Source for 700v 8uf filter caps

Discussion in '"Boat Anchor" & Classic Equipment' started by W7UUU, Jun 11, 2018.

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  1. KM1H

    KM1H Ham Member QRZ Page

    Without knowing the choke inductance and DC resistance plus transformer impedance everything is a WAG. I simply would not recommend 40uF and will you pay for a transformer and tube if they let loose?

    Not uncommon back then.

    By how much? And why stress the transformer. Mo is not always betta:eek::rolleyes:

    They call it a Pierce, not modified. The screen functions as the plate in a pentode.

    $55 wasnt that expensive for quality and not all Novices or new hams were crying poor mouth. Its long production life says Johnson was happy with the sales.
    At least it didnt fry transformers as did the poor design Heaths.

    The 5U4GA was released 4-23-54 with a 250 ma rating and with a T-11 bulb. The 5U4GB was released 4-30-54 with a 275 ma rating, a T-12 bulb, and fins on the plates so either could have been used in the Adventurer if the engineers thought it necessary or at some time during its 1954-63 production life.

    There was also a 5Z4 which was a 5U4 with a different pin out to keep people from swapping in a lower spec 5Y3 or similar. One of the original 5-7-35 new metal octal releases and appears to have been mostly on Philco sets and soon followed. by the 5U4G. It is in the 6L6 class as far as leaving skin behind on a hot one! The 5T4 is another 5U4 variant with a different pin out released by RCA in 2-4-37 to add more revenue. Other variants such as the hefty 5AT4 appeared as late as 1961 for high power stereo and other amps....BIG bucks today.

  2. N2EY

    N2EY Ham Member QRZ Page

    To a certain extent. What can be done is to do before-and-after measurements.

    Why would increasing the input capacitance to 40 uF cause the transformer and/or tube to fail? Do you really think the transformer in the Adventurer is operated so close to the edge of its ratings that such a change is more than it can take?

    If the power transformer is running that close to meltdown, then it should never be used on AM, particularly plate-modulated AM, because of the duty cycle of AM. Yet EFJ provides info on how to plate-modulate the Adventurer with an external modulator. So there must be considerable reserve in the power supply.

    Not good, either. The soaring key-up plate voltage can cause chirp and clicks.

    You mean you don't know?

    Then the Adventurer should never be run on AM.

    The Pierce crystal oscillator uses a triode. The modified-Pierce uses a tetrode or pentode. The "modified Pierce" name comes from the ARRL Handbooks and other sources.

    btw, here's an article which explains the advantages of different tubes and crystal oscillator circuits.

    The measurements made show that the 6AG7 in the modified-Pierce circuit gives the lowest crystal current yet provides plenty of output on both the fundamental and harmonics.

    I already mentioned the quality of the Adventurer, with its use of ceramic parts and real transmitting parts where others used less-expensive parts.

    "Crying poor mouth"? $55 in 1955 inflates to $511.81 in today's money.

    Ten years on the market, 6,142 Adventurers sold.

    The DX-35 and DX-4o transformers were simply not up to the job.


    IMHO a near-optimum design for a classic Novice transmitter was "65 Watts At Low Cost" by W1ICP (QST, March 1961). It used a 6K6GT crystal oscillator (but a 6AG7 could be used) feeding a pair of 6BG6GA sweep tubes (but other tubes could be used).

    The design used relatively low plate voltage (350-400 volts) from a TV power transformer. At 350 volts, 215 mA plate current would give the old Novice limit of 75 watts input. The low plate voltage meant AM BC capacitors could be used for both the tune and load caps.

    Of course neutralization would be needed, but that's no big deal. A typical TV power transformer would loaf along in such service.

    Jim, N2EY
  3. W7UUU

    W7UUU QRZ Lifetime Member #133 Volunteer Moderator Life Member Platinum Subscriber QRZ Page

    I love all the theoretical back and forth in discussions like this. It gives me lots of stuff to consider, think about, and Google.

    Meantime, I'm always, it would seem, the bloke on the business end of the soldering iron hoping all the advice bears out in a "good way" :)

    Caps should be here later this week and I'll see how it goes. In fact, it will be a separate thread - it's a transmitter that arrived fairly smashed up do to the choke coming unbolted in transit. The seller would have had no way to know it would do that - just a fluke. The choke took out the 5U4 and the large RF choke, as well as the choke busting up its own frame and wiring. So I figured I may as well upgrade the caps while I'm at it. It was "known working" when shipped - with video to prove it. So should be an easy fix.

    Thanks for all the great discussion and insight

    This is the very first Johnson transmitter of any kind I've ever owned - I plan to pair it with a spare Drake R4B I have on hand. Crystal control for how, until I rebuild my HA5 later this year.

    Either way, a nice setup I should think :)

    WA7PRC likes this.
  4. N2EY

    N2EY Ham Member QRZ Page

    Oh man! Sorry it got busted up!

    Do you have a replacement for the RFC?

    You're welcome.

    Note that the Heathkit rigs used choke-input filters, resulting in much better B+ voltage regulation. They just under-rated the power transformers.

    Very nice!

    The HA-5 is a really nice VF). Heterodyne type, which is unusual.

    Johnson made some really great stuff in from the late 1940s to the early 1960s. But they never made the transition to transceivers and SSB.

    EFJ did design an advanced SSB transceiver in the 1960s - the Viking Avenger. (The Avenger name was later reused for a Johnson VHF radio) It had a lot of advanced features - dual VFOs, all solid state except the final and driver tubes, decent performer. But it cost so much to make that it would have cost about double what a Collins KWM-2 cost at the time. So after some prototypes were made, the project was abandoned.

