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On Thu, 1 Mar 2018 at 17:21 Francesco <madowax@...> wrote:

Thanks Siggi, I have just tested every resistor you listed out of circuit,
they all test good and they are still in spec even the 1% tolerance ones, I
replaced R1878 when I received the scope, the previous owner butchered it,
probably the grid bias problem was there when he sold the scope, I also
replaced c1991, just to be sure it wasn't leaking. The only thing I found a
bit strange is the waveform from pin 7 of high voltage trasformer, the
sinewave seems a bit asymmetrical, however -300v test point is exactly at
-300V. Thanks again.
Regards
Francesco.

Hey Francesco,

well, now that you know the resistor values for sure, the next step would
be to measure the voltage drop over them in-circuit. I'd suggest leaving
the scope running for 10-15 minutes before you do so, as it's easier to get
consistent measurements that way. Alternatively you could short the
slow-start capacitor to get a consistent measurement in the stone-cold
state.

If you measure and report the voltage drops over R1994, R1881 and R1992, we
can do a bit of math and see whether the currents make sensible values.
Is it reasonable for you to do this with the grid bias pot at min and max
settings?

Note that resistors can go wonky in weird ways. In my 485, I found a
resistor that measured in spec on my DMM, but had voltage-dependent
resistance in circuit. A bit of a head-scratcher that one :).

Siggi

Found a large list of Tek MODS and their relative documentation:

The simple answer to this is that unless the output is terminated with 600 ohms it will be +6dB too high. Get yourself a BNC Y attachment and a 600 ohm attenuator from BroadWave Technologies, and be calibrated forever afterward!

EJP

Lee...

Thank you for your willingness to help out a fellow Tek 335 owner in need!!? :)

Thank you, Jeff, for offering your service, as well...

If I can help with postage or ?, please email me off list and I will be especially happy to assist in any way I can.

Phil

Hi Lee,


Thanks! I'll get to work on it as soon as the foot arrives!


My address:


Jeff Davis

12 Galora Lane

Ladera Ranch, CA 92694


319-431-3846 (cell)


Regards,
Jeff


________________________________
From: [email protected] <[email protected]> on behalf of Lee Houde <houdatto@...>
Sent: Thursday, March 1, 2018 2:26 PM
To: [email protected]
Subject: Re: [TekScopes] Back feet for 335 scope

Phillip Potter, Jeff Davis N0DY -

It would appear you two are on the same page so I would be more that willing to send my one good 335 foot to Jeff for modeling and creation of new feet. Jeff if you will pm me your address off group I will get the foot out in the mail ASAP.

Lee NV8YH

Phillip Potter, Jeff Davis N0DY -

It would appear you two are on the same page so I would be more that willing to send my one good 335 foot to Jeff for modeling and creation of new feet. Jeff if you will pm me your address off group I will get the foot out in the mail ASAP.

Lee NV8YH

Thanks Siggi, I have just tested every resistor you listed out of circuit, they all test good and they are still in spec even the 1% tolerance ones, I replaced R1878 when I received the scope, the previous owner butchered it, probably the grid bias problem was there when he sold the scope, I also replaced c1991, just to be sure it wasn't leaking. The only thing I found a bit strange is the waveform from pin 7 of high voltage trasformer, the sinewave seems a bit asymmetrical, however -300v test point is exactly at -300V. Thanks again.
Regards
Francesco.

Hi Phil,


Yep, that's me. And I did get your email and have sent a response.


What I do is entirely non-destructive. I just need to take measurements from the existing foot

Jeff
________________________________
From: [email protected] <[email protected]> on behalf of Phillip Potter <p.potter@...>
Sent: Thursday, March 1, 2018 1:56 PM
To: [email protected]
Subject: Re: [TekScopes] Back feet for 335 scope

Hi Jeff,

Are you N0dy? If so, I just emailed you about your 400 series feet.

If your process is nondestructive, maybe we can get Lee H. (on list) to
volunteer his one surviving complete foot for measurement...

I have a picture of the foot, upon which I have drawn (crudely) the
measurements, that I will put that in my folder on the server:



If it comes to pass that Lee would allow you to measure and print out
feet... he should probably be the one to receive your kind offer of
printed feet, not me, but I would buy a set from you.

