Topics

Tek 555 Capacitor Replacement List?


Matt Russell
 

I am curious if there is anyone on here that may have an idea on what capacitors to go through and change out to give an old 555 a good bill of health? I have an issue in the -150v supply and possible in the +100v also. I should be able to get that straightened out just fine.I think that what I will need the most help with is good like quality replacement parts as I really want to try to keep this as close to what Tek intended. So I do not know if there is someone on here that has a large quantity of NOS parts, but also what parts to use for replacements for the stuff that needs to get pulled out.
As always, I want to thank you all for your input, and willingness to try to keep these devices original, and running!
thanks, -
Matt


John Williams
 

Matt:

To start with, I am not in favour of replacing a bunch of parts Willy-billy. I would only replace a part if it is causing a problem. I start with a thorough inspection and analysis of trouble symptoms. I always check all supplies for ripple as well as voltage. But needlessly disturbing working circuits in my opinion is a bad idea.

As for replacements, I keep in mind that any part I find even so-called “new old stock” could be in worse shape than what’s in the scope. Capacitors age whether or not they are in use. The only exception I might make would be bumblebee capacitors which are easy to change and real new replacements are at hand.

I wish you good luck with your power supply.


John Williams
 

One of the first things I suspect are tubes and tube sockets of course. I have replaced far more tubes than anything else in the hundreds of scopes I have repaired. The sockets are often corroded to the point that contact is spotty at best. I remove the tubes in a circuit I am testing one at a time. Ideally I would test each tube individually by substitution and the tube tester both. I spray the tube socket liberally with contact cleaner before replacing the tube. If the substitute didn’t help I always put the original back as per Tek procedure.


Morris Odell
 

The only electrolytic I have had fail in my 555 was C760, a twin 40 uF unit that filters the +500 supply. That supply is stacked on top of the +350 supply so the caps only have to handle about 150 volts. An original type was unobtainable so I installed two 50 uF 350 Volt units under the chassis in the power supply where they can't be seen. In othe scopes I have seen failures in the pole capacitors across the voltage dividers that define the power supply voltages eg in the 555 C617, 740, 710, 682 and 650. These are all 0.01 uF and in relatively high impedance circuits. In early scopes they were black beauties or bumblebee caps that were prone to leakage thus moving the power supply voltages out of spec. If I see those types I replace them routinely with orange drop type polyesters rated at 630 volts.

Morris


John Williams
 

Yes I have had to replace C760 in both 551 and 555 power supplies. Fortunately I can switch some of the power supplies around for testing. I have boxes of electrolytic caps removed from Tek scopes and so far I have been able to find replacements that are still good.


Shaun M
 

John,

Good information in this thread. Would you mind sharing your testing protocol when utilizing either NOS or used (old) HV electrolytic capacitors? I usually do the following to determine good candidates: Visual inspection, gradual reforming, ESR, HV leakage test.

Thanks,

Shaun M.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of John Williams
Sent: Saturday, February 9, 2019 3:35 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

Yes I have had to replace C760 in both 551 and 555 power supplies. Fortunately I can switch some of the power supplies around for testing. I have boxes of electrolytic caps removed from Tek scopes and so far I have been able to find replacements that are still good.


John Williams
 

Sure Shaun. I would love to, but must point out that I am just a 74 year old guy who has learned only from limited experienc. I do believe strongly however that observation and logic are of utmost importance to me.

I do not have a capacitance tester. So I need to be very careful not to blow myself up. Before replacing a cap I check the rectifier output and very carefully inspect the 10 ohm resistor if there is one in the circuit. These will sometimes explode and sometimes just crack so they look ok. All the tubes in the circuit need to be checked.

If everything else looks ok I start disconnecting capacitors. When one is disconnected I connect the spare using clip leads. Often the cap will have a resistor across it to discharge it. If not I leave the cap in the circuit until it is fully discharged. I power up the scope making sure the clip leads are not touching anything they shouldn’t. Standing well back (in case the cap should explode) power on. I like to be ready to test as soon as the relay pulls in. If no change I resolder the existing cap back in and move on to the next one in the circuitry.

