Re: 7904 strange problems
The P31 conversion is done and looks great. Both CRTs are in very good shape and bright, with no burns at all. Still working on the other stuff. Will report next year.
Ed
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Re: Quarter-turn panel fasteners
Hi Richard. I have plenty of these. PM me your mailing address and I will send you a set of four. Do you need all parts for each one ie the screw, plastic part, and the little metal thingy?
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Re: probes for vacuum tubes scopes
Hi Jim. To be frank, it seems a bit premature to look for probe information when you don’t have a scope, and maybe don’t know what you are going to use it for exactly. It might be better to look for some help choosing and acquiring whatever type you decide on, and how you are going to get it. There are a few 535’s on eBay, but no indication of working or not. Prices seem to be around the $400 mark plus shipping. As far as probes go, I pretty much stick with the P6006. I have never had a use for 100x probes. When I was selling scopes I brought in a quantity of Chinese probes. They were pretty much the same as the Tek ones. Quality was good and they were quite inexpensive. I always use 4 foot ones, the six and nine foot cords always seemed to get in the way and snagged on everything on the bench. If you have one scope, a couple are all you need anyway.
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Re: 7904 strange problems
Ed,
My first thoughts after reading the descriptions are switch contact issues in the selector switches and or something in the routing logic that is on the back plane of the mainframe. If I remember correctly there are 3 IC's on the back plane that handle signal selection and routing. It sounds like one of those might not be receiving the correct signals or not outputting correctly for signal switching.
Zen
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-----Original Message----- From: [email protected] < [email protected]> On Behalf Of ed breya via groups.io Sent: Tuesday, December 31, 2024 2:42 PM To: [email protected]Subject: [TekScopes] 7904 strange problems I have this last 7904 up and running as explained previously. It showed several problems including readout loss, severe vertical compression, A-horizontal failure, and supply crashing when control lighting is turned off. I swapped in another readout board, which got that working about right. I'll have to slog through the rest. The vertical problem is very strange, and depends on the plug-in type, apparently. When I first fired it up, I put in a 7A26, 7A18, and 7B53 - the very same ones I had been using in the 7613 for diagnosing the PS for this unit. The compression was evident immediately, and I blamed the mainframe, but after some swapping around of plugs and holes and other 7A18s and 7A26s, I started to blame the 7A18, thinking it may have just crapped out coincidentally (this kind of thing has happened before). After enough combo trials, I realized the 7A18s were OK and confirmed their proper operation in the 7613. The 7A26s worked in both 7904 verticals, while both of the 7A18s had the same symptom with the line stuck near the bottom of the screen, barely affected by input signal or position controls. After more checkout, it seems the vertical display and triggering are fine in both slots using the 7A26s, and only the B-horizontal works properly. When "A" is selected, it crashes something and the display goes crazy, looking collapsed kind of like in beam-find mode, and missing parts. At this point I know the supplies seem OK, and the display looks good, with full control of intensity and focus. Has anyone seen things like these in a 7904? As I mentioned before, my notes from 2012 and also 2019 indicate that this was kind of a junker, with multiple problems existing or swapped into it, including the bad PS. Now that that's fixed, I get to revisit all of it together. The notes include stuff about the readout, the vertical and horizontal interface boards, suspecting one side of the differential signals missing, and that some plug-ins like 7D01 worked OK, while others didn't. Unfortunately, I didn't make very precise notes, so all I can tell is that these were some of the issues involved, but there's nothing about resolution of any problems. The strangest part I think is why certain plug-in types would work just fine and others not. Ed
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I have this last 7904 up and running as explained previously. It showed several problems including readout loss, severe vertical compression, A-horizontal failure, and supply crashing when control lighting is turned off. I swapped in another readout board, which got that working about right. I'll have to slog through the rest.
The vertical problem is very strange, and depends on the plug-in type, apparently. When I first fired it up, I put in a 7A26, 7A18, and 7B53 - the very same ones I had been using in the 7613 for diagnosing the PS for this unit. The compression was evident immediately, and I blamed the mainframe, but after some swapping around of plugs and holes and other 7A18s and 7A26s, I started to blame the 7A18, thinking it may have just crapped out coincidentally (this kind of thing has happened before). After enough combo trials, I realized the 7A18s were OK and confirmed their proper operation in the 7613. The 7A26s worked in both 7904 verticals, while both of the 7A18s had the same symptom with the line stuck near the bottom of the screen, barely affected by input signal or position controls.
