Ancestry

The family chronicles: Linoprint cover page

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With the chronicles related to my father’s parents completed, and the book decorated by hot embossing (see: The SCHRÖDLE Family Chronicles: decorative hot embossing) it is time to consider the decoration of a similar book about the parents of my mothers. Fortunately, the contents are nearly complete, but I didn’t want to do just another hot embossed front page. After some brainstorming, woodcut print seemed like a nice idea. Surely, I have no time and patience and skill to cut a complex plate from wood with knifes, but intended to use a digital design and than LASER-cut it into the material to general a relief suitable for printing.

First I tried to use actual wood, but the results were not that nice with ordinary plywood. The edges break off easily with thin elements.

Cutting is easy, I am using a Sculpfun S9 cutter with a blue diode LASER. The material is held to a metal plate with some magnets, there is no further workholding needed. Compressed air is used to blow away the dust and to protect the laser optics. All the fumes are extracted by a fan to an exhaust – the whole LASER cutter is in a protective enclosure..

After seeing the mixed results with wood, quickly ordered some “art supplies”, good old natural linoleum (don’t get the PVC type, this cannot be LASER cut and will emit toxic fumes!). Linoleum plate is made from linseed oil, wood powder, limestone filler and some additives. Just a few days later, two plates arrived. There is a very nice and particular smell of fresh linoleum in the workshop.

Before going to the endeavor of large format prints, good to start with some smaller test piece. Because of the thin beam, the engraving works best here at 10 lines per mm, 1300 mm/min speed. After a few minutes of engraving, a small cat relief was ready. The raw cut needs some treatment to remove the burned residues. First tried with an eraser, works well, but eventually a good method is to bead blast it with compressed air.

There are two kinds of paints, water and oil based. Water based paint has the advantage of fast drying and easy cleaning, but for the traditional look and ever-lasting persistence, oil based paint is preferred. After doing some research, the DALER-ROWNEY ADIGRAF seemed to be a good choice. A 250 mL can is just about 10 EUR and will last for many prints.

Next, we need a rubber roller. Using some piece of an old typewriter, cut to size and turned down to a little smaller diameter on the lathe, and with a simple wood handle attached, a sturdy roller was fabricated quickly.

The cut linoleum relief is stuck down to some old chipboard, and the printing setup is ready.

To my greatest delight, the first print turned out well. A lovely cat print. Just used my fingers to transfer the ink by circular motion.

The cat motive is good for experimenting: the quantity of ink, the uniformity of ink application, attaching the paper, transfering the ink, all needs some practise.

With many cats printed, it is time to engrave the big relief for the book cover page. The artwork went through quite some iterations, because I wanted to incorporate motives from my ancestors’ past, without it looking to fancy. Giving it a little worn and historic look, with simple elements. A certain variability of the ink application will give a nice individual touch.

The engraving took about 3 hours. Not fast, but for a very affordable 5.5 Watts LASER, fair enough.

Cleaned it out by bead blasting (soda glass beads of ~300 µm at 8 bars), and some manual work to cut it out with some tapered edges.

After the cat exercise, inking the relief worked pretty well and the first print gave a good result. Switched form 150 g/m2 paper to hard 250 g/m2 board to give the book some stiffness.

In no time several prints were made.

While the deep red color is a nice, it is lacking a little contrast. From very old books, like this copy from 1692 (which is one of the oldest in my library), a black-red color scheme is known, which has been also used for woodcut prints and similar, for example, for “ex libris” cards and other more art-oriented printing.

For inking, a small roller was needed. Rather than buying one, made it myself, this time from some paper pushing roller of an old printer (good that I keep a large assortment of parts in my basement…).

With a piece of steel wire, the small roller (also called a brayer) is ready for use.

To roll-out the ink to a thin layer, some pieces of old glass sheet attached to a wooden board are hand, because of their smooth surface and resistance to solvent cleaning (methylated spirits are good for cleaning of the oil based ink).

The inking is about three times the effort compared to a single-color print, but at least we don’t need to worry about the alignment of the paper when all two colors are printed at one, rather than consecutively.

The result turned out well, such a nice contrast of red and black!

Now, many prints have been made, and these need to dry thoroughly, which will take at least 5 days, better 2 weeks, for the oil based ink.