Things that make this dangerous: the caps in the -150 volt circuit are connected backwards. This means the metal can is hot. The cap will have an insulator under it and a paper or plastic sleeve around the can. Be careful of the hot cans and make sure if you replace it to get the polarity right and the insulation properly in place. I haven’t tried this but I believe that connecting one backwards it could go boom. Not good for the old ticker for sure.

This is not definitive as a test but I generally find it moves things along. One of the smaller electrolytic is located near the hv oscillator and is a bugger to get at. Also sometimes it is tricky to get the nut and lock washer back on when replacing certain ones. Otherwise it is just a matter of care and patience.

Hope this helps.

John


Roy Morgan
 

I have a diatribe on reforming electrolytic caps and testing other caps.

My dropbox is refusing to cooperate so I will email it to anyone interested.

Roy


On Feb 9, 2019, at 5:43 PM, Shaun M <shaun_merrigan@outlook.com> wrote:

John,

Good information in this thread. Would you mind sharing your testing protocol when utilizing either NOS or used (old) HV electrolytic capacitors? I usually do the following to determine good candidates: Visual inspection, gradual reforming, ESR, HV leakage test. ...
-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of John Williams...

Yes I have had to replace C760 in both 551 and 555 power supplies. Fortunately I can switch some of the power supplies around for testing. I have boxes of electrolytic caps removed from Tek scopes and so far I have been able to find replacements that are still good.

Roy Morgan
K1LKY since 1958
k1lky68@gmail.com


Matt Russell
 

Roy I am all ears as far as reforming caps
I am statesomattr@...
I do not want to go slamming a bunch of parts in this either, my issue is in the -150 volt supply, and possibly +100 supply
my hope is that I can get in tune with some of you guys whom have been around the block and do not mind lending information on these......I feel like I have been bitten by a bug all I think about is this scope and I am looking into purchasing more if they are out there(as long as the cash allows it)!


Matt Russell
 

wow, I am really glad you commented....I am also thankful for any information that you may have on these scopes. is there any other service documentation out on the web to do with the Tek555? as in voltage listings, anything other than what is in the manual and service book?


fiftythreebuick <ae5i@...>
 

Matt, I have a copy of the modification history for the 555. Beyond the early and later versions of the operator/service manuals, that's about all I know of. I "almost" had a nice prototype 555 indicator some decades ago but it was packed so badly when it was shipped to me that it was literally destroyed. Real heartbreaker....

One of mine has an interesting mod: it's a MOD 101D which provides for operation on 60 or 400 cycles. There were two versions of the 400 cycle option and mine is one of 20 that were made with this particular design. Thankfully I have the matching power supply as well. Not that I have anywhere to actually run it from 400 cycles!

The 555 has been my favorite scope ever since I saw one for the first time (1976) and I hope to keep one operational for as long as I am... :-)

Tom


Matt Russell
 

they are really an amazing device for certain. I know it is out of my league, but I will do all in my power to get this thing back to its normal operation. I literally saw a video about it and how it modulated it 6.3v heater circuit, and I just knew when I heard how it all operates, that I need to have one period. Any information that you have I will happily accept.


Matt Russell
 

Morris, these caps that you installed in place of the bumblebee/ black beauties, are these the Orange drop poly caps that are non polarized (P/N SBE715P 600V?) I just see that these black beauties(in my case) have a white or tan dot to the left of the script on the cap and that is on all of them.
it does not show in the schematic they are electrolytic, but I just can not be too careful in my mind. Thank you for all the help


Michael A. Terrell
 

It may indicate the outside foil, which is marked by a black line on the Orange Drops, if they are marked. The 715P is designed for pule applications, not coupling so it isn't marked on that series. In some applications it was used as somewhat of a shield, or part of a tuned filter when a wire was wrapped around it to create a crude RF filter.

Here is an example of modern caps with the outside foil marked:

<https://www.tubesandmore.com/products/capacitor-sozo-500v-nexgen-yellow-mustard-vintage>;

I no longer have any data on those oil filled paper 'Black Beauties' but most paper caps marked the outside foil.


