Henry 2k Restoration plate transformer options

Discussion in '"Boat Anchor" & Classic Equipment' started by G4LPL, Sep 16, 2018.

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  1. G4LPL

    G4LPL Ham Member QRZ Page

    looking for opinions, info, suggestions

    I have recently acquired an early Henry 2k console amplifier which I am restoring as far as I can. It's one of the original style amps 1963-65 with the resonant choke anode supply and a pair of 3-400Zs. It also has a the factory soft start. The amp was in poor cosmetic shape having been left standing unused and uncovered in someone's radio shack for a very long time. Apart from that it seems totally original. A lot of screws were missing indicating previous failed attempts at repairs.
    I have already gone through the RF deck and cleaned it up a bit. The tubes have date codes of 6618 and blank. The one without a date code is taller and has a similar envelope height to a 3-500z. Neither tube has any meter readable inter-electrode shorts and both filaments light up when I apply 120v to the heater transformer. On to the Plate supply!

    Not so lucky here! One of the main line fuses (12.5A) was blown. The amp is wired 220 using a metal cased 3 pin plug and what looks like a rubber insulated cable. No Ground! I've checked with a meter, the plate transformer, the resonating choke, the bleeder chain. All appeared ok and more importantly no dc path to the chassis. Both the resonating capacitor and the filter capacitor read the correct values with my el cheapo Chinese LCR meter. Time to put some volts on it. Plate transformer alone first. Using a Variac and no rectifier tubes in place I increased the voltage monitoring the secondary volts. As the secondaries passed 2000v I could hear a fizzing noise from the transformer can and the voltage became unstable. Hmmmm!

    The transformer is all but unobtainium. It's a weird thin and tall size and in a can of 1960s bitumen! Hammond manufacturing's offering as a replacement is $1000 and from the dimensions given won't fit on the chassis in the same space. W1ZM has closed his doors so having the original re-wound by someone who knows the transformer is out. I've tried contacting the various Henry people with no result. I have been in contact with Fred KC5RT (Northland Drifters), he used a commercially available Ameritron transformer on his last repair which utilized a doubler circuit. That would exclude the use of the current filter capacitor, choke, bleeder chain etc and probably reduce the weight of the psu by 50lbs.

    So: I've cooked the transformer can to remove most of the bitumen, soaked it for a week in diesel to soften the rest, cut the can off and liberated the transformer from it's goo! Taking pictures as I go I've removed the laminations, and unwound both parts of the secondary (it's split on the bobbin), removed the copper screen and both primaries to be left with the original bobbin which is still serviceable. To do this I made a rudimentary winding machine with counter.

    If you have read this far down, you probably need another hobby! I'm left with 3 main choices:

    1) Rewind the existing
    Pros:
    Will fit in the same place. I can wind it for 120/240 not 115/230 like the original. I can adjust the secondary volts for solid state rectifiers or even 3-500z tubes. Cost.
    Cons:
    Tedious, each secondary part is 3080 turns. Space, modern insulation will be thicker potentially so it might not fit in the window. No can or potting, maybe the end result will be noisy. Potential for other components to be faulty as work progresses.

    2)Find or build a plate transformer from scratch (C-core or toroid) with a tapped secondary to use full wave bridge rectifier.
    Pros:
    resonating choke, capacitor and rectifier filament transformer gone to make space on the chassis. Can use existing filter capacitor and bleeder chain. Consistent with tube upgrade.
    Cons:
    Not original. Will need mods to chassis. Cost

    3) Use Fred KC5RT's idea of a readily available transformer and construct a voltage doubler circuit.
    Pros:
    Uses off the shelf parts.
    Cons:
    All other existing components unused.Not original. will need mods to chassis. Cost

    Those are the options as I currently see them. My original goal was full restoration but that looks almost impossible at this point unless a 100% working replacement transformer appears on the market or I throw a load of money at it. Neither of these seem likely. Any positive suggestions or info would be welcome.

    Ian
    G4LPL
     
  2. WO4K

    WO4K XML Subscriber QRZ Page

    Contact John Birdlebough, K7BIT. He repairs Hanks.
     
  3. KM1H

    KM1H Ham Member QRZ Page

    Scrap the 50-60's era choke idea and go with a copy of any of the modern PS using just a capacitor filter. The Ameritron version is very reliable even in the AL-1500, all their senior amps use the same one.

    Carl
     
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    ^I'd go for that also.

    Without the choke, the bleeder power can be much lower, saving power and heat. Drill some holes.
     
  5. WB2GCR

    WB2GCR Ham Member QRZ Page

    Owning one of them, if I had the same problem, I'd look for a replacement transformer of similar
    ratings. Going to a cap input filter, maybe, but only if it was a C-L or C-L-C and then only if it was
    necessary to get the B+ voltage that I needed from a given bit of iron.

