Hallicrafters HA-1 Electronic Keyer

High Voltage Electronic Keyer from 1960

I've been interested in getting my hands on a Hallicrafters HA-1 since the first time I saw one online.  A 60 year old (as of this writing) all-tube keyer weighing in at 7.5 lbs.  Everyone needs one, right?

The HA-1 uses a mercury wetted relay capable of switching up to 500v circuits.  Wow!  It employs four 12AU7 tubes to perform the mark-space morse timing and uses an OA2 and OB2 tubes for power regulation.

They always auctioned for more scratch than I thought was reasonable or were so beat up that I assumed it had been buried in a damp basement since Eisenhower was president.

I finally won an auction for one that was in reasonable cosmetic condition and fully expected to have to overhaul the electrolytics and out-of-spec capacitors but I lucked out and received one that had been recently overhauled with new power caps and even had replacement polys.  The only issue was the the sidetone circuit was kaput because a neon bulb used in the relaxation oscillation circuit had broken its leads at some point (maybe during shipping) and was rattling around in the case when I received it.

Fortunately I had an old neon bulb in my junk box.  It was socketed rather than having the leads, but I soldered some leads to the socket and installed it where the other had broken off.  Wahlah, sidetone audio restored.

What an electronic keyer was like 60 years ago

After reading the manual and adjusting the circuit balance and element weighting, I had a go with it.  I found that it kept eating a DIT when it followed a DAH in a character like K or N.  I eventually realized that I was hitting and releasing the left paddle (dit paddle) before the current DAH was completing.  

A keyer without DIT / DAH memory

Then it hit me... this tube circuitry doesn't have an "memory".  Modern, digital keying circuits have a memory as to what paddle was pressed while the current element is being completed, but this old electronic keyer is using all its tube goodness to complete the timing for the current element.  So in the case of a DAH, it doesn't have a place to buffer that I've pressed and released the DIT key while it was completing the DAH.  I have to be holding the DIT paddle after it's completed the DAH for it to recognize and begin the DIT element. 

That really calls for a change in my paddle usage.  My brain needs to keep in mind the length of DAHs so that I don't rush and release a following DIT before the current element completes.  This is a bigger problem below 25wpm given the longer length of the DAHs.

The Hallicrafters HA-1 manual states that the keyer is different from other electronic keyers and requires "a knack" to use effectively.  I think I've discovered whereof it speaks.

I practiced for about 30 minutes and then tried some on-air CW QSOs.  They were rough.  Leaving DITS out of K's, C's, Q's and N's and other such letters really changes what you're saying... C's become M's... K's become M's (mmm... M&Ms)  N's become T's... Anyway, you get it.  Very frustrating for both the sender and the receiver.

As luck would have it, one of the stations I worked was also using an old Hallicrafters keyer.  Did I know because he was dropping DITs ?  No, I was telling him about the "new" keyer I was using and he responded that he was using one as well and went on to extoll it's virtues.  

So I plan to use it and not relegate it as a shelf queen.  I figure with enough practice it will actually improve my technique and probably improve my bug fist as well since it causes me to be far more conscious of my inter-element timing when forming characters.

Conclusion

If you have a good, modern keyer and don't need to key high-voltage tube gear, I can't really recommend that you run out and find a Hallicrafters HA-1.  But if your taste runs toward the eclectic and you want a really, large electronic keyer with no memory functions that consumes 30 watts of power whenever it's on and provides you with a wonderful tube smell, and also requires soldering to hook-up the line to connect to an external transmitter... then this is the key for you.

Plus it looks just like H.A.L. from the Space Odyssey 

That's all for now

73

So use a keyer with more wattage than your QRP station to get those extra DX contacts.

DE AA4OO

Space in Morse Code

Silence is Beautiful

The space between characters and words is just as important as properly forming the characters.

If you're rushing your characters the elements of one character will not be easily discerned from the next and the person your sending to will find it indecipherable and respond with a 73 and spin the dial.  I have a number of comments in my logs about operators who ran their characters and words together.  I tend to avoid those contacts down the log.

But, many of us, including myself, are guilty of rushing when we send, especially as a ragchew moves into the 3rd or 4th exchange.  I think the problem is that as the person sending the code, I know what I am sending and in the excitement of wanting to get out all the things I want to say and turn it over, I start to rush and begin compressing the space between my sent characters and words.  After all, it's very clear in my head what I'm sending, it must be just as clear to the listener, right?  Wrong.

