Topics

555 Attributes, facets, benefits and General Discussion

fiftythreebuick
 

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

Randy Newman
 

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@...> 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



Tim Phillips
 

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@...>
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@...> 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





bill koski
 

I've never seen a 555 up close and personal but I have a 556 that I bought for 25 bucks with the full manual at a HAM/Antique radio fest. From what I know it's very similar to the 555 but has it's own power supply built in.
Other than a vertical driver tube and maybe 1 or 2 other tubes I've been running it as I bought it. It had a single and a dual trace plugin with it. I've since acquired 5 or 6 plugins from a flea market for about 10 bucks each. All had tubes and needed little more than cleanup. I then got a single bay (535?) with another 4 complete plugins.
Checked out the plugins but not the scope itself yet.
Fortunately I got to all those plugins before any audiophiles did to strip the tube out of them. ( I'm actually a tube audio nut myself but would never strip a Tek unit for an audio project!!!)
I built a cart for the 556 and it sits next to my bench always ready for action.
It too has quite an inrush when turned on. I have an old analog TV in my office and before I did some rewiring I could watch the picture get narrower and lights dim when I switch on the 556!
It used to be a "Hey watch this" moment when I had friends over:)
I love using it. Though it's only rated for 50 MHz I've easily locked on 100MHz+ signals (heavily attenuated.)
The internal construction of those scopes is a work of art to look at in my opinion.
I've not done a calibration on anything yet but with the plugins I use most form the basic checks I've done things seem to be pretty close to nut on. I'm sure it's been decades since a calibration was done on anything and possibly much not touched since it left the factory.

BTW while I'm here I do have a 1L5 spectrum analyzer plugin that I bought (cost more than the 2 scopes and all the other plugins put together) I don't believe it is working. I've checked the FET in it and did find 1 lytic that was bad but it appears to still have some problems. I need to make an extension cable to check it further and then that may become a discussion for another time here other than to ask if there is any common things to look for that goes bad on those?

Roy Morgan
 

Some decades ago (2 or 3) I had a different dual trace scope but am unsure of the model number. It was the size of the 545 with no separate power unit. It had two vertical channels and time base without any plug-ins as I remember. The bandwidth was modest, meant for medical/physiology use.

It must have been the 502. Maybe I will discover it buried in my long-neglected storage unit.

Roy

Roy Morgan
K1LKY Western Mass

On Feb 26, 2020, at 2:33 AM, Tim Phillips <timexucl@...> wrote:

from Tim P (UK)
re the 555, I've often wondered why the timebases were made plug-in.

Chuck Harris
 

565 is what your are thinking of..

-Chuck Harris

Roy Morgan wrote:

Some decades ago (2 or 3) I had a different dual trace scope but am unsure of the model number. It was the size of the 545 with no separate power unit. It had two vertical channels and time base without any plug-ins as I remember. The bandwidth was modest, meant for medical/physiology use.

It must have been the 502. Maybe I will discover it buried in my long-neglected storage unit.

Roy

Roy Morgan
K1LKY Western Mass

Morris Odell
 

It sounds like a 502, which was my first Tek and I still have it stored away. It is a double beam with one timebase common to both beams. It's a little bit smaller than a 545. The vertical amps are built in and use very high quality low noise tubes that audiophooles would kill for. It was intended for biomedical use and the VAs are very sensitive, down to 100 uV/div and the bandwidth varies from 500 KHz down to 100 KHz at maximum sensitivity. I appreciated it at the time when I was working on audio stuff and RTTY modems etc but it's not really practical for other things.

Morris
--------------------------------
Roy wrote:

Some decades ago (2 or 3) I had a different dual trace scope but am unsure of the model number. It was the size of the 545 with no separate power unit. It had two vertical channels and time base without any plug-ins as I remember. The bandwidth was modest, meant for medical/physiology use.

It must have been the 502. Maybe I will discover it buried in my long-neglected storage unit.

 

Hi fiftythreebuick,

Your thread is quite informative about the 555, and the great satisfaction to own and use it..

