The Amp Garage

The feedback stage has a 470pF bypass on its 220k anode load, which would start rolling off gain above say 1kHz. The 2.2nF introduces a corner frequency at 22kHz, which is quite low. That seems to be too low to use to improve stability margin for one common compensation scheme where the network chan...

Yes tonally the amp may oscillate wildly and grossly depending on the speaker and leads used - its called unstable operation.

Thanks for taking the time to describe your experience :) Did your recent mods change the output stage in anyway that may have influenced the cathode fuse to nearly blow ? Did you have an input signal applied to the amp when you turned it on without a speaker load ? Normally the cathodes wouldn't ex...

One of the basic tests I do for any transformer I want to use, but don't know its origin, is for insulation resistance at say 1kVdc between windings, and between windings and core. That test is a quick form of 'hi-pot' test that would be done by a manufacturer prior to sale, and similar to a sparky'...

Did you match them into pairs at least for that price?

Given something like what you'd want would be quite niche, you could check with Scott to see if he has/would make a jig and gain unit for you. Ronald's uTracer has a distortion assessment tool which may get you the information you are after, but not for noise comparisons, and is a commercial partly ...

Perhaps well worthwhile looking through how Scott Reynolds has worked through that concept:
https://tavishdesign.com/

Mark, your first post indicated cat10 info, and that you recall doing calculations. That didn't sound like data, which is why I asked. There are a few academic/journal papers on the topic over the decades, but many require access. I recall another paper that went to measurement data on twist rate, b...

What data were you assessing to come to that view ?

Some refs on the topic:
https://dalmura.com.au/static/Predictin ... Cable.pdf
https://dalmura.com.au/static/Reduction ... twist.pdf

The chance of arcing is more common in single ended amps. I'd say an SE output stage is more prone too. The main reason is that there is no closely coupled half-primary winding (eg. with a PP OPT) to act as a local capacitance to soak up some of the energy that wants to instantaneously fly around. ...

Its just a ground for the first stage cathode. You can barely see the lugs of a terminal strip poking up above the chassis line where the RC for the cathode is mounted. Yes, but its not clear where that green wire goes to and if you have a single point chassis link somewhere, and how that relates t...

Did you power the heaters from a battery supply as an initial test item, to cross-check that the noise wasn't significantly ingressing by other pathways (such as B+ or ...). For heater related ingress of noise into the audio path, the method of dc elevating the heater AC supply only affects one tran...

Photo of pin 2-3 arc damage on ceramic socket in attached article on such protection issue.
https://dalmura.com.au/static/Output%20 ... ection.pdf

A quick PSUD2 assessment of a JTM45 with 350-0-350V secondary (effective 80R winding per side), with GZ34 into a 32uF filter with 5k simple load for 88mA continuous supply indicates a 250mA T IEC fuse in the CT link should have some margin to cope with a hot-start, and is operating at about 75% of c...