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Photo DSCF0213.JPG updated
#photo-notice
[email protected] Notification
The following photos have been updated in the Sampling with 3S2 album of the [email protected] group. By: Charles <charlesmorris800@...> |
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Re: 3T77 tunnel diodes (again)
Great progress, Charles ¡ª nice to see persistence win over Murphy!
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Cheers Tom Sent from my iThing, so please forgive typos and brevity. On Mar 5, 2021, at 4:41 PM, Charles <charlesmorris800@...> wrote: |
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Re: 3T77 tunnel diodes (again)
This afternoon I was busy tweaking the trigger circuit, especially the 10 ma leaded tunnel diode I'd tacked in place of the defective D42 trigger regenerator. Part of the problem was excessive lead length causing oscillations when not desired to free-run... anyhow I put the diode on the back side of the trigger board with very short leads (and very quick soldering). I also put the shunt R back to the original 5.1 ohms having belatedly considered that the 10 ohm film resistor may have non-negligible inductance too. So the bottom line is, the only change required to use a 10 ma TD was to add resistance from the DC bias pot, and to readjust everything in that part of the circuit.
I also discovered that my 1st comparator regenerator adjustment was critical. While I was adjusting that, the sampler came to life! The only remaining problem was that the sweep would not go farther than horizontal division 8.5 with any internal adjustment, or knob on the 3T77A. After considerable wasted time measuring points in the horiz amp (particularly the op-amp Q333/334 where the sawtooth developed a flat peak), the solution was simply to adjust the gain of the 3T77A, an inconspicuous recessed screwdriver adjustment. Forgot about that one! Of course that changed the time/division calibration... later I will go through the manual and set things in order. But it works better than it ever has, although I have to dance a rhumba on the trigger sensitivity and recovery time controls ;) I added three photos to the Sampling with 3S2 album (before fixing the sweep length and thus altering the equivalent time/div) of the fastest pulse I can make with the Tek 114 pulse generator, about 120 ns wide and 1 us rep rate. It compares very favorably with the bench scope display - I can measure the fall time at about 8 ns on the sampler which is definitely faster than what I see on the 7403... the bandwidth of the mainframe itself is limited to 65 MHz (5.4 ns), plus some effects from the 200 MHz 7A26 and the Chinese probe. Anyhow, now to calibrate the time base. I had made a quick avalanche pulser but its rep rate is too slow and irregular to get the 3S2 to trigger properly. I also have a GR oscillator that spans 220-920 MHz so I could use that for a source (of sine waves). |
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Re: 547 HV Transformer: Bill Schell rewind failed
Hi,
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Yeah, it looks like you're correct there were brown epoxy impregnated transformers in the 561B series. The manual I have (from Shannon Hill's collection) lists 3 different revisions of the transformer in the 561B. RPR & Transformer Diagrams show 4 different versions of the 120-0466-xx transformer. I did a little research against the transformer diagrams and what they were coated/impregnated with. 120-0466-00 ( to B099999 ) Epoxy 252-0089-00 (Un-curiously this is the same epoxy used on the 547 transformer 120-308.) 120-0466-01 ( to B159999 ) Silicone Varnish 252-0169-00, Silicone Resin 252-0198-00 120-0466-02 ( and up ) Silicone Resin 252-0213-00 & 252-0214-00 120-0466-03 ( ??? ) Epoxy 255-0479-00 The same 120-0466-00 was used in the 564B, and the 568, per the RPR. I found a couple of pictures of the -00 version in this EEVBlog thread: Looks brown to me... As Chuck said, mine, serial # B19xxx, is a -02, and Black. I can't speak further to -01, and -03, but definitely there were quite a pile of 561B/564B/568's made with now known bad epoxy. The 567 was mentioned at one point in the transformer discussions recently, per the transformer diagrams, the 567 transformer ( 120-292 ) was impregnated with wax 256-508 (neither epoxy, nor silicone). My RM567 is not in a position for me to look and confirm. That's my contribution to the thread.... Cheers! David On Fri, Mar 5, 2021 at 5:04 PM Chuck Harris <cfharris@...> wrote:
Hi David, |
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547 HV Transformer: Bill Schell rewind restored (was Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed)
?To set the record straight, I post this with a new title.
To you who reads only this post: After sitting idle for four years, my 547 with Bill Schell rewound HV transformer exhibited the classic HV transformer thermal runaway. I posted this fact. Then I kept the instrument warm overnight. Next morning it was fine again. It is still fine. It appears that although my transformer took on water, it baked right out and returned to excellent working condition. This is nothing like the problem with the original Tek epoxy formula, which is irreversible. I still hold Bill's work in high respect. Dave Wise |
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Re: Beeswax in Transformers
I didn't impregnate my low-tech 453 rewind. Hang on for ten more years, maybe you'll see a post titled "Dave Wise HV rewind failed" :)?
