Tuesday, October 18, 2016

More Junk Box Rigs

FPM20 Rebirth of the hallicrafters FPM300
10/28/2016 ~ New Power Amp Stage
 I have somewhat changed direction and added a 4 Watt Linear Amplifier Stage which uses a device I found in the junk box --a 2SC2075.  Had a board layout in my computer so about 10 minutes worth of work on the CNC mill and I had a new board. This is shown below. With 4 watts I can drive thru an intermediate amplifier the SB200 to about 600 Watts out. This is a signal that can be heard on 40 Meters all the way to the right coast from the left coast.
Schematic ~ the 2SC2075 is substituted for the 2SC2166 with no other circuit changes

The "As Built" amplifier ~ The metal case is the heatsink!

Looks like crap works like Hell!
You too can build rigs like this!
Pete N6QW


10/24/2016 ~ More refinements -- improving the power output.
Initially I set the carrier oscillator frequencies in the Arduino sketch to the values indicated in the schematics. The USB frequency seemed way off. A quick and dirty test is to set the mode to USB and normally speak into the microphone. The output was much lower than LSB. A second part of the test is to whistle into the microphone (the rig was connected to a dummy load) and the output noted. On LSB the whistle test produced about 1/2 the output on LSB as compared to speaking into the microphone. On USB the whistle test produced about 1/10 the output as compared to the LSB with voice.
Using a separate external oscillator for the carrier input I adjusted the BFO frequencies until the whistle test on LSB and USB was at the same power level and these in turn matched the output using speech. These values were much different from the schematic values. But then on closer examination of the circuit schematic for the BFO  both crystals had trimmer plus fixed caps connected across the crystals -- so the actual oscillating frequency was modified in production and different from the marked frequencies. In my rig the BFO is supplied by the Si5351 and the values are set in software. I suspect that I am really close but may be off by about 30 Hz on LSB, which I will further test to verify that hunch. 
These changes have resulted in greater output!  I switched the linear amp following the driver stage to the brick liberated from an Atlas 210X. Now I am easily seeing about 50 watts output and driving the SB200 produces about 450 watts on peaks. So we are cooking. This evening I had a QSO with a station in New York where I was running 50 watts and he had a KX3 cranked down to 1 watt. So with a modest power level you can have coast to coast contacts on 40M.
I am really excited about this rig! There are some plans in work to make this a two band rig covering 20 and 40 meters.
So far I have had about two dozen contacts with stations in California, Washington, Nevada, Utah, New Mexico, Arizona, Texas, Nebraska and New York.
Pete N6QW
FPM20 now working at 50 watts with an external amplifier!
10/23/2016 ~ The FPM20 is "Alive" and making QSO's
The rig went "live" on 10/22 and so far I have made about a dozen contacts. Some of the contacts were made using just the driver stage at 350 Milliwatts (this is the EMRFD variant with a 2N2222 and BD139). Several were made using the outboard SS amp running about 25 watts. One piece of DX was a QSO with a station in Nebraska. (KD7YUW) where I was running 25 watts.
This is how it looks but I desperately need to tidy things up.
This is the rig "as is" as of 10/23

This is the 350 MW driver stage and low pass filter.

Pete N6QW


Building a Junk Box Rig from a Commercial Transceiver Board.

In the photo below is a "breadboard" version of the FPM20. Essentially the heart of this rig is the main board from a hallicrafters FPM300 SSB/CW transceiver and the S Meter. I have added a 2N3904 Receiver RF amp stage, a band pass filter comprised of two 42IF123 10.7 MHz IF transformers padded to 7.0 MHz, a Si53551 providing the LO and BFO signals and a power supply board (the FPM used weird voltgaes0. Rounding this out is the SBL-1 that acts as a receive and transmit mixer stage. The audio output stage uses an LM-386-3.
In the video above the receiver was working but I got no output on transmit -- that is until I realized on the output chain (the final device on the board) consisted of a 40841 Dual Gate MOSFET. that has ALC applied to Gate 2. Upon close examination of another of the circuit diagrams I saw a note about ALC. On receive the voltage is "0" but on transmit with no signal applied the voltage was 6 volts supplied from the ALC circuit -- this was a negative ALC. As more signal (such as from over driving) is developed the ALC becomes less. I had applied no voltage to Pin 17 on the board so essentially the circuit was cut-off! I added a 5 volt regulator to Pin 17 on transmit and the circuit now works on transmit --and CW. The FPM 300 used a keyed tone for CW generation.
A new board will be built using my standard 2N3904 bi-directional circuit which acts as the RF amp on receive and the transmit pre-driver on transmit. There is sufficient output from the 2N3904 to fully drive the 20 Watt brick sold by CCI. This is why the rig is dubbed the FPM20. We are on our way.

