Audio Sine Wave Oscillator

[David G4EBT]

I fancied a little winter project and spotted a basic audio sine wave generator that appealed to me - not that I needed one, but I had most of the bits to hand. It covers two frequency ranges 15Hz – 2,200 Hz & 150Hz - 22 KHz, and two voltage ranges 0.01V - 0.24V & 0.1V – 2.4V. (I calibrated the voltage range in RMS rather than peak to peak volts). I had to alter the value of R1 to get it to oscillate as the wire-ended 28V/40mA stabiliser lamp I used was only 62R (cold) as opposed to the specified one which was 105R. Also, to get the voltage range to be 1/10th of the full voltage I had to use a 470k for R7 as opposed to the specified 47k.

Only a basic thing, but the sine wave looks respectable enough. (The pic shows a 20kHz sine wave). I found the design here:

http://www.bobsdata.com/audio_sine_w...tor/index.html

I fitted the PCB on spacers behind the front panel rather than horizontally, so I could make the box shallower. I designed a simple front panel along the lines of the original and when I’d calibrated it I printed it on blue card, encapsulated, then covered with a panel of 2mm acrylic.

I have an aversion to complex test gear which far exceeds my simple needs, and have always enjoyed building simple but adequate test gear such as this. For some years now I've housed my projects in purpose made comb-jointed boxes which I make on a home-made router jig from whatever hardwood I can scavenge - in this case, an offcut of a mahogany plank sliced down to 8mm on the band-saw.

Probably of limited interest, but I’ve attached a few pics anyway, including one of the component overlay which I had to work out and draw, because though the PCB artwork is on the website link, there was no overlay to show component placement. The only bits I had to buy were the little regulator lamp and the 50k dual liner pot (R5) - both ebay purchases. The rest of it is simply a rearrangement of bits from my 'spares box'(es) apart from the box itself.

Hope it’s of interest.

[Ti Pwun]

What a really lovely job! Excellent, in fact. Big thumbs up there.

[Denis G4DWC]

Brilliant. I just love the box.

Denis

[David G4EBT]

Thanks for your kind words guys. I know that there are two schools of thought about home brew - "build it rough like a rat's nest and see if it works, then tidy it up if it does" - or "build it neatly from the outset and if it doesn't work, debug it till it does" (hopefully!). As a consequence, over the years, because my practical abilities exceed my technical abilities, I've built countless projects that look neat but don't work, but rather that than to turn out junk

I'm still at it - I've just built a 'coil coverage test unit' based on a 1969 'Suggested Circuits' G.A. French design for testing the coverage of home-brew coils at various tuning capacitor settings. A handy device, which looks bonny in it's comb-jointed box with a nice front panel, but it doesn't (yet!) work. More on that in another thread, if ever it does.

[bikerhifinut]

Lovely workmanship. Professional is what I'd call it.
I can wire stuff together with a reasonable amount of competence but I'm about as hamfisted as it's possible to be when it comes to wood and metal work. And when it comes to the superb labelling on the panel...................

Respect.

[Aub]

Smashing job, well done!

[David G4EBT]

Originally Posted by bikerhifinut

Lovely workmanship. Professional is what I'd call it.
And when it comes to the superb labelling on the panel...................

Respect.

Thanks for your kind comments - much appreciated!

As to the front panel, my CAD skills are very basic - I just cobbled it together using MS 'Paint'.

[mpegjohn]

Great looking project. Well done.

[RadioRentals]

Looks, old, vintage and "factory" as our American cousins would say. Top job!

[Wendymott]

David.
A tip for front panels....I use my PCB artwork software, its easy for lines and text. Then either print on paper or clear acetate. I am still using DIPTRACE and it seems to do the job.
However your panel seems ok to me..

[Mike Phelan]

Brilliant, David, as usual! Yes, MS Paint is very much underrated. The internet version is even better.

[FrankB]

Most excellent job! I wished I had your talent for wood working, as I have many radio cases to repair.
BTW, Here many of the wooden pallets are made of oak, and it's a great source of wood for projects. I have used it a lot, and a friend made a beautiful table from the salvaged wood.

[Radio Wrangler]

Not only is it well-built and in a beautiful box, it's a good circuit as well. The website explains the resistor selection needed to get a light-bulb wien bridge working properly.

This is a vintage circuit, a technique invented by Bill Hewlett in the late 30's and used to start HP.

