Friday, November 28, 2008

Privatization, what is it good for?

It's been an interesting week. On Monday, in the UK Government's Pre-Budget Report, one of the less reported items was "reviews of the Met Office, Oil & Pipeline Agency...

So maybe, just maybe, in a few months my employer will no longer be owned by the Ministry of Defence.  Okay, for most folks in computing that probably doesn't seem like a big deal.  But for an organisation that's existed for over 150 years, that's a big change. Especially so for those employees who give the impression of having been there for most of that century and a half.

National meteorological services (or NMS's as we call 'em) are almost always state owned, and pretty much every country has one - even Somalia is trying to re-establish(*) one right now.  I doubt it's because having crazy bearded scientists  who claim to predict the weather is a source of great national pride, just that in an age of air travel, climate change, and  expectation that governments anticipate, rather than just deal with, disaster having a decent weather service is a necessity.

Anyway, now there's some new things for me to learn.  This looks to be a useful resource -


* Typing this "re" reminded me of a recent internal email advising staff who had signed a security document, that had since been amended, that they would be "asked to resign".  How we all laughed!

Sunday, November 23, 2008

Mullard 3 3

Almost exactly a month ago I "won" a "homebrew vintage amplifier" chassis on Ebay.  It looked to have a couple of decent quality transformers and I reckoned that it's hard to destroy them both accidently so bidding for what I reckoned one to be worth wasn't taking too big a risk.  Both turned out to be OK, but I decided not to use the mains transformer for the rebuild.

Here are the before photos -

From gadgets

From gadgets

And here's the rebuilt amplifier -

From gadgets

From gadgets

From gadgets

For schematics and project notes see Mullard three-three.

Saturday, November 08, 2008

Cheap triodes

Judging by the high prices valve (tube) amplifiers and their component parts are making on EBay these days the following notes might be of use to others.  As I've now managed to gather more than enough parts to build a Wireless World Quality Amplifier I should really get on with building it  - not buying yet more valves, transformers, etc.

Decent triodes seem to be unreasonably expensive at present.  OK, the likes of PX4, PX25, PX25A output triodes are bound to be pricey, more than £100 even for a used tube.   Which is why most folks on sensible budgets use output pentodes (or kinkless tetrodes, KT66) with the more extravagant using them as triodes, as in the famous Williamson amplifier.   

But... why pay more than a few quid for a used L63 (6J5G)?  Here's an old idea that might save valve amp experimenters a few pounds - 6Q7G was designed as a first audio triode for wireless sets, sure it's also got two diodes, but you don't have to use them.  When I bought my wartime Vortexion PAs one had a couple of 6Q7G the other used EF37A connected as triodes - see the datasheet that can be downloaded from the Virtual Valve Museum, Mullard give data for using this valve as triode or pentode.