Pete N6QW

Saturday, October 8, 2016

That's All Folks!

This is the latest and last posting on this blog. There will be no further blog entries!

Keep on melting solder.

Pete N6QW

Saturday, October 1, 2016

What is a VFO (variable frequency oscillator)?

The Variable Frequency Oscillator ~ aka "Grief in a Box".

Whether you have an appliance radio (store bought) or one that you made with your own hands somewhere buried in the innards is a variable frequency oscillator.  However if you are running a single channel fixed frequency device such as a crystal controlled transmitter or receiver then maybe that is not the case. The acid test is if you move a knob or mouse pointer and you are able to change the frequency, then you have a VFO. A special case may be the VXO which is a variable crystal oscillator which uses the properties of a quartz crystal to shift its frequency of oscillation over a small range. But the VXO usually has a knob adjusting a variable capacitor or a pot controlling a voltage variable capacitor.
But I really want to focus on the knob turning, mouse pointing variety of variable frequency oscillator. There are various ways to generate a variable frequency starting with the very early approach involving analog circuits where an inductor and capacitor formed the very heart of the VFO. When an inductor and capacitor are linked up, either in series with each other or in parallel, a resonant circuit is formed. If this combination is placed in an amplifier circuit and certain conditions are met with respect to internally generated feedback the circuit will oscillate at a frequency determined mostly by the  inductor and capacitor values. Other factors that impact the actual frequency of oscillation include stray capacitance and/or inductance as a result of component lead lengths. For these reasons most VFO construction tutorials stress short direct connections and isolation from other circuit elements.

There are many types of analog VFO circuits with names like Hartley, Colpitts, Clapp, Vacker, Seiler, Franklin, ECO. The difference among these types basically is how the L and C are combined (series or parallel), the method of achieving feedback, where the load is placed and finally the coupling to the load. Some of these circuits are very load sensitive and you will frequently see some sort of follow on buffer amplifier to isolate the actual load (such as a mixer stage or convertor stage) from the oscillator itself. Below are two examples of oscillators with the first being a Hartley and the second called a Vackar. [The naming typically follows the person who invented the circuit.]

The Basic Hartley circuit (parallel L and C)

Vackar Circuit with L and Co in Series
For those who have an insatiable desire to know where every nut and bolt is hiding there are many factors concealed in the bushes as to why the circuit oscillates. Some factors have to do with the physics of inductors and their response to  being charged and collapsing electric fields while others have to do with capacitance discharge rates and flywheel effects. I do not plan to cover these other than to recognize that certain conditions have to be met for an analog circuit to oscillate.
Here is part of why I used the term "grief in the box "-- getting a circuit to oscillate is but a slice of the pie as then the builder is confronted with keeping the circuit in the oscillating state over the desired range. When you twiddle the knob or move the mouse pointer the objective is to keep it oscillating over the entire tuning range. That does not always happen.
Another pie slice is oscillator stability which has several subsets. There is the "drift factor' manifest as either "initial turn on drift" where as the circuit elements heat up from a cold start the frequency will drift. This can be a very large amount in the range of several hundred hertz to kilohertz. Capacitors especially are subject to temperature drift and the inductor as well will respond to temperature changes.
Another drift factor is "long term drift" where after the initial "turn on drift", over time the frequency will shift albeit usually a smaller amount. Turn on drift as stated may be in order of magnitude of kilohertz whereas the long term may be 100 Hertz. Fifty years ago a few kilohertz drift was common. Today the Flex Radio Operators on 40 Meters will scream at you if your rig moves 10 Hertz -- so with progress there are some penalties.

