An 80 through 10 meter Ground Plane

The HF Ground Plane Antenna System employed at 

WD4NKA. 

I have been asked several times on the various FaceBook groups that I am party to regarding details regarding my roof mounted Vertical.  Rather than take up space on the several groups, I thought it more convenient for the reader... and more efficient... to simply write a blog entry and refer those interested in this antenna to this installment.

 

Firstly, the antenna itself is what I might call "Garden Variety".  You can find it in the antenna section of any Amateur Radio Handbook, going as far back as nearly a century.  A quarter wavelength vertical element and a counterpoise, normally a parallel connection of quarter wavelength (or 5% over) radial wires.... or tubing.... depending on the antenna dimensions.

 

Almost like an Inverted Vee on it's side.  The feed point is at the high current / low voltage node of the emitted wave assuming a quarter wavelength per "side", just as a center fed half-wave dipole.  A low impedance feed point, only unlike a dipole, something less than a balance feed.  This is why baluns, while frequently used for center fed dipoles when using unbalanced coaxial feed... are not usually used to feed verticals.  At least, not the quarter wave verticals I've read about or have built, or have seen mention of in the construction project instructions.

 

When a vertical is elevated from the ground, and it's radial "counterpoise" system likewise raised, the losses caused by earth is greatly reduced; fewer radials are required to sustain a decent counterpoise, sustaining a lower angle of radiation.  Various research papers indicate that as few as four, three, and in one case only two radials are needed for proper function of a raised ground plane.  Indeed, my memories of the half wave and 5/8th wave ground plane antenna systems popular with the CB community for decades bare this out.  Most only had three radials.  

 

Ground mounted verticals popularly had a requirement of 120 ground radials cut to 5% over quarter wavelength (or so).  An elevated ground plane system does well with radials cut right to a quarter wave.  In my opinion, an added 5% of length has really no bearing.  I've used both.  No difference.

 

My own Ground Plane is made Quarter Wavelength to 40 meters, employing a vertical element of 33 feet, with 33 foot radials.  The vertical element is made from telescoping aluminum tubing, the radials of insulated 14 gauge stranded copper wire.  I use five radials for 40m, and after about a year of experimentation, an extra addition of 3 to 5 radials cut to about 70 feet for use on 75 meters, wherein this antenna becomes a 1/8th wavelength ground plane at 75 meters.  More on this later.

 

Having used this scheme for decades, usually using used tubing from former antennas, I found that the windage normally experienced during our summer "monsoon" season induced a great deal of stress on my 33 foot "Space Needle" bolted to the gable end of the house on a push-up pole, and after about 20 years, it finally bent over during a tropical storm.  It took that long.

 

In 2019 I decided to rebuild the "Space Needle", as it is affectionately known in the neighborhood.  Only this time all new aluminum would be used.  It would be re-enforced, and it would be very, very secured.

 

 

 

This is the scale rendering I made on Macromedia "FreeHand", my fav vector IDE.  What you see is a 33 foot telescopic pole bolted to about three feet of mast using four saddle clamps.  A weatherproof gasket sealed aluminum box is also clamped to the antenna base serving as both a place to mount an SO-239 coax female jack, an insulated stand off to run a wire from the antenna base to the coaxial feed.  It would also serve as common to the coaxial ground, where the radial wires would ultimately be attached.  And so the parts were ordered, largely from DX-Engineers.

 

Also shown in the above drawing is a Sched 40 PVC pipe covering all but about a foot of the bottom tube, which is 1.5" in diameter.  There are end-caps at each end of this PVC pipe, the top cap being drilled out to 1.5" for the base tubing, the bottom being drilled with a small hole to permit condensation to escape, a "weep" hole.  The feed wire would be drilled through the base of the PVC pipe above the bottom end cap, and into the base tubing itself.

 

The purpose of the PVC is to help absorb the torque developed as the antenna flexes in the wind, and I have seen these antennas endure sustained 75-85 mph winds and higher gusts.  This re-design and "build" would be a bit stouter than my prior verticals, six telescoping 6 ft. lengths, the bottom tube being 1.5".  This makes for a fairly stout 33 foot extension with three feet of interplay between the tubing sections.  The greatest interleave is on the lowest and second to the lowest tube sections, decreasing toward the top.

