Test Equipment Anonymous (TEA) group therapy thread

[McBryce]

@McBryce I may well do that, but this is not the time right now. I have 4 or 5 pinballs that I need to finish, plus my other repair stack ...

Even better, there are a few pinball machines that did all the scores with Nixie tubes!

McBryce.

[tggzzz]

On the other side I attended the Keysight webinars about FFT. Interesting stuff, I report here my question and how they answer it:

Q: Does the 10MHz input on the high end Scope improve the FFT performance?
A: Hello Zucca, Thank you for the question. I am not sure if this would provide any improvement, I will check with the factory and get back to you via email.

Further answer:

I assume you refer to the 10MHz common instrument clock, typically used to synchronise instruments and which often come from a high-precision source. I checked with the factory and they state that think this would have very little effect. You wouldn’t notice a few parts/million difference in frequency measurements. Johnnie Hancock will be presenting a virtual seminar in early October on “Understanding Oscilloscope Specifications”. One thing he plans to point out is that although the scope’s time-base accuracy specification is often touted, it is overrated. There are many other factors that go into determining timing accuracy that are much bigger than time-base accuracy. He states the same can be said for frequency measurements in the frequency domain.

If you are referring to the 20MHz filter used in the oscilloscope front-end (hardware bandwidth limit filter): then this will have an effect - if you are only interested in frequency components below 20 MHz, this will definitely help. It should also improve the scope’s noise floor.

FFTs are boring

Here is a nice screenshot, especially when you try to count the number of digits in the frequencies



FFI see https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3000930/#msg3000930

[tonyalbus]

Okey this seller is onbeleveble..
i do an offer, low, we are starting.....
he puts a counter offer, i go inbetween which was also my max, and i told him...
we both walk away from the deal, no harm done...
after one day he comes back to me... to agree on my offer, he changed his mind...fine..
then he gives me 4 not 5 start becouse i offer to low....
    he came back to me, and i was a fast payer...i did my part
some sellers...

[bd139]

It’s just humans. Some of them are wired up wrong. Or have a burned out resistor somewhere.

[Ice-Tea]

That's just stupid. If you don't like the offer, don't accept. If you do, suck it up and be happy with what you get.

[tonyalbus]

It’s just humans. Some of them are wired up wrong. Or have a burned out resistor somewhere.

i hope he is wired enough to properly pack it... . or i end-up with 4 stars and a broken unit, because of this clown...
the tarts are not a problem, i was just supprized, i have 100+ 5 start so it will not show...
how this people think..if they even do..
don't sell the thing i am not forcing you..

[jonovid]

 multifunction 3 pin semiconductor passive component tester

the elegant case is a big improvement on the open pcb & 9volt clip of previous multifunction testers.
this unit has built in lithium battery. size? ...did not look any further
hold the test button to on/off.
came with 3 ic hook test leads red , black & green.
plus a USB to micro usb 15cm long cable adapter.
1 electrolytic capacitor & a red 3mm led.

this units are savior for those with innumeracy with building electronics.
-fail at high to mid level mathematical equations.

[tonyalbus]

multifunction 3 pin semiconductor passive component tester

the elegant case is a big improvement on the open pcb & 9volt clip of previous multifunction testers.
this unit has built in lithium battery. size? ...did not look any further
hold the test button to on/off.
came with 3 ic hook test leads red , black & green.
plus a USB to micro usb 15cm long cable adapter.
1 electrolytic capacitor & a red 3mm led.

this units are savior for those with innumeracy with building electronics.
-fail at high to mid level mathematical equations.

indeed looks a lot better!, nice

[Saskia]

@Zucca

https://www.ebay.de/itm/Sony-TA-E86B-Vintage-Vorverstarker/174396217750?hash=item289ad31996:g:ObgAAOSwaU1fOQfA

fantastic preamp.
Immediate buy if in working condition.

You are playing the Eve role and I feel like Adam... 



I have to take a pause of meditations and decide what to do...
Thank you so much!

am I at least playing it well ?

here, have an apple

I also have a Burmester 846 sitting somewhere in my closet that I may be tawked into parting with ...

[bd139]

Just grabbed an interesting thing off ebay. At £30 I figured I will bounce it more more even if it is naff to someone less lazy and/or more enterprising.



It appears to be a fairly competent looking homebrew HF spectrum analyser adapter for a scope. Based on the feature presentation it is probably one of the QST designs.

Seller is on holiday until Monday so I'll have to wait for a bit and see what the deal is...

[tonyalbus]

Just grabbed an interesting thing off ebay. At £30 I figured I will bounce it more more even if it is naff to someone less lazy and/or more enterprising.



It appears to be a fairly competent looking homebrew HF spectrum analyser adapter for a scope. Based on the feature presentation it is probably one of the QST designs.