RRFBCPYALLWXHRISSUNNYES88FRIGISIC756PRORUNNING100WINTODIPOLEUP66FTDESM8ERW8BJOK

The exchange above isn't far from reality and that's assuming the character spacing was good.  When the character spacing is rushed two characters become a different character or no character at all, and you sit there with your head tilted thinking "what in the world are they saying?"

Proper Space (Timing)

What is considered proper spacing?  Let's review some basics.  A DIT is counted as a single Morse Code element (think of it as a unit of time).  A DAH is counted as 3 times longer or 3 Morse Code elements (3 times the DIT time unit).  

Of course the length (time) of a sent DIT or DAH will change with the speed you are sending.  As the word per minute speed rises, the length of of DITs and DAHs decreases accordingly and vice-versa.  Unless you're using Farnsworth timing, but that's a different discussion...

Space between DITS and DAHS in a Character

Characters other than the E and T are made up of more than a single DIT or DAH.  Between each DIT and DAH making up a single character is space.  The space between each DIT and DAH making up a single character should be as long as a single Morse Code element... a DIT.  So there's a DIT's space of silence between every DIT and DAH in a character. 

"R" = DIT.DAH.DIT (where the '.' is the length of a DIT)

Space between characters within a Word

There should be 3 Morse Code elements of silence between each letter in a word, or silence the length of a DAH, at the speed you are sending.

"WORD" = W-O-R-D (where the '-' is the length of a DAH)

Space between Words

There should be 7 Morse Code elements of silence between each word you send.

"HERE<>ARE<>SOME<>WORDS" (where the '<>' is the length of a the M character)

The length of an "M" ??  Yes.  I was corrected about this in a video I made.  In that video I was counting the DITS and DAHS only, and said to count the inter-word space to be the length of the 'W' character because it is made of a DIT and two DAHS, but I was forgetting the space between the DITS and DAHS that make up the character.  A 'W' character contains 9 elements.  An 'M' contains 7 elements since it is 2 DAHS (3*2=6) plus the inter-character element that spaces them (1-element of silence) equals 7 Morse code elements.

How to Practice

If you use an electronic keyer it will take care of the inter-character spacing between the DITS and DAHS of your sent characters.  If you use a manual key you'll have to take care of that yourself.  You can practice by sending strings of DITS, listening to see if you are placing the same space between each DIT as the length of the DIT itself.  

To practice spacing letters in a word, get used to the length of a DAH (a 'T' character).  Send a T over and over making sure you have the space of the character and the space of silence equivalent.  This gets a bit more complicated with different characters.  An 'E' character is of course much shorter than a 'Z' character but you need to have the same amount of space after each before sending the next character.  I find that I tend to rush into the next character after sending a long character like an 'F 'or an 'L' and add too much space after short characters like an 'E' or 'T'.   If you use a decoder of some type it can be helpful in showing you timing mistakes.  Send into a decoder and see if it turns two of your characters into a different character (you rushed the timing), or see if it spaces the word out as if there's a word break (you're putting too much space between the letters).  It is a very humbling experience to send into a decoder.

Similar to working on letter spacing, spacing for words is potentially an even more important skill.  When we listen to Morse at speed the rhythmic sound of the characters in a word as a whole tends to tell our brain what we've heard.  If the next word is rushed then we don't process the first and miss the beginning of the next.  Practice sending the 'M' character at your preferred speed and get used to the amount of time it takes to send.  

One thing I've tried that works pretty well is setting the break-in timing of my transceiver to match the space I want between words.  At 20wpm the DIT length is between 50-60 milliseconds depending on the measurement you use.  So if I want to be sure I'm spacing properly I should have 7 time-units or 7*50 = 350 milliseconds break-in set in the transceiver.  Both my Elecraft KX3 and Ten-Tec Eagle support setting the break-in in milliseconds.  By being sure that I hear break-in occur between every word I know that I'm putting in a good minimum amount of spacing.  If I don't hear break-in occurring, it reminds me that I'm rushing my words.

