[TMC] SBE-3 question

[Duncan Brown]

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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