[TMC] SBE-3 question

[Chris Bolkan]

Thank you Duncan! I will keep those things in mind. Especially since mine
is a bit rough with some corrosion.

Best regards,

Chris
KI7NXY

On Tue, Feb 1, 2022 at 6:30 PM Duncan Brown <duncanancy at earthlink.net>
wrote:

> Chris.
>
> I worked on getting a SBE-6 (very similar to the SBE-3) going about 15
> years ago.  One problem I remember having was poor/intermittent grounds.
> One area was the tuning coils in the bandswitch area. Another was hum
> caused by the filaments using chassis for return. I think I ran wires
> from at least some (if not all) the "grounded" tube filament terminals
> back to the transformer "grounded" filament line.
>
> Good luck & 73,
>
> Duncan
>
> K2OEQ
>
> On 01-Feb-22 20:24, Chris Bolkan wrote:
> > Thank you Meir!
> > That makes sense to me and is what I needed to know. On to the next
> > oscillators, then onto other circuit blocks one by one!
> > I will probably have lots of questions as I go. :-)
> > Warm regards,
> > Chris
> > KI7NXY
> >
> > On Tue, Feb 1, 2022 at 12:27 PM Meir Ben-Dror WF2U <wf2u at ws19ops.com>
> wrote:
> >
> >> Chris,
> >>
> >> The waveform out of an oscillator without a resonant circuit in the
> output
> >> is going to look pretty weird and dirty, as it is full of harmonics.
> >> Look at the output of V126 (6AH6) as it feeds T127, which is a tuned
> >> circuit for 250 kHz.
> >> What you want to do, is to turn the two audio input channels OFF and
> turn
> >> the carrier insertion up, until you have a decent amount of 250 kHz
> signal
> >> visible at the plate of V126.
> >> You should see a reasonably clean sinewave there.
> >>
> >> Let me know how that worked out.
> >>
> >> 73, Meir WF2U
> >> Landrum, SC
> >>
> >> Get BlueMail for Android <https://bluemail.me>
> >> On Feb 1, 2022, at 12:55 PM, Chris Bolkan <bolkyboats at gmail.com> wrote:
> >>> Hi TMC lovers!
> >>>
> >>> I am currently trying to bring up a rough SBE-3 to operational
> condition
> >>> and need some help. I have no experience to pull on so I am hoping
> someone
> >>> on here has "been there and done that". I am starting by looking for
> the
> >>> most basic functionality...are the oscillators oscillating? The first
> >>> oscillator I am troubleshooting is the 250Khz sideband carrier (Z-103,
> >>> Z-108). It seems to me that this oscillator should be outputting a pure
> >>> looking sine wave. Mine is oscillating at the right frequency, and I
> >>> believe the final amplitude out of the cathode follower is
> approximately
> >>> correct, but the waveform is horrendous. Should it be a clean sine wave
> >>> like I think it should be or is it OK that it looks like $h1t?
> >>>
> >>> I've looked the circuit over, checked component values and believe
> there
> >>> are no out of tolerance resistors or leaky caps, but something just
> doesn't
> >>> seem right.
> >>>
> >>> It seems to me that if this oscillator is creating the (re)inserted
> carrier
> >>> it should be a pretty clean waveform. Any thoughts?
> >>>
> >>> Best regards,
> >>>
> >>> Chris
> >>> KI7NXY
> >>>
> >>>
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