When I hear break-in occur between every word I know that I'm putting in a good minimum amount of spacing

Conclusion

The silence you send is just as important as the signal.  Silence is golden

DE AA4OO

Regulated voltage for Regenerative receiver project

Mr. Regula-tor

Building a regenerative tube receiver seems to have been a rite of passage for all hams of yesteryear.  Although I built one from a kit (4-States QRP) as my first electronics project a couple years ago I thought I'd go for the real deal and build a vacuum tube regen receiver.

I'm building a design based around the 6SN7 tube. While I'm collecting parts and still locating a suitable chassis I decided to build a regulated power supply from the parts I have.  Anyone familiar with electronics could probably whip this together in no time, but being the electronics newbie that I am, it is a slow process.

I'm using a transformer from a 1950's Heathkit VTVM V-7 that I parted out. It supplies the 6.3V filament voltage from one set of windings (yellow wires)  those tested good. But the HV was an unknown as it was only half wave rectified when the transformer was used in the meter.  That meter's rectifier and power cap had gone bad so I didn't know what condition the HV side of the transformer.

Breadboarded using a full wave rectifier created with 4 diodes, buffered by a 22uF electrolytic and a 10k resistor, I saw 189 volts, with no-load out of the high voltage side of the transformer. The amount of current the transformer could provide was still an unknown. I tested temporarily with a 2.5kOhm high wattage resistor and saw 56ma of current provided with a voltage sag down to 130V but the core of the transistor started heating up.  Within half an hour it was over 120F so I discontinued that load test.

Fortunately, the regen circuit uses a ridiculously small amount of current for B+; about 4 to 5mA. Although I will likely change the audio side of the tube to deliver enough current for a speaker rather than the high impedance headphones in the current design, which may potentially double that to 10ma.  For the first incarnation I'll stick with high-impedance headphones.

The regen power supply requirements called for 6.3V@0.5A and 90V@4mA B+.  The B+ voltage  was based on using 10x 9V batteries and it stated that voltage wasn't critical but shouldn't fall much below 90V, going 12% above 90V should be OK.

Generally batteries are used with regenerative receivers because they are so sensitive to power supply noise, but I wanted to give the power supply a shot first and if it proves too noisy I can fall back to battery power for the B+ and just use the filament voltage provided by this transformer.

Since I have a OB2 voltage regulation tube I want to use. The OB2 regulates at 108V so that's what I'm going with.  An OB3 would regulate at 90V, but I don't have one of those.

OB2 in action... Glow baby, Glow!

Calculating the resistor drop

A voltage regulating tube like a OB2 ionizes gas to maintain the voltage at the tube's specification.  In the case of an OB2 it tries to maintain voltage at 108V.  It requires a starting voltage higher than what it will regulate to, but ultimately can only dissipate so much current as it drops voltage.  So, a resistor must be put in series ahead of the VR tube to limit the current it will have to dissipate.  The resistor must be able to handle the current flowing through it, so that must be calculated as well.  

The calculation for the dropping resistor resistance is:

Rdrop = (Vs - Vreg) / (Ireg + Isupply)

So, in my case:

Voltage supply (Vs) = 189V
voltage regulation (Vreg) = 108V
regulator current (Ireg) the OB2 requires 5mA to do its job = 5mA
supply current (Isupply) the actual current required by the 6SN7 up to ~ 5mA

So, (189V - 108V) / (0.005A + 0.005A)  comes out to a resistor value of  10,100 ohms.  10k is the closest standard size resistor and at 108V it should be able to dissipate 1.166 watts.  So I'll need a 10k 2-watt resistor.

Parts is parts

Running the regulated power supply with a 10k Rdrop resistor for a few hours showed the transformer stabilize at 92F degrees at 70F amb.  I was using a separate 27k 2-watt resistor to simulate the ~4mA load that the receiver will draw at 108V. 

As you can see on the newly restored, trusty Heathkit VTVM; the voltage was holding steady around 108V.  With that little current, the OB2 is not visibly glowing but with the lights out the violet colored ionization is visible.

Summary

I'm going to order a larger filter capacitor.  The only one I had to test with was 22uF 360V and I'd like to use higher capacitance value of 47uF with a more appropriate voltage rating of 250V.  I will also be adding 0.01uF caps at the input and output of the filter capacitor and I may add a 0.01uF across the OB2 pins 1/7 to further attenuate any RF noise.   

With the current values I'm seeing 50mA ripple on my regulated voltage.