 

 

 

This is the vertical when I had just put the tubing together and prepared the PVC and end-caps.  The saddle clamps are made from red oak, soaked in varnish and dried, about a three day process.  This shot shows the assembly bolted to a length of 1.25" diameter mast, used to "try" the U-clamp and Saddle assembly.  It was kind of tricky drilling out the saddles.

 

 

 

Here is a closer look at the four saddle clamps.  These oak saddles lasted about three years, and actually could have lasted longer had I not chosen to rebuild this antenna this summer (2022)  I had chosen to rebuild not for any flaw in the design electrically, but for construction and structural improvements.  This year, 2022, is projected to be an active hurricane year, and this antenna is heavy.  Too heavy for me alone to unbolt and lower.... then raise again several times in a season.  As such, the four-bracket bolt up seen here, although very successful, was destined to change.  But the antenna electrically remained the same.

 

 

 

This is a close-up of the top section of the PVC, showing the method I used to clamp the telescoping sections together.  I think the six 6-foot length of tubing cost about $125.00 in 2019 when I ordered them from DX-Engineers.  That price has gone up, but I would do the same today despite the cost.  When you used new parts and quality stainless hardware, there's a lot less to worry about.

  

This is a view of the vertical as it appeared in June of 2019.  Note that there is a coaxial RF choke in series with the feed.  This knocked out a lot of RFI.  The weatherproof aluminum box was not used at this point, a direct feed to the antenna base was used.  That aluminum box made it's appearance when I placed a coil in series with the feed to bring the swr down for use on 75 meter AM.  The introduction of that coil, and this antenna's use on 75 meters is a story unto itself, but that can wait for another time.

 

 

This is the grounding plate that I used for the first rebuild, and still use today.  A total of ten radials, six for 40m and four for 75m fanned out across the roof, from west to north to east.  The feed point is approximately 18-20 feet above average terrain.

 

 

 

Here is a shot of the aluminum box with the 75m series coil.  At first I used a switch to select 75m or 40m and higher.... but the feed point at 75 meters, using a few hundred watts on AM develops a high voltage, and soon the switch burnt out.  So I took this switch out and replaced it with an insulated stand-off connect as is on the top of the box.  I unscrew the wire coming from the antenna base from one ceramic stand off (with a stainless screw and wing-nut) - and bolt it up to the other, depending on the band.  This requires me to climb the "crows nest" each time I change from 75 meters to 40 meters (and higher).   Actually..... I like it that way.  It allows me to inspect the antenna each time I ascend the Crows Nest!

 

 

 

This was the "Space Needle" from 2019 to 2022.  And it performed very nicely, resonant to 40m and 15m naturally, and using a tuner for 20 and 10 meters easily.  On 75m, the coil brings the standing wave down to about 1.7 or 1.8:1, the residual reactance is tuned out by the antenna tuner, a Dentron MT3000A.

 

 

This year (2022) is projected to have an active hurricane season, and frankly, I'm getting too old to lug this beast up and down the roof each time a hurricane threatens.  Thus it was determined to change the mounting system to the mast, and while at it, replace the mounting hardware with stainless all around, and also re-enforce the gable fascia, and double the brackets holding the push-up pole.  The new mounting system would have a stainless pivot mount instead of the saddle brackets, a stand-off brace would provide the extra bracing at the four foot level of the base of the antenna, providing less coupling between the vertical radiator and the mast.

 

 

 

 

This is the new hardware used in the re-build of my ground plane.  New 14g insulated stranded wire for the radials, new stainless brackets (DX Engineers), new pivoting mounting bracket (also DX Engineers) and also not shown: new eve brackets for the mast.  It took about two months to gather everything together, and meanwhile the vertical came down, everything inspected to make sure all was doing well with the vertical itself.  The radial mounting plate was cleaned and polished.  New Y-lugs for the radials were obtained. Also the weather proof aluminum box holding the 75m matching coil was re-fitted with stainless connecting hardware.  

 

Essentially everything stayed the same electrically.  It is the same ground plane, only with better hardware and a pivoting mounting bracket to make lowering the antenna in case of a hurricane easier for an old guy like me.  I think the photos below will tell the rest of the story:

 

 

 

The new mast mount: the gable fascia was doubled for a more secure anchoring of the mounting hardware.  a lower bracket was added, and new stainless U-clamps were installed to better hold the mast in high winds.  The mast itself was sunk about 3 feet into the ground, and grounded using a series of 6-foot copper ground rods, also used to ground the station equipment.

 

 

This is the 75m matching coil and switching box.  The coaxial RF choke is mounted below the antenna feed.

