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Dynaco Stereo 35 replacement output transformers

Obviously there's a range of operation from class A to class B and a circuit can fall anywhere on that range. It's interesting that with perfectly linear devices, the only truly linear modes would be class A and class B - because AB would have a step change in the waveform slope at the transition to cutoff. (one tube stops contributing). As described earlier, the increase of transconductance with current (and the cathode's ability to conduct more than twice the idle current) greatly reduces this effect, typically resulting in a distortion null at a relatively high power. And of course, negative feedback reduces distortion further.

Real circuits can have other issues, with bias point shifting with a sagging power supply, and course the real-life loadline is not the one you drew on the graph, with circuit parasitics and varying speaker impedance. The problem components are the ones that aren't on the schematic - Miller capacitance, the limited inductance of the output transformer and its leakage inductance, stray capacitance and lead inductance that can give noise coupling and unwanted positive feedback. And that damn loudspeaker that refuses to be an 8 Ohm resistor!
 
I'm sorry, but referring to this as the "Class A region" is simply the lazy man's way of avoiding less appealing - but technically correct - rhetoric. It's a small region above cutoff, nothing more. I don't often object to the liberties people take with terminology, but this is different. Referring to this as the "Class A region" assigns characteristics that it doesn't deliver. Further, attempting to justify this shortcut through comparisons to poorly designed amplifiers or fringe topologies is ludicrous. It's a contrived phrase intended to convey meaning in a manner that dumbs down the entire concept of amplifier classifications. It's flawed, it's incorrect, and it's unworthy of the otherwise competent and technical members of this forum.

Jack
 
RMS watts are just watts calculated from RMS volts. As opposed to peak watts, which are calculated from peak volts.

TriodeLuvr said:
simply the lazy man's way of avoiding less appealing - but technically correct - rhetoric.
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this is an accurate description. I'm not concerned with being absolutely technically correct, just having enough of a working understanding to make things work without investing more effort than is needed to get to that point. I'm not writing a doctorate thesis here, just puttering with obsolete broken amplifiers and trying to help other people fix their broken stuff.

Tom Bavis said:
Transconductance (output current vs. input voltage) is not constant over the signal swing. (you see this as unequal spacing of plate curves) This creates 2nd order distortion... but in push pull, it cancels - as one tube decreases in transconductance, the other increases, so the sum is closer to the input signal than either alone .
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and this is also likely the technical reason why shared cathode resistors produce better results than individual ones in this sort of amplifier.
 
Would like to see updates from people who have tried the different Dynaco st35 output transformers available. I just received an amp that has the dynakit parts output transformers but stock pt. It was damaged in shipping so I’ll have to rebuild it and it has the dynakit parts bias board so I’ll retain that. And how do the updated transformers compare to original in terms of sound and performance?
 
pjrengineer said:
Would like to see updates from people who have tried the different Dynaco st35 output transformers available. I just received an amp that has the dynakit parts output transformers but stock pt. It was damaged in shipping so I’ll have to rebuild it and it has the dynakit parts bias board so I’ll retain that. And how do the updated transformers compare to original in terms of sound and performance?
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I To would like to know if there is a suitable st35 replacement >I have never seen a definitive answer about Musical supplies output transformer.Or any other offerings >Im wanting to upgrade my magnavox and would buy the musical supplies one right now if I knew it was a decent sounding replacement .Will someone Please post a response if they have used this opt .Thank you
 
Yes, it would be good to get the updated experience of people who had tried and listened to them in the Dynaco ST35 circuit, or thoroughly tested the output transformer Z565 clones vended by Musical Power Supply. Or others of the “modern” Z565 replacements.

I believe @nerdorama had plans to perform some testing on the MPS Z565 clones. I have not seen mention of it; did you get around to it?
 
I bought a pair but haven't used or tested them yet. If I remember correctly, it says on the MPS web site that Dave Gillespie had helped with some testing during his trials so I hope this bodes well for these transformers. I have several projects in mind that could use these but I won't be cloning a Dynaco.
 
Thanks for your reply and update. I hope you are right about the good omen of Dave’s involvement. I am looking forward to hearing the results of your testing of these MPS clone Z565 transformer when you get to it, since I lack the instruments and ability to test them myself. I guess there are several other potential users in the same boat.
 
If doing a magnavox I hope you are taking advantage of Dave’s circuits as well. They transformed my magnavox and I don’t need new output transformers now.
 
@pjrengineer, glad to hear about your positive experience with your Magnavox that didn’t need new outputs afterall. I am a believer in Dave’s mods and EFB.

In my case I used the OEM Z565 transformers from my SCA35 in the building of a brand new ST35 using Dave’s PCBs, new power transformer, new chassis, cage, etc. Now I am looking for replacement transformers that will fit the SCA35 to restore it to good function.
 
I have a pair and confirmed they will fit the SCA35 perfectly. Other than the PVC leads they are identical to the “real Z565s” in appearance and physical measurements.
 
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Has anyone used any of their other transformers? Need to grab the measuring stick and confirm but I believe they have a 6.6k transformer that fits the space I need it to fit for a 6L6 amp I'd like to build.
 
gadget73 said:
Has anyone used any of their other transformers? Need to grab the measuring stick and confirm but I believe they have a 6.6k transformer that fits the space I need it to fit for a 6L6 amp I'd like to build.
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So far I've only used his SE outputs for 6V6 and GU50 amps. Both amps measure extremely well for FR and also for THD.
 
spantou01 said:
@pjrengineer, glad to hear about your positive experience with your Magnavox that didn’t need new outputs afterall. I am a believer in Dave’s mods and EFB.

In my case I used the OEM Z565 transformers from my SCA35 in the building of a brand new ST35 using Dave’s PCBs, new power transformer, new chassis, cage, etc. Now I am looking for replacement transformers that will fit the SCA35 to restore it to good function.
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What new PT did you use? Dynakitparts is, sadly, still not showing these available. I have a set of Dave’s boards completed for a second ST 35 build and was looking for PT options - considering trying the MPS OPTs in this one although the Thermionic Lab ones get limited but positive comments - just hoping for easier delivery
 
It is a problem and I’m sorry I have no better advice. For my ST35 power transformer I will install a “NOS” replica transformer I bought from Triode, USA years ago when they still sold them. (I think it used to be called Triode Electric, when “Uncle Ned” operated it).
 
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