475/A not really ideal for audio, and some noise thoughts.


In the recent thread about using a single scope to do "everything", I
think it's worthwhile to make a few audio related points:

1. all 475's are noiser than any 465, so they are really NOT a good
choice for audio work, especially if low level signals are being
observed. They also respond to many spurious ambient signals when
connected to a high impedance node, so it can be quite irritating to
determine what's really there. YES, you can reduce the bandwidth to
reduce this effect, but then why have a 475?

2. both CRTs and internal parts are much scarcer for the 475's, so a
repair to the scope is not trivial or cheap.

3. I agree with the comments about the 7K frames and using a 7A22 for
real audio work, it is a powerful weapon. A 7603 with a 7A26 and 7A22
and a 7B53A is almost ideal for audio: huge screen, great performance,
no noisy fan, and it's STILL portable.

An important point about used 475's and 465's: many (>75%) are
missing the internal case ground fingers (removed for some unknown
reason by an earlier lazy technician), this makes them even NOISIER
than normal. There should be case ground fingers at both the vertical
amp side and horizontal sweep side. if you have a thick trace, check
this out!

all the best,

Robert Morein <morepub@...>

For audio, why not a 434?
It has 1 mv sensitivity.
With a sweep oscillator and the storage tube, you can get a nice graph of frequency response.
The scopes are cheap. Although speced at 25 mHz, they measure out to about 38 mHz.
They weigh 24 lbs, and were stated by Tek to be designed for rugged environments.

I think one has to really think twice about the "one scope fits all" idea.

Although this is a Tek scope group, I'd like to point out that there are other worthy scopes out there. I purchased a Leader LBO-518 at a Verizon auction for $55. It looked like a trashcan, but cleaned up nicely. Surprisingly, it was perfectly functional.
It's a 100 mHz scope with FOUR channels, dual time based, delayed sweep, and 1mv sensitivity.
Surprisingly, the scope does not appear to have a switching power supply, which is probably why it still works perfectly. Weight is under 20 lbs, and the knobs and feel are very familiar.

Sorry, Tek lovers. I couldn't help but mention it.

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