After more checkout, it seems the vertical display and triggering are fine in both slots using the 7A26s, and only the B-horizontal works properly. When "A" is selected, it crashes something and the display goes crazy, looking collapsed kind of like in beam-find mode, and missing parts.
At this point I know the supplies seem OK, and the display looks good, with full control of intensity and focus.
Has anyone seen things like these in a 7904? As I mentioned before, my notes from 2012 and also 2019 indicate that this was kind of a junker, with multiple problems existing or swapped into it, including the bad PS. Now that that's fixed, I get to revisit all of it together. The notes include stuff about the readout, the vertical and horizontal interface boards, suspecting one side of the differential signals missing, and that some plug-ins like 7D01 worked OK, while others didn't. Unfortunately, I didn't make very precise notes, so all I can tell is that these were some of the issues involved, but there's nothing about resolution of any problems.
The strangest part I think is why certain plug-in types would work just fine and others not.
Ed
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Re: probes for vacuum tubes scopes
A CORRECTION
I gave the wrong links for the "Radiotron Designer's Handbook". I gave links to the table of contents only, the full text is available, it is:
Radiotron 4th Edition:
<>
Radiotron 3rd Edition:
<>
Sorry for this, I didn't notice until I reveiwed my post later.
On 12/30/2024 9:12 PM, Richard Knoppow via groups.io wrote:> wave response. Beside scope specs also see the catalogs for probe specs.
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? Now, if you are going to explore vacuum tube amplifiers you absolutely need the "Radiotron Designer's Handbook" 4th edition. Available several places on the web for example:
<>
??? Books on this site are very well scanned and complete. They are free.
??? Actual hard copies are still available, do a web search. Personally, being quite old fashioned I prefer hard copy actual books but must settle for electronic versions where the originals are not available or are too expensive.
??? Earlier editions of the Radiotron are of historical and some practical insterest, the 3rd edition is available at the same site:
<>
??? There will never be another book like the 4th edition, an excellent compilation of audio design at about the end of the vacuum tube period.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
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Added photo album JFETs substitution for 12au6s in 575 curve tracer
#photo-notice
Anita Abranovic <anita.abranovic@...> added the photo album JFETs substitution for 12au6s in 575 curve tracer ( /g/TekScopes/album?id=299769 ) : Both horizontal and vertical amplifiers have these instead of matching 12au6s
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Tek 1103 Probe Power Supply FS
In very good mechanical condition, lights up when plugged in, controls and buttons seem to work.
$100 and I'll ship free (from Austin) CONUS only please.
I can't guarantee it since I don't have any probes / scopes that are compatible as far as I can tell.
Email if you want a picture.
Thanks!
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Re: probes for vacuum tubes scopes
A few things to consider when selecting probes:
Check the probe's compensation range against the input capacitance of the scope input.
For work in tube circuits check the max input voltage spec of the probe. Also consider how safe the probe is for high voltage circuits.
Lastly consider the attenuation of the probe against the v/dev range of the scope against the voltages in the circuits you're working on.
The Tek P6006, P6008, P6009 should be considered. The first two are 10x. The latter is 100x.
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Mark,
I listed the Multiplier and knob on eBay.
Barry
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Hi Joel,
Sorry to say, they are already spoken for. I will let you know if that changes.
Regards,
Barry
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Hi Barry,
I'd be interested in buying the remaining V/Div knob(s). The ones I have have lost the silkscreened numbers (1/2/5/10 V etc...). Will pay a reasonable price + shipping to France, of course.
Sincerely,
Joel Setton
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I just got an email from groups.io saying Dennis is due to be billed for
this.
1. Is Dennis still with us?
a. If no, groups.io need to be informed who should be billed
b. If yes, and he's not able to handle this, as above.
Cheers, David
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Re: probes for vacuum tubes scopes
I don't know of a reason to call the 535 best for audio work, but if so, I'd pair it with a 1A7 plug in for it's 10 uV/div sensitivity and variable bandwidth, 2nd choice 1A1 for 5 mV sensitivity with the two channels chained.? Haven't used a 500 series scope since the early1970's. For audio, I would much prefer the 5000 series scopes for solid state, large screen, and with a 5A22 plug in, the same 10 uV and variable bandwidth. 7000 series with 7A22 plug in also good. Of course this topic could be argued endlessly.
