Re: 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?
Yes, Tek engineers started to experiment and using TD as soon as they were introduced. Tek 544, 546 and 547 already they had TD in their circuitry.toggle quoted messageShow quoted text
I've gained expertise working and studying circuits in my TEK 3B4, 3T77, 3T77A plugins and 465 also.
TDs are very rare and hard to find, but the models used in 465 and 475 scopes (respectively 152-0125-00/01 and 152-0140-01) still can be found with some patience.
I've got two of these, Tek original, from a Greek surplus dealer for a reasonable price, about 40$ plus shipping, two years ago. One of these replaced the broken TD in my 3B4. The other is jealously guarded in my drawer with other Tek original spares, since the TD model 152-0125-00 fits equally well in #b4 and 465....
The only, very UNOBTAINABLE TD is the 1N3129, used in 3T77 and 3T77A sampling sweep units. My 3T77 had one TD dead.
After 3 years of fruitless search, the past year I finally decided to make the jump: I bought some russian TD, GaAs military, from an ukrainian dealer, carefully choosing and comparing their specs against the original Teks ones.
Then I changed the polarization network, to adapt the GaAs diode (Ge diodes has Vp-Vv of about 300-500mV, GaAs can be 800 mV or more, for the same Ip, so the polarization network must be modified accordingly)
After some hours of calculations, graph comparisons, measurements of TD curves on my curve tracer (a curve tracer I made especially for TD measurements), I changed some resistors in the 3T77 unit, put the russian GaAs TD in place of the original dead 1N3129 and voila! My 3T77 returned to live, with the same specs of the original: it triggers with sine wave signals up to 600/700Mhz and a mere 20 mV amplitude. With external trigger signal it works up to 1Ghz with no problems, in conjunction with my 3S1 sampling unit.
For the chronicle, two years ago I found ONE 1N3129 offered to the miserable price of $ 150 (I refused, damn... was gold or platinum? Or maybe, diamond?), while the russian diodes I've paid about $ 10 each
--- In TekScopes@..., "stan_katz" wrote: