From: info@turneraudio.com.au   
      
   Andre Jute wrote....   
      
    10,000kmpa is a bit ambitious at 68. I still ride the hills, but nowhere near   
   10K; but then I was never a roadie, so I didn't aspire to the big round   
   numbers.    
      
   Andre Jute    
      
   Well, the 10km++ a year was until about 2 months ago. I have genetically very   
   poor knees, courtesy of my dear departed mother, who was, like me, a plodder,   
   and who never rode a bike or ran anywhere. She prefered to look good on a   
   horse at Centennial Park    
   aged 25, super hot, but alas, no possible suitors noticed her there. Later she   
   drove, and walked and swam, but in very limited amounts. I inherited her   
   terrible knees combined with my dad's genes. He set a NSW schoolboy running   
   record for the Mile in    
   about 1926. He had a terrible temper I am glad not to have inherited, so ppl   
   tell me.   
   In 1994, a surgeon told me I needed new knee joints but also that I was too   
   young then. OK, I struggle on after giving up the building trade. I thought I   
   might learn a bit about hi-fi sound gear - a journey of wonderment.    
   In 2005, I could hardly stand up for longer than 5 minutes, and I needed pain   
   drugs.    
   But the surgeon gave me an arthroscopy to tidy&clean both knees, and next day   
   I found I had no pain, and a whole new life began with more confidence. In   
   2006, I got back on bike, and since then I've ridden about 100,000km, and I   
   had a very fine time with    
   a local ride group. Well, in June last year, while going up a very steep short   
   hill, I felt something "give" and sure enough I'd hurt a knee. Well, maybe   
   you'd expect that; it was an Irish hill, O'Conlon Crescent, and where shit   
   which could happen, and    
   it did happen.   
   Next doc, a young jerk said he wouldn't do an arthroscopy, and offered only   
   two joints, about $30k, plus all other costs, and he said I'd be begging him   
   for the knees soon enough. That was 15mths ago, no begging, but knees have   
   same symptoms as in 2005,    
   and scan reports fill 2 pages. No more bike because pain has returned, but now   
   chasing the doc who did me in 2005, appointment is Feb, and maybe in 10 mths I   
   get another arthroscopy, keep me going for maybe 5 more years. By then, other   
   things probably    
   will take me out. I need mobility because I live alone and the bicycle was the   
   finest wheelchair I ever used.....   
      
   Meanwhile, there is a FABULOUS Thai restaurant which opened 3 years ago just   
   nearby, and its my home away from my house, which I've never managed to make   
   into a real home. Being gregarious at 68 is mainly a useless quality because   
   most old ppl my age don'   
   t or can't or won't be friendly, and the few younger folks who turn up loathe   
   all ppl over 35. Good cafe's have limitations.    
      
   But I tinker with all sorts of stuff, with more time now because I ain't   
   spending 10 hours a week riding around, and I retired from working 50hrs a   
   week on old junk for less net wages than the dole. Wonderment can only be   
   stretched so far.   
      
   I get distracted, and this last month investigated the Gilbert Cell - using   
   tubes, very good for DSB without carrier, but hopeless for normnal AM.    
   I then discovered AM using an LTP with bjts, and modulating with emitter   
   current change, its the SS version of what HP did in about 1955 with their   
   Fantabulous HP606A RF signal gene - I have one, and it works fine - and it   
   uses all tubes and has a    
   balanced oscillator, and balanced LTP RF amp with cathode modulation with 6B4.   
   This piece of gear has 2 lots of tuned LC tanks on a rotating turret switch to   
   get 6 x F ranges between 50kHz and 65MHz, with ability for 100% modulation and   
   envelope THD < 1%    
   at 95% mod depth. My efforts so far with untuned circuits and bjts is 100kHz   
   to 4MHz, with about 5% THD at 2MHz.   
   HP used NFB to remove envelope THD with internal detector signal compared with   
   AF input signal. I've done that in an SE oscillator in about 2005, good, but   
   nowhere near as good as HP.   
   But, to apply about 20dB FB around the circuit where modulated carrier is   
   involved, and without tunes circuits, the darn thing just oscillates with   
   parasitics no matter what theoretical cures I think up and apply. Remarkably,   
   there isn't much online    
   which where others have had success.    
   But I've learnt, and some ideas just will not work, and to get my pathetic   
   attempts with bjts to work anywhere near as well as tubes in HP, I'd have to   
   use tuned RF circuits which have the magical quality of supressing parasitic   
   oscillations, because the    
   LC can only work at ONE F, not several, or allow broadband noise to occur.   
      
   I think electronics with soldering iron and old things is better than doing   
   crosswords because those only prod memory, making stuff to work prods problem   
   solving AND memory. Both need constant prodding, to delay insanity for as long   
   as possible.   
      
   Keep well, try to stay sane,   
   Patrick Turner.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)