John?? KK6IL
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On 12/30/2024 8:33 PM, Jim Ford via groups.io wrote: Hi, everybody.
So at some point I will take the plunge into vacuum tube audio, and according to George Lydeck on this group, the Tek 535A is the best scope ever for tube audio work.? Now, I figured out that the letter series and 1- series plug-ins, although not all of them, are the ones to plug into this mainframe.? I have that stuff on my Test Equipment Wishlist already.
OTOH, plugging directly into scope or plug-in inputs (assumed BNC, since I don't really want to go down the rabbit hole of UHF connectors) is probably not going to be productive, so I will need some probes.? Type N, SMA, 3.5 mm, BNC, and TNC are quite enough variety in my garage lab, thank you very much.
Try as I might, on TekWiki and the Internet at large, I cannot find anything specifically saying which Tek probes are appropriate for a vacuum tube scope such as the 535A.? Maybe this is tribal knowledge?? AFAIK, I have not used a scope with more than 1 tube, the CRT, (I was born in 1965, approaching 60 years old early in 2025), so the world was mostly solid-state by the time I was old enough to be playing around with scopes.? Come to think of it, all 5 of my current scopes have CRTs, and I don't think I've owned one yet with an LCD screen.? I'm in the 'tween generation, I guess.
Any recommendations for probes for a 535A?? Plug-ins also would be a good idea to know for the wishlist.
Thanks a bunch!
Jim FordLaguna Hills, California, USA
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Re: probes for vacuum tubes scopes
Thank you, John, Dave, and Richard!? Now that I think about it, I did see that P6006 probe mentioned on eevblog, IIRC.
Much appreciated!
Jim
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On Monday, December 30, 2024 at 11:17:57 PM CST, John Williams via groups.io <books4you4@...> wrote:
Hi Jim.? Always glad to encounter someone using tube scopes in this day and age. I design and troubleshoot with tube scopes as well, although I often reach for the 2465A. Now it would be hard to find a Tek scope that could not be used for audio work. My personal preference is for the 502 or 504. The 504 is cheap, nice and portable, and offers adequate bandwidth. There is no fan so they are very quiet.? On the downside they of course are single channel. The two channels of the CA are often very useful. The 530 series, the 531 and 535 both are good scopes for low frequency work, having a 15 MHZ bandwidth. However they do constitute a lot of scope for the application. They are big, heavy to move around, and noisy. They both are fairly complex, especially the 535 with delayed sweep, which I did not find very useful but it is there if you need it.? It is tricky to find one that doesn’t have its problems, especially considering the age. If something goes wrong fixing a problem can be tricky. Also getting one shipped without damage can be a challenge. But with say a CA plugin they are a fine instrument. They originally came with a 6006 10X probe, which I use with most of my scopes. I have a lot of parts for these scopes, so if you do get one let me know if you need something. Best regards.
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Re: Solder - Tin/Silver or Tin/Lead/Silver?
I’ve been using the WBT solder on all my Tek repairs and have had zero issues. But I bought my 1/2lb when it was $50 cheaper. And still have over half of it left.
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Re: probes for vacuum tubes scopes
Hi Jim. Always glad to encounter someone using tube scopes in this day and age. I design and troubleshoot with tube scopes as well, although I often reach for the 2465A. Now it would be hard to find a Tek scope that could not be used for audio work. My personal preference is for the 502 or 504. The 504 is cheap, nice and portable, and offers adequate bandwidth. There is no fan so they are very quiet. On the downside they of course are single channel. The two channels of the CA are often very useful. The 530 series, the 531 and 535 both are good scopes for low frequency work, having a 15 MHZ bandwidth. However they do constitute a lot of scope for the application. They are big, heavy to move around, and noisy. They both are fairly complex, especially the 535 with delayed sweep, which I did not find very useful but it is there if you need it. It is tricky to find one that doesn’t have its problems, especially considering the age. If something goes wrong fixing a problem can be tricky. Also getting one shipped without damage can be a challenge. But with say a CA plugin they are a fine instrument. They originally came with a 6006 10X probe, which I use with most of my scopes. I have a lot of parts for these scopes, so if you do get one let me know if you need something. Best regards.