    EFJ was eventually sold off in pieces to various other companies.


    Johnson named most of their rigs with rather - aggressive - names. Challenger, Valiant, Ranger, Thunderbolt, Invader, Adventurer, Courier, Navigator.....

    Only a few EFJ rigs didn't have such names - the Desk Kilowatt, the Five Hundred.....and that's about it.

    (insert appropriate Ole and Lena joke HERE)

    73 de Jim, N2EY
  5. W7UUU

    W7UUU QRZ Lifetime Member #133 Volunteer Moderator Life Member Platinum Subscriber QRZ Page

    Yessir! Thanks for asking.

    Photo below is how it arrived. I knew something was really wrong when I picked up the box and "heard things". But again, the seller would really not have expected the choke screws/nuts to undo themselves in transit. I was really pretty lucky, actually.

    The choke stayed connected. Had it fully ripped loose, it could have taken out everything.... variable caps, coils, 807, panel meter... granted, I do have spare 807 tubes and 5U4GB (per the cap upgrade) and could probably source other broken bits - but as I said - I got lucky.

    You can see splices on the PS choke - it had been removed sometime in the past, and reconnected or replaced.

    I don't know the actual value of the large RF choke - but I have a respectable supply of RF chokes and should be able to match it. Of course, if someone knows the actual uH value, that would help - but I'm assuming in the range of 2.5 uH or so. It really got chuffed in the shipping - very torn up, which surprised me given the choke never touched the 807 tube.

    So there ya go - yet another W7UUU project to "get on the air" - and you know I will do just that :) It's what I do :)

    My goal will be "Nostalgic W.A.S." within a year, paired with my Drake R4B


    Trashed Johnson.png
    Last edited: Jun 14, 2018
  6. SM0AOM

    SM0AOM Ham Member QRZ Page

    It is quite sad to see such damage, but as you said, a certain amount of luck was around anyway.
    Much more expensive components than a rectifier tube and a "garden-variety" RF choke could have been damaged.

    Which BA transmitter to be paired with which BA receiver is a quite tricky question;
    is the goal to optimise for authenticy or for performance?

    Performance-wise the Drake R-4B is way over the contemporary receivers that usually went with the Novice BA transmitter
    of this era, which usually were in the Hallicrafters S-40 or at the best SX-99 class.

    It feels somewhat like a m├ęsalliance to pair an R-4B with a lowly CO-PA, it somehow feels like it would be worthy
    of a somewhat more "classy" running mate... But to each his own.

    Just now I am into the same question; I was recently given two Eico 720s and one DX-40, all in decent working order.

    It would be nice to compose at least two 1960s' BA operating positions,
    using receivers that would have been appropriate for the period and level of ambition.

    This somehow rules out Collins 51S-1:s or R-390A:s, as well as Rohde&Schwarz EK07,
    Eddystone 880/2, Racal RA-117, Standard Radio SR25, Hammarlund SP-600 or Philips BX-925.

    Remaining options could be Drake 2B, Hammarlund SP-210X, Hallicrafters SX-101A, SX-24, S-76 or S-40B,
    British General Electric BRT-400S, Eddystone 740, National HRO-50, Max Funke RX-57 or maybe some surplus gear such as a
    Marconi CR100/2, BC-1147, BC-312 or 348.

    A trip to the BA receiver storage facility in the basement to overview the various possible running mates for the transmitters
    is a task to be undertaken...

    W7UUU likes this.
  7. N2EY

    N2EY Ham Member QRZ Page

    They must have been loose for that to happen.


    It's a 2.5 mH choke, per the manual. btw, the plate blocking cap, C9, is kinda small for the application (.0003 in the manual - only 300 pF). I suggest a .01 there. Has to be pretty HV - 1.4 kV minimum for CW.

    Note that the Adventurer doesn't have a "safety" RFC on the output. If C9 shorts, you could get full B+ on the antenna. (Neither does the Heathkit DX-20 - and the stock DX-20 doesn't have a mains fuse, either!)


    73 de Jim , N2EY
    W7UUU likes this.
  8. KM1H

    KM1H Ham Member QRZ Page

    You totally missed the point.
    When the 5U4 shorts it often takes out the transformer before the fuse opens.

    The Pierce is not limited to a triode and the Adventurer is still a Pierce. the modified version adds feed back for when a regulated screen supply is used which is correctly stated in the above link which Im very familiar with.

    That commonly quoted inflation "formula" doesnt show the true buying power of the 50's when a worker was able to keep a lot more of his salary.

    What you actually said was:
  9. KM1H

    KM1H Ham Member QRZ Page

    Theoretical PLUS practical experience from those with decades of experience in the repair side:cool:

    Show us the repair progress, I love your work!

    Ive been a Johnson fan since 1957 when I bought a used Viking I with matching 122 VFO. These days I have another V-I , plus a V-II CDC, Ranger, Valiant, and a 6N2. Along with 122 VFO's, a HA5, HT-18 and WRL 755A VFO's are used with other rigs.

    W7UUU likes this.
  10. KM1H

    KM1H Ham Member QRZ Page

    Period receivers in the middle range price class would be the National NC-109 (a real sleeper), NC-190 with SWL and ham dial selections, and NC-270. The HRO-50 was high end gone by 1952 and the 50-1 by 54. Coil changing can be a PITA plus you have to wait until the HFO stabilizes.
    Also the HQ-140X/XA, SX-100 MK2A.
    A Collins R-388 would likely be readily available over there and are dirt cheap in the US.

    I have an Eico 720 and finally found an affordable 730 modulator.


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