Various

Broncolor Primo: the photo flash is flashing again

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A very unusual and dangerous repair, a defective photo flash. This is a professional unit, for use in photo studios. Generally, these units work by charging a big capacitor bank to 300-400 VDC, and then discharging this energy in an instant through flash bulbs. This unit has 10 pcs. of 2450 µF capacitors, charged to 360 VDC. About 1600 Joule, which makes this unit very dangerous, I would strongly discourage anyone not familiar with power electronics to even open the case.

For its size, it is quite heavy unit, and has a 16 Amp fuse, it will recharge quickly, drawing substantial power for a short time.

Inside are 12 large capacitors, 2 for the charging voltage stabilization, 10 for the capacitor bank. After duly checking the caps and their safe discharge state, I tested them all, each individually. 3 were bad: 1 completely disconnected at the terminals, 2 with no capacity, worn out.

Flash capacitor need to withstand high discharge current, so we cannot just use any ordinary cap but need to source “flash capacitor” – found reasonably priced one from China, because there were other faults with this unit besides the capacitors, there was no reason to by expensive caps first, without knowing if this unit can be fixed at all. Unfortunately, there are no schematics available.

Studying the electronics, there is a primary thyristor (TXN1012) switch DC stage, a type of coarsely regulated power supply. This had a blown transistor in its control circuit. Failed by arcing. Fortunately, I was able to still read the color rings under a microscope, and replaced the part and an associated Zener diode. Also the thyristor and a MOSFET in the thyristor were replaced (the MOSFET tested good, but I didn’t want to take a risk).

The replacement caps have 2000 µF. 3x 2450=7350, 4x 2000=8000, so I decided to install 4 of the 2000 µF capacitors (2450 µF were not available easily). It results in about 5% higher energy in one bank, good enough.

After some hours of complicated failure search and repair, some very careful tests (checking if the caps load symmetrically, which they did), finally the green light of the “flash read” LED was lighting up.

The flash worked – but only for a short time, then: SMOKE from the flash box. Expecting the worst, opened it up right away. Surely, first removing the cables from the capacitor bank.

Inside of the flash box, 4 Xenon? flash bulbs, with spiral trigger electrodes. The high voltage trigger transformers are right inside the flash box. The smell is awkwardly familiar: an exploded Rifa safety capacitor. 0.1 µF, 1000 VDC.

Fortunately, it failed open, as it is supposed to, lots of bad smell but no damage or fire. There is one capacitor for each bulb, a total of 4 (2 sets).

I cleaned up the mess, ordered 4 original Rifa (now KEMET, but they still print “Rifa” on these), and soldered it all back together. The other 3 were electrically still good (tested for leak resistance several MOhm, and isolation test passed at 1000 VDC), but had many cracks so I replaced all capacitors.

Eventually, all is working again. There is a built-in studio light, quite fancy unit. Hope the repair will last for a while!

Various

ANENG MH15 Isolation Resistance Meter: a remarkable deal

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Typically, I don’t report about test equipment acquisition unless these are associated with repairs, but this time, I will make an exemption. I used to have an old isolation tester, but it has been playing up, and with the analog instrument, difficult to repair. So I checked about more recent instruments, mostly, to check electric installations and motors and similar, for isolation after repair. This requires a 1000 VDC test, because some isolation defects tend not to show up at low voltage.

After a quick search, I found an almost unbelievable offer, just about 25 EUR! Shipping included!

One week later, a badly packaged box arrived, in a plastic bag, but without major damage.

Inside, a handy soft case.

The instrument, the plastic is of good quality. The red plastic is a little hard so it will not absorb too much shock when you drop the device.

Immediately, I got some of the highest value resistors I have in stock, a Remix 1000 MOhm +-5 % resistor. This is good to 10 kV, so there is no problem or leakage when doing a 1000 V test (other resistors may be have voltage rating of 300 V or 500V).

At a first glace, very nice result. -2% within the tolerance of the part.

Checking the voltages, 1000 V is fairly accurate.

500 Volts, even better.

Some more deviation at 250 and 100 Volts.

The specifications are quite good. But eventually, the instrument is not used much to measure resistance, but to check for conduction when 1000 Volts are applied. Normally, it will either show >2000 MOhm, or a spark will fly and the high-voltage isolation test has failed.

