Another pic of the 254W rig

[W8ACR]

Here is another pic of the 254W rig looking through the glass, and a closeup of the antenna tuner.

Ron W8ACR

[W4AAB]

Those tubes look a lot like the H-K(Heintz and Kaufman) 254's I have.

[W8ACR]

Hi Joe,

Yes, the 254W is basically the same tube as the original HK-254. Eimac and Penta made the 254W's.

If you want to see some pics of the RF deck out of the cabinet, I had some pics in a post in the QSO section on Dec 13th 2010. Those pics show a different front panel, but the RF deck is otherwise the same. Do a search on 254W and it should come up.

Ron W8ACR

[Opcom]

Won't that tube fit in the same socket as the 250TH and has the same filament voltage?

[W4AAB]

Yes, it does on both counts.I have the original article in RADIO from the 1930's when H&K introduced the 254, with a schematic diagram.

[w5omr]

Here is another pic of the 254W rig looking through the glass, and a closeup of the antenna tuner.

A couple of questions, Ron...

1) The (2) HK-254's are in parallel?  Pi-L circuit?
Regardless, why is the plate choke so far away from the tubes?  I Thought those lines were supposed to be as short as possible, along with some parasitic chokes in the B+ leads to the tubes to prevent parasitic oscillation.  Maybe I'm picking on nits, here... but every rig I've ever come across, has had the plate choke between a pair of tubes, or in the middle of more than 2.  Not that I'm saying that because it's been done like that for a hunnert years, that's the way it SHOULD be, or is SUPPOSED to be, just that I've never seen it done differently.  That's my only reason for asking.

2)  I notice the big B&W butterfly Tuning cap, paralleled with a split-stator cap.  Nice setup.  That's what's in the final of my rig, with the swinging link coupling the RF out to an antenna/xmtr impedance matching device in the name of Heathkit SA-2060, feeding 600ohm open wire line.  The question is, can you go from 75 to 40m simply by removing the vacuum capacitor?

[w5omr]

Won't that tube fit in the same socket as the 250TH and has the same filament voltage?

5.0v but at 7.5amps.  Full spec sheet can be seen at
http://scottbecker.net/tube/sheets/114/h/HK254.pdf

Interesting... I wonder why they call it a 254, when the plate dissipation is only 100w?

[Ralph W3GL]

   If you are referring to the RF Choke there on the right side of the chassis.
   that's the choke across the output that is standard practice for pi network
   circuits.

    If you look closely you will see the top of the shunt feed choke there in
    front of the right tube...

    The parasitic chokes are in the grid circuit and that copper strap to the
     plates is "short" for a single band amplifier designed for 160.

     Properly grid neutralized, it should  be stable as a rock...


   

[W2PFY]

I Thought those lines were supposed to be as short as possible, along with some parasitic chokes in the B+ leads to the tubes to prevent parasitic oscillation.

At these low frequencies he can get away with his layout. If you were to do the same thing on 40 meters there may be a problem. Another thing that would allow you to get away with long interconnections is the use of a single frequency or more accurately a single band.   

[KM1H]

H&K made some nice tubes which is why Eimac bought them. Id kill for a couple of 1254's

The 254 is midway between a 100TL and 100TH and very similar to the VT-127A as far as specs.

Ive a pair of 354C's in a 15M monoband amp also running in parallel to a pi-net as is the 250TH's 160-20M amp.

I also have a pair of H&K 6146B's and have wondered who actually made them? They say USA.

Carl

[W8ACR]

Ralph is correct. The B+ RF choke is mounted in front of the tubes, and is barely visible in the picture. The larger RF choke on the right of the picture is at the output end of the pi network. It is there, as I understand it, to shunt DC voltage to ground in the event of blocking capacitor failure. I used VHF parasitic chokes on the grid leads, but with a single band 160 meter RF deck, I didn't think it would be necessary to have parasitic chokes on both grid and plate leads. There is a schematic of the RF deck in my earlier post on this subject back in December.

Regarding the antenna tuner. It will tune the dipole on 160 and 75 meters. I remove the vacuum cap for 75 meter tuning. The large split stator capacitor on the left is used to resonate the link coil at the input end of the tuner. The sections are connected so it is not being used as a split stator. I understand that a receiving variable may be used at this position, but I was not sure, so I put in the bigger capacitor.

I had this rig on the air last night and it worked well for the first two transmissions. I started to get some arcing somewhere in the rear of the chassis on the third transmission, so I'll have to figure out why. Probably won't be too hard to figure out and fix. I noticed the plate structure of the tubes turned red during the arcing indicating increased plate current.

Ron W8ACR

[W2PFY]

I would like to know the science of that glowing of the plates when it arcs over. I think during the fault the tank circuit must be totally out of resonance? Any ideas?

[4cx250]

Hello All!

     Why every last watt? Why not just rate it at 250 watts?

     I have seen that in car adds here in Detroit. The car companies are rating their outfits at every last horsepower.

