Friday 26 February 2010

TubePad and a Working AF Final

After seeing a few interesting looking schematics on the 'net I decided to check out TubePad

I THOUGHT it was a schematic capture / circuit drawing package for valve applications - but in fact it claims only to be "free for use share-ware library of images which were created by Gary Johanson, WD4NKA". You have a bunch of image files of component outlines, "clip art"-style images of components and schematic elements, all of which are intended to be pasted into a drawing package such as paint and "wired up" using line drawing - not exactly what I had expected.

I used to prefer PowerPoint as my default drawing package - but I made the dumb mistake of upgrading to Office 2007 recently and haven't really used PP 2007 yet. After a very long struggle with PowerPoint 2007 (took ages to learn how to set default line colour to black, etc) I was able to draw up the schematic of the little ECL 86 amplifier I had cooked up on my "test bed"..

Here it is, in all its glory...

As an experiment, I also knocked up an ECL86 as a new device in EAGLE (my favourite PCB package). It took me less time to build this device and produce the schematic than to get up and running with the TubePad alternative...

The circuit is my own - but it was arrived at by experiment and plagiarism (there are lots of similar designs on the 'net). Please don't copy this for use as an audio amp or a little guitar amp - it is set up as a low power solution only! (Perhaps I will get around to designing that stereo PCL86-based amp some day).

I guess the TubePad version looks kind-of pretty but I don't think I'll be using it much!

Having documented the AF amplifier (in the schematics above) I built a copy of it in the not-so-superhet chassis...

...and I'm pleased to report it works a treat - with none of the motor-boating of my first rushed attempt. Here's a close-up of the ECL86 doing its thing for all the tube fetishists out there

I am listening to the 80m CW band THROUGH SPEAKERS even as I type - great fun!

...-.- de m0xpd

Thursday 25 February 2010

New Audio Stage

Those who have followed the story of the development of my experimental (not-so-)superhet (Blogs passim) will recall that I had too little overall gain to use the receiver with a loudspeaker - despite confirming operation with headphones.

In the quest for MORE GAIN, I decided the best option was to replace the existing pentode AF final stage with a triode-pentode tube, allowing a whole extra gain stage without adding another valve. In truth there are at least two other motives at play here...

1) I resented using the valuable EL84 valve in this application (I have a BTH stereo amplifier that uses EL84s in push-pull and I would rather hold the valve as a spare for that system)
2) I am interested in exploring the ECL80/82/84/86 devices, both for Tx applications a la Hans G0UPL et al and for AF amplifiers, particularly as I've got quite a few PCL86s in the collection.

So... I knocked up an ECL86-based amplifier for the SuperHet, which both worked and didn't!

It worked in the sense that I could now use the radio through the speaker - but didn't work in the sense that turning up the volume caused "motor-boating" instability. Despite some experiments with modifications to get rid of the low frequency instability (exploring the usual approaches of reducing the inter-stage coupling at LF, improving power supply de-coupling, etc) I couldn't sort it out in the cramped conditions of the receiver chassis. This prompted the construction of a single-ended triode/pentode amplifier "test-bed", seen here in close-up.

A scrap sheet of aluminium has 4mm sockets for all the important connection (except input via a RCA/phono) and a B9A base. The transformer is actually a reverb driver spare from my Fender Super Reverb amplifier, which I use for guitar and my Rhodes piano.

After a few minutes messing about with the circuit (which would have been a frustrating task on the receiver chassis) I had a nice-sounding, stable amplifier, seen here in operation on the bench...

"Plans" for the future of this prototype are twofold:
First, I'll copy the amplifier in the receiver chassis.
Second, I'll experiment some more with the circuit, to finalize a design for a stereo PCL86-based amplifier.

The first will be done soon (maybe at the weekend), but don't hold your breath waiting for the second - I've got a lot of other ideas competing for my attention!

...-.- de m0xpd

Friday 19 February 2010

Temporal aberrations and the nutter on the bus

Having (nearly) recovered from the journey home from ZL-land, fate has placed me back in HB for a few days. Taking a ridiculously early train from Lausanne towards Geneva Airport (where I have a date with SleazyJet) I found myself drifting in and out of sleep.

Perhaps it was the semi-conscious state which made me laugh at something...

