Date   
130 LC meter

Bob Albert
 

Is there anyone familiar with this unit? I have one that isn't working and have traced the problem to the variable oscillator not oscillating.

It's plate voltage is too low but everything seems good otherwise. Too low for enough gain to oscillate. The tubes are good and the transformer resonates. There is less than one volt on the plate of V4A.

Re: 130 LC meter

Craig Sawyers <c.sawyers@...>
 

Have you checked the smoothing capacitor on the power supply? Mine was open circuit.

Craig

Is there anyone familiar with this unit? I have one that isn't working and have traced the problem
to
the variable oscillator not oscillating.

7834 HT transformer rewind?

 

I may have located a company in UK that can handle the rewinding of these
transformers.

It won't be dagger cheap - they gave me a ball-park figure of about GBP100
plus tax and delivery, but that was without seeing the winding
specification which I have just emailed to them. I'll let you know when
they say once they've had a chance to look at the document.

David

Re: 7834 HT transformer rewind?

Brian
 

That is good news to hear , some years ago I went to a company that said they could wind a 549 transformer , in todays money it cost about the same -- but it didnt work when I got it ?? . I was never able to discover why
Brian

On Saturday, 19 October 2019, 13:14:02 BST, David C. Partridge <@perdrix> wrote:

I may have located a company in UK that can handle the rewinding of these
transformers.

It won't be dagger cheap - they gave me a ball-park figure of about GBP100
plus tax and delivery,  but that was without seeing the winding
specification which I have just emailed to them.  I'll let you know when
they say once they've had a chance to look at the document.

David








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Re: 130 LC meter

Jack Wills
 

My Tek 130 had several Sprague Black Beauty capacitors in the oscillator
circuit

All were bad. I've had enough trouble (and been shocked enough) with these
caps
that I replace them on sight.

On Sat, Oct 19, 2019 at 1:05 AM Craig Sawyers <c.sawyers@...>
wrote:

Have you checked the smoothing capacitor on the power supply? Mine was
open circuit.

Craig

Is there anyone familiar with this unit? I have one that isn't working
and have traced the problem
to
the variable oscillator not oscillating.




Re: 7834 HT transformer rewind?

Mlynch001
 

David,

I would be interested in a quote for the HV transformer of the Type 576 as well. The winding specs are readily available, unfortunately, the ferrite cores are not. There are very likely some buyers for a "factory built" replacement HV transformer for the 576 as well. Just throwing that out there, as this subject has already been thoroughly discussed in another thread.

--
Michael Lynch
Dardanelle, AR

Re: 7834 HT transformer rewind?

Chuck Harris
 

The 7834 transformer is an all-in-one transformer, and as
such it has all of the power supply windings, and the EHT
on a single core.

It is a cornucopia of wire sizes, taps, tapes, and wedges.

The winding machine would have to be started and stopped
two dozen times before the entire winding would be finished.

There are many in the 7000 series that are similarly done,
among them the 7904, 7934... The "A" scopes went back to
the separate Power and EHT style of design.

-Chuck Harris

Mlynch001 wrote:

David,

I would be interested in a quote for the HV transformer of the Type 576 as well. The winding specs are readily available, unfortunately, the ferrite cores are not. There are very likely some buyers for a "factory built" replacement HV transformer for the 576 as well. Just throwing that out there, as this subject has already been thoroughly discussed in another thread.

Re: 7834 HT transformer rewind?

greenboxmaven
 

Has anyone investigated the compatability of transformers or cores from Tektronix televison studio equipment? I really don't care for the idea of trashing that gear, but I can't imagine any of the 480I archival and transfer studios wanting the vacuum tube versions of them. In addition to the transformers, the CRTs (IF they are not run to death) might be adaptable to replace smashed, missing, or dead ones, and the knobs are compatable with many older scopes. Maybe some conversations with broadcast engineers could locate a few to find out. Also, I heard years ago Conrac was the television division of Tektronix. Was this true? I do know there were gazillions of Tektronix wavefrom monitor/ 8 inch Conrac picture monitor combos in factory built rack trays used in TV studios.

Bruce Gentry, KA2IVY

On 10/19/19 11:18 AM, Mlynch001 wrote:
David,

I would be interested in a quote for the HV transformer of the Type 576 as well. The winding specs are readily available, unfortunately, the ferrite cores are not. There are very likely some buyers for a "factory built" replacement HV transformer for the 576 as well. Just throwing that out there, as this subject has already been thoroughly discussed in another thread.