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Re: probes for vacuum tubes scopes
The handbook for the scope should tell you its input impedance which will tell you what probes it can use. Typical scopes have 1 megohm input but not all. Probes can provide voltage range extension which is accompianed with increased impedance, i.e. a 10X probe will give you 10 meg impedance. Probes usually also have some means of compensating for capacitance, usually an adjustment on the probe to optimise its square wave response. Beside scope specs also see the catalogs for probe specs.
Now, if you are going to explore vacuum tube amplifiers you absolutely need the "Radiotron Designer's Handbook" 4th edition. Available several places on the web for example:
<>
Books on this site are very well scanned and complete. They are free.
Actual hard copies are still available, do a web search. Personally, being quite old fashioned I prefer hard copy actual books but must settle for electronic versions where the originals are not available or are too expensive.
Earlier editions of the Radiotron are of historical and some practical insterest, the 3rd edition is available at the same site:
<>
There will never be another book like the 4th edition, an excellent compilation of audio design at about the end of the vacuum tube period.
BTW, I also have the original Australian edition (in hard copy) and the American edition has everything and is excellently reproduced so there is no advantage to searching out an original.
I bought a 4th when they first came out and wore it out. I have since gotten two used ones beside the PDF version.
Lots of other tube audio books at Tubebooks.org
I wonder why the Tek 535A is considered so good for audio?
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On 12/30/2024 8:33 PM, Jim Ford via groups.io wrote: Hi, everybody.
So at some point I will take the plunge into vacuum tube audio, and according to George Lydeck on this group, the Tek 535A is the best scope ever for tube audio work.? Now, I figured out that the letter series and 1- series plug-ins, although not all of them, are the ones to plug into this mainframe.? I have that stuff on my Test Equipment Wishlist already.
OTOH, plugging directly into scope or plug-in inputs (assumed BNC, since I don't really want to go down the rabbit hole of UHF connectors) is probably not going to be productive, so I will need some probes.? Type N, SMA, 3.5 mm, BNC, and TNC are quite enough variety in my garage lab, thank you very much.
Try as I might, on TekWiki and the Internet at large, I cannot find anything specifically saying which Tek probes are appropriate for a vacuum tube scope such as the 535A.? Maybe this is tribal knowledge?? AFAIK, I have not used a scope with more than 1 tube, the CRT, (I was born in 1965, approaching 60 years old early in 2025), so the world was mostly solid-state by the time I was old enough to be playing around with scopes.? Come to think of it, all 5 of my current scopes have CRTs, and I don't think I've owned one yet with an LCD screen.? I'm in the 'tween generation, I guess.
Any recommendations for probes for a 535A?? Plug-ins also would be a good idea to know for the wishlist.
Thanks a bunch!
Jim FordLaguna Hills, California, USA
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
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Re: probes for vacuum tubes scopes
Jim
The Tek catalog from March 1967 is what you need. I've had one for years and its one of the best single references for the 500 series stuff that you will find. I see its available on Tekwiki - lots of data on appropriate probes and plugins.
DaveB, NZ
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Jim Ford via groups.io Sent: Tuesday, December 31, 2024 17:33 To: TekScopes — 开云体育 Subject: [TekScopes] probes for vacuum tubes scopes Hi, everybody. So at some point I will take the plunge into vacuum tube audio, and according to George Lydeck on this group, the Tek 535A is the best scope ever for tube audio work. Now, I figured out that the letter series and 1- series plug-ins, although not all of them, are the ones to plug into this mainframe. I have that stuff on my Test Equipment Wishlist already. OTOH, plugging directly into scope or plug-in inputs (assumed BNC, since I don't really want to go down the rabbit hole of UHF connectors) is probably not going to be productive, so I will need some probes. Type N, SMA, 3.5 mm, BNC, and TNC are quite enough variety in my garage lab, thank you very much. Try as I might, on TekWiki and the Internet at large, I cannot find anything specifically saying which Tek probes are appropriate for a vacuum tube scope such as the 535A. Maybe this is tribal knowledge? AFAIK, I have not used a scope with more than 1 tube, the CRT, (I was born in 1965, approaching 60 years old early in 2025), so the world was mostly solid-state by the time I was old enough to be playing around with scopes. Come to think of it, all 5 of my current scopes have CRTs, and I don't think I've owned one yet with an LCD screen. I'm in the 'tween generation, I guess. Any recommendations for probes for a 535A? Plug-ins also would be a good idea to know for the wishlist. Thanks a bunch! Jim FordLaguna Hills, California, USA
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John Williams
David C. Partridge
Eric Boyle