Michael A. Terrell

-----Original Message-----
From: Matt Russell <statesomattr@gmail.com>
Sent: Feb 11, 2019 12:12 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

Morris, these caps that you installed in place of the bumblebee/ black beauties, are these the Orange drop poly caps that are non polarized (P/N SBE715P 600V?) I just see that these black beauties(in my case) have a white or tan dot to the left of the script on the cap and that is on all of them.
it does not show in the schematic they are electrolytic, but I just can not be too careful in my mind. Thank you for all the help


Renée
 

beware there are a number of caps that the line does not indicate outside foil , seems like it is just the side that indicates where to begin reading the info.
I have a number of newer orange drops where the marker is incorrect.
Renée

On 2019-02-11 3:17 a.m., Michael A. Terrell wrote:
It may indicate the outside foil, which is marked by a black line on the Orange Drops, if they are marked. The 715P is designed for pule applications, not coupling so it isn't marked on that series. In some applications it was used as somewhat of a shield, or part of a tuned filter when a wire was wrapped around it to create a crude RF filter.

Here is an example of modern caps with the outside foil marked:

<https://www.tubesandmore.com/products/capacitor-sozo-500v-nexgen-yellow-mustard-vintage>;

I no longer have any data on those oil filled paper 'Black Beauties' but most paper caps marked the outside foil.


Michael A. Terrell


-----Original Message-----
From: Matt Russell <statesomattr@gmail.com>
Sent: Feb 11, 2019 12:12 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

Morris, these caps that you installed in place of the bumblebee/ black beauties, are these the Orange drop poly caps that are non polarized (P/N SBE715P 600V?) I just see that these black beauties(in my case) have a white or tan dot to the left of the script on the cap and that is on all of them.
it does not show in the schematic they are electrolytic, but I just can not be too careful in my mind. Thank you for all the help


Michael A. Terrell
 

I saw a project online to build something o identify the outside foil. It may have been Mr. Carson's Lab on Youtube.

Another thing to watch out for: Sprague uses a 2 in a circle for their branding, but some people advertise other brands as Sprague that are missing their branding.


Michael A. Terrell

-----Original Message-----
From: Renée <k6fsb.1@gmail.com>
Sent: Feb 11, 2019 11:55 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

beware there are a number of caps that the line does not indicate
outside foil , seems like it is just the side that indicates where to
begin reading the info.
I have a number of newer orange drops where the marker is incorrect.
Renée

On 2019-02-11 3:17 a.m., Michael A. Terrell wrote:
It may indicate the outside foil, which is marked by a black line on the Orange Drops, if they are marked. The 715P is designed for pule applications, not coupling so it isn't marked on that series. In some applications it was used as somewhat of a shield, or part of a tuned filter when a wire was wrapped around it to create a crude RF filter.

Here is an example of modern caps with the outside foil marked:

<https://www.tubesandmore.com/products/capacitor-sozo-500v-nexgen-yellow-mustard-vintage>;

I no longer have any data on those oil filled paper 'Black Beauties' but most paper caps marked the outside foil.


Dave Wise
 

Identifying outside foil: (1) Audio generator across cap, set below transition frequency; (2) Sniff around cap with signal tracer; (3) Do this with cap wired both ways; (4) Whichever is quieter has outside foil grounded.

It's possible to make a cap without a clearly identifiable outside foil (think stacked-foil), but doing so using the wound type of construction requires willful perversion.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Michael A. Terrell <mike.terrell@earthlink.net>
Sent: Monday, February 11, 2019 9:06 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

I saw a project online to build something o identify the outside foil. It may have been Mr. Carson's Lab on Youtube.

Another thing to watch out for: Sprague uses a 2 in a circle for their branding, but some people advertise other brands as Sprague that are missing their branding.


Michael A. Terrell


-----Original Message-----
From: Renée <k6fsb.1@gmail.com>
Sent: Feb 11, 2019 11:55 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

beware there are a number of caps that the line does not indicate
outside foil , seems like it is just the side that indicates where to
begin reading the info.
I have a number of newer orange drops where the marker is incorrect.
Renée


Colin Herbert
 

There is an easy way to identify the outside foil, if it exists, with only common workshop things - I hope most of us have at least one oscilloscope? Just connect the capacitor across the input and grab the cap in your fingers without touching any of the bare wires. Try this with the capacitor connected both ways and the way where the most noise is seen has the outside foil connected to the signal lead. As the meerkat says, "simples".
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Michael A. Terrell
Sent: 11 February 2019 17:06
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

I saw a project online to build something o identify the outside foil. It may have been Mr. Carson's Lab on Youtube.

