ad: davisrope-1

Heathkit DX-35

Discussion in '"Boat Anchor" & Classic Equipment' started by K1OIK, Jan 17, 2022.

ad: L-HROutlet
ad: l-rl
ad: l-BCInc
ad: Radclub22-2
ad: L-MFJ
ad: Left-2
ad: Left-3
ad: abrind-2
  1. N2EY

    N2EY XML Subscriber QRZ Page

    Hold on a moment there.

    You removed the plate cap of the 6146 and operated the transmitter that way?

    If so, why?

    A screen-grid tube should NEVER be operated with screen voltage and no plate voltage, because doing so can easily result in excessive screen current and a useless tube in a short time.

    It would be more informative if you specified what those pins are - Triode #1 grid, Triode #2 plate, etc.

    But some are. And the rest can usually be calculated.

    The modulator sections of the DX-35 and DX-40 are similar, so it would be helpful to compare manuals.

    Have you traced out the wiring and circuitry and compared it to the schematic? If not, why not?

    Have you taken resistance readings and compared them to what the resistance should be?

    That's nice - but why do you keep telling us that?

    You get a tax deduction for all donations, right? But the person who buys what you sell doesn't get the deduction.

    So why do you keep mentioning it?

    You mention not donating to ARRL often. Why?

    Please explain what your donations to charity have to do with fixing old radios.

    Consider that if you really want to fix old radios, you need to work smarter, not harder.
     
    W7UUU, W1BR and AC0OB like this.
  2. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    I too support St. Jude and have actually visited them, but back to the DX-35.

    I assume you have removed the 12AX7 speech amp tube to make sure that the oscillations are NOT coming from it?

    The reason for removing the 12BY7A Driver stage tube was to remove all RF from the system since the oscillator and the driver are in DC series. NO driver, no RF. Removing the Final was to insure it was not stressed with no RF on it's control grid and with the presence of screen voltage.

    I will purchase the DX-35 from you for what you paid for it plus some extra for your St. Jude fund within reason. My email is current.

    I just don't like to see these early Novice rigs languish! :(

    Pheel





     
    Last edited: Jan 22, 2022
    N2EY likes this.
  3. K1APJ

    K1APJ Premium Subscriber QRZ Page

    Posting this against my better judgement, but a few minutes of internet search revealed the attachment, which gives a general outline of troubleshooting the DX-35, including tube pin voltages.

    What frequency is the oscillation?
     

    Attached Files:

  4. K1OIK

    K1OIK XML Subscriber QRZ Page

    Wow, great post. I will get to work on it. Thanks a lot.
     
  5. K1OIK

    K1OIK XML Subscriber QRZ Page

    With the 12BY7 removed on the scope set for 0.5 milliseconds there are three sawtooth type wave forms in excess of 50v P/P on pin 1 of the 12AX7.
    With the 12AX7 and the 12BY7 removed there is no oscillation on any pins. The 12AX7 may not be the origination of the oscillation, just a player in the process. It looks like I am not the first one to troubleshoot this as several capacitors in the circuit look new as I checked to see if built as drawn.
    I don't recall what I bought the DX-35 for. It was bought last October at a hamfest. I started donating to St. Jude instead of the Salvation Army when one of their truck drivers told me what they do with non-monetary donations.
    The DX-35 will not be parted out. It will be sold fixed or with a notice of modulation issues.
     
  6. N2EY

    N2EY XML Subscriber QRZ Page

    And that works out to what frequency?

     
  7. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page


    Then it will not be fixed. Why sell anything that is not properly fixed?

    Remove both the 12BY7A Driver AND the 12AU7A modulator tube AND the Final as was previously requested.

    Short the mic input jack, not anything else. Scope again Pin 1 of the 12AX7A. If there is still an oscillation on Pin 1 then suspect the previous owner has mucked it up by the incorrect placement of components and has created a positive feedback situation.

    You still haven't stated if you checked the 12AX7A circuit or the 12AU7A circuit components and their placements (physical location) against the schematic or the assembly manual.

    You must analyze one stage at a time when troubleshooting in order to eliminate as many variables as possible.

    This is simply commonsense troubleshooting which by now should be apparent to you.

    Some on here want a quick fix without properly understanding circuit operation.