 

 

 

The four saddle brackets were replaced by a combination of the pivoting base and the stand-off clamp at the four foot level. (photo shot before the 75m coil was mounted.)

 

 

 

This is a closer look at the base and stand-off clamp.  I was in the process of installing the switch box when I took this shot.  The 40m radial wires were also laid out after this photo was taken.

 

 

 

A photo of the re-installed radial mounting plate.  This plate holds ten radial connects.  Five are for 40m, the remaining five will be for 75m.  Or.... I may do six for 40m, and four for 75m, depending on how much wire I have on the spool (500 feet.)

 

 

 

And here you go!  The last three shots pretty well sum up the project.  Preliminary testing on 40, 20, 15 and 10m show that everything is operational.  I have yet to lay out the 75m radials, but that will happen the next rainless- thunderstorm-less day I have off to work on it.  Hopefully by August.  It's good to have the "Space Needle" back up again!

 

de wd4nka

Deltona, FL

SW Volusia Co.

 

Gary's Awesome Adventures in Amplitude Modulation (AM Radio Transmission & Reception) :

Prepping the Johnson Viking Ranger for Station Use, Part 4. 

 

There are a number of reasons to install a PTT (Push To Talk) relay into a Johnson Viking Ranger, not the least of which is to save wear and tear on the "Operate" switch.  Without a PTT switch, it is, of course, possible to do AM phone, just rotate the switch between Phone and Standby.  And that will work.  However, these rotary switches were not meant for constant off and on operation!  They were designed to be positioned and parked for a while, like a band switch.  The original Potter & Brumfield relay switch was recommended by Johnson as the relay of choice, and recently I discovered that some Rangers actually came pre-wired for this relay.  Mine was.  Either that, or whoever did the wiring did an absolutely professional job soldering the wires in place, wrapped and taped the wires above deck near where the relay was to be installed in pre-drilled holes to place the mounting screws... but never actually installed the relay switch!!   The tape used to band these wires was yellowed and brittle with age, as if whenever the taping was done was about the time the radio was made.

 

Cruising about the internet forums informed me that indeed, some factory Rangers were, in fact, pre-wired.  That was news to me.  If anyone has documentation to this effect, please let me know at wd4nka@gmail.com.  I'll post the documentation to my blog.  Until then I will classify this bit of information as a definite maybe.

 

Potter & Brumfield relay switching aside, D-Labs has come out with a better solution that accomplishes two design goals: to provide a non-drill solution for PTT switching, and to solid-state the low voltage rectifier.  The wiring is at most at least as intensive as the original PTT wiring plan indicated on pages 19 and 20 in the Ranger Operations manual.  As it turns out, all but two of of wiring required for the K1 or K2 relay is already in place if installing in a pre wired Ranger such as mine, if yours is not, said wiring is not all that hard.  Only two solder points were actually challenging, but as I will share in this installment, there are work-arounds to make things easier.

 

First, let me share D-Lab's video covering the K1 installation.  This will apply to the K2 as well.  For what you get, they are well worth the money!

 

 

 

 

Terry's video shows the basic installation of the K1 relay.  Later, he produced the K2 relay, which is the same as the K1, with the same wiring, but the K2 provides for two more switch functions which can be utilized according to the installer's discretion.  You can key a transmit light, you can kill screen current in the modulators when the modulator is switched off, you can key an ACR, any number of things.

 

I purchased the K2 relay, although I had no immediate plans on how to used these extra relay ports.  Probably at a future date I'll look into keying an ACR, but the jury's out.  Maybe later I'll tackle that, but for now, I just wanted a PTT relay, and yeah, nice to reduce some heat by SSing the low voltage relay.  I am not very comfortable SSing the 5R4 HV rectifier simply because the components in place are designed around the voltage drop of this rectifier.  Since it is high voltage, and since there is little to no VR drop using silicon diodes, that B+ rail will be significantly higher.  It's not such a big deal with the low voltage rectifier.  So I opted to keep the 5R4 in place.

 

The next video is for D-Lab's K2 relay.  It's worth watching even if the basic rely wiring is identical to the K1.  Terry gets into what to do with the extra relay ports, which may spark some ideas.

 

 

 

Wish I could get my daughter to do one of my videos with me.  Oh, well......

 

Terry pretty much covers the installation, and I'll not repeat everything here in this installment.  What I have endeavored to do is address a couple snags I ran into.   Like I said, my rig came pre-wired for the Potter & Brumfield relay, which is close to the wiring of the K1/K2 relays.... but not identical.