Yet another form of drift is the result of poor mechanical construction of the VFO. If your inductor flops around --the VFO will change frequency. If you move your hand near the inductor it will change frequency and even blowing cold or hot air on the inductor will change the VFO frequency. You get the drift (pun guys).
Other issues include "FMming" a term often applied to certain older boat anchor inexpensive commercial appliance radios that lacked good voltage regulation. Typically these vintage radios featured 500 watt sweep tubes and with a marginal power supply on voice peaks the VFO regulation suffered. The result is the SSB signal frequency that varied with voice peaks --thus frequency modulation. Before we leave VFO voltage regulation that is an issue in itself as the lack of adequate voltage regulation results in frequency drift.
A similar problem was when the VFO was built  "al fresco" with no shielding such that the output RF signal was being picked up in the VFO circuitry and this results in distortion. 
Hopefully now you understand why I call it "Grief in a Box"! But in examining all of these maladies there is a general approach that cures many of these problems and most of the cures are physical in nature. So for those contemplating building an analog VFO behind the schematic is a host of factors that if properly addressed  will assure a success. Lets us examine some of the physical factors.
  1. The components themselves are one factor. Use NPO temperature coefficient capacitors and use multiple caps in parallel. Capacitors have AC current passing through them which cause a heating of the cap. If you have say a 100 PF cap in parallel with a 50 PF variable cap to set the band range then use ten 10 PF caps in parallel as then each caps is drawing 1/10 the current and the heating of each individual cap is dramatically reduced. While you are at it the 50 PF variable must be a double bearing type (supported at both ends). This keeps the cap linear and not subject to vibration. Old style brass capacitors work the best but may not be readily available.
  2. Inductors are very subject to temperature and mechanical impacts. Air wound inductors seems to be the best BUT how you mount them may negate their otherwise excellent properties. Frequently the inductors are wound on a grooved ceramic core or on a cardboard form that has been varnished. Keeping an inductor away from the chassis or walls of an enclosure is an art. Ceramic pillars are often used for this chore. One other approach is to super glue the air wound inductor to a 1/4 inch thick piece of plexiglass which is then mounted on the pillars.
  3. Physical isolation is another factor. High quality VFO's are built in shielded enclosures and power is fed to the VFO via "feedthrough" capacitors. The signal output is best done utilizing SMA connectors. Real die hard VFO builders will put the Inductor and Capacitor in one box and the electronics in another box where the two boxes are interconnected with a short length of RG174/U 52 Ohm coax. This approach isolates any heat from the frequency determining elements.
  4. The build itself should utilize short direct connections over a common ground plane. This is where a Manhattan style build could result in an extremely "solid" VFO. For best results do not utilize Zener regulators but instead a three terminal type such as the 78L08. That is another point use the  minimum amount of voltage to sustain reliable operation. This reduces  circuit heating thereby impacting the drift in the least amount possible. Further amplification of the VFO signal can be done externally.
  5. Mechanical factors must be addressed wherein any vibrations or mechanical movement will cause movement of  components in the VFO itself. One the earliest frequency agile ham transmitters was the self-excited Hartley oscillator which frequently used a type 45 tube. Essentially this jewel was a keyed VFO built on a wooden breadboard. This was a pure example of "al fresco construction" . Literature of the time cautioned that the operator must place the transmitter on a shelf above the operating table as the mere act of striking the Morse key would transmit vibrations to the transmitter and the signal would vary in frequency based purely on the movement of the key. The physical isolation solved that problem. The second caution was to insure the antenna was taut --- if the antenna moved with a breeze it would present a variable load to the oscillator and the frequency would shift. A hefty mechanically sound enclosure serves two purposes: one is to shield the VFO and secondly to reduce the impact of mechanical vibrations.
  6. Voltage regulation is key as mentioned earlier. Resist using Zener diodes and resort to stout three terminal regulators. You ask why? -- Most of the three terminal regulators feature internal temperature compensation to keep the output constant --Zener diodes do not. Very sophisticated regulation circuits will keep the output constant even when subjected to wild swings in the input side. Lack of voltage regulation and heating of the circuits (especially with tube type vfo's) frequently resulted in a chirpy signal especially if one were keying a VFO for CW operation. The message here is to use the lowest voltage practical to sustain oscillation as this facilitates maintaining the applied voltage and reduces the device dissipation which in turn generates less heat.
  7. Once you have the VFO built typically some sort of gear reduction drive mechanism coupled with a mechanical readout like a circular dial is fixed to the capacitor shaft. Careful alignment is required so that no stresses are introduced into the capacitor shaft (ie binding) such that the assembly lacks smooth tuning. This takes time to get it right!
  8. Finally --don't be greedy! Select a reasonable tuning range like 500 kHz for your VFO as this satisfies several factors one of which is stability and another is linearity. The ultimate goal is to have the same degree of movement at one end of the VFO range produce the exact same increment of change at the other end. Did I mention that a smaller range facilitates the use of reduction drives to give you "fine tuning". 
The above cover much of the well known cautions and tribal knowledge in analog VFO construction and if you are looking for a simplification in building an stable analog VFO --there is none! There is much effort involved if you want to have a stable VFO. Translate this to hours and days of work versus a hour with some wire wrap tools and 30 Minutes writing some code for an Arduino. Unless time is well spent on analog VFO construction you will have grief in a box!

