[R-390] Tek 500 series CRO s

[Pete Lancashire]

One of the best resources for the older Tek gear is two Yahoo groups
TekScopes and TekScopes2

The 547 HV transformer has been pretty much reverse engineered and
there is one member the
last time I was visiting the group was rebuilding them. They are all
failing due to moisture.

They are one amazing piece of Tek gear from the BA period.

-pete Ex Tekkie

On Sun, Apr 1, 2012 at 12:08 AM, bernie nicholson <vk2abn at bigpond.net.au> wrote:
>
>
> Hello John  and everyone ,  over the years I bought hundreds of 500 series cro s from the Government Auctions here in Australia , Back in the 70 s and 80 s .      A common fault I found with the 547 s   is the filament winding for the CRT going down to earth , Rather than replacing the whole transformer I used to connect up  a separate  well insulated filament transformer [the cathode is about 1500Volts above earth , This fixed the problem , The commonest fault I used to find in all the 500 series  Cro s was  Failed open circuit dried out  Electrolytic  Bypass cap for the 50Khz osc. in the  Eht supply   the Oscillator  tube has grid leak bias  and as the 50Khz wanders around the chassis the output drops off , and the Bias gets less dissipation goes up and eventually the tube plate glows red  ,symptoms the Trace is bright when first turned on then gets dimmer after about 5 minutes  goes out altogether , I Got to know these units pretty well , Overall they were pretty good the
>  547 s had a Tunnel diode trigger circuit , The tunnel diodes used to fail , there is one in each timebase ,so the other could be changed around to check the fault , and the Miller time base could be tricky, I remember one very difficult to find Fault , I ended up Meggar testing Every cap in the ''A'' timebase , One 500Pf cap measured 300Megohms , when I replaced that it worked  perfectly  ,the miller timebases rely on the tubes internal capacity to oscillate , and it doesn't take much to stop     Regards   Bernie  Vk2abn                                       My web page http://vk2abn.millen.id.au
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