Seller is on holiday until Monday so I'll have to wait for a bit and see what the deal is...

interesting....

[Cerebus]

Yeah have checked it already. They are good fortunately. I’ve got a bag of 1N270’s around somewhere which would work (poor man’s 1N34A  )

10 pieces for EUR 3.84 including shipping is not that expensive. Imho. 

https://www.ebay.de/itm/291935959284

Hmm. Buying 1N34A diodes is a bit of a shit show to be honest. Some sellers sell other cheap Ge diodes as equivalents. They don’t have the same steep curve as the proper ones and way too much capacitance. And then there’s the lot selling small Schottky diodes as 1N34A’s.  The popularity is defined by the ubiquity of the things in articles spanning back 50 years now I suppose. This has given them a holy status along with the 40673 dual gate MOSFETs and other devices. This in turn leads to supply being gobbled up by chancers trying to make a quick buck (like me  ) and prices increasing. Then attractive low cost options appear which really aren’t 1N34’s.

But 100% of the time you can throw a 1N270 in there. And those are cheap.

Another lore diode is the holy mixer diode, the HP 5082-2800. Which is exactly the same as an ST 1N5711 but commands a 20x price tag 

This is why I hate watching people spend on a specific part. On another forum I saw someone pay £30 for a basic TO3 pass transistor because it had a different number to 2n3055 written in it...

To be fair, pretty much any circuit that has been designed to have something better than a 2N3055 is going to have problems with substituting in a 2N3055 - the world's worst power transistor - but yeah, pretty much anything that meets h_FEmin and P_tot ought to work for a pass transistor.

I'm of the school that says it's a bad design if you can't substitute almost any BJT in a circuit with something very roughly similar and get a working properly biased stable circuit. Sure, you might miss on some critical applications (e.g. THD on low distortion power amplifiers can rely on having the right output transistors to get 0.001% THD rather than 0.01% with any old thing that's to hand) but for most things with non-critical, not pushing the envelope, design criteria then almost anything with suitable V_BCEO, h_FEmin/h_femin, F_t and P_tot ought to work by design.

As a matter of practice I use LTSpice's "AKO:" BJT model statement (along with modelling strays) to try substituting transistors in most of my designs precisely to try and make sure that I keep the above true. I am far from a paragon of circuit design (quite the opposite in fact) but I ain't lazy.

[tggzzz]

I'm of the school that says it's a bad design if you can't substitute almost any BJT in a circuit with something very roughly similar and get a working properly biased stable circuit. Sure, you might miss on some critical applications (e.g. THD on low distortion power amplifiers can rely on having the right output transistors to get 0.001% THD rather than 0.01% with any old thing that's to hand) but for most things with non-critical, not pushing the envelope, design criteria then almost anything with suitable V_BCEO, h_FEmin/h_femin, F_t and P_tot ought to work by design.

I don't disagree, but when you are pushing designs to the limit you often end up relying on some "peculiar" parameter that is only found in one device. That is a problem when the device becomes unprofitable to make.

FFI, have a look at some of the discussions on sci.electronics.design. There's some very high quality info there, if you manage to avoid the politics!

Alternatively, have a look at the tables and "designs of the masters" in TAoE and the x-Chapters.

[bd139]

To be fair, pretty much any circuit that has been designed to have something better than a 2N3055 is going to have problems with substituting in a 2N3055 - the world's worst power transistor - but yeah, pretty much anything that meets h_FEmin and P_tot ought to work for a pass transistor.

I'm of the school that says it's a bad design if you can't substitute almost any BJT in a circuit with something very roughly similar and get a working properly biased stable circuit. Sure, you might miss on some critical applications (e.g. THD on low distortion power amplifiers can rely on having the right output transistors to get 0.001% THD rather than 0.01% with any old thing that's to hand) but for most things with non-critical, not pushing the envelope, design criteria then almost anything with suitable V_BCEO, h_FEmin/h_femin, F_t and P_tot ought to work by design.

As a matter of practice I use LTSpice's "AKO:" BJT model statement (along with modelling strays) to try substituting transistors in most of my designs precisely to try and make sure that I keep the above true. I am far from a paragon of circuit design (quite the opposite in fact) but I ain't lazy.

Completely agree with your assertions on substitution. If you keep normalised parameters for a basic BJT reference model and do not rely on specific device characteristics then you can't go wrong. I'm slightly obsessed with designing feedback circuits so this is quite good fun to push as much as you can out of shit transistors

Not tried AKO. That's interesting. Will play with that today.

