The Amp Garage

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...

As RG indicates, adding a fuse is not a straight-forward task, and I'd suggest is quite a technical effort to appreciate what faults can be protected against and how the added fuse would respond. If you've had to replace PT's, then there may be incentive to do such a technical assessment when adding...

This is delving into hazardous testing, which you may not have done before, in which case imho you should work with a competent person to raise your experience. The commonly used technique is to insert a 1kΩ resistor in series with the filter cap and clipping a handheld multimeter across the resisto...

Measure the leakage at rated DCV. Measure the ESR. Measure the capacitance. Look for deformities. Fairly simple, but it takes time. It can be done by lifting one leg with care, and can be done using the amp's power supply when you have a variac and use a series resistor for current sensing.

If you notice some hum/ripple getting through the SE amp to your speakers then one way to suppress B+ ripple is to parallel a 'tuned' capacitor across the choke to form a ripple trap. The parallel LC forms a brick wall for 2nd harmonic to mains frequency, which is the major ripple component.

Yes that is a reasonably well known power supply 'technique'. The other advantage of that input capacitor is that it alleviates solid-state diode switching noise by lowering dV/dt at that node. Perhaps better to use UF4007, instead of 1N4007, for that application too. Not such an issue with valve re...

I'd also suggest the polarity of the 10uF 50V ecap in series with the coring diodes is showing the wrong polarity.

I find it strange that some happily measure and set output stage tube currents etc to better than 5-10% accuracy, and spend many $$ on tubes, but don't take the time to measure mains ac current at idle, and when cranked, for their nominal mains AC voltage, and then buy and use an appropriately value...