A bit over 50mA ripple

After I get the new capacitor and get the 0.01uF caps in play to filter out noise, I'll hook it up to the oscilloscope to check for ripple.  I'll update the post at that time.


That's all for now....

So lower your power the old fashioned way, using a voltage regulator tube.

72/73
Richard, AA4OO

Heathkit Art

Heathkit HP-23A and IM-11

I had just buttoned up a HP-23A, after testing its transformer. A fellow ham gave it to me for parts. 

This old stuff looks cool, so I took a pic with the phone and thought I'd share. 

Feel free to use as a desktop background, but if you use it in on the web or publish provide proper attribution.

Metering High Voltage on the cheap

🗲 Heathkit VTM model IM-11 🗲

I recently got a taste for restoring and using vintage vacuum tube radio equipment.  Using equipment that requires 800+ volts for making QRP transmissions is counter-intuitive to the spirit of QRP ham radio, but it's part of my journey as a ham, so I'm writing about it.  Bear with me.  Once I receive a near fatal shock I'm sure I'll move back to 12v powered equipment again.

Until then...

One of the first issues I ran into while testing the power supplies I restored for my vintage gear was how to measure voltages beyond the range of my digital multi-meter.  Most consumer grade digital multi-meters (DMMs) can only measure up to 500 volts then display an error, or stop working altogether.  Previously, I was able to measure voltages over 500V by making a voltage divider out of two 100k 1w resistors and taking my measurement from the middle of the two resistors, but it was precarious in use and added even more danger when working with this old equipment.

I'd looked at getting a DMM capable of measuring high voltage, but the recommended ones, like a Tenma 72-1055 Benchtop Digital Multimeter, start around $100.  Used Fluke meters are even pricier.  I'm sure buying a more professional DMM would be a wise investment.  As I've evidenced many times; wisdom is omitted from my DNA.

So what did hams of yesteryear use?

Behold... Vacuum Tube Volt Meter

Vacuum Tube Volt Meter

This Heathkit VTVM model IM-11 was available at my local Hamfest (Rarsfest) for 5 dollars.

Debugging

Five dollars is not a princely sum, but as with most things purchased from a hamfest, it required some attention.  

The 55 year old 16uFd@150V paper, electrolytic power filter capacitor was likely a ticking time bomb so I replaced it with a modern capacitor for safety concerns.  The closest one I had was a 33uFd@160V radial electrolytic.  I don't think double the capacitance will be a problem for a filter capacitor, it will just make the transformer work a little harder when it's first turned on. I calculated the initial charge time and it's 393ms vs 190ms for the original cap. I think the 10k resistor and transformer can handle the extra 200ms heavy load on power up.

A few wires inside the meter had come loose from some very sparse solder points and a one intermittent connection in the range switch was especially troublesome to track down.
The biggest mystery to solve was oversensitive resistance readings in the Ohms mode.  I replaced the C-cell battery in the battery cup and while I had it out I glanced at the + connection for the battery in the cup.  I appeared to have oxidized at some point in the past and was discolored.  I scraped it off until I saw shiny bits and thought all was good.  I spent more time tracing the circuit and thought I had a problem with the switch itself or the 9x resistors in the range circuit, as suggested in the troubleshooting section of the manual.  The problem turned out to be that oxidized bolt head that formed the positive battery connection in the battery cup.  Scraping it had not provided electrical contact.  In fact, when I removed the bolt (after having to disassemble the circuit board from the meter for the 2nd time), I filed down the head of the bolt  and could find no conductive metal left.  I'm guessing that a former leaky battery had converted the entire head of the bolt to a very hard, yet non-conductive material.  I've never seen anything like it before and it proved to be a useful lesson.
I had to find a replacement bolt and that lead to working on my lawn mower and then mowing the yard... not sure how that progression occurred...  Eventually I got the new bolt in the cup, the circuit board re-installed.  Ohms tested accurately, put it all back together and noticed the #50 pilot lamp had stopped working (sigh).  I removed the innards from the case one more time and got the pilot bulb settled (I think it's required to balance the filament circuit).  While I had it apart for the umpteenth time, I decided to reconnect the 1/4" plug that a former owner had disconnected while keeping their original modification allowing 1 mega-ohm to be switched in for the outermost probe when DC functions are selected but switched out when AC or Ohm functions are chosen.  I wanted to allow use of an original VTVM probe used in the 1/4" plug with its built-in 1 mega-ohm resistor.