I'm of the school that says it's a bad design if you can't substitute almost any BJT in a circuit with something very roughly similar and get a working properly biased stable circuit. Sure, you might miss on some critical applications (e.g. THD on low distortion power amplifiers can rely on having the right output transistors to get 0.001% THD rather than 0.01% with any old thing that's to hand) but for most things with non-critical, not pushing the envelope, design criteria then almost anything with suitable V_BCEO, h_FEmin/h_femin, F_t and P_tot ought to work by design.

I don't disagree, but when you are pushing designs to the limit you often end up relying on some "peculiar" parameter that is only found in one device. That is a problem when the device becomes unprofitable to make.

The grand consolidation of semiconductor companies in the last 30 years is a fine example of the crippling decline in the availability of the special devices.

However we gained things like MMICs and magic IC blobs that replace the entire functional unit. This is commercially viable but eliminates skill and everyone plays lego instead. Which is boring.

[Cerebus]

I'm of the school that says it's a bad design if you can't substitute almost any BJT in a circuit with something very roughly similar and get a working properly biased stable circuit. Sure, you might miss on some critical applications (e.g. THD on low distortion power amplifiers can rely on having the right output transistors to get 0.001% THD rather than 0.01% with any old thing that's to hand) but for most things with non-critical, not pushing the envelope, design criteria then almost anything with suitable V_BCEO, h_FEmin/h_femin, F_t and P_tot ought to work by design.

I don't disagree, but when you are pushing designs to the limit you often end up relying on some "peculiar" parameter that is only found in one device. That is a problem when the device becomes unprofitable to make.

FFI, have a look at some of the discussions on sci.electronics.design. There's some very high quality info there, if you manage to avoid the politics!

Alternatively, have a look at the tables and "designs of the masters" in TAoE and the x-Chapters.

One of the 'designs of the masters' examples they give is the 34401A ADC design. That is notable in that it designs out a lot of the stuff that could lead to critical reliance on component characteristics. Basically it comes down to "the voltage reference must be long term stable and this small set of resistors must be long term stable and this capacitor and op amp need to OK (but not critical)". I cobbled together an implementation of that ADC on a cheap plug-in breadboard with the components I had to hand and an Arduino and was getting readings that were stable to 6 digits over several hour periods.

At the other end of the spectrum is measuring nanovolts and femptoamps where, even designing out as much as you can, you end up relying on the characteristics of some very particular devices and any substitution would fail on either noise or leakage grounds.

[Cerebus]

However we gained things like MMICs and magic IC blobs that replace the entire functional unit. This is commercially viable but eliminates skill and everyone plays lego instead. Which is boring.

Precisely. This is why I still design stuff from scratch, not because I need to but because it's not boring. It's much more fun to try and design out the awkwardnesses and difficulties than pour over manufacturer's parametric searches to find a magic black and silver box that does what you need.

[mansaxel]

However we gained things like MMICs and magic IC blobs that replace the entire functional unit. This is commercially viable but eliminates skill and everyone plays lego instead. Which is boring.

On the other hand, to hacks like me, the for-audio IC's like DRV134 or THAT 1200 -series are a godsend.

Yes, I've copy-cat'ed TL072 circuits as well, that also perform slightly better with 5532's substituted (and to some extent demonstrate the part replaceability we seem to agree on being good), but those custom IC's are wonders. 

The various class-D power amps like the one mnem posted about are another interesting part type, but I'm less intrigued with them.

[Saskia]

However we gained things like MMICs and magic IC blobs that replace the entire functional unit. This is commercially viable but eliminates skill and everyone plays lego instead. Which is boring.

Precisely. This is why I still design stuff from scratch, not because I need to but because it's not boring. It's much more fun to try and design out the awkwardnesses and difficulties than pour over manufacturer's parametric searches to find a magic black and silver box that does what you need.

it also keeps you mentally fit.

[bd139]

I'm of the school that says it's a bad design if you can't substitute almost any BJT in a circuit with something very roughly similar and get a working properly biased stable circuit. Sure, you might miss on some critical applications (e.g. THD on low distortion power amplifiers can rely on having the right output transistors to get 0.001% THD rather than 0.01% with any old thing that's to hand) but for most things with non-critical, not pushing the envelope, design criteria then almost anything with suitable V_BCEO, h_FEmin/h_femin, F_t and P_tot ought to work by design.

I don't disagree, but when you are pushing designs to the limit you often end up relying on some "peculiar" parameter that is only found in one device. That is a problem when the device becomes unprofitable to make.

FFI, have a look at some of the discussions on sci.electronics.design. There's some very high quality info there, if you manage to avoid the politics!

Alternatively, have a look at the tables and "designs of the masters" in TAoE and the x-Chapters.