    Pheel
     
    Last edited: Jan 22, 2022
    W1BR, N2EY and W7UUU like this.
  8. K1OIK

    K1OIK XML Subscriber QRZ Page

    Sometimes I sell things at a reduced price to someone who is more adept at troubleshooting.
    With the 12BY7, 12AU7 and 6146 removed on pin 1 of the 12AX7 there is 6 v p/P an uneven sine wave on the 2-millisecond setting.
    Voltage measurements:
    With all tubes in but the 6146.
    12AX7
    1. 185 2. zero 3. 2v 6. 85v 7. -0.4 8. zero
    Should be from manual
    1. 160v 2, zero 3. 1.8v 6. 95v 7. -0.8 8. zero

    12AU7:
    1. 400 2. zero 3.36 6. 400 7. 77 8. 150
    Should be:
    1. 425 2. zero 3. 36 6. 420 7. 35 8. 60
     
  9. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Why change the scope settings? Go back to the original setting and report the period and amplitude of this waveform on Pin 1.
    Mode should be AM without KeyDown. Is this with the mic jack shorted? You didn't confirm this step.

    With the 12BY7, 12AU7 and 6146 removed on pin 1 of the 12AX7 there is 6 v p/P an uneven sine wave on the 2-millisecond setting.
    Voltage measurements:
    With all tubes in but the 6146.

    The above doesn't make sense Burt. Do you see the contradiction?


    How did you get these voltages with the tube out? You never said you put the tube back in its socket.

    You still haven't stated if you checked the 12AX7A circuit or the 12AU7A circuit components and their placements (physical location) and the wiring against the schematic or the assembly manual. This is a basic step in any troubleshooting and should be done before going further.

    Pheel
     
    Last edited: Jan 22, 2022
    N2EY likes this.
  10. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

  11. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Been reading the mail on this very interesting thread, but I'll jump in with my two cents. With very few exceptions, all old radios (receivers or transmitters) have been tinkered with by someone who should have avoided electronics as a hobby. And former kit radios are even worse -- many of them were built incorrectly from the start and the mistakes can be hidden in the wiring. For that matter, even the commercial manufacturers have been known to have made mistakes. I would like to amplify what Pheel (and others) has said. With any boat anchor restoration work, tracing out the relevant wiring against the schematic is absolutely, positively essential before deciding what to do about anything. Everyone has their favorite method, but mine is to print out the the schematic in sections and then trace the radio out, marking where I've been with a highlighter. I will sometimes mark the component in the radio with a tiny dot of ink from a fine-point sharpie and then look to see if any EXTRA components have been added.

    I'm not sure that fixing up old shortwave transmitters and receivers is anything to engage in for resale purposes of any kind -- the work is just too intense to do it to turn a buck. There's no such thing as doing a quick once-over, popping in a new set of tubes, and calling it good as new. And some of these boat anchors will eat you alive if you're on a timetable.

    Hope this is helpful!

    73 - Steve, KW4H
     
    N2EY likes this.
  12. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    For darn sure you had better have a love for bringing vintage equipment back to life and not for the resale value.

    I recently sold my updated/upgraded Viking II-CDC for a paltry price only because this older gentleman had one when he was younger and wanted to relive memories. I probably put 120 hours of labor and $200.00 worth of parts into it and sold it for about 1/4 of the total costs.

    Pheel
     
    K1OIK, KS4W, N2EY and 3 others like this.
  13. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    I think a lot of us fix up boat anchors because it's a great learning experience (every piece of equipment is its own puzzle) and there's a lot of memories involved with tube radios. I restored a HRO-60 last year that was a nonfunctional mess. Every single circuit had to be traced out by hand, some areas rebuilt from scratch because someone had botched it up terribly. Had the case refinished and I relettered the front panel. I would only consider selling it to the right person who wanted the memories because there's no way in hell I'd ever recapture the parts costs or even a fraction of the labor involved. My point is that we do this stuff because we love it and we don't want to see these old beauties go to the dump.

    Steve.
     
    KS4W, N2EY and AC0OB like this.
  14. K1OIK

    K1OIK XML Subscriber QRZ Page

    I am not doing this to, "turn a buck", with the time already expended it is a loss. It is a challenge. I make a lot more trading in the stock market, at least until the last few weeks. Tomorrow I will address the help that was recently posted. I also found an electrolytic connected to pin #3 of the 12AX7 disconnected, probably by someone trouble shooting. This is not going to the dump. 90% of what I get or more gets fixed by me without coming here.
     
  15. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Disconnected from what? You need to be more forthcoming with your information and more descriptive.

    That 2uF cap is there to stabilize bias and to prevent a loss of gain at the second stage, since they needed all the audio gain they could get to modulate the 12AU7A.


    Pheel

     
    N2EY likes this.

Share This Page

ad: M2Ant-1