    The original iron has the filament windings on the same core. Separating them is a good thing,
    but requires some sort of mounting arrangement in the pedestal.

    As far as rewinding, afaik WZ1M is still going rewinds?

    One could rewind the iron by hand, but it takes time, a jig and a lot of copper wire... fwiw, there was
    a neat 1950s Hints & Kinks or short article on rewinding HV iron using segmented windings that were
    made up using stand alone segments that were then stacked up on the core! This added to the HV
    breakdown resistance. Neat idea, think of doughnuts of wire + insulation stacked up on the core...
    Always wanted to try it. :D

    Since there is a lot of height available, one could find two transformers and potentially stack them
    to get the current rating.

    Dunno if I would consider a doubler...

    Ymmv.
     
  6. G4LPL

    G4LPL Ham Member QRZ Page

    Thanks for the responses so far:

    That's the way I'm favoring at the moment, probably rewinding the original core to use a 4 diode bridge and utilizing the current filter capacitor.

    Good point. The last thing I need in Florida is another heat source. I found an article here https://www.qsl.net/i0jx/supply.html on resonant choke circuits and reducing the bleeder current

    Not in this iteration of the amplifier, the filament transformer is in the RF deck so no real complication in that area.

    Unfortunately Gary has retired and not taking on any more rewinds. He's trying to sell the business as a going concern I believe

    Now it all makes sense! I couldn't understand why there were 2 cardboard formers and the secondary one was in 2 halves. Both formers are rectangular in section. The primary one having a copper shield over the primary winding which gave an oval finished section. The much larger secondary coils were wound separately on half length thick cardboard rectangular formers and glued in place over the secondary. The corner voids were filled with bitumen when the whole thing was potted.

    I'm probably going to rewind it for a 2000v secondary and 120/240 primaries, use a 4 diode bridge and the existing filter capacitor and reduce the bleeder current significantly.

    One problem regarding the rewind is the turns per volt differs between the primary and secondary windings. The can says 115,115 or 230 for the primary, each winding was 118 turns so 1.026 turns per volt. That makes the core's Tesla rating about 1.3 on a good day. The secondary is supposed to be 2800,0,2800, each half of the winding was 3078 turns which is 1.099 turns per volt. Quite a difference! When I original put volts on the transformer to test it, at 115 volts on the primary the half of the secondary that wasn't fizzing had an open circuit voltage in excess of 3000 volts, which is consistent with the primary turns per volt but not the label on the can and way too high for a pair of 3-400s unless there's significant loss through the tube rectifiers. Any ideas?

    Ian
    G4LPL
     
  7. KM1H

    KM1H Ham Member QRZ Page


    With a cap only you need about 20-25 uF total for good SSB dynamic regulation with an adequately sized transformer. I dont know if the original core is up to the task as the tuned choke did a good part of the regulation. Remember that it is a early 60's product and the lamination material is old school which is another strike against it.

    What is the DC resistance of the windings?

    For AM I suggest another 10 uF or so to reduce the carrier hum. I use a string of 8 330 uF 450V 105C Snap- In caps in the various commercial amps I use for CW/SSB/AM and can see the improved SSB IMD on the spectrum analyzer on those with marginal transformers....which is about the norm:rolleyes:

    Ive had Heyboer rewind several decent cores as well as new builds and have always been pleased.
    https://www.heyboertransformers.com/

    Carl
     
  8. G4LPL

    G4LPL Ham Member QRZ Page

    The original core is 2.5 by 1.75 inches, the window is 6.0 by 1.25 inches. It's made up of 2 'E' sections, a long one and a short one, not your regular 'E,I' type. I'm guessing making it long and tall was due to accommodating all the other stuff on the chassis. I've looked at using a pair of C=cores to wind on also, that might be a way to go. Cost of materials to wind myself would be around $250.

    I didn't measure the DC resistance of either winding. The secondary was burned on one half and for all I knew until I opened it the other half could have been the same. The primaries are sitting in the scrap bin coiled up so I could measure those. They were wound of 14 awg square section wire.

    The current filter capacitor is a 20 uF 4kv paper. It reads 20 on my LCR meter but that's no guarantee it works I know. If it works all well and good, if not I'll resort to the electrolytic chain. IIRC last time I built a plate supply from scratch (in the late 80s!) I used 8 470uf @ 450v which is consistent with current practice

    I've looked at a number of rewind sites but the shipping costs these days cost about the same as the wire to do the job.

    Ian
     
  9. AC0OB

    AC0OB Subscriber QRZ Page

    Hi Ian,

    I upgraded my power supply in the Henry 2K-4 about 5 years ago as per the PDF below, and it has been very reliable.

    I hope this helps.


    Pheel
     

    Attached Files:

  10. G4LPL

    G4LPL Ham Member QRZ Page

    That's what I'm aiming for apart from the voltage which is way too high for a 3-400z!
     

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