    FREQ CONTROL switch set to UNLOCK
    This option allows the SB-401 to operate as an "independent" transmitter without the transmit frequencies to be controlled by the
    receiver.

    The 8 individual crystals are NOT required when the SB-401 transmitter FUNCTION and FREQ CONTROL switches are set for
    option #2 listed below:

    Option #2
    FUNCTION switch set to TRCV (Transceive)
    FREQ CONTROL switch set to LOCK
    This option allows the SB-301 receiver to control the SB-401 "transmit frequency". This option requires the connections shown on
    page 105 Figure 4.1B. Other Heathkit SB receivers such as the SB-300 and SB-303 can be used in this option.

    There is no 3rd option to allow the SB-401 to control the SB-300/301/303 receiver's frequency. Heathkit never included that option in the
    FREQ CONTROL switch setting in TRCV.

    73
    Mike W5RKL
     
  7. KB1FGC

    KB1FGC Ham Member QRZ Page

    Mike thanks for reply.I saved what you said and it will help out when I get ready to test on the air.I sometimes words things a little oddly but I think I was on the right track,your explanation helped me understand it a little better though.Nice to have this forum:).I have Option 2,I don't have crystals in the 401,But have 8 in the 301.There are some things I don't understand yet about tubes rigs so I am gonna have to read up on the Manuel--My first Tube rig-lol.
    Rich
     
  8. W5RKL

    W5RKL Ham Member QRZ Page

    Hi Rich,

    I recommend you spend some time studying/reading the SB-401 manual's "Circuit Description" section. There you will find discussions
    about each stage along with the schematic of each stage so you can see how the circuit is wired/constructed, and how each stage works
    with follow-in stages to ultimately produce an RF output.

    You also should spend time studying the SB-401 Block Diagram. There you will see how each stage connects to other stages. You will
    also, see how the FREQ CONTROl switch settings change the oscillator signal paths in TRANS or TRCV.

    Hopefully, you have the complete SB-401 assembly manual.

    You should also learn how vacuum tubes work. I recommend you download and read "Basic Radio Course" by "John T. Frye at the
    the following link

    https://w5rkl.com/wp-content/uploads/2015/02/Basic-Radio-Course.pdf

    There are chapters on vacuum tubes and how the various "types" of vacuum tubes (Diode, Triode, Tetrode, Pentode, and Pentagrid)
    work.

    73
    Mike W5RKL
     

Share This Page