My single-beam 547 has an adjustment for trace rotation. in the dual-beam tube, unless it is very precisely machined, how is it possible to independently rotate the traces to bring them together in alignment?

Ernesto

fiftythreebuick
 

Hi Bill-

You're right, there are similarities between the 555 and 556, and a good number of differences. For one, the original version of the 555 is all tubes while the 556 is hybrid. The bandwidth difference is 30 mc vs 50 mc. They use the same plug-in units.

One difference that I like in the 555's favor is the design of the high voltage supply. The 555 uses the older style of xfmr and the HV circuit is not sealed in a box. All of the ones that I have had and worked on have been quite reliable!

I also like the plug-in timebases. Put one on an extender card and there is very good service access.

The 21/22 timebases have a really handy auto-level trigger function that's really convenient as long as you're within the bandwidth that the circuit can handle, while the 21A/22A have a really good tunnel diode-based trigger circuit that will trigger on almost anything. Using a Type O Plug-In Unit in one beam as a trigger conditioner even gives you better ability to trigger on difficult signals, with the ability to keep an eye directly on the trigger signal on the extra beam that the O is installed in.

And as mention, it's an extremely pleasing to operate unit!

Tom

On Wed, Feb 26, 2020 at 06:44 AM, bill koski wrote:


I've never seen a 555 up close and personal but I have a 556 that I bought for
25 bucks with the full manual at a HAM/Antique radio fest. From what I know
it's very similar to the 555 but has it's own power supply built in.
Other than a vertical driver tube and maybe 1 or 2 other tubes I've been
running it as I bought it. It had a single and a dual trace plugin with it.
I've since acquired 5 or 6 plugins from a flea market for about 10 bucks each.
All had tubes and needed little more than cleanup. I then got a single bay
(535?) with another 4 complete plugins.
Checked out the plugins but not the scope itself yet.
Fortunately I got to all those plugins before any audiophiles did to strip the
tube out of them. ( I'm actually a tube audio nut myself but would never strip
a Tek unit for an audio project!!!)
I built a cart for the 556 and it sits next to my bench always ready for
action.
It too has quite an inrush when turned on. I have an old analog TV in my
office and before I did some rewiring I could watch the picture get narrower
and lights dim when I switch on the 556!
It used to be a "Hey watch this" moment when I had friends over:)
I love using it. Though it's only rated for 50 MHz I've easily locked on
100MHz+ signals (heavily attenuated.)
The internal construction of those scopes is a work of art to look at in my
opinion.
I've not done a calibration on anything yet but with the plugins I use most
form the basic checks I've done things seem to be pretty close to nut on. I'm
sure it's been decades since a calibration was done on anything and possibly
much not touched since it left the factory.

BTW while I'm here I do have a 1L5 spectrum analyzer plugin that I bought
(cost more than the 2 scopes and all the other plugins put together) I don't
believe it is working. I've checked the FET in it and did find 1 lytic that
was bad but it appears to still have some problems. I need to make an
extension cable to check it further and then that may become a discussion for
another time here other than to ask if there is any common things to look for
that goes bad on those?

bobkrassa
 

Tom's mention of using a Type O as a trigger conditioner is interesting. I'd appreciate hearing more about this. Modern scopes have menus for this but they are opaque.

The 556 is a wonderful scope but when it needs work, access is quite difficult for people with larger hands.

The display on a 556 is 6 x 10 cm per beam with a 4 cm overlap while on a 555 it is 4 x 10 per beam with a 2 cm overlap.

Some time ago there was a very informative message in this group about not mixing A and non-A time base plug ins in a 555. As mentioned, they are designed for access not swapping.

Weights are different. The 556 is a single compact unit that weighs 83 pounds even without plug ins. This is fine if you can handle the weight without damaging yourself or the scope. On the 555, the indicator weighs 68 lbs and the power supply 45 lbs. You certainly need more bench space to work on them because you can't do much diagnosis without having the two parts connected, but the somewhat lower weight and the accessibility make a difference.