For completeness, also checked a 200 Ohm, 0.1% resistor. 1.5% deviation is the specification of the MH15, and deviation found is 0.25%, very good.

All in all, a great instrument for the occasional user, and one more reason to not skip isolation resistance tests.

Various

Rohde&Schwarz URE RMS-Voltmeter: analog digital communication

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Recently, I got more R&S instruments for repair than ever before. This time, an URE RMS-Voltmeter. It can measure AC and DC voltage, in true RMS values, from 50 µV to 300 Volts. 0.5% basic error. So it is about 1% accurate, with a frequency response from 10 Hz to 20 MHz.

It showed a failure message, “error d” which is a combination of errors that aren’t a good sign. So I was not sure how to approach it first. Checking the manual, I decided to proceed first with some basic test to see if the analog circuit is reacting to commands. A simple test involves the check of the reference voltages: there are 1 V, 10 V, 0.1 V and other voltages derived from a main reference on the analog board, and by digital command you can switch either of these to a test point. However, I could not get all of these voltages switched correctly.

Doing some analysis of the logic chips and circuit, the analog board didn’t get a valid command – there was no signal on the A0 address bus. Tracing back the signal path, this bus originates from an optically isolated driver circuit on the CPU board.

There are 12 optocouplers, fortunately, socketed. So I changed the B12 (A0) and B11 couplers, and indeed, the reference voltage issue showed a different behavior. Obviously, something in wrong with these couplers. I tested a little, and replaced the B12 coupler by a 4N28, and this brought the unit back to life, without and failures. Run the self-calibration (necessary to remove a wire bridge to execute calibration command).

Then, after checking more carefully, decided to replace the 4N28 by a 4N35, because this is a part of virtually identical performance to the (obsolete and old type) of optocouplers installed in the unit. Also checked the signal integrity and slopes with a scope, can’t see any difference of the new B12 coupler to the other couplers.

One major advantage was that I got a whole file with all big schematic copies, easy to work with it. I like to put these on the floor for easy reference without damaging the paper.

A final test with a precision level generator. All seems good, even after a few hours there is barely any drift.

Various

L33 Thermal fuse: inner workings

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Recently, I had a project that required a reliable thermal fuse. There was little space to accommodate the classical axial versions, so I did some investigations and settled for the L33 type fuses. These come in various temperature versions, here, the 130°C limit, rated 2 Amps, 250 Volts.

The main components are the 2 wires, a plastic case, and some resin. Having never studied one open, I disassembled a few good ones.

Clearly, the resin is filled to certain level. At the top, there is a bridge between the wires, made by low-temperature melting alloy (having tin, bismuth, indium and related metals).

The alloy is quite substantial, likely to be able to handle 2 Amps of current.

Triggering it with heat gun, the alloy melts, and there is enough space in plastic case that it forms a drop, effectively interrupting the circuit.

While the devices studied showed very good consistency of construction, a little overfilling with resin may result in the thermal fuse not opening, I hope the manufacturer has this parameter under strict control. For the 10 pieces I have, the weights measured on a precision balance where quite uniform at least. But if you get such critical parts from some doubtful sources, better you do some tests first and be sure they are reliable.

Various

Rohde&Schwarz NRT Power Reflection Meter: tantalum issues

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Recently, I got this very nice instrument – a Rohde&Schwarz NRT “Power Reflection Meter”. It is designed to measure transmitted and reflected power, a quite handy instrument used for the installation of cell phone antennas, etc.

This unit was received with a label “completely dead and burned”, but it turns out that the damage was not all that bad.

Some quick survey showed that there is a 12 VDC power supply installed, which is connected to the main board by a cable. On the main board, there are three capacitors in parallel for the 12 V bus. One of these had burned out, only pieces and black smoke remained. The board looked damaged, but after careful removal, there was no problem with the board found. Used some methylated spirits to clean the mess thoroughly. There one thin trace underneath one of these capacitors, so better don’t work on it with coarse tools or in a rush. I dissected it under the microscope. The ground connection pad of these capacitors has no heat relieve arrangement, but the caps are soldered to the heavy ground plane – a strong soldering tool will be needed to melt the solder in adequate time.