     Why? Is that how things are done now?


Tnx,

[N0WEK]

Ran across this...

http://scottbecker.net/tube/sheets/114/h/HK254.pdf

There is a very nice push/pull amp circuit down a page or two.

Also this...

http://cgi.ebay.com/Eimac-254W-HK254-100TH-1-4-Kilowatt-trans-tube-NOS-/310305434764?pt=Vintage_Electronics_R2&hash=item483fa52c8c

[W4AAB]

That is the same circuit that the original article from RADIO by Faust Gonsett used.Carl, let me see how many 254's I have, and I may trade them for an 833 if you have one(I am looking for spares for my BC-339.
                                                           Joe W4AAB

[W2PFY]

Joe W4AAB BC-339

Joe, do you have any pictures of that rig inside and out?

[Steve - K4HX]

Does the 813 have 813 watts dissipation?   

Interesting... I wonder why they call it a 254, when the plate dissipation is only 100w?

[W3GMS]

That is the same circuit that the original article from RADIO by Faust Gonsett used.Carl, let me see how many 254's I have, and I may trade them for an 833 if you have one(I am looking for spares for my BC-339.
                                                           Joe W4AAB


Hi Joe,

I have a BC-339 that use to belong to Glenn, K3TKF (SK).  Its in my garage and pretty heavy to move downstairs in the Ham Shack.  Your the first person that I have heard other than myself that has one!  The 3 phase plate transformer is really quite a site!

Regards,
Joe, W3GMS
     

[W2PFY]

Joe W4AAB BC-339

Joe, do you have any pictures of that rig inside and out?

would ether one of youse guys post some pictures of that transmitter? I for one, sure would like to see it

[W4AAB]

I haven't hauled it home yet. Thing weighs 1670 pounds!! I got to pour a slab of concrete to build a building around it.I have all the tech manuals.

[W2PFY]

I haven't hauled it home yet. Thing weighs 1670 pounds!! I got to pour a slab of concrete to build a building around it.I have all the tech manuals.

Well here's your chance to make a documentary of the move. I'm happy to hear that another large military transmitter escaped the scrap yard. Most of the big old nice stuff was junked outright or torn down to make other less significant transmitters or amplifiers.

I own a Westinghouse MW-2, 2-30 meg transmitter soon to go back on the air again.

[k4kyv]

When I was over in Africa I cannibalised five BC-339s.  Shipped the meters, variable caps, HRO type dials and some of the other parts home, and hand carried nine 833As home on the plane with me.  At that time (1970) they weren't so hyper-paranoid and let me store my box of tubes up front in a little compartment behind the cockpit door during the flight, and didn't freak out when I insisted on no-one handling the box but me.  I couldn't ship any of  the heavy stuff, but certainly would have liked to have had the big cabinets.  I did ship a bunch of 872As and 4B32s, which arrived intact, but wouldn't trust the 833s. The 3-phase plate xfmrs were left behind; they would make good ship ballast.

I regret shipping only a couple of the big 900pf/900pf split stator loading caps and leaving the others behind.  They are very heavy solid brass and I was too cheap to pay shipping costs - now kick myself to this day every time I think about leaving them in the scrap yard.

I did pick up another 339 locally about 15 years ago.  I still have the cabinet and all the parts except for the plate xfmr, but if I ever try to do anything with it, it will probably be something homebrew of my own design, using more scroteful RF output tank components and neutralising caps, and capable of 160m .  The stock rig is only designed  to go down to about 4 mc/s, and no modulator, and not designed to withstand the peak voltages of plate modulated AM. It was designed to be used for CW and RTTY.  I thought the balanced push-pull pi network output circuit was clever; would work right into a balanced 600Ω line. I stripped the lead sheathing off the HV cable and now use it in my HF-300 rig.  That's something else I wish I hadn't left behind in Ethiopia, the best HV cable I have ever seen.  Also the jumbo size old buzzard style pilot lamp jewels.

Mike, W4AAE (then NI4N) picked up a 339, modified it with a larger plate tank variable, built up an 833A modulator for it (in a second cabinet about the same size as the transmitter) and put it on 75.  Later he sold it all to someone in the northeast who put it on the air, but I heard on the band only once.  Don't know if the guy still has it or whatever happened to it. I think he sold the whole thing for about $500. After the transmitter was moved out, Mike noticed a crack in the concrete floor of the garage ham shack running through the spot where the transmitter sat.

[KM1H]

That is the same circuit that the original article from RADIO by Faust Gonsett used.Carl, let me see how many 254's I have, and I may trade them for an 833 if you have one(I am looking for spares for my BC-339.
                                                           Joe W4AAB

Joe, Im looking for a H-K 1254

Carl

[W4AAB]

I stand corrected on the 1254. Not sure if I ever sw one. The 354 is the biggest H&K I ever saw.
                                      Joe W4AAB

[KM1H]

Its their version of a 750TH

Carl