Do output transformers "saturate"

[Helmholtz]

I admit I purposely challenge people ...

Fine, but then you shouldn't have a short fuse when someone asks a critical technical question.

[Mike K]

Fine, but then you shouldn't have short fuse when someone asks a critical technical question.

I admit I was a bit miffed about you bickering with Greg about something that really had no practical use to the OP. I think it was obvious from my first response. You also continued to deter the notion of what I said without any evidence on the matter, despite some being given in the counter. That annoys me. I'm fine with admitting that. The method you have stuck in your head may be the most effective or efficient but it doesn't mean it's the only way.

[Chuck H]

I'll boldly claim that Teemu is propagating that same myth in his book by not clarifying. Why can you not accept that?


Listen, you're defending Teemu, not the idea. I'm attacking the idea which was propagated by said author - his name is only attached to said idea by authorship. If an author cannot claim responsibility for what is published, then they should not publish. End of story. I don't know how much experience you have with publishing technical papers, but you want to convey it a certain way. And you continue to do so.


I don't know Teemu, I didn't know he was a member of this forum, I have NO vested interest in his or discrediting anything but what I wrote.

Enough! In the work Teemu states:

“Hartley Peavey Whitepapers Chapter 3 – TransTube” acknowledges five characteristics, which are typical for tube amplifiers. These are output transformer’s saturation during overdrive (which causes bandwidth to change dynamically), bias drift during overdrive, asymmetric clipping in multiple gain stages, power supply sag and its effects as well as high output impedance and its effects.

Later he discusses how the circuit is implemented and mentions that it is imperfect in simulating actual output transformer saturation. At an earlier point he mentions that achieving output transformer saturation in a tube amp might require an OT rated for half of what it should be. Certainly he's not implying that guitar amps are commonly made that way.

Apparently you and I took something different from the reading. What I saw was a discussion of the TransTube circuit and how it works. Including considerations about it's failings. Nothing more. Are publications that detail medieval medical practices promoting leeching and the four humors?

You tried to pull back and imply you were questioning Peavey. Now that I made it so that was no longer a possible diversion you're trying to say the author of a discussion is promoting the work and questionable in his credibility and understanding by association?

What you SHOULD do is just say "OK. My bad. Didn't really mean it that way." and move the hell on. But you don't seem to have that ability. I don't know what sort of problems this mannerism has caused you elsewhere but I'm not going to let you bring those problems here. I'm out of patience now. This is not the sort of thing that should have to be explained ten ways. I honestly think you may enjoy being intentionally provocative and instigating offense and reactions to it. I'll be watching you for that behavior. That is my last word on it.

[Mike K]

I did not try to pull back and imply anything. I've questioned the effect which no one has yet to come up with an actual plausible explanation for except to say that I should somehow apologize for pointing it out. I'll apologize if it seemed like I put blame on someone who didn't deserve it, but it seems to me from reading that section of the book that it is simulating an actual effect, as I said multiple times, but you, Chuck, have said you don't care about but only want to focus on me and putting me in my place. You've 100% focused on that and have only had reactionary responses to any criticism of said author. I think maybe this paper should be peer reviewed before it is touted as proper learning tool, because as I see it, it contains misleading information.

I know you want to ban me, but I'll simply leave. I joined this forum out the fact that I truly did think it was purporting misinformation without any actual experience, and that made some people mad. And now again, I'm seeing the same thing and I'm being asked to grovel to keep my place.

[loudthud]

Output transformer saturation has been discussed here several times before and as I recall, it was dismissed as a myth.

There was an instance where a novice builder used a transformer intended for push pull operation in a single ended amp and had virtually no output. It was assumed that DC current saturated the push pull OT thus no output.

[Helmholtz]

The pdf is the first edition of Teemu's book.
Chances are that there's at least one newer, revised edition.
Maybe teemuk wants to clarify himself.

Generally I think the book is a treasure, giving a wealth of good information.
Still wondering why it's free.

[Mick Bailey]

The topology of the amplifier is possibly the main limiting factor in whether an OT would saturate. My synth will produce a 15v P-P output from ultrasonic down to a sub-1hz frequency (with the VCA DC coupled), but even with a tube keyboard or bass amp it's unlikely that a signal of low enough frequency and great enough amplitude would reach the output transformer to saturate it. Maybe of the OT was grossly under-specified and the circuit topology capable of reproducing the first octave there would be a clear audible effect. Mainly a guitar's lower frequency would be tamed to reduce mushy intermodulated notes in most amps by selecting appropriate coupling caps.