David

[David G4EBT]

I’ve had a couple of requests from people wanting to build this project but who are having difficulty finding a source of the wire-ended 28V 40mA bulb used as a stabiliser. They're readily obtainable at £1.90 for two, post free from an e-bay supplier from whom I obtained mine. The e-bay link is here. Several types of bulbs are listed, so make sure that you select 28V 40 mA:

http://www.ebay.co.uk/itm/Sub-miniat...-/390808042128

For anyone who doesn’t use ebay or paypal, I assume that the supplier would be happy to accept a cheque with a covering letter. The full postal address is:

Rich Electronics (Breconjess),
Rich Farm,
Hendredenny Ganol,
Caerphilly CCB,
CF83 2RL.

I’d reiterate that I had to alter the value of R1 to get the circuit to oscillate as the wire-ended 28V/40mA stabiliser lamp I used was only 62R (cold) as opposed to the specified one in the original article, which was 105R when cold. The original article outlines in detail under ‘how it works’ as to the role of the stabiliser bulb, and how to alter the values of R1+R2 should the circuit fail to oscillate.

Also, I’d reiterate that to get the low voltage range to be 1/10th of the full voltage I had to use a 470k for R7 as opposed to the specified 47k.

Maybe there was a factor of ten typo in the original article?

I’ve attached the PCB artwork that I used. The board is 12cms wide x 11cms high.

Hope that may resolve a few questions and assist anyone who may be considering building the project.

[Karen O]

I just love homemade stuff like that and I would be proud to turn out something that looks so good.

My woodworking skills let me down - so much so that I buy things like bread bins and egg cupboards from a local home wares shop. It's either that or build another of my tea crates

[David G4EBT]

Originally Posted by Karen O

I just love homemade stuff like that and I would be proud to turn out something that looks so good.

It's not as tricky as it may look - it only calls for basic woodworking skills - nothing too fancy!

I hope it isn't drifting a bit too far off topic for the forum, but just to say that all that I use to make my comb-jointed boxes for test gear and the like, is a cheap DIY router with a 6mm bit, and a home-made jig made from scrap ply.The router fits to the jig, and the jig is held in a vice. It's from a design by the late Roy Sutton which features on a DVD entitled 'Making Router Jigs and Gadgets'. It's many years old and was originally on VHS. It's available from here, though not cheap:

https://www.tooled-up.com/artwork/Pr...ENpage_187.pdf

Anyone with rudimentary woodworking skills can make such a jig. For anyone interested, there are some pics and explanations that I posted here:

http://golbornevintageradio.co.uk/fo...comb+joint+jig

Youtube videos abound on the topic of 'comb joint/finger joint/box joint' jigs, some using table saws, others using router tables, such as this one:

https://www.youtube.com/watch?v=eKEB-BIq9qI

Mindful that this is a vintage radio forum - not a woodworking forum - if anyone would like more info, maybe a PM would be more appropriate than further posts on this aspect of the project?

[Radio Wrangler]

There's quite a bit of woodwork involved in vintage radio, just as there is soldering and various other skills. That oscillator circuit, done with valves dates back to a patent in about 1938, which is good and vintage.

I've seen some very nice re-veneering on here as well as people making replica 20's radios, but I've not yet seen anyone replace a full cabinet lost to worm.

DAvid

[David G4EBT]

I guess the best example is the Ekco TSC48 TV cabinet which Colin, ('Retired') restored, which involved more work than building a new cabinet from scratch because the original one was in such a poor state. It was covered in detail under a thread entitled 'A Restorer's Dream', which is here:

https://www.vintage-radio.net/forum/...g+a+TV+cabinet

It was a very long running thread, which involved repairing, veneering, and French polishing the cabinet.

A few posts which have pics in of relevance are numbers 13 (the original state of the cabinet), 160, 165, 229, 236 and 272, which shows the finished cabinet.

Colin also re-veneered and French polished a Barker 88 radio with book-matched burr walnut veneer. Not a task for the fainthearted!

[Radio Wrangler]

Yes, I remember the thread on Colin's Barker 88. A gorgeous job!

David

[Radio Tech]

Hi David

I had a go at building this but tried all sorts of values in R1 but could not get it to oscillate so I put a small additional circuit that employs a 2N3819 with its drain attached to pin 2 of IC1a and a 56k resistor in R1. The small circuit has a 4.7k resistor from drain to pin 2 the source to ground the gate has a 4.7k to ground with a 0.47uf cap in parallel and also from the gate a 1n418 with 560r to pin 1 of the IC

Best wishes

KEN