Phil



On 3/1/2018 1:36 PM, Jeff Davis wrote:

Hi all,


I'd be willing to undertake the 3D modelling and printing with a durable nylon material if I could get my hands on a reasonable existing foot to take measurements from. I've already developed models of 465/475 and 453/454 feet that are near identical replacements for the existing feet.


In exchange for the use of your foot, I'd be happy to provide a set of nylon printed feet gratis to upgrade your existing feet. I would then make these feet available to the community through the same channels I use for my 465/475 and 453/454 feet.


PM me if interested.


Thanks,
Jeff


________________________________
From: [email protected] <[email protected]> on behalf of Phillip Potter <p.potter@...>
Sent: Thursday, March 1, 2018 12:34 PM
To: [email protected]
Subject: [TekScopes] Back feet for 335 scope

Hello all,

The feet on the rear of my 335 are crumbling apart, literally!

I talked to Walter at Sphere and he has nothing even close, and searches
on the net reveal nothing... so, I am coming to the group to see if
there might happen to be someone who has any extra rear feet (Tek PN
348-0425-00) or even just one, that could be spared (or loaned?) to me
as an example of a complete foot? I don't know if they could be 3-D
printed or cast, but I don't have even one that is complete... mine are
all crumbled.

Here is a picture of what it looks like (borrowed from the internet):



Thanks for any suggestion or help you can provide.

Phil

Hi,
I have one of these with no disks, has anyone got a sample waveform disk they can upload to the files section please? I haven't checked what format the disks use, I guess an imaging tool such as Dave Dunfield ImageDisk would cater for it.

Regards,
John

Hi Jeff,

Are you N0dy?? If so, I just emailed you about your 400 series feet.

If your process is nondestructive, maybe we can get Lee H. (on list) to volunteer his one surviving complete foot for measurement...

I have a picture of the foot, upon which I have drawn (crudely) the measurements, that I will put that in my folder on the server:

/g/TekScopes/photo/33014/2?p=Name,,,20,1,0,0

If it comes to pass that Lee would allow you to measure and print out feet... he should probably be the one to receive your kind offer of printed feet, not me, but I would buy a set from you.

Phil

Hi all,


I'd be willing to undertake the 3D modelling and printing with a durable nylon material if I could get my hands on a reasonable existing foot to take measurements from. I've already developed models of 465/475 and 453/454 feet that are near identical replacements for the existing feet.


In exchange for the use of your foot, I'd be happy to provide a set of nylon printed feet gratis to upgrade your existing feet. I would then make these feet available to the community through the same channels I use for my 465/475 and 453/454 feet.


PM me if interested.


Thanks,
Jeff


________________________________
From: [email protected] <[email protected]> on behalf of Phillip Potter <p.potter@...>
Sent: Thursday, March 1, 2018 12:34 PM
To: [email protected]
Subject: [TekScopes] Back feet for 335 scope

Hello all,

The feet on the rear of my 335 are crumbling apart, literally!

I talked to Walter at Sphere and he has nothing even close, and searches
on the net reveal nothing... so, I am coming to the group to see if
there might happen to be someone who has any extra rear feet (Tek PN
348-0425-00) or even just one, that could be spared (or loaned?) to me
as an example of a complete foot? I don't know if they could be 3-D
printed or cast, but I don't have even one that is complete... mine are
all crumbled.

Here is a picture of what it looks like (borrowed from the internet):



Thanks for any suggestion or help you can provide.

Phil

Hi Lee,

I have been considering making a mold, but I am going to have to learn how... If I can figure out how to do that, without harming the example, I will get back to you on this...

Thanks for offering such a valuable piece... as it seems they are "unobtainium" these days!

Phil

Ps thanks to all who have made suggestions, so far... I am going to follow up on them.

On 2018-03-01 3:34 PM, Phillip Potter wrote:

Hello all,

The feet on the rear of my 335 are crumbling apart, literally!

I talked to Walter at Sphere and he has nothing even close, and searches
on the net reveal nothing... so, I am coming to the group to see if
there might happen to be someone who has any extra rear feet (Tek PN
348-0425-00) or even just one, that could be spared (or loaned?) to me
as an example of a complete foot?? I don't know if they could be 3-D
printed or cast, but I don't have even one that is complete... mine are
all crumbled.

Here is a picture of what it looks like (borrowed from the internet):

/g/TekScopes/photo/33014/1?p=Name,,,20,1,0,0

Thanks for any suggestion or help you can provide.