Re: 130 LC meter

Bob Albert
 

I have spent lots of time and lost lots of sleep over this.  I got up in the middle of the night last night and discovered that the problem appears to be a defective tube socket.  Not the best news but I'll probably bite the bullet after a few more tests.
I measure a variable resistance from one tube pin to ground, and see a spiky noise coming from the next stage.
Bob

On Saturday, October 19, 2019, 01:05:56 AM PDT, Craig Sawyers <c.sawyers@...> wrote:

Have you checked the smoothing capacitor on the power supply? Mine was open circuit.

Craig

Is there anyone familiar with this unit?  I have one that isn't working and have traced the problem
to
the variable oscillator not oscillating.

Re: 7834 HT transformer rewind?

Mlynch001
 

Chuck,

You are a cornucopia of knowledge!

Thanks!

--
Michael Lynch
Dardanelle, AR

TDS544A major surgery - CRT issues

Ed Breya
 

A few years back, I reported on restoring a TDS544A that had the capacitor plague on the acquisition board. That part worked out OK, but a couple months or so later, the HV transformer in the CRT circuit arced and was non-recoverable (way too much charcoal inside). Ever since, I have managed to keep using it though, with an external VGA display - nice and big, but awkward. At the last flea market of this season, a picked up a TDS540 carcass for cheap, figuring maybe I could swap out the displays and restore the 544A to full operation.

The 540 was just the guts with no can, but otherwise complete, and marked "won't start up" or something like that, so I figured typical PS trouble, and the display was likely OK. It turned out the PS and display were in fine shape, but the acquisition board indeed had the plague, so bad that it crashed the supply. I tried to clean it up as usual, but it did not recover enough. It all fires up, with a nice bright display, and passes the self-tests except for the dreaded acquisition failure.

I have decided to go ahead with the display swap, and let the 540 be for the spare parts dept, but thought I'd check here for any advice before starting. The main issue is that the 544A has the color-shutter, while the 540 is straight monochrome. Is the same CRT/display unit used in both? I vaguely recall seeing online somewhere that the shutter may be glued to the CRT - that would spoil the whole deal. Does anyone know if this is the case?

I'm up at the farm this weekend, so don't have access to all my usual tools and equipment, and I didn't think to bring all my notes and info from working on this before. The original shot display is still in the 544A (but unhooked), so I didn't even even experience removing it. I assume the front all has to come off, then the color-shutter and CRT out the front, and the rest out the middle after everything is opened up. If the shutter is bonded to the CRT, then the only other option is to leave the assembly in, and just replace the HV PS section - if it's compatible. Does anyone know if the CRTs are the same in this regard? I recall that before the 544A's display crapped out, the CRT seemed old and dim, so I'm hoping this new stuff will go right in. On the other hand, it's possible that the poor brightness on the old one was a symptom of the HV transformer going bad, so maybe it's in better shape than I thought.

Anyway, just thought I'd ask if anybody happens to know quick answers to these questions. I've got both units here, ready to start once I clear some usable space and gather up some tools. I'd like to wrap it up tonight, one way or another - tomorrow will be occupied with the water tank and other outdoor projects.

Ed

Re: TDS544A major surgery - CRT issues

Harvey White
 

To the best of my knowledge. the displays are much the same, the difference being the LCD shutter feed from the MB.  From what I know, the LCD shutter is "fastened" to the display with an intermediate gel, and one problem is that the gel goes odd, perhaps dries out.  I know that there is at least one instance where the gel was rather laboriously scraped out, and the system was restored.  If the CRTs are identical, you may wish to just simply replace the display boards.

Not a quick answer, because I don't know (I have a 540 and a 640), wish I had a 544 or a 644 for just the color capability when running an external display, but that's the best I can do.

Harvey

On 10/19/2019 8:11 PM, Ed Breya via Groups.Io wrote:
A few years back, I reported on restoring a TDS544A that had the capacitor plague on the acquisition board. That part worked out OK, but a couple months or so later, the HV transformer in the CRT circuit arced and was non-recoverable (way too much charcoal inside). Ever since, I have managed to keep using it though, with an external VGA display - nice and big, but awkward. At the last flea market of this season, a picked up a TDS540 carcass for cheap, figuring maybe I could swap out the displays and restore the 544A to full operation.

The 540 was just the guts with no can, but otherwise complete, and marked "won't start up" or something like that, so I figured typical PS trouble, and the display was likely OK. It turned out the PS and display were in fine shape, but the acquisition board indeed had the plague, so bad that it crashed the supply. I tried to clean it up as usual, but it did not recover enough. It all fires up, with a nice bright display, and passes the self-tests except for the dreaded acquisition failure.