I desoldered not only the bad guy, but also the adjacent capacitor, to test its performance and value (there is no schematic). These are 100 µm low ESR caps. I found it appropriate to replace two of them by one 470 µF electrolytic capacitor, plus, a 10 µF multilayer ceramic capacitor in parallel. Saving money to buy 100 µm small-size tantalum that are difficult to hand solder without risking damage.

One intriguing part came up during repair, a 78ST105S regulator, which is there to provide a 5 V rail from the 12 V input. Quite a nice part, now obsolete, but first time a ever saw such design. It is essentially a high efficiency voltage regulator, easy to use, but it has a buck circuit installed to get higher efficiencies compared the customar 7805 regulators.

Some quick check of isolation resistance and the power supply (without anything connected) – it provided stable 12 VDC to a test load, so the shorted cap didn’t cause any damage to the supply. The moment of truth: switching on the NRT instrument. Working fine.

To complete the unit, I will need to see where to get an affordable NRT sensor. These don’t come cheap. List price is 3800 EUR each, used units go anywhere from 500-2000 EUR. Definitely, expensive.

Miscellaneous

Christmas Bakers: Dominosteine – dominostones

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This year a good friend has been asking me to prepare “Dominostones” together. It is a kind of German special Christmas cookie, which is normally purchased at supermarkets because fast machines can make these things much more accurately and faster than human had. However, always up for a challenge. Handmade goods of such rare nature will also be a handy gift.

First, we have to make a thin dough base.
120 g of honey (cheap honey is OK)
30 g of sugar
1 tablespoon of mixed spices (cinnamon, etc., use gingerbread spice)
100 g of wheat flour
100 g of heavy rye flour
1 egg
3 g of ammonium bicarbonate (“Hirschhornsalz”) dissolved in some warm water (10 ml)
3 g of potassium carbonate (“Pottasche”) (dissolved in a little it of warm water)

Warm up the honey a little in the microwave to make it liquid, dissolve the sugar in it. Some little remaining sugar is no problem. Add a mixture of the flour and spices (best, pre-mix as dry powder), add the egg. Add at one side the dissolved ammonium bicarbonate, mix a little, add the potassium carbonate solution at the opposite site (don’t mix these two things together).
Let the dough rest for a few hours (wrap it tightly with cling wrap; not too cold, say, 15-20°C).

Use a good pan with some anti-stick paper, be sure to roll it to a uniform layer. The size of my pan is 43×32 cm. Similar size will also work.

Bake approximate 8-10 minutes at 200°C (upper/lower heat; air convection oven you may try 180°C).

Let it cool down.

Take about 600 g of apricot jam (screen it through a mesh to remove any solids), add 150 g of water with about 9 g of agar-agar (a pale powder). Boil for 2 minutes. Let it cool down with occasional stirring, but don’t let it get firm. Apply to the dough base in one go. First leave a little distance (say, 0.5 cm) to the edge, then apply more and more ensuring that it doesn’t flow down. If to liquid, wait a little, however, it is best to apply all in one operation, to avoid forming layers of gel that can later separate.

After some cooling, apply a marzipan layer.

400 g of marzipan (baking marzipan)
150 g of powdered sugar (not icing sugar or similar mixed products, must be 100% pure powdered sugar)
Kneed the marzipan and sugar to a uniform mass by hand. This takes some effort. First work in 1/3 portions, then combine all together. First, it looks as if it cannot mix, but after a while, it will. Roll this material to a thin layer large enough to cover the full pan. Use small quantities of flour to prevent sticking.

Cut the combined layers. I like to double-stack them: dough-gelly-marzipan-dough-gelly-marzipan. It is recommended to make so nice bite size pieces, not too small. It is an item served in single-piece quantities.

Cover with chocolate, by dipping them first, piece by piece, in chocolate and removing excess chocolate with a wood stick or similar tool. It is important to liquify the chocolate glaze in water bath, don’t overheat it.
About 400 g of chocolate (dark is preferred) will be needed.

Finally, put them in a box for safe storage. Otherwise, they may get eaten faster than you believe. Better to store at about 15-18°C, constant temperature. Don’t put in the fridge.