 

Most of the wiring involves accessing the front wafer of SW4, patially above deck, partially below deck.  There are two black wires soldered onto clip 8 of SW4 (front) wafer... the wafer closest to the front panel, the one behind the (rear) wafer.  These are to be removed and soldered onto the black wire pre-wired onto the K1/K2 board.  These two wires were in fact removed, only in a rather round-about manner, and fed below deck where they were soldered together and covered with rubber tubing. Another wire was soldered to this joint and fed above deck, and taped off.   A wire ran from clip 8 of this same rear wafer, accessed from below deck, and fed back up above deck, wrapped and taped off.  I noticed that these wires, all black, were the exact same wires used for all the black insulated wiring done on this rig!  Clip 5 goes to the white wire pre-soldered to the relay board, and again, a black wire was already soldered into place, fed above deck, and taped off.  Wow, this was gonna be easy!  All I had to do was solder a wire onto SW4 (front)'s clip 8, run a wire from pin 2 of the mic jack (a cap to ground was already in place) to pin 4 of V-12, and boom!  Ready to go.

 

Then I looked at where this pin-4 was.  Hidden under that big log of a variable ceramic resistor (R35), and that resistor was bracketed into place, and the screws that held those brackets were danged near impossible to reach.  Since that resistor (R35) is pretty fragile.... I needed to think this one out.  Here's what resulted:

 

 

 

 

There it is.  R35.  One bracket behind a choke, the other tucked up under the lip of the chassis, where none of my tools could reach well.  The brackets are screwed through the rear apron of the chassis, through the bracket mounting holes, the lock washer and nut bolting up from the inside.  I did manage to get a needle nose in there to just loosen the nut from the inside, assisted by counter turning with a screwdriver the screw from the outside.  At length the screw came out, my finger keeping pressure on the nut so it wouldn't drop.  That pressure was enough for it to stick for a couple seconds on my finger, enough to remove it from the scene.

 

 

 

 

The screw was then pulled out from the back, and the bracket removed.  You can see that R35 is grounded at one end via a soldered eyelet that is held by the bracket screw.  No... the resistor isn't cracked.  Believe it or not, that line you see on the resistor is a reflection.  Trust me.  I had to look twice when I saw this photo on my I-Phone.  

 

One nice thing about these mounting screws is the use of lock washers.  On the other side of the resistor I could just turn the screw from the back of the rear apron, just enough to allow me to move R35 upward, and clear the way to access pin 4 of V12.

 

 

 

 

Here is a photo of R35, moved up just high enough to clear V12.  Even though things are still a little cramped, it was at least reachable by the soldering pencil.

 

 

 

 

 

Here is a close-up of V12.  Pin four is the vacant pin at the 1-oclock position, and is clear of anything soldered to it.  The wire soldered to it came from Pin 2 of the mic socket, and was threaded across the chassis to this point, as near to the chassis as possible.  It is the only really long wire run in the transmitter.  The task remained to put R35 back where I found it.  That wasn't going to be easy since the bolt is beneath the chassis edge-lip, inaccessible for any of my nut drivers and other handy tools.

I discovered that a wooden barbecue skewer could thread an 8-32  washer.  This would be what I would use to position the nut from the inside.

 

 

 

 

This solved the holding of the nut from the inside under-deck of the chassis, but the screw had to be re-inserted through the rear apron, and the resistor ground eyelet placed between the bracket and the nut and lock washer.

 

 

 

 

This was solved by taping the screw in place temporarily, for which I used both hands to hold resistor, bracket, lock washer, eyelet and nut in place.  The tape was subsequently removed after everything was tightened.

 

With the audio wire in place, I moved on to the last remaining wire pre-soldered to the K2 relay, the Red wire.  This would go to SW4 (front) clip 6.

 

 

 

 

Yeah, right.

 

This was one congested place!  You can see the earlier mentioned two wires that were removed from SW4 (front) clip 8, soldered together, and the single black wire soldered to this pair, leading to the upper deck, eventually connecting to the pre-soldered K2 relay's black wire.  You can see the heat shrink insulation to the left, before I wrote "black" on it, and slid it over this junction and shrank it.  But you can barely barely even see SW4 (front)'s clip 6!  Soldering here could hardly be considered.  Not with my 20 watt soldering pencil.  I made a close inspection of the switch, both above and below deck.  No hobbyist with average soldering equipment is going to safely solder a connection to this clip as it is.  I was faced with a major task of removing, some how, some of this congestion and then re-soldering all of it.  That was not in the cards, gang.