Above all feel free to add your additional comments on how to avoid "Grief in a Box".

Pete N6QW

Wednesday, September 21, 2016

Taking a Break!

Are you tired of seeing me post about my rigs?

9/28/2016 ~ Some recent updates

I have often said that most of my rigs are experimenter's platforms and the Junk Box Rig stands as an example of that approach. Everyday I look at possibilities for improvement --some changes are in the negative column but many are in the positive direction. Usually I employ the concept of TFMS when "peaking and tweaking" a rig. Oh almost forgot TFMS is an old timer term for Tune For Maximum Smoke. Well in this case when I had the rig outfitted to run 700 Watts out (Yes, Virginia, that is not QRP) I found that I got a report of splatter. One of those Flex Guys saw me pop up on his 60 inch color display and he reported I was very broad and splattering over onto other frequencies.
He was absolutely right! If you are running QRP at one watt --there may be splatter that is hardly noticed but magnify that 700 times and you will notice that your signal is broad and spilling over the normal bandwidth. A simple adjustment of the microphone gain can cure that problem. So out comes the scope and I was indeed flat topping and lowering the gain didn't actually impact the PEP output but did immeasurably improve the signal quality and cleaned up the spectral purity. For reference purpose a 1 watt signal is 30 dBm and a 700 watt signal is  58.5 dBm. So you will hear that very large elephant in the room!

Once I reduced the microphone gain, the Flex guy was  happy and so now I was happy too! WE have a responsibility as hams to put out the cleanest signal possible! I am now ever vigilant to not let that happen again. The positive side was that my PNP audio amp was no wimp and I had a gentle reminder about flat topping and splatter.
Rummaging through the junk box I found a 2SC2166 on a board and swapped out the 2SC2075.  Now 5 watts out is an easy goal. I also made a change on the driver board where normally the EMRFD circuit has a 2N3904 driving a 2N3866 but in my circuit I have a 2N2222 driving a BD139. In the emitter lead of the 2N3904 (my 2N2222) there is a 22 Ohm resistor to ground. I replaced that resistor with a 200 Ohm pot. The center wiper is connected to ground and the top lead is connected to the 2N2222. This enables me to adjust the stage gain. When I drive the 100 watt intermediate amp ahead of the SB200, I have it set so the Junk Box Rig outputs 1 watt as that is about the max level input to the intermediate amp. In the TFMS QRP mode (without any amplifiers) I can adjust that pot for 5 watts output from the 2SC2166.
On 9/27/2016 I made a 400 mile hop to San Francisco from my QTH near Los Angeles running 1 watt out on 40 Meters. Not a lot of signal strength but readable. But I must confess that 40M QSO's to the mid-west are much better running 700 watts!
Recap: Beefier RF Transistor, Watch for Flat Topping, Variable RF Output, QRP QSO's.
Pete N6QW

9/21/2016 Revised Microphone Amplifier and plot. (See Comments)

Revised Schematic to limit the frequency response.

Output Plot of the revised shematic

Here is a chance to tell me what is on your bench and if you have attempted to build any of my projects.

Pete N6QW

Saturday, September 3, 2016

40M Junk Box SSB Xcvr in a Blue Case

The Blue Junk Box 40M SSB Is Alive!

9/15/2016 ~ Continued -- Listen to the Junk Box Radio...

9/15/2016 ~ Junk Box Experimenter's Platform

Ever wary of unwanted frequency mixing schemes and picking an IF too close (harmonically) to another band, I decided to change out the Yaesu 3.180 MHz Crystal Filter. The second harmonic of the BFO is at 6.4 MHz which is in my opinion too close to the 40M band with just the simple Band Pass Filter I am using. Adding a better BPF (more poles) or changing the IF would of course provide better solutions to my concerns. Still another solution would be to use dual conversion approach to mitigate the problem.