This is such a common malady that a few people have developed
replacement feet.

One reference is /g/TekScopes/message/144184

And I've bought a few sets from Fred Usack on ebay, and can vouch for
him (I don't know if he is on TekScopes):




These are for other models, but given some basic measurements, Fred (or
others) is likely able to produce feet that are compatible with your
model, even if not identical to the originals.

--Toby

Phil

Why not "print" a foot and use that
to make a mold. Then you can cast
them in more robust material.

73. Dick, W1KSZ

On Thu, Mar 1, 2018 at 1:59 PM, Malcolm Hunter <malcolm.r.hunter@...>
wrote:

It can be done. I've 3D printed feet for the 465 based on this model I
"designed" based on the original feet:
. Printed in PLA, they are
functional but I wouldn't bank on them holding out for every day use.
Someone with a bit of 3D modelling ability and an original foot should be
able to craft a suitable replacement for the 335 too. Printed in something
a bit more durable would work and even if they weren't as good as the
original, you could have plenty of spares.

Malc

On 1 March 2018 at 20:34, Phillip Potter <p.potter@...> wrote:

Hello all,

The feet on the rear of my 335 are crumbling apart, literally!

I talked to Walter at Sphere and he has nothing even close, and searches
on the net reveal nothing... so, I am coming to the group to see if there
might happen to be someone who has any extra rear feet (Tek PN

348-0425-00)

or even just one, that could be spared (or loaned?) to me as an example

of

a complete foot? I don't know if they could be 3-D printed or cast, but

I

don't have even one that is complete... mine are all crumbled.

Here is a picture of what it looks like (borrowed from the internet):

/g/TekScopes/photo/33014/1?p=Name,,,20,1,0,0

Thanks for any suggestion or help you can provide.

Phil

It can be done. I've 3D printed feet for the 465 based on this model I
"designed" based on the original feet:
. Printed in PLA, they are
functional but I wouldn't bank on them holding out for every day use.
Someone with a bit of 3D modelling ability and an original foot should be
able to craft a suitable replacement for the 335 too. Printed in something
a bit more durable would work and even if they weren't as good as the
original, you could have plenty of spares.

Malc

My 335 has ONE good, complete foot that I would loan out in the hope it might lead to the production of four new replacement feet.

Hello all,

The feet on the rear of my 335 are crumbling apart, literally!

I talked to Walter at Sphere and he has nothing even close, and searches on the net reveal nothing... so, I am coming to the group to see if there might happen to be someone who has any extra rear feet (Tek PN 348-0425-00) or even just one, that could be spared (or loaned?) to me as an example of a complete foot?? I don't know if they could be 3-D printed or cast, but I don't have even one that is complete... mine are all crumbled.

Here is a picture of what it looks like (borrowed from the internet):

/g/TekScopes/photo/33014/1?p=Name,,,20,1,0,0

Thanks for any suggestion or help you can provide.

Phil

On Thu, 1 Mar 2018 at 02:00 Francesco <madowax@...> wrote:

Ok I have checked the Voltage at Q1980 collector, with r1878 full CW (max
grid bias) = 60V, with r1878 full CCW (min grid bias) = 120V, so there is
the correct range but shifted of 13V more or less. Q1980 test good out of
circuit.

Well, this shifting does seem to be your problem - especially if you're
measuring this at power-on, as the slow start should increase the nominal
voltages by ~10V initially. So if you're measuring this in the "cold"
state, you're more like 20V low.

I don't know where this is coming from, but there aren't very many
candidates.
If R1994 has drifted low, that'd do it.
If R1881 or R1992 have drifted high, that'd do it.
If R1878, the grid bias pot had high contact resistance or resistance to
ground, that'd do it.
If C1991 was leaky, that'd do it.

I think you'd best trace this by the currents to and from the Q1980 base
node. By measuring the values of R1881, R1992 and R1994, then measuring the
voltage drop over them, you should be able to to suss this out.

Good luck,
Siggi

forget to add some pictures:

Use this picture to make the scale. Think new scale looks good and will work. Make 3 different types to try the illumination under the scale.
I think the better one will be with the foil on bottom of the scale , but will try all.
Now will try to find a time to make new metal knob and to install all.
Thanks to all!