Ancestry

The SCHRÖDLE Family Chronicles: decorative hot embossing

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The major project besides all the work in the electronics lab and mechanical workshop here has been the writing of the family chronicles and ancestry research, starting with my father’s side: the grandparents SCHRÖDLE and REITSAM. Now as the draft has been completed, I have put further thought to the publishing. The specialized contents won’t justify a large printing operation with many copies, so the book will be done by digital print rather than professional offset printing. Also, there may be some corrections necessary after the first print, therefore I don’t like to print to many pieces that then need to be corrected, but will only print the copies needed. Binding will be done by a spiral binding machine that I have recently purchased used, a heavy-duty version of a spiral binder that I have owned for years to make small “user manual” booklets and similar.
For the cover page, I thought it is a good idea to not only print it black and white, but to give it some nice appearance by gold print.
Golden letters can be printed by various means, but the best result is obtained by hot embossing. A heater metal (or special polymer stamp) is pushed into the paper, with a hot printing foil in between. The foil has multiple layers: a PET carrier, a layer of gold-colored aluminum, and a heat activated glue. Where heated the the embossing stamp, the foil will stick to the paper and the gold layer will transfer to the paper when the hot print foil is peeled off.

While the theory is easy, the challenge is to do the hot embossing in the home shop without a specialized machine. I have some experience with milling brass stamps that I have made for some friend years back, CNC milled. But with current case, I would need a 90×50 mm brass block, which I didn’t have in stock, so I took some hard aluminum alloy instead. Durability is no issue anyway, because I will need less than 100 copies anyway.

After preparing the stamp block (it will be directly heated by two 180 Watts 230 Volt heater cartridges, 10 mm diameter, 80 mm long), I set it up on my CNC mill to cut the letters. Don’t forget that all must be mirrored!

The program has many lines, but all no problem with LinuxCNC, which can handle machine programs of essentially any size.

First, roughing out the main parts, with a 3.8 mm endmill, 1.5 mm deep. You could also use a 2.5 mm endmill, but from experience, it is ok to just mill away the major gaps and cut the other areas by am engraver tool.

The fine engraving is done with an approx. 60 degrees engraving single-lip cutter. Surely, my CNC’s spindly is not fast enough for this, using about 2800 RPM where I should run at 10000, but the feeds were adjusted to roughly 140 mm/min, to get away with the “slow” rotation. The single-lip cutter (made from K30 tungsten carbide) is holding up well in hard aluminum and leaves a shiny cut even without any lubricant.

For a test print, I heated the metal stamp on a hot plate. It has some crude temperature regulation, so it is not difficult to control the temperature.

The supplies prepared: some pieces of paper (always use the actual paper you want to print on), some cut strips of heat printing foil (this foil I have purchased more than 20 years back, a mid-sized coil, many meters because it is petty thin), and a thermometer to sense the temperature of the block while heating (the green wire is the thermocouple).

The printing itself, I did on the print press. It is recommendable to print on a piece of thick paper or cardboard, to have a certain depth of the impression. You can also print on a flat and hard surface, but the result is then less impressive. Temperature, pressure and time need to be established by trial and error, say, 180-200 degrees centigrade, intermediate force, and just a few seconds are a good starting point. Too hot printing will damage the foil and paper, too cold printing will give bad transfer and low durability, too high pressure will give unclean corners and edges, and too long printing will result in transfer to areas that are not letters, leaving a “dirty” print. You can check with an eraser: a good hot embossing will not be affected by using a soft eraser on it. If the gold comes off, either the paper is not good, the temperature is too low, or you are not pressing hard enough.

At an angle, there is a nice reflection. This is printed with a semi-matte gold foil, I will also try a shiny reflective gold foil. But I guess my grandparents would have been happy with any style of gold print.

Various

LH0021CK Power Opamp: an analog autopsy

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From an earlier test equipment repair, I had two broken LH0021CK power amplifiers, both died because of a design issue with an YIG driver board (lacking distance of a heat sink from a board trace leading to an occasional short circuit).

The LH0021CK are +-12V output, +-18V input, 1 Amp capable devices, and if treated nicely, they will last 40+ years of service. Still available today, despite being obsolete, at prices ranging from 10 to 300 EUR a piece. These were quite common parts in high-end controllable power supplies, servo drivers for scientific instruments, and similar apparatus.

