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About trobbins

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  1. Addicted to music, As you can see from the recent photo you posted, the earth bar is where the protective earths are distributed from. There is only one local connection between earth and neutral bar. The neutral bars are nowadays typically segmented to allow earth leakage detection on certain load circuits, but not on others. AS3000 is and has been the reference for sparkies to work from. Caution is needed when posting on AC circuits, as non-competent people may assume that posted advise is accurate and safe and according to regulations.
  2. Can you please correct your diagram - protective earth distribution won't come from the main neutral bar.
  3. Toby, It's unlikely to be too different in the main part of the amp, and quite likely to be related to a different input source, or someone's idea of 'an improvement'. If you mark up the schematic, showing the differences then it should be relatively easy to work through what is happening. Perhaps if you don't work from the component labels on the tag board, and just work from a schematic - as the tag board labels are obviously not correct. Given its age, you would be well served to do a thorough restoration and to add some protection parts in, if you have done that before? Ciao, Tim
  4. Sounds fine then - a good outcome. It's not your neighbours fault. They are allowed to generate, as the utility has allowed them. It's just a paradigm shift over the last decade from domestic houses being only power sinks. Luckily, most well made and designed valve audio equipment have primary voltage taps, and valves are very tolerant of operating levels.
  5. Australia standardised for 230VAC decades ago - previously the utilities were required to meet 240VAC +6% distribution. Domestic PV installations are the typical reason you are observing voltages approaching 240V + 10%. Utilities are typically restricting new PV installations when capacity is sufficient to raise line voltage above +10%. You could complain to your electricity supplier, and say that you have equipment that is only rated to 230V+10% = 253V, and so put pressure on them to modify the distribution voltage down one notch. You could also ask them to state what their formal distribution voltage range is (they may formally state that they operate to 240VAC + 10%), and what their policy is when distribution voltage exceeds that range. As suggested, the heater voltage in a valve pre/amp is the key issue, as it should not exceed 6.3V + 10% = 6.9VAC for reliable and stress-free operation.
  6. Another perspective is how little amplifier power can one get by with for acceptable listening. If the start was a 90dB/W/m flat response speaker (not yet going in to the multiple speaker aspect, as the THX reference indicates levels are set for individual channels), then a typical reduction for seating position in a domestic location is circa 10dB, and a 16W max continuous (before clipping) amp would reach 92dB. If one was fine with 80dB average listening SPL, and perceived that 12dB peak-to-average was pretty good for general audio sources, then circa 15W amplifier channels is a somewhat fair compromise. That would then raise the issue of whether source material can be nicely limited, whenever that was transiently required, so as to co-ordinate with the amplifier rapid rise in clipping distortion. It would also relate to speakers that were more optimised for higher efficiency, flat response, than for peak SPL (where growing distortion and compression possibly gets clouded by the ear's inherent distortion and compression and lack of appreciation of detail).
  7. No and yes. No, the valve itself won't degrade due to minor vibration. Yes, you will use the valve rather than resign it to the spares bin. Vibration could be from within your amp (eg. from power transformer), or from the speakers, or the tram passing by, or ....
  8. Can you recall what testing on a tester you did when tube rolling? And did that extend to checking the default test amplifier for valve operating bias voltages, and distortion levels with resistor loading, and noise floor levels for microphonics when passing loud levels to the speakers ? I guess without those extra measurements then the story of how the different tubes may sound could be clouded in uncertainty.
  9. Subjective comments are fraught with uneven playing grounds. It's often best to at least pass any tube-rolled part through a valve tester, or to make at least some basic measurements in circuit, to confirm that each and every valve tried is nominal for starters, and doesn't surreptitiously have substantially mismatched halves, or move the operating point in the circuit far from nominal, or show abnormal distortion levels. Some insight in to the operating circuit would also help, but that wasn't provided by soundfan for his comparisons. If one assumed that the operation did not cause large voltage swings on the 6SN7 (as per a driver stage to a power amplifier), then a nominal vintage 6SN7 would be introducing <<0.1% THD, and so it would be technically suspicious that valve comparisons would be audibly detectable. The other major uncertainty that is usually intangible is the level of microphonic output when doing a listening test. I can't imagine that many have checked their set up for microphonic influence, where they have specifically looked at a spectrum analyser response of the output signal at highish listening level as input signal is swept through the audible spectrum.
  10. It appears that the cause of the mechanical hum hasn't properly been resolved, although the Tortech path has led to a solution. A higher mains voltage may well be the cause - as that would lead to a mains current waveform with increasing peaks, and a higher rms current level and higher levels of harmonics, which can exhibit as transformer mechanical stress and humming. Using a spectrum analyser app on an android phone can provide 'detail' on such an audible hum. Borrowing a beefy single-phase variac, and using one of those piggy-back cheapo mains voltage/current/watt meters can be a simple means to confirm that increasing mains voltage level from say 230V to 250V causes the change in audible hum. There is no information to say that the power transformer is a toroid type and susceptible to dc disturbance on the mains. The suggestion of using a dc blocker would be a means to confirm that. The Tortech test may have alleviated either/both of the above. One other possibility, as we don't know the internal circuitry, is that the amplifier is loading the power supply excessively as mains voltage increases. The result may be indistinguishable from that of a power transformer starting to experience saturation, and would need a current probe/oscilloscope to assess the waveform shape.
  11. The 6X5 could be arcing inside under certain conditions - that could be contributing to fuse blowing and audible noise and higher dissipation in the tube and hence base cracking. Do you have ss diodes in series with each valve diode anode?
  12. There are some good semi-technical summaries of how to choose a SUT. The link below is worth a read. Unfortunately the best outcome does require 'tuning' of the SUT output, with a snubber network usually required to ensure minimal ringing. Similar to an oscilloscope probe needing its compensation adjusted to get a good square wave, or a power transformer secondary winding optimally snubbed using a quasimodo type tester. That test situation is probably the nub of why so many observe such a wide difference in performance when they simply just connect a SUT and think it should perform perfectly 'out of the box'. You may also be able to find a vintage microphone transformer for a couple of dollars that also suits an MC SUT. That may appear a little aesthetically displeasing, but the performance of some would I suggest be very good indeed, and they were very well made. For example a commonly found mic transformer is from Zephyr (who advertised in RTV&H) with 50 and 350 ohm inputs, and 42k output - the 350 ohm input provides an excellent 11:1 turns ratio. The PA amp manufacturers also used stock mic transformers - STC had a CL5244-2 with the same spec as that Zephyr. Some mic transformers used a higher turns ratio - AWA used octal valve holder mounted transformers such as 1TW14012 - although its 18:1 ratio would really only suit lower output carts.
  13. In England in the mid-1950's, HMV had the flagship model 3000 range radiograms - they included a standard Williamson amp.
  14. One aspect to note is that distortion of the peak part of a signal waveform (ie. furthest excursion from the bias point) increases as the signal approaches the voltage rail limits, especially the zero current region in SE and in PP (for one side going in to cutoff). A pure class A would normally operate well away from cutoff region, whereas a PP transitions through that region as the 'class A' max level is reached. So in general the load line operation is optimised to be in quite different regions for amps designed just for class A compared to amps designed for class AB where there is an initial portion of operation in class A.
  15. Lining the port or adding absorption near the internal mouth may have a benefit in alleviating any pipe self resononant effects, especially if the tube is large enough to not exhibit airflow issues, but has a self resonance low enough to be in the speaker operating bandwidth.