Test Equipment Anonymous (TEA) group therapy thread

[bd139]

Anybody want to start a sweepstake on what frequency BD's new headphone oscillator will start up at? 

I doubt it will be much use for this thread: https://www.eevblog.com/forum/projects/challenge-thread-the-fastest-breadboard-oscillator-on-the-mudball/

The answer is a surprisingly low 12Hz (!). Never seen anything oscillate that slowly before!

Genuinely surprising. If I'd had to pick a number I'd have been upwards of the 70MHz that my last effort scored at about 0.5 F_t of the output trannies. As you'd mentioned arrays, and the trannies that come in arrays (and are still available new) go from an F_t of 300 MHz up to the Gigahertz region, I'd have punted at least 200 MHz.

I’m using 2n3904 discrete transistors on the prototype so around 300MHz. I was expecting that as well. However the thing is properly loop compensated and there’s extra Miller capacitance added to shape the response and phase and slow them right down. I have got some HFA3096 arrays here good to 8GHz ft 

I have my suspicions on what it is. Further investigation ensuing after bacon is consumed.

[Saskia]

@Zucca
look here:
https://www.ebay-kleinanzeigen.de/s-anzeige/quadral-amun-phonologue-mit-verstaerker/1465604763-172-9274

[PA0PBZ]

if i trust my handwriting from 25 years ago... i found it....
no qlue if it works or not... with all those KV's it runs on, its prob. not staic sensetive or is it?

Did I just spot an AZ4 (or AZ1) in there?

[med6753]

thanks for the hint. TBH I had that stuff serviced by a professional repair tech and would expect the tubes to be ok.
Also did not want to mess around with these power amps as I don't have schematics, have zero experience with tubes, and would not know what I would be doing.
Given the fact, that those amps are 5k apiece, the expense to risk ration did not seem to be worth it.

Tubes aren't hard. Think of them as large and glowing FET's and you get their basic function. Signal path is usually grid to plate with the cathode providing the electrons. You just have to remain aware of the voltages involved. Small signal areas generally no higher than +150V on the plates. But in the power amp area now you are talking serious ouch voltages of +300V upwards to even +600V. High kill factor.

And then you have sweep circuits or RF circuits if you're talking analog CRT TV's, CRT scopes, transmitters, etc. Serious no go territory for me unless I have no choice. Rubber gloves and one hand behind my back. And HV probe at the ready.   

[Saskia]

this is exactly the point. I don't have enough experience with that, and a 5000€ power amp is the wrong gizmo to start experimenting.

It's like flying. you feel safe in vmc, never ventured into IFR, and start pushing your limits, and when you are not careful, you are suddenly in imc, and shortly thereafter quite dead.

[med6753]

this is exactly the point. I don't have enough experience with that, and a 5000€ power amp is the wrong gizmo to start experimenting.

It's like flying. you feel safe in vmc, never ventured into IFR, and start pushing your limits, and when you are not careful, you are suddenly in imc, and shortly thereafter quite dead.

Understood. I grew up with vacuum tubes so I'm comfortable with them. It was all I had to work on. That baffling solid state stuff came later. 

[Cerebus]

Anybody want to start a sweepstake on what frequency BD's new headphone oscillator will start up at? 

I doubt it will be much use for this thread: https://www.eevblog.com/forum/projects/challenge-thread-the-fastest-breadboard-oscillator-on-the-mudball/

The answer is a surprisingly low 12Hz (!). Never seen anything oscillate that slowly before!

Genuinely surprising. If I'd had to pick a number I'd have been upwards of the 70MHz that my last effort scored at about 0.5 F_t of the output trannies. As you'd mentioned arrays, and the trannies that come in arrays (and are still available new) go from an F_t of 300 MHz up to the Gigahertz region, I'd have punted at least 200 MHz.

I’m using 2n3904 discrete transistors on the prototype so around 300MHz. I was expecting that as well. However the thing is properly loop compensated and there’s extra Miller capacitance added to shape the response and phase and slow them right down. I have got some HFA3096 arrays here good to 8GHz ft 

I have my suspicions on what it is. Further investigation ensuing after bacon is consumed.