I opted to change the IF frequency as I had a spare 9.0 MHz GQRP Club SSB Filter. The change from 3.180 involved unsoldering two wires and the mechanical removal of the filter from the board. The Z in/out of either filter is 500 Ohms, thus requiring no change in the matching transformers. Insofar as Arduino code changes, about a total of eight entries and that was it. Since the LO is above the incoming there is a sideband inversion so the lower frequency BFO frequency is used to receive LSB (8.998500 MHz) and USB uses the upper 9.001500 MHz Carrier Frequency. The changes went FB and we now have an IF of 9.0 MHz. I now would feel more comfortable in moving the rig to 20 Meters. BTW total elapsed time was about 30 Minutes for the hardware change out and the software modifications / loading on to the Arduino Pro-Mini.

This is the beauty of my approach to building a rig. Changes both in hardware and software can be easily made without a complete disassembly of the radio. It is truly an experimenter's platform.

Pete N6QW

The Junk Box SSB Transceiver is now fitted with a 9.0 MHz Crystal Filter from the GQRP Club

A Close Up of the Junk Box SSB Rig Front Panel -- You gotta love that blue!

9/12/2016 ~ Making Contacts
The one nice facet of our beloved hobby is to make contacts and hopefully by what I have done with the last several transceiver projects is to inspire others to "take up the iron". Perhaps one of the most powerful ways that can be done is by using the rigs on the air. I have actually spent more time on the air in the last several weeks than I have all year long. True much of my operation has been in short bursts like 20 minutes here and there -- but the results have been many fold. Not only have I met some really great people; but the interest level has ramped up with many inquiries about the rigs I have built. Perhaps one or two will be inspired to build their very own rigs.
Pete N6QW
9/8/2016 ~ Ramping up the Power!
Yesterday I added some switching circuitry so I could simultaneously key up the Atlas 210X "brick" and my SB200 Linear Amp. I am happy to report I can now put out about 600 Watts into my droopy dipole. This now should give me a shot at working coast to coast with the droopy dipole.
Another critical part of the tests were to make sure I wasn't tripping (or ripping up)  the security alarm, telephone system, sprinkler system or the cable TV. All is clean and so the grounding, shielding and good wiring practices have paid off.  
I am very pleased at the performance of this radio and now with winter coming on want to do some serious 40M operation. I note that in the early morning hours I am routinely hearing stations in Japan and Indonesia on 40M SSB. So that is another goal to make contact with these station and I feel possible with this rig and the amps. I hardly ever run it at 3 watts so I guess my QRP award is in jeopardy of being revoked.
Pete N6QW

9/7/2016 ~ Some observations and updated information

I continue to be amazed at the performance of this "Junk Box Rig". Signal reports affirm its good quality signal and nice sounding audio which does seem to have some added "sparkle" to the sound. I attest the audio reports to spending some time in improving the frequency response of the PNP microphone amplifier. A bit of time with LT Spice pays off in big dividends.
You can't imagine my surprise several days ago where about six stations in a row contacted me for details about my rig and how it was built. There is no finer compliment than to hear your station being called by others. With a bit of tuning and some improvements I now get about 115 watts out using the linear amplifier "brick" liberated from an Atlas 210X SSB transceiver. This power level now enables easy QSO's into the mid-west and western Canada with my "droopy dipole" installed on my postage stamp sized Southern California lot. A better antenna would definitely extend the range into the east coast on a regular basis. So the antenna does count. In fact typically the second question after the usual first question about the rig is what kind of antenna are you using?
Extensive use of a radio will often identify "issues" and so it was with the Junk Box Rig. I found that after an hour or so of operation the rig would not return to receive after a lengthy transmission and at times even though the rig would go into transmit -- there was no output signal. The problem was traced to the solid state switch. I found that when this occurred the SN7400 IC which was wired as an inverter was "hot"  to the touch. Not just warm; but burn your finger hot. So my fix was to install a small 12VDC SPDT relay in lieu of the switching board. Problem fixed and a simpler solution. The radio no longer suffers from that hang up. But it does beg the question as to why? I will do some further bench evaluation --but in keeping with the theme of this rig --the relay is what I found in the junk box -- and even though the relay is small its contacts are rated for 3 Amps DC at 32 Volts --so plenty of head room.
To seem repetitious often when we challenge ourselves to find solutions by using what we have an end result which is often better than simply flipping out the plastic and buying new. I have quite a few boat anchors and aside from the KWM-2, this rig hears better than most of those radios of old. With a bit of scrounging and some horse trading this rig can be built for less than $150. The frequency generation part, BFO, encoder and the LCD can be bought for about $20. The SBL-1 Double Balanced Mixers can be purchased from RF Parts for about $16 and the Iron Powder and Ferrite cores add about $10. The real bang for the buck is the pleasure of saying my rig is homebrew built by me!
So what is on your bench???????
Pete N6QW

It has been one week since we made the first contact with the 40M Junk Box SSB Xcvr and I am happy to report that the hunk of junk has now been given a proper and fitting home.