I have decided to go ahead with the display swap, and let the 540 be for the spare parts dept, but thought I'd check here for any advice before starting. The main issue is that the 544A has the color-shutter, while the 540 is straight monochrome. Is the same CRT/display unit used in both? I vaguely recall seeing online somewhere that the shutter may be glued to the CRT - that would spoil the whole deal. Does anyone know if this is the case?

I'm up at the farm this weekend, so don't have access to all my usual tools and equipment, and I didn't think to bring all my notes and info from working on this before. The original shot display is still in the 544A (but unhooked), so I didn't even even experience removing it. I assume the front all has to come off, then the color-shutter and CRT out the front, and the rest out the middle after everything is opened up. If the shutter is bonded to the CRT, then the only other option is to leave the assembly in, and just replace the HV PS section - if it's compatible. Does anyone know if the CRTs are the same in this regard? I recall that before the 544A's display crapped out, the CRT seemed old and dim, so I'm hoping this new stuff will go right in. On the other hand, it's possible that the poor brightness on the old one was a symptom of the HV transformer going bad, so maybe it's in better shape than I thought.

Anyway, just thought I'd ask if anybody happens to know quick answers to these questions. I've got both units here, ready to start once I clear some usable space and gather up some tools. I'd like to wrap it up tonight, one way or another - tomorrow will be occupied with the water tank and other outdoor projects.

Ed



Practicing "Safe RF" RF: DC block, RF Attenuator and/or limiter?

Konrad Roeder -- WA4OSH
 

My primary interest in my new (used) Tek 492BP spectrum analyzer is to test ham radio transverters, linear amplifiers, filters and antennas with a return loss bridge. At my job, we're urged to always practice "Safe RF" to prevent damage to sensitive RF instruments. I'm not quite ready to buy a DC Block/Limiter that costs as much as what I spent on my Spec-An, but I still would rather blow a fuse than my beloved Tek 492.

Tell me more about what DC blocks, limiters and/or external attenuators you use on your instruments when making measurements.
--Konrad

Re: Practicing "Safe RF" RF: DC block, RF Attenuator and/or limiter?

Tom Gardner
 

If you spent less than $21 on a working Tek 492, you are lucky :)

The Minicircuits BLK-18-S is small enough to be fitted internally, and has a bandpass of 10-18000MHz. Internal fitting means it can't be forgotten and can't be knocked off, but different internal cables may change the overall frequency response.

A DC block isn't a panacea, but it is a useful prophylactic.

https://www.minicircuits.com/WebStore/dashboard.html?model=BLK-18-S%2B

On 20/10/19 05:40, Konrad Roeder -- WA4OSH wrote:
My primary interest in my new (used) Tek 492BP spectrum analyzer is to test ham radio transverters, linear amplifiers, filters and antennas with a return loss bridge. At my job, we're urged to always practice "Safe RF" to prevent damage to sensitive RF instruments. I'm not quite ready to buy a DC Block/Limiter that costs as much as what I spent on my Spec-An, but I still would rather blow a fuse than my beloved Tek 492.

Tell me more about what DC blocks, limiters and/or external attenuators you use on your instruments when making measurements.
--Konrad

Re: Practicing "Safe RF" RF: DC block, RF Attenuator and/or limiter?

Greg Muir
 

Konrad,

If you are not extremely familiar with using a spectrum analyzer for the applications that you mention, here are some suggestions.

1. Do not connect a transmitter or any high RF level directly to the input of the spectrum analyzer. I have seen people do this several times not knowing the proper procedures when using an analyzer for RF signal analysis. The result can be very costly in repairs to the instrument.

2. Either built-in or external overload protectors are nice but they do have their limitations mostly from a maximum RF power level. Some external devices may be slow enough so as to allow a significant power level to pass on to the test equipment before activating protection.

3. If the situation permits, use an antenna connected to the spectrum analyzer. This can be done if you are not performing precise testing of power levels and such or not overly concerned with harmonic and spurious levels.

4. If you must connect to the output of a device under test to the analyzer input, utilize an in-line power attenuator to reduce the RF to a level lower than the maximum allowed for the spectrum analyzer. (Example: https://birdrf.com/Products/Test%20and%20Measurement/Attenuators.aspx). Calculate the attenuation required in relation to the RF power level you will be measuring.

