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Heathkit HP-23A + SB102

Discussion in '"Boat Anchor" & Classic Equipment' started by TERROR_BYTE, Jun 21, 2020.

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    I have a Nice Heathkit setup that Ive pieced togetther via ebay and such.

    I have begun the task of replacing old components with new of better or equal vaules (heathkit did run them close to their max wattage specs)

    I have replaced the 4x 150uf carboard tubed caps with 100uf 450v (what I had on hand)
    Replaced all diodes with 1n4006 600PIV ones from the 57-27 types

    I replaced the breaker with a 3A modern one vs the 2.92 A one (seemed stiff, worried it wouldnt trip )

    That being said, my HV voltage seems to be under the 800V that the receiver SB 102 sees.


    I had replaced the 2x 20uf caps on the board and the other 2x Electrolytics on top the LMO cage C304
    I had found a wildly out of spec 22K that read 44K on the Audio board (by V14) R316
    replaced the 7W 2.5K ohm with a new 10W one (though its only burning 3W) R305

    Issues thus far:
    -Bias Pot wont adjust the bias supply (stuck on -107V instead of 110v)
    -Audio output is much lower after replacing the caps / R on the audio board

    B+ is 290V not the 300V

    I went over the Resistance measurements and found it close to the ball pall .

    Before replacing the 2.5K it was Open (so I suppose B+ wasnt flowing to half the rig) 150V rail

    Setting the device to Calibrate and USB/LSB actually does get a squeal as I near the 0 on the dial Finally , though USB/LSB seem 1 notch to the left or right of the 0.

    I can hear the static out of the headphones just fine. though it seems after replacing the cap and Resistor the gain just isnt coming out of the speaking from the PA tube

    I heard that the 10R at the Finals 6148 tubes go bad , would I need to test em out of circuit and not wrapped around the Cap, they show 1.5 in circuit but I think they are all linked in the schematic

    the 100R to pin 3 of the finals is in spec, the only R that seemed really bad was the 2.5K 7W that was replaced.

    I would like to wire this to a 4 pin as the 2 pin jacks are hard to comeby and my Turner mic is 4 pin.
    (any help with that would be awesome)

    What are my next steps

    SB-102 Schematic

  2. W7AMI

    W7AMI Ham Member QRZ Page

    Please be very careful working on this radio. The voltages present can be lethal.

    What are you using for a meter?

    There are 6 of the 10 Ohm resistors tied in parallel across the cathodes and suppressor grids of the 6146 tubes. So the total resistance should be 1.66 Ohms. That is with in 10% tolerance of your measured value and probably close enough given that your meter could easily have that much or more error in the measurement.


    Thanks for the Reply , Been really eager to get this rig up in the air (at least Rx ) while I study for my License.
    The lethal voltages in this are common for tube gear, higher than the average guitar amp :eek:

    I have worked out the issue with low audio output : (Needed to use a real antenna )
    I had a burnt out 2.5K 7W on the audioboard that was denying the transciever the LMO operation. Once I got that up, I replaced the 1K 7W with a 10W

    I cant get the meter ALC to zero as it sits too high at S6.

    I did the bulletin replacement of R 100k to 82K for this

    I wired my Turner Expander 500 to work with the 4pin plug that I installed on the Heathkit
    My makeshift antenna can now receive on 40m,20m,15m, but anything else is tricky (its a Inverted V about 10ft off the ground sloping to 6ft about 45ft each side)

    the 10R reading at 1.6 is reasonable and checks out. I do not see any grid current when the relays engage so I think Tx is not operational.

    And my common complaint is the dial slipping.

  4. W7AMI

    W7AMI Ham Member QRZ Page

    I cant get the meter ALC to zero as it sits too high at S6.

    Do you mean ALC or S Meter. The mod you mentioned is for the S Meter circuit.
  5. KK6IYM

    KK6IYM Ham Member QRZ Page

    First read the manual. There is a lot of information on troubleshooting and operation of the transceiver. When I restore one of these transceivers, I follow the alignment procedure in the manual. This is how I find the faults. If a step can't be performed properly, then I investigate the reason. Once the radio is fully aligned, you should be able to tell what needs work. Sometimes grid current won't show up until tuned circuits have been adjusted. Don't try and align the radio out of order--at least until you have had a few of these cross your work bench.


    KE4OH likes this.
  6. AI3V

    AI3V Ham Member QRZ Page

    Uh, stop replacing parts at random and troubleshoot the rig?



    I need to get a hold of the alignment tool (something nylon not a metal alenkey)

    then I can verify the alignment of the radio.

    My first steps was to remove / replace any out of spec and burnt out Resistors /caps

    Ive followed the Impedance measuring and found most in the ball park but some of the diode test in the manual gave me higher impedances or the same regardless of polarity:

    V9 Grid (pin5) = 3.9K
    Pin7 of V3 = 0 ohm

    CW jack = 63.4 (should be 50k)
    CW Jack Reverse (diode) = 48K (should be 30K)
    CW Jack TUNE/LSB/USB = 391K (should be 80K) Diode

    8R Jack 5.2R should be 0.7R TUNE
    Spare A = inf (ok)
    Spare B = inf (ok)
    ALC Jack = 7.6K (should be 5-100)(gnd chassis)
    ALC Jack = 6K (should be 20K) Diode (poz = chassis)
    ALC Jack =2M (should be 3 ) Diode USB /LSB
    Phone Patch Jack (1 M) (OK) TUNE
    Power Plug Pin1 22K (should be 13K)
    Power Plug Pin2 0 (ok)
    Powerplug Pinn 3 (35-40K ) (should be 35K) TUNE
    Powerplug Pinn 3 (35-46K ) (should be 25K)
    PowerPlug Pin4 (960K) should be 1M TUNE
    Pin 5 =0 (ok)
    Pin 6 = 1R (ok)
    Pin 7 = 0.7R (ok)
    Pin 8 = OL (should be 50K)CHASING THIS DOWN
    Pin 9 -11 = INF (ok)
    Pin 9 to Pin 10 = inf (ok)

    Pin 9-Pin10 (OFF/PTT/VOX) = 0 OK

    RFOUT = 1.9R (should be 0.2R)
    Phones + Phones VOL = 14R-600R
    Mic1 Jack=1M (ok)
    Mic2 =0 (ok)
    Mic2 =690K (should be 500K) LSB.USB.CW
    RF GAIN (leg2) (0-68K) (should be 10-70K)
    AF Gain (leg2) (0-500K) (OK)
  8. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    This is an alignment issue. However, after fifty years the USB/LSB crystals have probably aged and drifted. You may or may not have enough adjustment available on the respective coils. Even if you can't get them to zero perfectly, it's not critical.


    Going over the impedance / Ohm Meter readings in the manual to re-verify its in range. Page 94 in the manual + onwards

    Seems I got a high 1M at pin1 of the Power connector when it should be 13K , now to check that one (BIAS Supply )

    Its at 15K when the BIAS pot is reset its in the ballpark of 10%
    Last edited: Jul 2, 2020


    Following more impedance measurments:

    ALC Jack is giving me 7K regardless of polarity

    Ive traced it back to the FINALS

    with probe on chassis and the ALC jack , it should be 5-100R
    I read 7K ,

    Reversed Polarity is same, I think its at D903

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