Switzerland - of course - has a reputation for several things, amongst which are the precision of its timepieces and the punctuality of its railways. It was the ironic conjunction of these two which amused me so much in my slumbers at Geneva station...

The Swiss Federal Railway System uses a station clock which is recognized as a design icon. It was, apparently, designed by one Hans Hilfiker (1901-93) and is now copied in watches, Swiss souvenirs etc..

Whilst peering out of the window, waiting for my train to advance towards the airport, I noticed that Swiss railway time, as told by Hans' iconic clocks, isn't the regular, linear story one might expect. Rather, the passage of "time" is rudely interrupted as the second hand reaches the vertical at the top of the minute.

There, mysteriously, time stands still for (what seems to a casual, sleepy, stationary observer like me) several seconds.

No wonder Swiss trains leave "on time"!.

Strangely, this irregular time-keeping isn't reflected in a random sample of Swiss Railway timepieces on the net. All other things being equal, we ought to see most of the clock photos with the second hand in the upright "time stands still" position - but we don't...

Obviously artistic considerations amongst those more excited by a design icon than a chronometer have biased our photographers to make their exposures with the second hand in relatively improbable locations (the probability density function having a "spike" at the upright twelve o'clock position).

To redress the balance, here's my clumsy iPhone snap of one of the clocks at Geneva Airport station, showing 7:01 am (little wonder I was tired). Note the second hand just visible in its proudly erect maximum likelihood position!

Whilst we're on the subject of public transport, Jasper Carrot had a sketch years back (when political correctness was still a twinkle in the killjoys' eyes) entitled "The nutter on the bus". It told how Jasper felt a certain class of fellow traveller always gravitated to the vacant seat next to him.

After this morning's journey I'm beginning to feel a certain sympathy with Mr Carrot, as a young couple with coughs and sneezes honoured me with their proximity in an otherwise un-crowded carriage. Unfortunately, though English speaking, they hadn't benefited from our Department of Health's advice (this version from 2007)...

... which has been such a consistent message that I (foolishly, it seems) thought it was now just a matter of common courtesy rather than disease control.

Suddenly all those girls in Asian airports wearing face-masks don't seem quite so stupid.

Get well soon, fellow travellers.

...-.- de m0xpd

Saturday 13 February 2010

The moon is up and over ... Maungakiekie

Today is my last day in New Zealand, which I marked by a trip up "One Tree Hill" - a volcanic peak south of Auckland's downtown area...

View Larger Map

The hill has achieved some global fame as result of the eponymous track on U2's album "The Joshua Tree".

That track also (apparently) inspired a TV series of the same name of which I know nothing - save that it is produced by the network responsible for other bright points on the apogee of high culture such as "America's Next Top Model" - 'nuff sed.

There once stood a single tree on the summit (the clue is in the name) but it was twice attacked by crazed Maori activist tree surgeons (in 1994 and 2000), so all that remains is a stump - visible in the following photo...

North Head is visible to the right of the photo, Mt Eden (another volcanic peak) is "above and to the left" of the stump and Sky Tower and the downtown "CBD" area is further left still.

Talking of all these volcanos, the Auckland War Memorial Museum includes an interesting exhibit "A Land on Fire" depicting what might happen in Auckland if one of these sleeping giants wakes up again. Auckland residents should look here if they want something to worry about!

Instead of a conspicuous single tree, the summit does at least sport a nice obelisk...

and a memorial to Sir John Logan Campbell, the "Father of Auckland".

Time to say farewell to the glorious southern hemisphere summer and head back to the UK. I don't mind the 13 hour time difference so much - but I do resent the 23 degree temperature difference!

...-.- de m0xpd

Saturday 6 February 2010


Just been rattling around the 'net and I stumbled on HamSphere , which is a sort of web-based shortwave simulation.

Downloaded the software and registered for an account (you get a free 3-day license - no idea what the costs are after that) and was soon running a simulation of a modern transceiver...

There's DSB voice mode (presumably for those with too much to say) but also CW!

I heard a CQ from 2hs413 (HamSphere can issue its own "call signs") and answered it - it turned out to be Scott in Michigan. Soon after that, Sam, vu2usa called me from Bangalore.

Don't get me wrong - this is never going to replace the "real thing". But it is one hell of a good game when you're stuck in a Hotel on the other side of the world on a business trip (ZL, in my case). All you need is your PC and your internet connection.

