Yorkie's 'PW Testmaster' c 1982

[pwdrive]

I've only got about ten radios but still I can't move without tripping, nice OP meter by the way, a handy piece of test gear, I'm on the lookout for one at some point.

Lawrence.

[AlanBeckett]

They seem to turn up fairly regularly, but the price can be very variable.
Yes, they are very useful 'cause you've got a reference, and I've never found having Marconi written on a piece of gear to be a disadvantage.
Come in Al

Alan.

[Joe]

Here's the details:-

  PW Test-master.pdf (Size: 8.16 MB / Downloads: 50)

- Joe

[Bushbaby]

Great piece of work.

Another item to add to my round to it pile.

Regards

Rob

[Yorkie]

Many thanks to Joe for tidying up my scan of the original article and for uploading it to the forum.

Mark H mentioned quite correctly that by now some of the carbon composition resistors used for substitution and in the bridge will doubtless have drifted high, so out of curiousity, I've tested the resistors and caps, with the following results:

Resistors:

Should be: %age over or under
10k - is 11.1k = +11%
33k - is 36.2k = +9.7%
100k - is 114k = +14%
330k - is 330k = 0
1M - is 1.111k = +11%
3M3 - is 3M15 = - 4.5%

Caps:

100pF - is 85pF = - 15%
1nF - is 795pF = -21%
3nF - is 3N36 = +12%
10nF - is 10.75nF = +7.5%
30nF - is 31.7nF = +5.6%
300nF - is 330nF = +10%
iuF - is 1.02nF = +2%
5uF - is 6.28uF = +12%
25uF - is 32uF = +27%
100uF - is 340uF = +240%!

I guess that after 30 years, bearing in mind that some may even have been NOS items rather than brand new when it was made, and weren't close tolerance types, nor were they selected on test, it's what we might expect to have happened over time . The whole point of test gear is for it to be accurate, so were I building such a project now, then I'd carefully select and components used as 'standards' to make sure they're close tolerance ones.

Interestingly, the oscillator frequencies are virtually bang on 1kHZ and 1 MHz. The 465kHz is 463KHz, and could be made spot on by melting the wax and tweaking the coil. It tends to confirm that with most IFTs using close tolerance stable silver mica or polystyrene caps, unless the 'phantom twiddler' has been at it, most IFTs in radios won't have altered much since they left the factory.

Oh well, it kept me occupied for a good few hours building it, and that's what I've enjoyed doing since a schoolboy in the mid 1950s. As I've passed through life I've come to realise there's little correlation between money expended and enjoyment derived. I guess in part that comes from having grown up in the 'make due and mend' and 'cut your suit according to your cloth' mentality. The only debt we've even had was our mortgage - never taken out a loan, never not paid off our credit card each month, never been overdrawn, never hankered after anything we can't afford.

Rambled and dribbled Yorkie.

[Mark Hennessy]

Brilliant - thanks David and Joe

David's version is definitely neater than the prototype built by the author!

[Mark Hennessy]

Hi David,

Those aren't too bad - I've seen plenty be high by 25-30%. Interesting that the 330K is spot-on. I have a massive tub of those particular resistors, and find them to be excellent - I use them as replacements in vintage transistor radios as they look reasonably "period". Quad used them in their amplifiers (certainly the ones I've seen), so they must have been reasonably OK...

Whenever I measure a vintage electrolytic, if it's basically working, the value is always well-over the stated value. Not so with modern caps. I guess that back then, they erred on the side of caution. IIRC, the tolerances were always unequal - e.g. -10%, +50%.

Regarding IFTs, my experience agrees with you. I rarely tweak undisturbed IF cores, and if I do, any improvements are always marginal. But I generally need to adjust the oscillator - however I suspect this probably has more to do with the trimmer capacitors than the coil...

If you haven't already seen it, some of my DIY can be seen on my website:

http://www.markhennessy.co.uk/electronics.htm
http://www.markhennessy.co.uk/audio.htm

All the best,

Mark

[Joe]

David's version is definitely neater than the prototype built by the author!

He puts us all to shame.

- Joe

[Mark R]

If you haven't already seen it, some of my DIY can be seen on my website:

http://www.markhennessy.co.uk/electronics.htm
http://www.markhennessy.co.uk/audio.htm

All the best,

Mark

Some nice projects on there Mark, very nice indeed!

cheers Mark

[Yorkie]

Very inspiring Mark! Wonderfully designed, executed and written up.

Most impressed - not just with the finished projects, but the drawing of the circuits.

When I build my 'Test Master' CAD software, or even home computers were still yet to come, I laboriously used Letraset rub-down transfers to make the front panel. I'm rather ashamed to say that despite there being many excellent drawing packages nowadays, which several forum members have mastered, were I to build something like the Test Master again, I'd probably have to resort to Letraset. What an admission to have to make in this day and age