Whew!

All-in-all, I probably spent 8 hours getting all the functions on my $5.00 meter to work, replacing old parts, undoing mods and aligning it for proper DC and AC readings.  It's a good thing I don't count my time in the cost of these projects, otherwise I could have purchased a couple Fluke meters for the cost of my time.

What's the fun in buying something that works right the first time when you get it home, huh?  Are we hams, capable of solving problems, or appliance users?  Actually, it would have been nice if it worked without new parts and repairs, but I digress.

Back to the story

This meter can measure up to 1500 Volts 🗲 

The main reason I purchased this is to measure the high voltage in my tube equipment power supplies and 1500 VDC should just about cover it.

Although this meter uses a C-cell battery for measuring resistance, it runs off service mains to power the tubes which control the meter circuitry, so it must be plugged in to be used. 

I love the look of its old "Gran Tran" power transformer inside the VTVM.  They just don't make'em like they used to.

Wiring, lots of wiring

This model was made by Heathkit, from 1961 through 1968, and used typical point to point wiring of the time, making circuit tracing loads of fun.

Point to point wiring makes for interesting circuit tracing 

Shiver me timbers, it's got decks

Fun fact:  When reading the schematic it will refer to "decks".  A "deck" is a wafer section.  When there are stacked sections as there are in the function and range controls the "front deck" is the one closest to the knob (front of the case) and the "rear deck" is the one furthest away, or in the case of working on it, the one closest to you.  When there are more than two decks, as is the case with the range control, it will refer to the "second deck".  As you'll likely guess by now, that is the second "deck" or wafer disc from the front of the instrument.

It also refers to "front half" and "rear half".  The "half" is referring to a side of the deck, so in the case of "front half" it refers to the side of a particular deck facing the front of the instrument, while the "rear half" is the side of a deck facing back (or toward you).

Clever voltage divider circuitry, what could possibly go wrong in this triple stack of wafer switches?

The left knob controls on/off and meter functions while the right knob controls the rather elegant voltage divider.

A knob for every function and a function for every knob.  NOTE: do not plug your headphones into the 1/4" jack on the front unless you want to experiment with personal electro-shock therapy.  Better, yet, don't plug your headphones in there.

Not clearly shown in this photo, voltage divisions up to 1500 volts supported

"...Weighed in the scales and found wanting"

Ok, how many of you understand that completely unrelated biblical reference?

I haven't used a meter like this since I used to plan my VFR flights using an E6B.  My modern, digital multi-meter is fairly idiot proof in terms of reading the results.  My DMM auto-ranges and displays the correct unit of measure along with the reading on its display.  It works well for a dummy like me.

A VTVM on the other hand, has a number of scales that must be interpreted based on whether you are reading DC, AC or Ohms.  Additionally, you have to pay attention to the range chosen.

Choose a reading... any reading, just use the correct scale
Note: the needle isn't at zero in this photo because I had just plugged it in before taking the picture and the tubes hadn't warmed up.  Ah, the joys of vacuum tube powered equipment

The voltage markings for the range switch refer to the full scale reading.  Resistance is the top scale, but let's ignore that because we're talking about measuring voltage...  The second scale from the top is Voltage.  Even though it appears to refer to DC for the numbers on the top and AC for the numbers on the bottom of that second scale that's not what's going on.  The second scale is for both DC and AC.  The numbers on the top are when you are using a range that is a multiple of 15, such as 0-1.5V 0-15V 0-150V 0-1500V.  The numbers on the bottom of that scale are for the ranges using a multiple of 5, such as 0-5V 0-50V 0-500V.   Clever eh?

You have to do a bit of math.  For example, if you if you're using the 1.5V range take your reading and move the decimal place one to the left.  So, a reading of 8 would represent 0.8V in the 1.5V range, while it would actually represent 8V in the 0-15V range and 80V in the 0-150V range, etc.  See, hams were smarter in the 1960s.

Always start with a range larger than what you expect the voltage to be and reduce the range for a more accurate reading if it occurs in the lower 3rd of the range.  The voltage divider set by the range knob is protecting the circuits so if you have it in too low a range and apply high voltage, bad things will likely occur.