I just need to figure how to hook up a key to let me really send morse (rather than have the computer interpret keyboard input).

...-.- de m0xpd

"Sweet as, Bro"

NZ 38 whisked me on to ZL-land where much has changed - Newmarket railway station has moved a few hundred metres, and they've even changed the name of my favourite local cafe.

Fortunately, they still serve up latte IN A BOWL...

I don't know if this is just an Auckland thing or a wider Kiwi thing - they certainly play up the Kiwi identity with that national icon a "silver fern leaf" in the froth...

After a couple of days in the office, I am now enjoying some R&R on the weekend in the Southern Hemisphere summer.

Today I took a trip on the ferry to Devonport...

View Larger Map

which is a really nice little "seaside town" offering an escape from the city environment in Auckland (not that Auckland is at all oppressive).

Looking back from the ferry gave a good view of the Auckland skyline, including the amazing Sky Tower...

Looking North-East, I could just make out Classique - the 22 meter cutter operated by Captain Mel - she is swinging from her mooring and only just visible in this snap from my iPhone (inside the red circle).

I sailed on Classique on an earlier trip to ZL in 2007...

Here's Classique at anchor in Man o' War Bay off Waiheke, where we spent the night...

Back to today's visit...

I walked along to North Head

where there are the remains of some old gun emplacements, protecting Auckland harbour from invasion. Nowadays the guns are rusty relics and the headland gives good views over to Rangitoto (the volcanic island that dominates the harbour)...

and back towards Auckland...

I finished the trip with a walk up to the Devonport Naval Base and visited the Navy Museum which was worth the walk - especially as entry is free!

After the ferry trip back to Auckland and some snooping around the NZ America's Cup boats, I strolled back to the curiously named "Britomart" public transport hub...

to catch the train back to Newmarket and my Hotel - great day!

...-.- de m0xpd

Thursday 4 February 2010

Hua Qiang Bei Lu Technology Market

Took the train from Kowloon up to Lo Wu and entered BY-land at Shenzhen on Sunday 31st Jan. The border is pretty civilized on a Sunday – last time I was there it was Monday morning and was a heaving, hurrying mass of humanity.

Highlight of the visit to BY was a trip to the Hua Qiang Bei Lu technology market – a vast area of retail and wholesale electronics outlets.

I was walking around with my eyes and mouth wide open – just like my first visit to Hamley’s, the London Toy store, forty-something years back. Think Dayton and Friedrichshafen rolled into one and you get some idea of one corner of this place. It even extends over multi-storey buildings…

Inside there is everything from family-run stalls selling components to organisations who will manufacture a product to your design in drops of 100k units.

I turned down the 5W dual-band handie for less than £50 (the fist is mightier than the voice) but fell for some high voltage electrolytic capacitors for my valve games (blogs passim) from these people…

and some LCD displays for the frequency counter circuit I use. Oh yes – I also couldn’t resist those 78L05s for tuppence a throw!

Here’s some of the haul from a short afternoon stroll around the market ...

Next time I go (April) I’ll be taking a bigger suitcase!

This trip, which has reached proportions of almost a “world tour”, continues with a flight to ZL on Wednesday 3rd – watch this space!

…-.- de m0xpd

vr2/m0xpd meets Häagen Dazs

So – now for a little travelogue…

Arrived in Hong Kong on the afternoon of Saturday 30th Jan, after the usual exhausting flight (made better by great service from the Air New Zealand crew) and transferred to the Harbor Plaza Metropolis Hotel in Kowloon.

During the transfer I noticed for the first time the number of container ports in and around Hong Kong – add them together and you get an operation big enough to make Felixstowe look pathetic!

I checked into an upgraded suite, which gave me the real benefit of access to a cocktail bar happy hour (which, mercifully, lasted longer than an hour) with great views over the harbour towards HK…

…and the dubious benefit of Häagen Dazs theming – which is easy enough hanging on the wall above the bed…

… but impossibly distracting as a frame for the TV…

Unfortunately, the fridge was empty too!!!

Next on the itinerary is China.

…-.- de m0xpd

Wednesday 3 February 2010


Well, after all the fun and games with the IFTs you may remember I finally built a Wobbulator.

The "glitch" in the first response captured with the device was traced to a flyback issue (the point where the voltage controlled oscillator flies back from the top of its sweep to start over at low frequency again).