________________________________ From: [email protected] <[email protected]> on behalf of Chuck Harris via groups.io <cfharris@...> Sent: Friday, March 05, 2021 9:48 AM To: [email protected] Subject: Re: [TekScopes] Beeswax in Transformers Hi Barry, It isn't a coating, but rather an impregnation. The beeswax, or epoxy is drawn into the spaces between the wires to add additional insulation, and to keep them from moving. If you don't add an impregnant, corona effects may eventually break down the insulation... in my experience, *will*... -Chuck Harris n4buq wrote: I'm curious why transformers (in particular, this transformer) benefit from a coating - beeswax or otherwise. Is it to damp sympathetic vibration at the operating frequency/frequencies? |
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Re: Modifying W Plugin to use 6DJ8 Tubes
Background:
Production below S/N 7000 uses a pair of 8056 Nuvistor at the input. At 7000 they are replaced by a dual JFET. V114 is on the A (plus) side, V214 is on the B (minus) side.?? One section is a cathode follower that bootstraps the first-stage amp anode or drain, the other section is the top half of the second-stage hybrid transistor-tube cascode amp. V124 is current sinks on the first-stage cathodes or sources. Update: I'm still investigating powering 6DJ8's, but I also experimented with a couple of common 12V tubes. First I tried 12AT7. It's a no-go. The cascode top's grid bias is Q154's Vce. 12AT7 is only 0.5V, so Q154 doesn't work. Then I tried 12AU7. Like 8416, it's about 2V and Q154 is happy. 12AU7 works! Albeit with reduced 3dB bandwidth. I see 22MHz with 12AU7, and 20ns rise time. Compare with the spec: 26MHz and 14ns. I see a flat top on the square wave. I didn't bother adjusting amplifier HF comp. Maybe I can speed it up. I see 33MHz with 8416. Common-mode rejection spec is 500:1 at 500kHz; both tubes make 1000:1. (Just for fun I tried 20MHz. Atrocious with either tube. Don't throw out your Type G.) It's a simple mod. Unless you're a purist or a stickler for specs, I say go for it. To modify your Type W to use 12AU7: 1) Cut off XV214 pin 9 solder tail. For assembly convenience Tek ran a component lead through it. This 8416 pin is internal shield but for 12AU7 it's the heater center tap and must be disconnected. To reach the solder tail to cut it, I had to lift the grounded terminal next to the socket, with a skinny right-angle #1 Phillips. This step is backward compatible. 2) Add 1200 ohms 2W across the V114-V214-V124 heater string. I hooked one end to the chassis end of R290 and, with a wire, extended the other to XV124 pin 4 . To pass shake test, add a tie point at the flying end of the resistor. 3) Adjust DC Level. I hit spec with R280 at minimum R, i.e. full CW. (Same as 8416.) 4) Adjust amplifier HF comp. I have not done this. Dave Wise My signal sources were HP 8640B and HP 8601A. Using an HP 436A/8482A power meter I confirmed less than 0.5dB variation from 1MHz to 35MHz. ________________________________ From: [email protected] <[email protected]> on behalf of Dave Wise via groups.io <david_wise@...> Sent: Tuesday, February 23, 2021 9:28 AM To: [email protected] Subject: Re: [TekScopes] Modifying W Plugin to use 6DJ8 Tubes In post #108873 (/g/TekScopes/message/108873</g/TekScopes/message/108873>), David Hess suggested wiring 6DJ8's in parallel and running them off 6.3VAC from pin 13-14. Unfortunately, that's out. Pin 13-14 is elevated to +100V and that will exceed the heater to cathode voltage rating on V124. To recap, today I see exactly two approaches. One, reverse a transformer. Unless you get lucky and find one with 6V and 18V windings like the 1A4's 120-0481-00, you have to wind your own, or put up with wire sized for 110V, i.e., at least 20VA even though the load is less than 4W. Two, run a switching power supply off +225V. I will investigate this if the 12AT7 sub fails. |
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Re: 547 HV Transformer: Bill Schell rewind failed
Chuck Harris
Hi David,
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Thank you for the picture. The 561B tranny shown is in black epoxy, which isn't usually a problem, and has turret posts, which adds to my expense. I will probably keep the tranny open frame, and use an FR4 terminal board to handle either eyelets, or turrets... likely eyelets. -Chuck Harris David Holland wrote: I directly emailed Chuck a picture of the 561B HV Transformer from my |
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Re: 547 HV Transformer: Bill Schell rewind failed
I directly emailed Chuck a picture of the 561B HV Transformer from my
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B19xxx. (I hope he didn't mind.) But I'll also freely admit it is a fairly late SN'd 561B. David On Fri, Mar 5, 2021 at 2:50 PM Chuck Harris <cfharris@...> wrote:
Hi Charles, |
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Re: 547 HV Transformer: Bill Schell rewind failed
Chuck Harris
Hi Charles,
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I would imagine so, but I don't have anything that shows what the 561B transformer looked like, nor how it mounted. The 561A is the old style as was used in the 545 etal before epoxy was used. It has micarta boards that fit into the core window to insulate the filament winding from the core. One of the family used a similar transformer, but stuffed it into a drawn aluminum can with clear silicone RTV to insulate. That might be more of a challenge, due to the wires all coming out through the can's opening... High voltage, low voltage all mingled together. -Chuck Harris Charles wrote: Does that include the 561B? I need one, once you start winding again :) |