The 2N3904/6 (in array form) and the HFA3096 were exactly the two ends of the spectrum that I was thinking of. I was playing (in simulation only) with the HFAxxxx arrays for some active differential probe designs a while back - must get back to it at some point.

[tonyalbus]

if i trust my handwriting from 25 years ago... i found it....
no qlue if it works or not... with all those KV's it runs on, its prob. not staic sensetive or is it?

Did I just spot an AZ4 (or AZ1) in there?

i'll have a look tomorow... getting ready for a night in the Datacenter... changing some iron..

[Saskia]

oh great, good luck

[mansaxel]

i'll have a look tomorow... getting ready for a night in the Datacenter... changing some iron..

I usually can get to the datacenter stuff in normal working hours, but not user access networks or broadcast gear. That's only after the last news broadcast for the evening, and only if I promise to ask the night staff in the news room if Trump, BoJo, or Lukashenko have done something stupid first...

Edit: Trimmed quotes. Also, Trump, BoJo, or Lukashenko always have done something -- the question is whether this particular instance is newsworthy.

[tonyalbus]

 
so far for not buying untill i am done playing with my todo pile...
again someone wanted to empty its basement...please help me get rid of this old meters
i could not resist... DC need to wait until i finisch this deal... and done 
my catch from last weekend and just now...
and no am not ritch... just unbelaveble good deals

Marconi 2955   partsn   2x front 1x met knobs
rekenmachine   classic   
Frequency counter   Thandar   TF200
SignaalGenerator      130 Mhz
Multimeter   fluke   8010a
Multimeter   handykit   mk-601
Multimeter   fluke   8012a
Multimeter   fluke    8050a
Multimeter   fluke   8010a - parts
Multimeter   fluke   8000 2x
Multimeter   fluke   8600
Frequency counter   ?   1920

the mailman will hate me by now..

[tonyalbus]

i'll have a look tomorow... getting ready for a night in the Datacenter... changing some iron..

I usually can get to the datacenter stuff in normal working hours,

most of the time it can be done in daytime, but not everything is hot swap or hot spare, we are a small company... then its night work
buts its an adventure every time 

[McBryce]

this is exactly the point. I don't have enough experience with that, and a 5000€ power amp is the wrong gizmo to start experimenting.

It's like flying. you feel safe in vmc, never ventured into IFR, and start pushing your limits, and when you are not careful, you are suddenly in imc, and shortly thereafter quite dead.

Tubes are still something you should look into (if not on this particular device). I avoided them for years due to the voltages involved, but discovering Nixie Tubes soon put a stop to that.

McBryce.

[Specmaster]

Anybody want to start a sweepstake on what frequency BD's new headphone oscillator will start up at? 

I doubt it will be much use for this thread: https://www.eevblog.com/forum/projects/challenge-thread-the-fastest-breadboard-oscillator-on-the-mudball/

The answer is a surprisingly low 12Hz (!). Never seen anything oscillate that slowly before!

DOH! duped.

[Saskia]

@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 ...

[mnementh]

i'll have a look tomorow... getting ready for a night in the Datacenter... changing some iron..

I usually can get to the datacenter stuff in normal working hours,

most of the time it can be done in daytime, but not everything is hot swap or hot spare, we are a small company... then its night work
buts its an adventure every time 

Yeah; this is the joy that is my day job...

mnem
And y'all wonder why the ol' TinkerDwagon is a bit tetched...   

[bd139]

The 2N3904/6 (in array form) and the HFA3096 were exactly the two ends of the spectrum that I was thinking of. I was playing (in simulation only) with the HFAxxxx arrays for some active differential probe designs a while back - must get back to it at some point.

They are rather nice little ICs. However quite fragile as I found 

Well I won. The issue was decoupling (tggzzz will be laughing at this and the prototype layout) and missing zobel network which was causing it to squeg. After a little motorboating due to missing compensation capacitor I got the turd polished. Also found out even at way too loud a volume it'll quite happily drive an 8 ohm speaker with 3904/3906 output pair without getting dangerously warm so I swapped that in.

So schematic, a fairly standard discrete opamp. Feedback path / gain setting through R10/R9. C1 decreases bandwidth in the loop. C7 adjusts low end response. C6 adjusts high end response. Phase flips have no gain



Prototype:



Reasonable power gain from 600 into 8 ohms! It'll push out quite a bit more than this but this is loud enough.