Here's a decent response of one of my experimental IFTs in close-to-critically coupled tuning, made with the Wobbulator...

Having gone to the trouble of brewing up the Wobbulator and finding it useful, I decided that I would put it in a box for longevity and ease of use...

The front controls...

... give me manual frequency selection (via the knob), manual / swept frequency (switch at lower left) and low / high impedance output (switch at centre). Speaking of high impedance, it is so high that the shunting capacitance of a 1meter coax connector becomes very significant in measurement - I'm learning all the time in this strange, high impedance world!

Having enjoyed more success with the experimental IFT homebrewed with axial RF coils than with home-wound coils on sewing machine bobbin formers (described here , I made a second "axial IFT"...

... and popped it into the valve superhet project (blogs passim).

The result is pretty convincing - best performance so far (although still with too little overall gain - working better into headphones than speakers). I could use the Wobbulator to measure an IF response in situ (this is important, given the effects of stray capacitances etc mentioned earlier)...

Must dash now - got a bout of business travel to attend to!

To tell you the truth, I made this post from the Thai Airways Royal Orchid Lounge in Hong Kong Airport during the business trip - but that's another story. Come to think of it, Bill Meara has a "travelogue" section on Soldersmoke, so perhaps I'll post some travelogue too!

...-.- de m0xpd

Capacity Housing Crisis

Here’s a sad little story for you…

I can’t say why it is but – ever since I started dabbling with electronics at the age of 10-ish – I have always accommodated resistors in more luxury than their passive cousins the capacitors.

I can’t say why but there are a few obvious factors…
1) I used to have more resistors than capacitors so housing the large number was more pressing than housing the few
2) when I was young I could figure out the colour code and so identify resistance values but found the mysteries of capacitor labelling more confusing. A resistor of known value is easier to place into pigeon holes with others of nearby value, whereas an unknown capacitor is harder to place.
3) Colour-code aside, I had the ability to measure resistance with a simple multi-meter – but had no capacitance meter (indeed, I still don’t). All the excuses about housing the named and known before the unknown above apply again.
4) To my simple mind, a resistor was always a resistor – whereas capacitors differed not only by value, but also by type. How could I manage all these ceramics, electrolytics, tantalums, polyesters, not to mention all those unidentified components with no measurable resistance which just HAD to be capacitors?
5) I can’t think of the fifth excuse – let’s just say…

The consequence of all the excuses above is that capacitors were always a jumbled, homeless mess, whilst resistors lived in luxury.

Fairly early on in my hobby “career” I got some sets of drawers which allowed me to separate the decades into a sort of “E3” series. Now I use a slightly expanded “E6” series of drawers with internal dividers to give me a unique place for all the E12 values from 10 Ohms to 1 MOhm.

One of the troubles with getting into radio homebrewing rather than the mix of AF and digital I played with before is that capacitors (and even inductors) take on a much more important role. It became such a trouble that it actually reached that threshold which triggered me into action the other weekend…

I decided to start a housing project for the ceramics! It doesn’t solve all the housing crisis for reactive passive components at m0xpd but at least it is a start.

Here’s what I was struggling with …

A stock of ceramics on bandoliers,

which became tangled up whenever you took your eyes off them, were difficult to find and involved the frustration of edge cutters or tearing (often leaving glue deposits on the wires, making them difficult or smelly to solder) before use.

A similar stock of ceramics in zip bags,

which were difficult to sort through and difficult to open / close.

Plus - if I’m honest - I even had a big zip bag with a lot of ceramics I’d used once in a circuit and then removed – I was too lazy to find the right bag, so they all ended up in the big “pot luck” bag.

It was taking too long to find the right capacitor and the “pot luck” bag was getting too big, so something cracked in side and I stopped off at the Stockport branch of Maplins and made the rash purchase of two Component Storage Boxes (order code: AN38) at the reasonable price of £1:99 a piece.

These have three rows of six compartments each row – giving me space for all E6 capacitor values in each decade – one box covers the pico’s and one the nano’s. I even went so far as labelling the whole collection…

It is an improvement – but I can see a couple of issues emerging already:
1) I’m going to have to buy some more stock to fill those unsightly empty compartments
2) I’ll swear impressively when I drop a box with the lid open.

I guess this is a small price to pay HI HI

…-.- de m0xpd