Old school needle gauge.  There's a lot going on behind that needle.  It operates very smoothly.

Sporting some temporary probe hookups

Making probes

This meter did not come with probes. I bought another older VTVM pretty cheap, for parts from a famous auction site because it was advertised as having a full compliment of probes, but alas, they were not usable. Even the 1/4" plug from those probes was a bust. However they did come with rebuildable probe "ends"  

I used a RG-58 cable as the high voltage DC wire using only the center conductor and grounding the shield even though it is not used as the ground return. I also placed a 1/4 watt 1 mega-ohm resistor at the tip of the probe to limit any current through the probe cable.  That cable terminates in the 1/4" plug and is wired such that it is out of the circuit in the Ohms position. I secured the cable into the probe body with some glue and used two layers of shrink wrap as a strain relief.  I also put some shrink wrap near the probe tip as a bit of extra insurance.

 I used a spare DMM cable for the outer positive banana plug feed used by the AC and OHMS circuit and made a heavily insulated cable with an alligator clip for the ground probe that goes to the other banana plug. 

The outer probes are used for measuring resistance, AC and low volage DC. The center probe is used only for high voltage DC positive. Both positive probes would not be connected at the same time (as they are in the image below), and would present a shock risk if they were both connected when measuring voltage.

Summary

If you need a way to measure high voltage or are looking for a really eccentric meter to make common measurements harder than they should be get one of these VTVMs.  They seem to be commonly available at hamfests and on famous auction sites for under $10.

Dazzle your friends next time they ask you to measure something for them, by whipping this not-so-little-puppy out of your back pocket and powering it up.  As you're making your measurements quietly repeat "Mmmm, yes.  Mmmm yes, I see now".    They'll have no idea what you're referring to and be quite impressed.

That's all for now...

So lower your power and measure it with the low-range on your snazzy Vacuum Tube Volt Meter

72/73

Richard AA4OO

Remote VFO - Knight V-44

Everyone needs a remote VFO from 1955

Late night eBay surfing, and poor judgement led me to bid on a Knight V-44... and unfortunately won it...

Note to self: Never browse eBay just before you go to sleep

The 1955 remote VFO was unique because it had a built-in power supply.  It's also interesting that its base oscillation frequency is in the 160m band.  Using harmonics from the base frequency means it doubles for each subsequent band (x2 for 80m, x4 for 40m, etc.)  That doubling means it also multiplies the drift.  Specified drift is 300Hz an hour.  That doesn't sound too bad, but multiply that by x6 up in the 10m band and holy-smokes, it's drifting 1800Hz an hour.

That's gonna make operating CW like a game of chase, or hide and seek after every exchange.

This is gonna be fun.

Surprisingly the big dial is actually operating the variable cap through a reduction gear and it's very smooth

Uses 4 tubes. Power supply up top, VFO circuits in the bottom to minimize impact of heat from the PS. 

Power supply

old electrolytic power filter cap  must be replaced

10k 7watt resistor had failed

Replacement bits

The 450v electrolytic cap must be replaced for safety reasons. All the other components measured within 10% of specifications except for the 10k 7w resistor connected to the OA2 tube. It had gone up into mega ohms of resistance, which is likely when the VFO was taken out of use.

Handwritten notes inside the chassis indicated the VFO tubes had been replaced in 1977. Until I get the replacement parts for the power supply I won't know the condition of the tubes.

Plans

I plan on using this with a Homebrew transmitter that I may build sometime this summer.

Surprisingly, it outputs 10 volts of signal, so I may also build an output filter and use it as a QRPp transmitter on its own.


The possibilities are endless.

Update 3/21

Repaired

The replacement parts arrived from Mouser...  A 500v 47uF electrolytic capacitor and a 10k Ohm 7-watt resistor.  The new high wattage resistor is tiny compared to the giant, defunct resistor that was in there before, and of course the capacitor was about 1/3rd the size of the original.  I used some spaghetti on the capacitor leads since the lead lengths were so much longer with the replacement cap.  So the power supply section was now repaired.