Pretty good eyeballed linearity:



Fairly decent step response at the cone!



Now to carefully measure it across the entire response frequency span. Which I can't be arsed to do tonight.

Well that's the first thing I've built from scratch for a long time and I'm enjoying it so far.

I am missing that SDS1202X-E now though if I'm honest 

Edit: ran some Queen through it and made a shit speaker box 



Actually sounds ok through that feeper. I will invest in this idea further. It's a shit load better than an LM386 anyway.

[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.

[bd139]

Quick teardown. Fluke 85RF probe. This came with the dead 8050A I bought. Unfortunately some gorilla broke it at some point so I had to tear it down for repair. Currently epoxy is setting...

The scope probe tip is nothing to do with the RF probe. Not sure how it got in that photo 



I may try 3d printing some RF probes in a similar fashion at some point.

[tggzzz]

Well I won. The issue was decoupling (tggzzz will be laughing at this and the prototype layout)

Actually I'm irked.

I thought I posted a snarky comment to the effect that there is are these things called capacitors and motorboating - but I can't see it. Maybe my good taste got the better of me; no good deed goes unpunished.

Nevermind. I've bookmarked it as for ammunition in my next "solderless breadboards are the work of the devil" post - and there will be others, sure as eggs are eggs.

[bd139]

Yes it’s worthy of that. I was going to do the whole thing on FR4 but I was using a breadboard to test DC operating points and it was just there begging for me to be lazy. I got away with it.

I suppose in this case the gain is that if you design it on the shittiest possible medium then it should work fine when I do the final build on FR4.

But not before I’ve thoroughly muntzed the design!

Edit: you do sort of have to know how to get away with it which is the point. Also while you’ll not see me doing things that aren’t compensated to buggery or really really slow on breadboards.

[med6753]

Quick teardown. Fluke 85RF probe. This came with the dead 8050A I bought. Unfortunately some gorilla broke it at some point so I had to tear it down for repair. Currently epoxy is setting...

The scope probe tip is nothing to do with the RF probe. Not sure how it got in that photo 


I may try 3d printing some RF probes in a similar fashion at some point.

You may want to check those 1N34's before buttoning it up. The Gorilla might have blown them up too.

I do have a whole crap load of 1N34's if you need them.

 

[bd139]

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  )

[Specmaster]

The 2N3904/6 (in array form) and the HFA3096 were exactly the two ends of the spectrum that I was thinking of. I was playing (in simulation only) with the HFAxxxx arrays for some active differential probe designs a while back - must get back to it at some point.

They are rather nice little ICs. However quite fragile as I found 

Well I won. The issue was decoupling (tggzzz will be laughing at this and the prototype layout) and missing zobel network which was causing it to squeg. After a little motorboating due to missing compensation capacitor I got the turd polished. Also found out even at way too loud a volume it'll quite happily drive an 8 ohm speaker with 3904/3906 output pair without getting dangerously warm so I swapped that in.

So schematic, a fairly standard discrete opamp. Feedback path / gain setting through R10/R9. C1 decreases bandwidth in the loop. C7 adjusts low end response. C6 adjusts high end response. Phase flips have no gain



Prototype:



Reasonable power gain from 600 into 8 ohms! It'll push out quite a bit more than this but this is loud enough.



Pretty good eyeballed linearity:



Fairly decent step response at the cone!



Now to carefully measure it across the entire response frequency span. Which I can't be arsed to do tonight.

Well that's the first thing I've built from scratch for a long time and I'm enjoying it so far.

I am missing that SDS1202X-E now though if I'm honest 

Edit: ran some Queen through it and made a shit speaker box 



Actually sounds ok through that feeper. I will invest in this idea further. It's a shit load better than an LM386 anyway.

Q4 is?

Edit, Volume,Bass Treble etc?

[Specmaster]

Quick teardown. Fluke 85RF probe. This came with the dead 8050A I bought. Unfortunately some gorilla broke it at some point so I had to tear it down for repair. Currently epoxy is setting...

The scope probe tip is nothing to do with the RF probe. Not sure how it got in that photo 



I may try 3d printing some RF probes in a similar fashion at some point.

It was photo bombing