from Tim P (UK)
re the 555, I've often wondered why the timebases were made plug-in.
Was it just for servicing, or was someone at Tek thinking about specialised
units (TDR, sampling, etc)?
According to Stan's book, the only variants were the 21A / 22A with
improved triggering.


On Wed, 26 Feb 2020 at 06:44, Randy Newman <randy.n.at.home@gmail.com>
wrote:

Just to chime in. I got a 555 some years back with 2 CA, and a D. I have
since added a W, and 1A7. I’ll not mention the initial price, as it was
phenomenal. The crt has the purple/blue phosphor for photographic
use....beautiful, sharp trace. I also have 3 7000 series scope, but really
enjoy the 555. Also love the dual-beam feature!

On Tue, Feb 25, 2020, 3:18 PM fiftythreebuick <ae5i@netdoor.com> wrote:

Ernesto expressed interest in a thread about the Type 555, so let's see

if

it'll fly! :-)

For any bench project within the vertical bandwidth of the 555, it's my
favorite oscilloscope and has been since I used one for the first time in
1976. I'll never forget the first time I ever saw one. I had been

using a

502A and a 533A on an instrumentation project and went into the

instruments

lab to get a different plug-in unit for the 533A, and when I opened the
door, there, in the middle of the room, on a 500/53A cart, was a 555!
Well, the heavens opened, the sun broke through and the angels sang and I
instantly knew that one day I *HAD* to have one! I used it as the main
scope on the remainder of the project that I was working on and

immediately

found it to be my favorite of all the scopes I had ever used. It was

less

than a year later that I was unpacking my first one.

I really enjoy the versatility of the mainframe. With the entire range

of

letter and 1 series plug-in units available, you can do just about

anything

with it. The fact that it's dual beam is quite handy. I have done
comparisons using a 1S2 in each beam, so as to have two identical TDR
traces at the same time. Being able to have a spectral display and a

time

domain display of a circuit on the same screen simultaneously is

extremely

convenient, particularly for screen photos. Using either a pair of Type

M

plug-in units or a pair of Type 1A4 Plug-in units gives 8 traces (not 3

or

4 full function traces and more that are only logic or without full
sensitivity/etc) that are all identical and all with the same
functionality. Being able to watch the timing of 7 different points in

an

instrument has been EXTREMELY handy before, for me.

Plus, it has the attributes that are found on most other 500 series
mainframes: razor sharp trace from a non-mesh CRT, controls big enough

to

be very convenient, the finest design possible, best choice of materials
possible, etc, etc....

The first one I ever got turned out to be a bit of an oddity: it's a
MOD101D, which means operable on 60 or 400 cycles! I have the info and

the

parts, and one day I hope to get the subchassis fabricated for the rest

of

the frequency switching circuit and finish restoring it. There were only
20 of them made like that one.

A bit of useful repair info: if any of the large 10 ohm carbon resistors
in the bottom of the power supply ever fail, don't replace it with a

metal

film resistor. My buddy tried that and it turned out that the metal film
resistor could not take the inrush current when the unit was powered up
from cold, and would blow open intermittently. We put an old carbon
resistor back in and never had another problem. We also took a look at

the

inrush current with a storage scope and it was quite significant.

Well, hope this starts a fun thread!

Tom AE5I