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Re: 547 HV Transformer: Bill Schell rewind failed
Chuck Harris
Hi Bernd,
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Since the winding pattern is entirely under computer control, I can wind anything that goes on the cardboard former that tektronix used. The only other issues with models other than the 547/545B, is termination. Small wires are easy, lugs or pins are harder. My highest priorities are 545B/547, 647A/B, and 576. Anything that uses the same mounting as the 545B/547/647A/B transformers should come essentially for free. -Chuck Harris widgethunter via groups.io wrote: Chuck;Am pleased to see that your ambitious undertaking is coming to fruition.I know that many Tek owners, who weren't so fortunate as to be able to keep their scopes working, are eagerly awaiting the day.We talked about this in terms of a side business, initially.If you are able to rewind other models, as well, you may be busy enough to get there, after all these years.Bernd |
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Re: Looking to ID a diode in a 1S1 sampling plug-in
Hi Sean,
Since you have a very early model 1S1, you might be interested in checking out whether your vertical board uses "pellet parts." See: /g/TekScopes/topic/74982135#168407 /g/TekScopes/topic/75088746#168713 The serial number of my 1S1 is in the 700s and I see regular discrete components on the underside of the vertical board, as in the picture snapdiode took, which suggests that maybe Tektronix gave up on the "pellet parts" idea. (Even in the photo on page 4-8 of the manual it looks like R4 and R5 are mounted in the normal fashion.) In trying to figure out the history of embedding discrete components under the traces in a PCB, I found a site saying it was still considered a "cutting edge" practice in 2014. So if Tektronix was doing it back in 1965 I wonder if they were one of the first. |
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To Beeswax or not to Beeswax: that is the question.
Hi All:
Yes, there are some threads about beeswax... and many more posts about beeswax, in other threads too... usually about using beeswax in/with transformers. In this tread, I want us to try to get to the bottom of the topic. I have a feeling, it'll be like herding a clowder... but here goes. -- Roy Thistle |
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Re: 547 HV Transformer: Bill Schell rewind failed
widgethunter
Chuck;Am pleased to see that your ambitious undertaking is coming to fruition.I know that many Tek owners, who weren't so fortunate as to be able to keep their scopes working, are eagerly awaiting the day.We talked about this in terms of a side business, initially.If you are able to rewind other models, as well, you may be busy enough to get there, after all these years.Bernd
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-----Original Message-----
From: Chuck Harris <cfharris@...> To: [email protected] Sent: Thu, Mar 4, 2021 4:45 pm Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed Hi Bernd, All indications are that my new machine is going to do an even better job than the best I could do with the old manual machine. As an example, I was able to get 2/3 of the way to a full wind without using the rosin/alcohol mixture that I developed to enhance the wire's friction... Using the rosin/alcohol, I am there already. And, I will be using beeswax. I'm glad to hear the prototype is still soldiering on.? Soon, I may be able to get you the winds I promised oh so long ago... -Chuck Harris widgethunter via groups.io wrote: My memory certainly hasn't improved with age.Not much else seems to have, either...But, the beeswax thing I'd be willing to put money on - fwiw. |
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Re: Tektronix 2230 - no readout
Hi Bert,
I also have a Salae clone. Used it once to reverse engineer a display of a VHF radio, a Motorola MC Micro. The story is on my blog (in Dutch): As there are not many countries where they speak Dutch: I live in Belgium, Flanders, not so far from the Northsea. Aha Michigan, so Dr. Pol is one of you neighbours ;-) Your a bit to far away to visit... I have been doing some more research today. Sorry for all the Tek lovers, but this scope is not very service friendy. You have to unscrew several things, isolate the PCB's with cardboard and/or newspaper to be able to measure on certain boards and be lucky not to provoke shorts. BTW:I found out you can test the scope without the GPIB option if you put P9107 (located 5B in schematic 10) in the other position, that way the reset from the GPIB board is inactive. One thing I did not check previously: the 5V ref A and B, as well as the +5V on the vector and I/O board are OK. Also checked point by point the flat cable between these boards, as well as the ribbon cable to the motherboard. There is no activity on the X and Y vector pins going to the multiplexer 4053. I am a bit running out of idea's. Do you have any more? greetings, Harry |
Mike Yepes
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