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About JimL

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  1. The current through the bias trimpots is the sum of the currents through the two tube sections, which is determined in the stock amplifier by the plate output resistors, the positive voltage supply and the fact that the plate voltage (ideally) is 0 volts. Since the nominal positive voltage supply is +320 volts, and the summed plate output resistor is 66 kilohms, by Ohms law the current through each tube section has to be 325/66k = 4.85mA, so for two tube sections (per channel), the total current is 9.7mA. 10mA is close enough for calculation purposes.
  2. The required wattage for the bias trimpots can be calculated easily. For the trimpots, the current is approximately 10 mA (approximately 5 mA per tube section), and the resistance is 2 kilohms, so the maximum power through them is I*I*R = (.01)*(.01)*2k = 0.2 watts. Using the rule of thirds, this means that any trimpot that is rated at 0.6 watts or more is fine.
  3. The safety resistors are a good idea even without the CCS mod. The easiest place to put them is at the PCB board - just de-solder the wire going to the output socket at the PCB and interpose the safety resistor between the PCB hole and the wire. Agree with Pars and Fitz comments re electrolytic caps. Replacing 100 uf caps with 330 uf caps should be fine as long as they physically fit - that includes the lead spacing, since the power supply caps are right up against the PCB so the lead spacing has to be the same. The brand shouldn't make a significant difference in sound unless the
  4. No particular brand recommendations. It is safe to install a larger capacitance as long as the voltage and size specifications are maintained. Larger capacitance is similar to slightly stabilizing the power supply voltages and allows the circuit to work a bit better. The amp should be off long enough to discharge the power supply caps, which you can check by measuring the residual voltages on the power supply caps - as long as there are only a few volts left you are fine. Note that because of variations in the AC line voltage and heat drift, there is going to be some c
  5. As electrolytic caps age they have a gradual decrease in capacitance and an increase in series resistance, but it is unlikely that you can tell that by listening. At some point as it approaches its end of life, the risk of the capacitor shorting out will increase, but again until it happens I don't know of any way to determine exactly when it will happen. That's why I recommend just replacing them all as routine maintenance. Kind of like replacing the oil in your car at specified maintenance intervals. If you don't do this, you are risking a catastrophic failure if the capacitor shorts out. Be
  6. For the electrolytic caps, if they are original they should be replaced as they are nearing, if not at the end, of their life. The most important things are the voltage rating needs to be the same or higher than the originals, and the size and lead spacing has to be similar so they will fit in the space. The brand is not really important as long as the electrical and physical parameters are similar. In some cases (i.e. the four big power caps) you can find caps with higher capacity that will fit in the same space, which can be an upgrade. In terms of tube replacement, both Hirsch a
  7. Just saw this and went to the Bottlehead link in the first post. From what it says, it seems like the output stage uses plate resistors and 10mA/channal standing current. They do use their C4S CCS in the design, but apparently not in the output stage. I should point out that the SRM-T1 series uses plate resistors with 9.6mA/channel, and without the CCS mod is not very happy driving the SR-007s. I would expect similar problems with the Bottlehead amp.
  8. JimL

    Speaker Porn

    Does say something about residual value though, doesn't it?
  9. Surprised nobody has mentioned the liquid midrange and ribbeting bass.
  10. I'm impressed (eye-roll). I read all seven pages of the Warwick Acoustics brochure and didn't learn one useful thing about the design other than it is balanced, which I assume means that it has two stators like every other electrostatic driver other than the Sonoma One. The specifications didn't include power draw, voltage or current output, or sound output capability, although the bias voltage is impressively high,. The chassis is significantly larger than the Sonoma One so I assume it has greater current capacity but there are no visible heatsinks, so I very much doubt it has the current dri
  11. As I recall, HI-FI+ also raved about the Trilogy H1, which was basically an Egmont at a ridiculous price. Ignorance is not always bliss.
  12. Yes, I just checked, so does appear to be a scam. However, there was this completed listing on eBay: https://www.ebay.com/itm/Trilogy-H1-Energiser-With-Free-Stax-SR009-Headphones-Worth-3199-UK-Warranty-/184083907188?hash=item2adc418274%3Ag%3AnJYAAOSwHX9d4W3L&nma=true&si=B5Bq21v%2B%2B7bRiJlbkPbCND2CIOo%3D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557 Price was 3750GBP including SR009 "worth 3199GBP" so the seller was saying the amp is worth 550GBP.
  13. Well, this is interesting. On eBay right now is a Trilogy H1 plus SR-009 for a Buy It Now price of $3000. https://www.ebay.com/itm/Trilogy-H1-Energiser-With-Brand-New-Stax-SR009-Headphones-Exceptional/324103691049?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 Given that used SR-009s are going for around $2100-2300 on eBay (most recent completed transactions that actually were sold), this means the seller is willing to let a 5000 GBP amp go for $700-900. And he has >6000 transactions so appears to be legit.
  14. JimL

    Amplifier porn

    Yes, the joke at the time was the ultimate cheap Linn system was an LP12 into two strings attached to tin cans.
  15. So, a used HiFiMan Jade II amp in excellent condition (according to the seller) just went for $633 Canadian (approx $480 US) plus shipping on eBay. Given its list price as best I can determine from an internet search is $1599, the value is really holding up (NOT).
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