Tek 453

IMG_3520

This was actually the first scope I got as “an Adult”.  I think I paid about $100 for it about 6 years ago.  Since then, it’s been my daily use scope, since it fits atop a rolling art-cart under my bench.

Everything works great, except the B sweep only triggers on ‘starts after delay’, not ‘triggerable after delay’, which means there’s something fishy towards the front end of the B trigger circuit.

Great write-up of 454 triggering diagnosis here. Punch-line: it was the tunnel-diode.

Also suspected Nuvistor v633, type 8393.  Substitution with a claimed-good tube didn’t change the issue, so I’m suspecting it less, but unfortunately I can’t locate the test parameters for the the 8393.
Found it for the 6cw4 (same pin-out?)
Tube    Plate  Bias   Fil.    Meter   Sig.     Selectors                 R.P.       Remarks
6CW4  C        7L     6.3   32        4         03050-0010-706    1430      Tr;X4.

Boom – An 8393 is a 7586 w/ a 13.5v filament.  So, for the TT-1:
Tube    Plate  Bias   Fil.    Meter   Sig.     Selectors                 R.P.       Remarks
8393  O        7L     12   36        4         03050-0010-706    1140      Tr;X4.

UPDATE 5/3: Everything around that Nuvistor seems OK, but nothing is coming out of it, with either the original or replacement.  They both test dead.  So either:
1) I’m testing them wrong, and it’s something else in the circuit, or
2) I have two bad 8393s.
replacements en route, 3 for $45.  Damn these things are getting expensive.

I also realized that this Nuvistor is a part of the signal chain when in XY mode, which I could never get working.

UPDATE 5/8: Replacing v633 Nuvistor fixed the X/Y mode, but ‘B’ is still not triggering on it’s own, so there’s still some drama in the triggering circuit.

 

 

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