Another thing to watch out for: Sprague uses a 2 in a circle for their branding, but some people advertise other brands as Sprague that are missing their branding.


Michael A. Terrell


-----Original Message-----
From: Renée <k6fsb.1@gmail.com>
Sent: Feb 11, 2019 11:55 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

beware there are a number of caps that the line does not indicate
outside foil , seems like it is just the side that indicates where to
begin reading the info.
I have a number of newer orange drops where the marker is incorrect.
Renée

On 2019-02-11 3:17 a.m., Michael A. Terrell wrote:
It may indicate the outside foil, which is marked by a black line on the Orange Drops, if they are marked. The 715P is designed for pule applications, not coupling so it isn't marked on that series. In some applications it was used as somewhat of a shield, or part of a tuned filter when a wire was wrapped around it to create a crude RF filter.

Here is an example of modern caps with the outside foil marked:

<https://www.tubesandmore.com/products/capacitor-sozo-500v-nexgen-yellow-mustard-vintage>;

I no longer have any data on those oil filled paper 'Black Beauties' but most paper caps marked the outside foil.


fiftythreebuick <ae5i@...>
 

Matt, whatever you do, don't give up on it! You'll love the scope once it's running right.

The service manual is your friend. The circuit description really does contain what you need to know to troubleshoot the various sections of the scope. Those are the most complete, well written manuals that I have ever seen for anything. My favorite tool for working on the power supplies in a scope like this would be another scope with a differential comparator vertical unit installed. A 545A with a Type W, or a 7623A with a couple of 7A13s or something similar.

Please don't hesitate to contact me off-list if I can be of any help!

Tom

Matt Russell
Feb 10 #154276

they are really an amazing device for certain. I know it is out of my league, but I will do all in my power to get this thing back to its normal operation. I literally saw a video about it and how it modulated it 6.3v heater circuit, and I just knew when I heard how it all operates, that I need to have one period. Any information that you have I will happily accept.


Glydeck
 

Here is the video and it does seem to work.

https://youtu.be/BnR_DLd1PDI

George

On Feb 11, 2019, at 10:31 AM, Colin Herbert via Groups.Io <colingherbert=blueyonder.co.uk@groups.io> wrote:

There is an easy way to identify the outside foil, if it exists, with only common workshop things - I hope most of us have at least one oscilloscope? Just connect the capacitor across the input and grab the cap in your fingers without touching any of the bare wires. Try this with the capacitor connected both ways and the way where the most noise is seen has the outside foil connected to the signal lead. As the meerkat says, "simples".
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Michael A. Terrell
Sent: 11 February 2019 17:06
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

I saw a project online to build something o identify the outside foil. It may have been Mr. Carson's Lab on Youtube.

Another thing to watch out for: Sprague uses a 2 in a circle for their branding, but some people advertise other brands as Sprague that are missing their branding.


Michael A. Terrell


-----Original Message-----
From: Renée <k6fsb.1@gmail.com>
Sent: Feb 11, 2019 11:55 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 555 Capacitor Replacement List?

beware there are a number of caps that the line does not indicate
outside foil , seems like it is just the side that indicates where to
begin reading the info.
I have a number of newer orange drops where the marker is incorrect.
Renée

On 2019-02-11 3:17 a.m., Michael A. Terrell wrote:
It may indicate the outside foil, which is marked by a black line on the Orange Drops, if they are marked. The 715P is designed for pule applications, not coupling so it isn't marked on that series. In some applications it was used as somewhat of a shield, or part of a tuned filter when a wire was wrapped around it to create a crude RF filter.

Here is an example of modern caps with the outside foil marked:

<https://www.tubesandmore.com/products/capacitor-sozo-500v-nexgen-yellow-mustard-vintage>;

I no longer have any data on those oil filled paper 'Black Beauties' but most paper caps marked the outside foil.