For what is worth, they are still current at ONSEMI. I hate them with a passion, they create more problems then they solve (due to the poor diode choice and integration), YMMV. Until the Thermal Track BJTs came to the market, I though I know how to thermally compensate a BJT output stage, now I'm no longer so sure.
Self's various Blameless are Lin topology.
I don't have Linn's amplifier schematics to compare to Blameless.
No they are not. Lin's was a single gain stage design, while Self's TWO gain stage designs were actually invented by Thompson.
I've called the single AC Vsource loop gain test the "Simple Middelbrook" version
the combined I, V "bidirectional" measurement loop gain probe is often refered to by Tian - for his article on it
Middelbrook actually has a "final solution" to loopgain/feedback element sensitivity measurement in his Generalized Feedback Theory tools "GFT"
General Feedback Theorem (GFT) explained
https://sites.google.com/site/frankwiedmann/loopgain
even older "opening the loop" methods are sometimes seen - you can put a Mega Henry inductor in series with the feedback in Spice and hopefuly get DC stabilization but also the see the "open loop" AC gain at higher frequencies
better accuracy requires loading the circuits on each side of the cut with replicas of the normal cirucit load
the combined I, V "bidirectional" measurement loop gain probe is often refered to by Tian - for his article on it
Middelbrook actually has a "final solution" to loopgain/feedback element sensitivity measurement in his Generalized Feedback Theory tools "GFT"
General Feedback Theorem (GFT) explained
https://sites.google.com/site/frankwiedmann/loopgain
even older "opening the loop" methods are sometimes seen - you can put a Mega Henry inductor in series with the feedback in Spice and hopefuly get DC stabilization but also the see the "open loop" AC gain at higher frequencies
better accuracy requires loading the circuits on each side of the cut with replicas of the normal cirucit load
H.C. Lin article, Electronics, Sept 1956
http://techpreservation.dyndns.org/beitman/abpr/HCLin_Quasi-Compl-Amp_Elec-1956-9134.pdf
http://techpreservation.dyndns.org/beitman/abpr/HCLin_Quasi-Compl-Amp_Elec-1956-9134.pdf
Clearly ON we're not moving the volumes needed to maintain the product. Might also be they needed to move fabs or assembly centre and the cost of re-qualifying was not justified.
In any event, I am pleased I stuck it out with my SOT23 temp sense and thermistor. The bias stability is very good.
Thanks for sharing. I don't think this is the blameless type circuit, but nevertheless, I think it is of historical importance. Kind of also makes one realize how far things have progressed in the last 50 or 60 years.
Hi Bonsai,
Have you published any details on your SOT23 temp sensor? How was it mounted in thermal contact with the relevant semiconductors?
Thanks,
Ian
I am sometimes fascinated by the vast philosophical differences between valve and solid state designers. For example:
Conventional wisdom in solid-state land
"It's important to incorporate effective protection circuitry to prevent the output devices being damaged when the amplifier's output is short circuited."
Conventional wisdom in valve-amp land
"WTF kind of moron short circuits the output of their amplifier?"
Seriously. The bottle-heads spend how much on their 300Bs and suchlike, but would never dream of adding any protection circuitry to keep their investment safe from accidental abuse. Meanwhile the solid state guys can't sleep nights for worrying about the health of their output transistors, most of which cost less than a decent cup of coffee.
Yes, I know tubes are a lot more rugged, but they're not invincible. Heck, some valve amps will self-destruct just because you switched on the power with no speakers connected.
WowI believe the real future will be developing the DSP technology to the point of being able to completely deconstruct any archival musical material -- Lexicon were going great guns on this, but stuffed up and the project was aborted -- effectively separating all the strands into as many tracks as seems reasonable. Then, just reassemble as suits the individual, feed into as many speakers as you like, remix all the classic albums into a version that sounds good to you. Everyone can become a studio recording engineer, able to play with the virtual microphone feeds to their heart's content ...
tubes cannot deliver more current then the cathode can emit....
while BJTs in theory are limited by the sky ( in mundane territory junction temperature) and strange enough tubes are also limited by temperature
of the anode plate. When the anode gets hotter than the cathode game over.
In practice the output transformer gets saturated and that is the protection circuit.
Surely the essence of the 1975 Middlebrook technique is that it accounts for the impedance at the test point with 2 measurements and not just a Vsource? This use does not do him justice.
The Middlebrook "final solution" seems identical in its loop/feedback element model to the Tian probe. It differs in its incorporation of a direct transmission element past the feedback loop that modifies the closed loop response but not the return ratio(loop gain). At least, that's what I understand so far, lots to study there.
Best wishes
David