Testing the TK Tar Baby

[TinselKoala]

TK,

Do you know what the output supplies are in the F43?  I am assuming that they are close to +/- 40 volts or so.  If so, the MPSU's were being pushed a bit hard regarding their V rating.  I would consider the 2SD669/2SB649 pairs I mentioned.  They have a higher V rating (the A versions even moreso).  Likely it was the V rating of the MPSU's that got you in to trouble in the first place.  Even though the 2S parts are only 1.5 amp devices, they will likely suffice.  Even with a full 40 volt offset at DC (I think you said it would do +/- 40 volts) into 50 ohms and with a little bias, you would still be under an amp.

No, not yet, I haven't had a chance to work on it today other than the parts run which was a bust. My supplier doesn't have any of the likely replacements.

Look at the board and trace from the 50R output.  See if you can find a couple diodes going from the amp side of the 50R trace to the rails.  If you cannot find them, I would consider adding them.  These would protect the output section from overvoltage by dumping any voltage in excess of the output supply to the rails.  I would to use a pair of fast 3 amp diodes with a PRV of 600 volts or so.

What does the unit have for the 50R?

Let me know how it's going.

PW

There is a maze of big 2 Watt carbon resistors between the output transistors and the attenuator switch. It looks like 2 series, 2 parallel of 50 ohm 2 Watt carbon resistors.

There are 8 diodes associated with the two final output transistors, going from their bases over to these 50R resistors. I can't read their numbers. Some of them are reverse biased; Zeners maybe. Here's where I like to look at schematics.
I dunno what these are doing.

[picowatt]

No, not yet, I haven't had a chance to work on it today other than the parts run which was a bust. My supplier doesn't have any of the likely replacements. There is a maze of big 2 Watt carbon resistors between the output transistors and the attenuator switch. It looks like 2 series, 2 parallel of 50 ohm 2 Watt carbon resistors.

There are 8 diodes associated with the two final output transistors, going from their bases over to these 50R resistors. I can't read their numbers. Some of them are reverse biased; Zeners maybe. Here's where I like to look at schematics.
I dunno what these are doing.

TK,

Sounds like a switched T or L pad.  Many more modern gens put the pad before the output to reduce parts/current handling at the pad switch (i.e., cost).  However, this setup is nice on a low THD gen as THD and noise are attenuated as the output is stepped down.  Not so important on a higher THD FG.

Again, I would not go with less than 80V parts...

PW

[PhiChaser]

Hi Guys,

That's an amusing series of posts.  It seems that TK et al want to protect their identities.  I solemnly promise NOT to exploit my knowledge of your own IP address MilesUpInTheAir.  I'd LOVE you to join.  We need you to start a thread on 'pure nonsense'.  That way you can exploit your true genius.

And little TK - just a quick reminder - lest you lead poor PhiChaser up the garden path by pretending you're getting significant OU results - YOU NEED TO USE A RECHARGEABLE BATTERY.  That is IF you want to take advantage of all that negative voltage across that battery.  I'm not sure that the one you're using on that little pocket version number - can cut it.

You poor readers are being so UTTERLY DUPED.  You need to wake up and smell the coffee.  Our own forum will at least give you a true picture.  This thread is PURE spin.  From beginning to end.  And it cannot END soon enough.  Little TK's disaster with his function generator is amusing.  But his anxiety to hide his results is now no longer intriguing.  It's downright dishonest. 

Regards,
Rosemary and
Rosie Pose
respectively.  LOL.   

Er... I never said the TB was OU. TK never said the TB was OU. TK said quite the opposite in fact. Repeatedly... He was trying to lead me somewhere?!? Huh?
What are you going on about Rosemary?? Again, just a bit out of context, a bit out of touch with reality, a bit touched... Really.
You are STUCK to the Tar Baby muhahahahaha! Jeeze, you really don't get it do you? So damn funny it is a shame you don't get it...
"...little pocket version number..." A touch of jealousy there Ainslie? Admit it, you couldn't build the Altiods rig TK built, even if you DID understand it.
Go talk to yourself on your own site Rosemary, I would LOVE to read your daily diatribe into madness...
PC

[TinselKoala]

OK... power supplies check out, +/- 30, +/- 15, and +/- 5 volts, all within a few mV.

Waveshapes, frequencies, and all other oscillator functions also check good on the oscilloscope. Whew. All except the DC offset... that looks like it's handled right at the input to the final amp stage. I'm getting a response but not the magnitude expected.... I'm sure that will clear up when I get the final output stages put back together.

So it's just the final output amp that's fried, probably just the two transistors too, but I'll replace all four if this internet order goes through.


A friend today just gave me a bunch of old equipment. 2 HP 5381a frequency counters, 80 MHz very basic, working, and I have an immediate application for one of them, my gyro levitation experiment needed a RPM counter and now it has one. Also an HP 8640B signal generator, for RF work, but it has a power supply fault in the +5 and the -20 volt regulated supplies, probably easy to fix. I don't need something like that very often but it makes a nice doorstop.
And an ancient Q-meter, Boonton Radio Corp. 260A. Real mad scientist stuff.
Also he gave me about ten thousand (no kidding) ceramic and mica capacitors plus about 20 big electrolytics, a dozen brand new 50k 10-turn wirewound pots, a handful of turn-counting knobs, and about a hundred little toggle switches, DPDT, SPDT, SPDT CO, SPST. Brand new in original packaging. And a bunch of Analog Devices modules, instrumentation amps from the looks of them, also some old Nixie panel indicators.... he used to work for Praxis, making NMR machines, and when they went out of business they gave him a bunch of their bench stock.... and now I've got some of it. I'll never need to buy another miniature toggle switch, at least.

[picowatt]

OK... power supplies check out, +/- 30, +/- 15, and +/- 5 volts, all within a few mV.

Waveshapes, frequencies, and all other oscillator functions also check good on the oscilloscope. Whew. All except the DC offset... that looks like it's handled right at the input to the final amp stage. I'm getting a response but not the magnitude expected.... I'm sure that will clear up when I get the final output stages put back together.

So it's just the final output amp that's fried, probably just the two transistors too, but I'll replace all four if this internet order goes through.


A friend today just gave me a bunch of old equipment. 2 HP 5381a frequency counters, 80 MHz very basic, working, and I have an immediate application for one of them, my gyro levitation experiment needed a RPM counter and now it has one. Also an HP 8640B signal generator, for RF work, but it has a power supply fault in the +5 and the -20 volt regulated supplies, probably easy to fix. I don't need something like that very often but it makes a nice doorstop.
And an ancient Q-meter, Boonton Radio Corp. 260A. Real mad scientist stuff.
Also he gave me about ten thousand (no kidding) ceramic and mica capacitors plus about 20 big electrolytics, a dozen brand new 50k 10-turn wirewound pots, a handful of turn-counting knobs, and about a hundred little toggle switches, DPDT, SPDT, SPDT CO, SPST. Brand new in original packaging. And a bunch of Analog Devices modules, instrumentation amps from the looks of them, also some old Nixie panel indicators.... he used to work for Praxis, making NMR machines, and when they went out of business they gave him a bunch of their bench stock.... and now I've got some of it. I'll never need to buy another miniature toggle switch, at least.

TK,

Glad to hear the supplies and osc section are still working.  The 30 volt rails are the output section I assume.  With the 80 volt parts their is about 20 volts of headroo relative to the MPSU06/56 ratings.  Don't drop to 60 volt parts.

Regarding the offset, what range are you seeing?  About a half or a third the normal output swing?

As for all the parts and equipment, that's a great friend to have!

PW