Bob Krassa AC0JL

John Williams
 

Hmm 555. Interesting topic. The scope that was the last gasp for tube technology. The top of the oscilloscope food chain. The end of an era for sure. I have worked on and with the 555 since 1966. As far as dual beams go, I have three 555s, three 551s, two 556s and 6 or so 502s. The 555 was not particularly innovative in terms of technology but it was a marvel of packaging by the engineering design teams. Think about putting two complete CRTs in one envelope. Put two 545s in one box. Make the box taller to accommodate the delay lines and time bases. There’s no room for the power supplies you say ? No problem, put them in a satellite box. While you’re at it, regulate the heater supply. Make a cable to go between the boxes, keeping the primary wiring interlocking. Split the power transformers between the boxes to distribute their weight. Perfect. To fit in the sweeps, use transistors to cut down the size. Create plug-ins to make servicing possible. Later, make “A” versions with better triggering.

However the 555 was an ecological disaster. It uses huge amounts of electricity, most of which it turns into heat. Due to the large amount of heat, two very noisy fans are required. With 106 tubes, regular service is a must. Units being used intermittently came in every 6 months for performance checks and calibration. Scopes in 24/7 use came in every month for service. Spare tube stock ran into the hundreds. They were a pain to move around the building let alone ship. Still it appealed to the engineering types for whom it was designed.

The 556, while similar, is a different animal altogether. The common element is the plugin interface. But it still has 37 tubes + crt and hundreds of discrete transistors. Still it performs much the same as the 555 with a smaller footprint and no connecting cable. Harder to service than the 555 but requires a lot less service if any. It does have a very thicker manual however.

For the 555s I have complete sets of tubes including spare CRTs. I have a spare power supply (nib) and spare time base plug-ins. I have sets of extenders for everything. I have made up cable extenders for the plug-ins and the power supply. One of the scopes has a P16 crt which is very rare.

Sadly now the 555 is hard to get unless someone is incredibly lucky. The tubes are an attraction for scavengers. The aura around them makes anyone with one for sale think they should fetch as much as the budget for a minor country. Plus they are a bear to get packed and shipped. I guess the moral here would be “if you have one keep it.” Owning one is like owning a Saturn rocket or an ICBM.

fiftythreebuick
 

Hi Bob-

Thanks for adding all of that good info! Good assessment of the weigh-1-or-2 piece issue. I can move the two pieces of a 555 much easier than the single piece of the 556. I need to have an overhead crane installed in my shop... <laughing>

The Type O trick has been useful to me on more than one project when trying to trigger on something difficult to lock onto. Depending on what the problem is as far as obtaining a stable lock, you can easily have an adjustable differentiator, and adjustable integrator or a trigger amp with non-linear gain, etc, etc, etc. By building your own module to plug into the Type O, you can get even more creative. And the nice thing is that you have a complete oscilloscope sitting right there to monitor the "trigger processor" output with... Then considering that you can trigger the the A timebase from your "conditioned" trigger and then delay the B timebase, you have another tool with which to isolate what you want to see.

Tom AE5I

On Sat, Feb 29, 2020 at 09:01 AM, bobkrassa wrote:


Tom's mention of using a Type O as a trigger conditioner is interesting. I'd
appreciate hearing more about this. Modern scopes have menus for this but
they are opaque.

The 556 is a wonderful scope but when it needs work, access is quite difficult
for people with larger hands.

The display on a 556 is 6 x 10 cm per beam with a 4 cm overlap while on a 555
it is 4 x 10 per beam with a 2 cm overlap.

Some time ago there was a very informative message in this group about not
mixing A and non-A time base plug ins in a 555. As mentioned, they are
designed for access not swapping.

Weights are different. The 556 is a single compact unit that weighs 83 pounds
even without plug ins. This is fine if you can handle the weight without
damaging yourself or the scope. On the 555, the indicator weighs 68 lbs and
the power supply 45 lbs. You certainly need more bench space to work on them
because you can't do much diagnosis without having the two parts connected,
but the somewhat lower weight and the accessibility make a difference.

Bob Krassa AC0JL