One of the 'designs of the masters' examples they give is the 34401A ADC design. That is notable in that it designs out a lot of the stuff that could lead to critical reliance on component characteristics. Basically it comes down to "the voltage reference must be long term stable and this small set of resistors must be long term stable and this capacitor and op amp need to OK (but not critical)". I cobbled together an implementation of that ADC on a cheap plug-in breadboard with the components I had to hand and an Arduino and was getting readings that were stable to 6 digits over several hour periods.

At the other end of the spectrum is measuring nanovolts and femptoamps where, even designing out as much as you can, you end up relying on the characteristics of some very particular devices and any substitution would fail on either noise or leakage grounds.

There's always hand selection for some parts. Buy several thousand and measure them.

There's one item that bothers me regularly on that front. The HP427A. The JFET in the impedance converter was a fairly early one and has a whole load of temperature dependent leakage. To control the impedance high they actually inject that leakage back into the gate using a similarly leaky diode. That's fine until either the JFET or the diode goes phut and then you have to find a substitute 

Precisely. This is why I still design stuff from scratch, not because I need to but because it's not boring. It's much more fun to try and design out the awkwardnesses and difficulties than pour over manufacturer's parametric searches to find a magic black and silver box that does what you need.

Spot on. For the use case I have for this audio amplifier, a relatively simple current boosted opamp would do the job. But that doesn't have any art involved. Even if I can't reproduce something as good as a commercial unit, which is always true, I can at least say I had a hand in the entire process. The more sweat and tears, the more connected to the physics and the outcome you are.

Difference between an operator and a creator. Which is why amateur radio sucks. It's all operators and cargo cults.

[tonyalbus]

Difference between an operator and a creator. Which is why amateur radio sucks. It's all operators and cargo cults.

This supprized me too to be honest, i was out for 25 years, but kept my lfull icense...
25 years ago all hams were electronics freeks and had the first computers..and the axam had a proper technical one, je allmost needed to know the TRX by its components level.
i am member of a few ham groups... and most of the new hams, just like talking and have no idea about the radio itself..
i was kicked out of a ham group becouse i posted a video of a teardown of a TRX and the modurator received complains it was to technical...
i will never anderstand those hams.

[edit] was not kicked out, but asked to but less technical videos.... i left, that was not my group..

[Cerebus]

it also keeps you mentally fit.

Fit, yes. Whether fit includes sane is very much open to debate. 

[bd139]

Difference between an operator and a creator. Which is why amateur radio sucks. It's all operators and cargo cults.

This supprized me too to be honest, i was out for 25 years, but kept my lfull icense...
25 years ago all hams were electronics freeks and had the first computers..and the axam had a proper technical one, je allmost needed to know the TRX by its components level.
i am member of a few ham groups... and most of the new hams, just like talking and have no idea about the radio itself..
i was kicked out of a ham group becouse i posted a video of a teardown of a TRX and the modurator received complains it was to technical...
i will never anderstand those hams.

That's about right. The local club here is about the same.

I did consider starting a technical only club online but I really don't have the time or the motivation for such things.

[Specmaster]

Spara, I have found the root cause of poor readings in my HP 3478A. It was the Front/Rear Switch that has gone bust, only the rear works fine.

Shall I buy a new switch or a switch contact cleaner ?

Its always worth trying the switch contact cleaner option first. That switch normally sees very little action so it is more than likely to no more than just dirty, contacts which switch cleaner and operating the switch, once dosed with cleaner should clean up very nicely.

[tonyalbus]

Difference between an operator and a creator. Which is why amateur radio sucks. It's all operators and cargo cults.

This supprized me too to be honest, i was out for 25 years, but kept my lfull icense...
25 years ago all hams were electronics freeks and had the first computers..and the axam had a proper technical one, je allmost needed to know the TRX by its components level.
i am member of a few ham groups... and most of the new hams, just like talking and have no idea about the radio itself..
i was kicked out of a ham group becouse i posted a video of a teardown of a TRX and the modurator received complains it was to technical...
i will never anderstand those hams.

That's about right. The local club here is about the same.

I did consider starting a technical only club online but I really don't have the time or the motivation for such things.

Don't bother.... it will drain you...those times were...
find a nice TEA club and just hang there 
much better for your mood

[mansaxel]

i will never anderstand those hams.

That's about right. The local club here is about the same.

Some of the members in the club where I went for my license have a little sub-gathering they call "Valve Junta" where they try to wake up and restore old valve gear, mostly related to radio. That's indeed technical. One of the members is the technical editor of the swedish ham magazine. A lot of the hams I know also are working at our variant of GCHQ, the "FRA". You don't get in there unless you've got the lightbulb on top of your shoulders correctly fitted, and that shows.

Then, of course there are the usual closet misogynistic (mostly because acting like an asshole towards women was OK when they were young) rag-chewers on 2 m. You can't win them all.