View Single Post
Old 2nd Dec 2015, 11:35 pm   #94
Phil G4SPZ
Dekatron
 
Phil G4SPZ's Avatar
 
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,342
Default Re: Test equipment for valve radio repair

Quote:
Originally Posted by David G4EBT View Post
...Worse still if we apply an AVO 7 (or any 1,000 OPV meter)...
Don't forget that the Avo 7 is actually 500 OPV until the divide-by-2 button is pressed! The other thing to remember is that the Avometer's scale and movement can be read accurately right down to a couple of percent above zero. Pre-1936 service sheets often refer to voltages being measured with a Universal Avometer on the 1,000 volt range - the Avometer of that era was no better than 167 OPV, but the loading of 167 kilohms on the 1kV range was still light enough to permit meaningful readings of just 20 or 30 volts to be taken and compared with expected results. The 'sensitive' Avo 7 from 1936 onwards must have seemed a real relevation to the service engineers of the day! For an excellent treatment of meter loading (and a lot more) the PW Publication 'Are The Voltages Correct?' is a good source of guidance for the beginner. PW did tell me that they were planning to re-publish this, but I'm not sure if that's happened.

That's a very impressive signal injector/tracer, David. I built one many years ago, nothing like as good as yours of course, but I found I never had cause to use it. For audio, a finger or a screwdriver blade (applied with due care) often injects enough audio to check whether a stage is working, and an old battery-powered PC speaker serves as a workable signal tracer. For RF, I find that a reliable source of modulated RF at a known frequency is almost indispensable, although like many contributors I certainly don't need to use one on a daily basis.

Phil
Attached Thumbnails
Click image for larger version

Name:	Are the voltages correct.jpg
Views:	226
Size:	113.1 KB
ID:	116374  
__________________
Phil

“The place where optimism most flourishes is the lunatic asylum” - Havelock Ellis

Last edited by Phil G4SPZ; 2nd Dec 2015 at 11:52 pm. Reason: Picture added
Phil G4SPZ is offline