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.
- Wikipedia Entry
- tekWiki on tunnel diodes
- replacement for 4.7ma tunnel diodes available on eBay, type GI304A, 10 pack en route.
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.