I also replaced the 2-blade, non-polarized, ungrounded, un-fused 1950's power cord with a 3-pin grounded plug and added a 1-amp/250v inline, replaceable fuse.  So hopefully there's a reduced risk of death or fire now.  Electrical safety didn't seem to be foremost on the minds of kit builders 60 years ago. The size of the 3 wire power cable and it's much thicker insulation didn't fit the opening in the back of the VFO as both the power cable and the VFO output come through the same hole, so I had to remove the insulation and use heat shrink to get things to fit.  Additionally the large in-line fuse holder didn't fit well inside the VFO housing so the wiring is quite a bit more cramped in there than it was before.

After the components were replaced and the wiring was complete I plugged it in... no-smoke.  Then I flipped the repaired switch (the phenolic disc for the on-off switch was broken in half when I received it), and wallah! The indicator light lit up through its pretty little blue jewel eye.  So I knew the transformer was supplying 6.3v for filament.  I heard a low hum from the little transformer and then the tubes began to glow.  The OA2 was glowing it's pretty violet color, and no bad smells were emanating.  I was ready to button it up and begin calibration.

The sparse instructions directed me to back out the tuning slug for the 80m band nearly to the end and screw in the slug for the other bands all the way, so I did so.  I set the trimmer caps C1 and C2 to their fully engaged positions.

I carefully re-installed the front face holding the VFO and PS sections it in its heavy-duty case, taking care to get all the new power cord/fuse wiring inside the VFO section from binding up on the sharp edges of the case as it went in.  In screwed in the plentiful 10 screws that holds it together and Bob's your uncle.  Well, maybe Bob isn't your uncle but I just wanted to say that.

I had already attached an RG-58 coax to the output inside the VFO and run it out the hole with the new power cord, so I then installed a BNC connector on the end of the RG-58 to make hookup easy.  I like BNC connectors because they are secure and I have lots of adapters for different connectors.  I then connected the VFO output to my Elecraft CP1 RF coupler and terminated the other end with my ugly dummy load.  I connected the RF coupled cable to the Oscilloscope and turned everything back on.

Calibration

I let it warm up 20 minutes or so.  The cabinet does not get very warm, just about 15 degrees above room temperature.  That's actually a good thing, from what I've read.  If the VFO is at room temperature then it's more susceptible to the variations of that room temperature.  Having the case stabilize above room temp can make the VFO more stable.

I had my frequency counter attached to an output from the oscilloscope.  In the 80m band setting with the VFO dial set to 3.5 Mhz the freq-counter was reading around 1.75'ish.  The VFO primary oscillation roams around the 160m band and generates the first harmonic in the 80m band.  The freq counter had trouble tracking due to all the harmonics, and the output on the oscilloscope was not very pretty because it was showing the primary frequency with the first harmonic interfering.

I was unable to properly calibrate the VFO using a frequency counter, due to the interference from the harmonics, so I turned on my SDRPlay, software defined radio.  It can display up to 10 mHz bandwidth but for this test I was displaying 2 mHz bandwidth so that I could easily see the harmonic for the band I was calibrating.

That made quick work of calibration.  I adjusted the variable capacitor C1 (near the bottom left hand side of the VFO) for the 80m band and adjusted the one above it for the remainder of the bands.  I was able to verify that adjusting the VFO dial in the CW portions of the bands was extremely accurate with regard to frequency.

It appears to work like a charm.  I hooked up a key and even sent some test messages and listened to them on the SDR.  I'd been advised to not key the VFO directly because it tended to chirp but frequency stability was much better than I expected.  Over the course of an hour that I was calibrating I saw very little drift after the initial warm-up.

Here's a little video demonstrating the completed calibration...

That's all for now .

So, warm up your Tubes and spray some RF into the air.

73
Richard ,AA4OO

Need a Vacuum Tube?

Superstore for Vacuum Tubes

When I started restoring my Heathkit HW-101 I thought it might be difficult to find replacement tubes.  I initially only looked on eBay for tubes but then I was directed in a boat anchor forum to the vacuum tube superstore... findatube.com

Bob Dubush offers tubes at prices well below what you'll find on eBay.  When you order from findatube you'll receive NOS (new open stock) tubes in their original boxes and may receive them in a nifty original store display box...  Ah I can smell the 1950's

 He also carries hard to find tubes like the 6GW8 at far better prices than what you'll find on the 'Bay.

So if you've been looking for a good source for all your classic vacuum tube needs visit...

That's all for now...

So fire up that high voltage power supply and warm your shack the old fashioned way

73

Richard AA4OO