[Gregg]

After all those years I have yet to see a guitar amp OT that goes into saturation. In guitar amps under normal circumstances the OT does not saturate. It can saturate when fed very low frequencies which the guitar amp doesn't usually generate. Since this is not the case you won't see any saturation. On the video attached you can see how intentionally induced saturation looks like and when when it starts. Also note that this was a toroidal OT.

[DrGonz78]

The pdf is the first edition of Teemu's book.
Chances are that there's at least one newer, revised edition.
Maybe teemuk wants to clarify himself.

Generally I think the book is a treasure, giving a wealth of good information.
Still wondering why it's free.

It’s so easy to setup an Amazon account to publish your book. I will post my brother’s theory book on a separate thread. But today it’s much simpler to publish and these companies will print and ship the book quickly.

[teemuk]

I think I've posted to couple of OT saturation topics here, even posted some scopeshots. Personally, I'm not a "believer" in it. I mean, it does happen (occasionally) but the effects are actually rather detrimental introducing abrupt high order harmonics and the waveform looks like parts of it have been chopped off randomly. Generally it needs very high voltage and very low frequencies that just not are present in tube guitar amps. It's not an effect to seek after.

NFB in an amp might increase bandwidth of a poor OT in some designs and when NFB collapses during clipping the bandwidth reduces. This is not saturation of course.

Peavey "Saturation" is just a generic diode clipping circuit with generic frequency-selective gain control. I don't know why Hartley even brought up the OT saturation concept. Clearly the circuit does nothing to emulate such or even the imaginary idea of such that the Hartley whitepapers discuss.
Yes, "Saturation" circuit has a hi-pass effect implemented to the gain control, like virtually every other high gain distortion effect has a HPF. HPF is just "fixed" to the gain control and doesn't have any dynamic interaction with amplitude or frequency content like real saturation should have. It's just a generic distortion circuit.

[g1]

I think I've posted to couple of OT saturation topics here, even posted some scopeshots. Personally, I'm not a "believer" in it. I mean, it does happen (occasionally) but the effects are actually rather detrimental introducing abrupt high order harmonics and the waveform looks like parts of it have been chopped off randomly. Generally it needs very high voltage and very low frequencies that just not are present in tube guitar amps. It's not an effect to seek after.

I'm linking a few of the threads where this was discussed and you commented. I think they will give Mike K a better idea of your thoughts on the Peavey statements.
Some pictures are missing and there is a broken link, but I think they all refer to this page: https://www.turneraudio.com.au/SE-ou...ns-calc-3.html

https://music-electronics-forum.com/...mer-saturation
https://music-electronics-forum.com/...mer-saturation
https://music-electronics-forum.com/...-design/50025-

[Helmholtz]

Wow, what great and exciting discussions you had on the MEF in those days!
So sad I missed most of that.
Definitely should have joined way earlier, but was just to busy with my manager job.

[SoulFetish]

I'm with Helmholtz on this one. The book is a treasure.

[trobbins]

Somewhat related is an effort I made last year to force a PP output stage to effectively saturate the output transformer, as a way of demonstrating voltage transients on the primary winding and how to manage such over-voltage transients using a MOV. I started with an open-circuit secondary condition on the output transformer, and drove the quad 6L6GC output stage with a 30Hz squarewave for just 2 cycles, and captured the plate voltage and cathode current waveforms of one of the 6L6 on a storage scope. My concern wasn't per se to assess the OT core characteristic, but the simplified test conditions allow some assessment and awareness. A brief write-up and scope plots are presented on page 14 of the linked doc (link doesn't work so go to https://dalmura.com.au/static/Output...protection.pdf ).

Under these test conditions, at turn-on the plate rapidly swings the primary winding voltage to nearly B+ (ie. plate swings to nearly 0V), and then that primary winding voltage collapses (ie. plate returns to B+ level) as effective winding inductance collapses. The cathode current starts from zero and follows the 6L6 anode curves for Vgs=0 (and the given screen voltage) from effectively the 0,0 origin, rising to about 400mA and then falling somewhat after the plate voltage has rapidly collapsed.

It looks like I could have raised the test frequency to circa 60-70Hz and still achieved the conditions of collapse of primary winding voltage - and that situation may have made the over-voltage transient energy greater as the half-winding current would have been greater at the point of turn-off.

[Helmholtz]

Excellent contribution to topic!
Showing severe OT saturation at extreme conditions (low frequency, square wave, no load).

The cathode current starts from zero and follows the 6L6 anode curves for Vgs=0 (and the given screen voltage) from effectively the 0,0 origin, rising to about 400mA and then falling somewhat after the plate voltage has rapidly collapsed.

Wondering about the reason for the falling cathode current.
Maybe sagging screen supply?