Finally, I cracked these open – not anticipating the fragile ceramic substrate inside.

I pieces together a picture from multiple images, because this part is a little too large for my microscope, and too small for other cameras to see it clearly.

The datasheet provides an internal circuit diagram, but is there really a 741 opamp inside? What about all these resistors?

Checking the parts, indeed, there are 4 discrete transistors, laser-tuned resistors (you can see the burn lines of the laser to adjust the value of the resistor in processing of the circuit, some have even two tuning lines), and an opamp die.

Eventually, I opened two of the broken parts, an old one, golden case, and a newer one, silver case, both made by National Semiconductors. There are some small differences of these parts, also related to the circuit. The resistance values are rather similar, but the newer part (shown in the picture) has an additional resistor at the COMP input. Both parts have no connection of GND to the negative supply input of the opamp – this is apparently a mistake in the schematic shown in the datasheet, because the circuit wouldn’t work if there is such connection.
The newer part seems to have a small diode chip (marked light blue), but checking it just gave a 0 Ohms value. Maybe just spacer for wire bonding.

The failure mode is clear for both parts – the SC+ bond wire is blown (with molten ends clearly visible), and the Q4 power transistor shot.

Clearly this part could save a lot of space in the old days, replacing it with discrete parts would take about 5 times the space (1 large TO-3 NPN, 1 large TO-3 PNP, 2 transistors, one TO-99 Opamp, and several resistors…. I have been successfully replacing these parts with TDA2030A audio amplifiers, they seem to be be a good substitute, even if they may lack some detail performance characteristics (eventually, the TDA2030A has even higher power and better bandwidth, say, 100 kHz vs. 20 kHz).

Some detail study of the opamp die showed that it is indeed a National Semiconductor part, 741H printed on it, and the shape of the capacitor (the light colored silver area in the middle) is the shape of the typical National 741.

Various

Blaupunkt OSTIA Home Radio: revamping an old beauty

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As a family heritage, we ever had an old radio from my great-uncle (brother of my grandfather) named Modestus, and ever since I can remember is had been standing in the bedroom of my parents. Eventually, it was no longer used there and moved into my mechanical workshop where it still serves to play background music while I am operating machines.

It was build some time in the early 70s, and is based on germanium transistors – to be precise, 11 germanium transistors. The sound is not bad given the relatively simple circuit. However, in the last year it must have suffered some degradation of the FM tuner, because this tends to drift, and the reception is not clear always. Especially in winter, switching it on after a “cold” start, it needs some re-tuning after about 30 minutes of operation. A little inconvenient. Rather than spending a long time trying to fix an old FM tuner, I decided to take another approach – adding a new digital (PLL) tuner.

In my stock of old parts I had a no longer used PCI TV card, which incorporates a Philips FM1216MK tuner, a combination TV and FM tuner use a TSA5523 PLL, and can operate from a single +5 V supply (because of an internal DC-DC converter).

The card is a combined ISDN-TV-FM card. The tuner can be easily desoldered. Control is by i2c bus, two wire interface. Some libraries exist, but I didn’t use those. Rather straightforward to send the bytes needed to set the frequency and to do some more configuration needed. The tuner has a stereo decoder, but I operate in mono mode – there is only one speaker in the OSTIA radio.

A quick setup with a i2c LCD added for debugging. Using a Arduino Nano3 board clone with an ATMega168p microcontroller. But any microcontroller will do.

Now, integrating the new tuner to the OSTIA – my objective was to not destroy the old beauty, integrate minimally invasive. A first attempt to use the build-in transformer failed, because it could not provide the roughly 200 mA current needed for the Philips tuner.

To feed the audio signal, I cut a bridge on the board (which carries the FM audio from the old tuner), and injected the audio from the new tuner via a 100 nF foil capacitor.
For control of frequency, there is no an incremental encoder on the back of the radio (I rarely change the station if at all), and when you push on that encoder, the last frequency set is stored in EEPROM. The LCD has been disconnected, not needed during operation.

Finally, the OSTIA back at its accustomed place in the workshop. Reception is good and stable now, all frequency locked to a small quartz crystal.

Certainly this radio now has no longer just 11 transistors – maybe 500 transistors now!