 

With a flashlight, and with moving some of the wires a bit, I could find the green and white wire that was soldered to the clip 6.  According to both the pictorial and schematic provided by D-lab, this green and white wire ran directly to pin 3 of the 6146.  I looked at the schematic to see if there were other points along the way, or any terminus connections I needed to be concerned about.

 

 

 

 

The schematic shows that green/white wire carrying the screen voltage to the 6146's pin 3, also to the clamp tube (6AQ5)'s pin 5.  Any where you tap along this line, the same voltage is seen.  RF is bypassed.  And while there is plainly printed on D-Lab's instructions to NOT solder the relay directly to pin 3 of the 6146, I could find no real reason why!  Another alternative would be to fish that green/white wire out of it's harness... which carried a gazillion other wires, and tap it... yet another mess.  Frankly, there was no good solution.  Soldering directly to clip 6 was clearly a disaster in the making.  On the video Terry said "it's do-able".  It may be on his early model Ranger, which has no key circuit sub-chassis, but in mine it would have been a mess.

 

So.... yeah, sorry.  I ran a wire down to pin 3.  

 

Shoot me, D-Lab.  I'm a scofflaw.  

 

But in retrospect, I still see no reason why not to, and to date I have had no issues in operation.

 

 

 

 

Maybe it's because I'm a home-brewer.... I'm used to things like this, tapping a rail somewhere along a  bus.  D-Lab never explains on the video or in print why tapping the 6146 screen-line is verboten.  I could just as well have tapped at that terminal strip to the left.  Or at the clamp tube.  Or at shunt resistor R16.  It made no measurable difference.  So use your own judgement, dear Reader.  And if down the line I do develop an issue associated with this, I will post and edit to this installment.  As it is, I am writing this installment well after the fact, after many QSOs using this Ranger, and the relay has performed flawlessly.  So has the Ranger itself.

 

'Nuff said.  

 

Meanwhile, above deck....

 

 

 

 

 

 

These are those pre-installed taped off wires I mentioned earlier.  Under deck they are connected where they need to be, and labeled as to which relay wire colour they attend to.  The key circuit deck was removed just prior for the wiring and the threading of these wires back up to the upper deck.  It is subsequently re-installed.

 

 

 

 

I mentioned these wires as being labeled.  Here is how I did the labeling: all the wires were pulled below deck at one point, with heat shrink slid over all squegg splices.  The associated wire colour is written on the heat shrink tubing itself.  After shrinking, these wires are fed back above deck as I just described, and wired to a terminal board which I mounted on the key circuit sub-chassis deck utilizing pre-drilled holes which happened to be a perfect match for one of my milsurp terminal boards.  Almost as if it that very teminal strip was meant to be there.  

 

 

 

 

It all went together nicely.  Everything connected in an organized manner.  You can see the K2 relay installed, and the terminal strip that I mounted using pre-existing holes.  After this, the relay was tested for function without the 5R4 installed.  Afterward the 5R4 was plugged in.

 

Let me mention at the point the accessory plug, which I had to secure and wire up.

 

When I bought this Ranger, it had no accessory socket.  When I made the need known. one of the members of the Amplitude Modulation Classics FB group spotted me the male Amphenal plug.  I ordered the shell cover for it from eBay, and at the same time I ordered the two-pin Amphenol mic plug, also from eBay.

 

The wiring of this plug is simple, and I will post the wiring diagram, per manual schematic, also a couple shots of the finished accessory plug :

 

 

 

 

With the K2 Relay finished and tested, it was time to button everything up, slide the cover onto the Ranger, bolt her together, and run her into a dummy load and check things out.  But there remained yet one more thing to put together...

 

 

The D-104 mic.  This was as simple as 1-2-3.  Black and shield grounds to the plug shell (I tucked it under the spring which runs under the plug's collar, a good firm connect.  Audio goes to pin 1, and the mic's key runs to pin 2.  With that complete and installed, I gave her the "Smoke Test".    She passed with flying colours.

 

And she's still flying.

 

In summary, let me add that I did do one audio mod, which was recommended by Charles Rauch W8JI, and linked at Greg Latta's site.  Here, Charles writes:

Change  C-52 from 500 pfd to .02 mFd
OK, this is about the only major worthwhile effect, since it will bring low frequencies up several dB. In my own rigs, I've found that a change from 500 pF to .01 uFd was far more than enough.

