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EMRR's Achievements

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  1. The triode would have to account for Miller effect, the pentode, not. That's why you see it in many broadcast amps.
  2. Yep there's a GE regulated power supply that started as 6B4G pass tubes, switched to 6Y6 with no other changes.
  3. The bolts are from the horn side. If you mount the horn on the front you can’t get to the bolt holes to put the driver back
  4. The mounting bolts for driver/horn are inaccessible unless the top panel is off the La Scala. You could mount while assembling a cabinet easily.
  5. I've had the same GZ34 in a 1966 Fender guitar amp since I got it in the mid-80's, still going strong. It may be the original tube for all I know.
  6. EMRR

    Bob Crites RIP

    RIP. Glad I had at least one phone conversation about some crossover design questions. Very straight no nonsense answers. Thanks Bob!
  7. I ran the LSR28P powered versions for years, great speakers.
  8. I do a fair amount of restoration and modification work on old broadcast tube gear, many of which require experimentation and making of response measurements while live. Things with outputs up to 10W. That's never bitten me. Go slow and don't touch anything until you've thoroughly assessed all the Murphy's waiting to strike. Tube gear should have bleeder resistors built into the power supply, they should be a balance between minimal current draw impact in of themselves when powered on, and reasonably rapid bleed down of high voltage once turned off. Once bled down, they also prevent any memory voltage from rising, as is possible in an amp lacking a bleeder. Almost all the old pro broadcast gear I work on is this way, and voltage measurement confirms a lack of stored voltage within a pretty short period of time. Safe to work on! I also own an Ampeg V4B bass amplifier (four 6L6 type amp, 100W) I've had to work on several times. Higher voltage (700ish?) and much higher current. That's bit me before, even following the one hand rule. Extremely painful. High power amps are an entirely different matter. But, if you're only working on the preamp section of that amp, voltages and currents are much lower, might startle you but that's it. Think about WHERE in a circuit the highest current draw potential is, keep it foremost in your mind I have a Hewlett-Packard 300V power supply that actually frightens me: 1.5A current capacity. Have never seen a need to turn that (arc-welder) on. Not sure what possessed me to acquire it!
  9. The only time I have seen a measurable audio difference in a film coupling cap was a case of an 80 year old cap in radio broadcast gear that had been powered on at least 50 years. ESR was high, like 80 ohms, and there was an obvious loss of treble because of it. Otherwise, I hear things that seem different, I may measure semi-inconsequential ESR differences, but I've not seen an audio response difference. I've measured plenty of high ESR that don't have response differences, and sound fine, all in high impedance tube circuits. Have I measured distortion between various caps in the same type circuit? Multiple types of circuits? Apples to apples? No, there's not enough time in the day for that rabbit hole. Maybe if I aspired to be a cap salesman!
  10. The slow trickle charge idea at least is relevant, like batteries. I have Western Electric collector friends who insist on re-forming 80+ year old electrolytic filter caps, apparently very very slowly (weeks) with much success. Not for me though.
  11. I have some RCA broadcast push-pull-parallel 45 amps I hope to get across the restoration finish line before much longer. They claimed "25W peak without objectionable distortion", seems wishful thinking! Particularly with modern full range speakers. At least the La Scala will barely need a thing from them.
  12. EMRR

    Dhl did it

    You have to wonder. It would seem with the JBL's they went for performance over durability. How much does any company do towards durability in shipping for audio electronics? I'd guess not much until there's a problem trend.
  13. EMRR

    Dhl did it

    Not true, but you need those little devices that register impact force in the box to prove it. Any void inside anything with heavy parts is space which allows parts to move internally when impact occurs, and you have to expect 6 foot box drops, which may land perfectly on one side of a box with no signs showing. All the vintage audio I sell gets panels removed and insides stuffed with bubble wrap, with instructions for removing it once received. Otherwise transformers shear off their mounts, or distort chassis, or speakers look like the above. Sometimes there's nothing you can do; I purchased JBL LSR28P speakers new years ago, and it took 3 shipments from the factory to get an undamaged pair at my door. The first two attempts had perfect looking factory sealed boxes, and the tweeters were mangled from impact force.
  14. My benchmark experience was in restoring three RCA broadcast consoles, needing 24 total 12AY7 tubes, 6 in high gain positions needing lowest noise. I did 40 hour burn-in of about 36 tubes using the lower gain preamp channels, because they were multiples of the same circuit, and another reason I'll come back to. I then made noise measurements of the lots and marked the boxes. I found an overall noise variation of about 20db, and these were all new tubes from the same lot. Most fell in the same tighter window, about 6dB variation. The 6 quietest went in the high gain channels, the next best into the low gain channels, at which point they beat the noise spec in the manual by several dB. Back to the burn-in. On the first 2 passes I also put tubes in the high gain channels, which draw much higher current. I found those tubes were much noisier after burn-in, and no other position changed their noise level. It seemed to be a permanent effect of the burn-in conditions. Had I just loaded new tubes and gone for it without taking measurements, noise would have been worse than spec. For most people, finding a tube dealer who does reliable and applicable audio noise tests on tubes is worth the extra cost. Unless you have a burn-in bank of some sort, you'll spend forever rolling the dice. On trying other tube types with different gain levels, remember lower gain does not mean lower noise. It may seem lower noise because there's less gain amplifying the front end noise. That may serve the purpose, but it's apples to oranges. If you want to be sure of preamp noise, short the input. If the noise goes away, it's coming from the source, not the preamp.
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