This is how it all started!

Using my Harbor Freight metal break I made some brackets to provide support to the front panel

The rig base is a piece of copper clad board 10.5 inches long by 8 inches wide. Here we see the front panel/support brackets installed on the base plate assembly. I used my manual mill to make the front panel.

This was an exercise to determine how all of the boards would fit in the case

The boards are all mechanically installed and the wiring is everywhere.

Here the wiring is about 85% done

Oblique view showing the various boards.

The Junk Box Rig sitting next to its older brother the Nu-Rig. Love that Blue!

The Junk Box Rig is now fully functional.

Front Panel close up!

Innards: Driver Board, Final and Solid State switch

Band Pass Filter, Bi-Directional Amp, Main Board, Si5351 and Microphone Amp.

Left Oblique View.

Right Oblique View: Audio Amp, TR Relay,Linear Amp Switch and Low Pass Filter

Power Amplifier. The device is mounted directly to the bottom copper plate (insulator used). We have 84 square inches of copper heat sink.
I now have connected this rig to the "brick" liberated from an Atlas 210X. With 3 watts of drive I get over 100 watts out. Since finishing this rig today I have made 5 contacts running the amp --- all excellent reports. Three of those contacts were into the mid-west.
What are you waiting for --get cracking on your junk box rig! Soon I hope to make a video so you can listen to this wonderful radio. This also has been a great experience for me in using what you have -- my 1st thoughts were to buy a chassis --ouch at $30 I figured there had to be another way and there was.
Pete N6QW

Friday, September 2, 2016

40M Junk Box SSB Transceiver Microphone Amplifier

Exploring PNP Transistor Microphone Amps

This is a first for me in terms of using PNP transistors for microphone amps. In fact more recently it was a first for me to use a single NPN transistor as a microphone amp. For the longest time my standard building block was the NE5534 for microphone amps.
On the air signal reports for the Junk Box rig were very good with the added comment that there seemed to a favoring of the highs with very little in the way of low frequencies. Well Duh, a couple of minutes with an LT Spice Simulation confirmed the why this was so. This post will explore the why.
[I should note that I have a bag of vintage PNP audio type transistors that I have often wondered what can be done with these treasures of old? Now I know!]
I ginned up the circuit I was initially using and it worked and just moved on but given the reports of the lack of lows I actually simulated the original circuit and found that there was a substantial lack of gain (like 10 to 15 dB) for frequencies below 1 KHz. Above that frequency things were much better.
Since there were no LT Spice Library entries for the 2N996 I picked the 2N4403 and then verified the same results with a 2N3906. Two capacitors play a key role in boosting the low end response and those are C1 and C4. Initially I had C1 at 100NF and C4 was 10 ufd and of course we could see that lack of the low end response. With a bit of cut and try these final values of 10 and 100 ufd, really boosts the low end. Now there is less than about a 3 dB change from 300 to 3000 hertz. I used a generator with a 100 millivolt output and swung the frequency from 10 hertz to 5000 hertz.
For those picknitters in the readership the + side of the 10 ufd is toward the signal input and the minus toward the base. On the 100 ufd, the + side is connected to the emitter of the device. I installed a socket on this board so I can actually turn this into a PNP transistor checker. For those who are still uncertain about electrolytic cap polarity-- the answer is to purchase and install non-polarized electrolytic capacitors.
A little more than the 15 minutes I spent with LT Spice could even further improve the low end so that the circuit is flat to 5 kHz. At this point I say Basta and just move on.

Schematic of the PNP Microphone Amplifier

Finally for the doubting Thomas crowd here is the expected performance of the circuit. I should also caution that R4 is really a 10K Trim Pot and the 220 NF (0.22 ufd) cap is connected to the center wiper. The output end of the 220 NF is paralleled with the audio amp input where both are connected to pins 3& 4 of the SBL-1.

Projected Output from the PNP Microphone Amplifier Stage.

The bottom line is that the PNP Microphone amplifier stage is good for about 20 dB of gain over the audio range and confirms the suitability of the device in homebrew SSB transceiver projects. Somehow many of us sort of gravitate to NPN devices --but good circuits can be built using PNP devices.
Pete N6QW