 

Having changed out C52 between the first and second audio amps in the speech amplifier, I have received audio reports that range from "very nice" to "smooth" to "great!".  I'll leave it there, gang.

 

That's all for now.

 

de wd4nka

 

Gary's Awesome Adventures in Amplitude Modulation (AM Radio Transmission & Reception) :

Prepping the Johnson Viking Ranger for Station Use, Part 3. 

 

I took the liberty of posting Greg Latta's photo of the line plug and fuse mod, because, frankly, his photo was better than mine, and also there's not really that much involved.  

 

 

 

The fuse holder is ordered from Mouser as indicated on Greg's parts list.  I also ordered the three conductor cord while I was at it.  Simply follow the original cord connects, and wire the cord's ground to...well... ground!  You can also get a partial view of the HV filter caps and equalizing resistors.  Again, I did the very same thing.  I could find no better arrangement.

 

 

I found I had a little variance in the positioning of my particular fuse holder.  I don't know if Mouser started stocking a slightly smaller base holder or not, but I was able to place mine a tad more vertically with plenty of clearance and accessibility.  Apart from this, again, I followed Greg's suggestions entirely.

Having done the re-cap, next I took on: the much feared Chernobyl Resistor!  That famed 18K resistor, also known as "R3", that strikes fear in the psyche of all Ranger owners.  If resistors could talk, this one would sound like Boris Badenov!!  

 

 

 

 

 In all fairness, it's rep is well to pay heed to.  The collapse of R3 can cause damage to the VFO, and you don't want that.  Nosir-eee.

For this, I needed to remove the keying circuit sub chassis and remove all the tubes in the area including the two rectifier tubes to have room for the screwdriver.  Any terminal strip screwed onto the plate which faces the key circuit sub chassis should be removed as well.  After removing the cover plate, what you will see is what the above photo shows.  Boris Badenov's hide-out.  There he is, sneaky little devil, in the lower right.  Don't be fooled by the brown-grey-orange tricolour, its really the colors of Pottslyvania.  Fearless Leader probably has a cam hidden in there somewhere.  Probably as stash of Molotovs as well.  Proceed with caution.

 

 

Here's a closer look.  As someone on one of the Facebook Groups pointed out, it looks brand new!  It probably would have been years before it actually broke down.  But discretion (and and ounce of prevention!) is the better part of valor, says I, and I chose to replace it with a 5-watt wire-wound.  Also from Mouser.

 

 

I opted to install the replacement resistor under the deck but near to the VFO entry port, because while I wanted the heat to be conducted away from the VFO (there is some varying points of view on this), I am not really comfortable with long wire lengths being strewn hither and yon.  So, borrowing a convenient screw already there to ground one of the new electrolytics, I installed a new terminal strip on which to place the new resistor.

 

And there it is.  Looks good, easy to access, in an un-cluttered space.  Should I have used an 8 or 10 watter instead?  Maybe... but it's better than the 2-watt resistor that was there.

 

So, what's the story behind this critter?  Let's look at the math.  (this is a cut and paste from one of the forums dealing with the subject.  It was just easier to do this than to have you think I actually  sit down with the schematic and do this stuff.  I do, when it comes to homebrewing or reverse engineering unknown mods.... but this fella already had it laid out.  Colour me lazy.)

The (in)famous "Chernobyl resistor" (R3) is used to drop the 300 volt line to 150 volts. So there is 150 volts across it.

From this we can determine the current flow:

I = E/R

E= 150 volts

R = 18,000 ohms

I = .00833 amp or 8.33 mA.

This is reasonable because the 0A2 has a minimum current of 5 mA and the oscillator tube screen draws only an mA or two.

Now for the power dissipation:

P = E I

150 volts times .00833 amp = 1.25 watts

So a 2 watter is theoretically big enough.

 

...ahh, but over the years, guess what begins to alter value with heat?  Yeah, that 18k/2 watt won't stay 18k forever. and 67 years is a long time to dissipate.  Ohms lost means increased current and increased heat.

 

Yeah, replace that.   Whether in the VFO or outside, choose your poison.  The point is to protect your historic gem, there.

 

That's it for now.  More to come, including the installation of D-Lab's K2 PTT/ SS rectifier.

 

de wd4nka