5. If access to the transmission line is possible, use an indirect method of looking at the RF such as a signal sampler or something similar. These devices connect in-line and have a capacitive probe (sometimes adjustable to set the sampled signal level) with a sample port to connect the analyzer to. To see what is offered Google “RF signal sampler.” But you must be careful because some sampled signal levels may exceed the analyzer safe RF input level so use of an in-line attenuator between the sample port and analyzer may be required.

I carry a field kit containing various attenuators with different attenuation and power levels. Much of my work involves dealing with large broadcast transmitters that have included RF signal sample ports on their transmission lines. But many of these ports will have several watts of power at the sample connector so it is standard practice to initially install attenuators in the line connecting the spectrum analyzer until the power level can be determined. Then any unneeded attenuators are removed to bring the signal up to the proper level required for testing.

For off-line testing I also utilize RF terminations (dummy loads) anywhere from 50 watts to 35 kW. In this instance I again use in-line signal samplers and various attenuators to match the sampled RF to the spectrum analyzer.

Since I start with an excessive amount of attenuation to begin with, I never worry about overloading the spectrum analyzer input nor any other device that I may be using in my tests. If you don’t know what RF level you are starting with it is much safer to start with a huge amount of attenuation then reducing it until you reach the proper level.

I seldom if never use the method of connecting any high RF power device directly to the analyzer input through attenuators.

Greg

Re: Practicing "Safe RF" RF: DC block, RF Attenuator and/or limiter?

Tom Gardner
 

On 20/10/19 08:35, Greg Muir via Groups.Io wrote:
I seldom if never use the method of connecting any high RF power device directly to the analyzer input through attenuators.
(Much sensible advice deleted for brevity)

I'd add that if you are using switched attenuators, be sure you understand the attenuator's characteristics when switching, as will be seen by not only the source but also the spectrum analyser.

Re: 7834 HT transformer rewind?

Vintage Test
 

Hi Dave,

I have a pair of 7834’s with duff HV transformers - always the EHT winding - and remember someone on the old Yahoo group had successfully rewound one of these. However, I have called and emailed several manufacturers of ‘custom’ transformers, only to be knocked back when they saw the complexity of the winding details. I toyed with the idea of removing the EHT winding and driving a mosFET and one of those cheap Chinese HV transformers from the inverter drive - seem to think it’s about 26KHz - but never got around to it🙁

Cheers,
Mel

--
you can never have enough oscilloscopes, DMMs, valve testers or soldering irons . . .

Re: 7834 HT transformer rewind?

Craig Sawyers <c.sawyers@...>
 

Hi Dave,

I have a pair of 7834?s with duff HV transformers - always the EHT winding - and remember someone
on the old Yahoo group had successfully rewound one of these.
I remember that. Whoever it was posted some pictures of the process.

Aha - found my copy of it. A 3-page pdf dated March 2015.

Must have got it from the pictures files on Tekscopes.

Craig

Re: 7834 HT transformer rewind?

Craig Sawyers <c.sawyers@...>
 

OK - it was Karin in 2015. The whole thread is here
https://groups.io/g/TekScopes/topic/7655243#114241

So somewhere lurking in the picture archive is the rewind photos he took.

Craig

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Craig Sawyers
Sent: 20 October 2019 10:41
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7834 HT transformer rewind?

Hi Dave,

I have a pair of 7834?s with duff HV transformers - always the EHT
winding - and remember someone on the old Yahoo group had successfully rewound one of these.
I remember that. Whoever it was posted some pictures of the process.

Aha - found my copy of it. A 3-page pdf dated March 2015.

Must have got it from the pictures files on Tekscopes.

Craig



Re: Practicing "Safe RF" RF: DC block, RF Attenuator and/or limiter?

Konrad Roeder -- WA4OSH
 

Greg,
To test amplifiers at work, I use a 50 Ohm attenuator with enough attenuation loss that the spectrum analyzer and power meter run near their "sweet spot". For most lab instruments that tends to be around 0-10dBm or 1-10mW. So to test a 50 Watt amplifier, I use a 40dB attenuator on the output side. For the input of the amplifier, I use a coupler to sample the input signal. I add the offset of the attenuator loss to my reading. The input power may already be at a low level like 0dBm, so the coupler might give me a signal at -30dBm for example. In the same way, I add the coupling factor loss to my reading.

But I still want to guard my spec-an against a DC bias should I have a leaky cap or a bias-tee connected for some odd reason. I also use a power limiter should my coupler or attenuator fail.

--Konrad