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  1. Bauhausler

    Not around here much any more. Traveling 200 days/year. Drop in when work allows.

    Not around here much any more. Traveling 200 days/year. Drop in when work allows.
  2. Bauhausler

    6DJ8/ECC88 Transconductance measurements on Hickok tester

    Agreed that Gm varies with A-K voltage and current. That's true with all tubes. So the chart on the tester should indicate what transconductance should be 100% for the test conditions applied by the tester. But for every other new small signal triode I get the specified target Gm with the...
  3. Bauhausler

    6DJ8/ECC88 Transconductance measurements on Hickok tester

    So it might be oscillation that causes the Gm measurement to be off. i usually don't work with high Gm tubes, but I'm sorting 6DJ8s to make a White cathode Follower OTL headphone amp. I could make up a 9-pin plug/socket adapter, but I have never used ferrites. Any references for where to buy...
  4. Bauhausler

    6DJ8/ECC88 Transconductance measurements on Hickok tester

    Thanks. That makes a lot of sense. When I test high value tubes like a batch of MOV KT88 I make up my own test rig so I can measure bias voltage, Gm, etc. But I've had pretty good luck with all other 9-pin dual triodes on this tester. I'll look into it some more.
  5. Bauhausler

    6DJ8/ECC88 Transconductance measurements on Hickok tester

    Inaccurate roll chart data was my first thought. I know people have documented errors in Hickok settings before. Probably the Bias knob setting is wrong. If I discover there's a mistake I'll post here.
  6. Bauhausler

    Headphone Dilemma with tube system

    If you want to go full DIY this thing I designed for Make Magazine sounds good. http://makezine.com/projects/bass-bump-headphone-amp/ To run it from a line input rather than from a lower impedance source change R8 from 100 Ohms to about 5K.
  7. Bauhausler

    6DJ8/ECC88 Transconductance measurements on Hickok tester

    Maybe someone knows the answer to this. I use a Hickok 533A tester. I believe it's pretty accurate because new tubes always test near the target transconductance. That's for small signal triodes and power tubes. But I always get out of range readings for 6DJ8/ECC88 tubes. The tester says...
  8. Bauhausler

    Schematic bleg: Knight KA-55

    Cleared out, all the way back to 2006.
  9. Bauhausler

    Heathkit W-5M First Tube Amp Rebuild

    It's important that those 330 Ohm cathode resistors be matched within 1%. The actual power dissipation there is 0.045A^2 X 330 = 660mw each, so a 7W part is way overkill. Probably chosen for stability rather than dissipation. I had one broken one so I subbed in matched 330 Ohm 3W metal films...
  10. Bauhausler

    Heathkit W-5M First Tube Amp Rebuild

    Thanks, Doug. Your word carries a lot of weight with me because you're an engineer and you measure things. $12 is pretty cheap for a quality 6L6 type. Before I used any of these in an amp I'd run each sample up to maybe 450V/50ma cathode current and monitor the G2 current. Any units with...
  11. Bauhausler

    Heathkit W-5M First Tube Amp Rebuild

    Yes, I read about them. The 6BG6GA swap has been around for over 10 years. As I said, these particular tubes may be fine at higher voltages and powers. But as much as possible I prefer to run things within manufacturers' specs when expensive transformers are at risk. I recognize that actual...
  12. Bauhausler

    Heathkit W-5M First Tube Amp Rebuild

    If you're concerned about long term reliability another thing to consider is the line voltage. A lot of gear designed 50 years ago assumed a nominal line voltage of 115VAC or lower. Today many places have line voltage 120VAC or higher. This could result in higher power dissipation in the...
  13. Bauhausler

    Schematic bleg: Knight KA-55

    Thanks, I found it on the SAMS page and will purchase the download. I don't know when I will get to these amps. I have literally dozens of restorable tube amps and receivers and have to be fussy about which one I tackle first.
  14. Bauhausler

    Heathkit W-5M First Tube Amp Rebuild

    SND is selling Philips 6BG6GA tubes as 6L6GC/7027 replacements. Like a lot of TV tubes, this tube has a screen voltage rating (Philips spec) of 350V. In the W-5M the screen voltage will be 450V. Also the plate power diss rating is 20W rather than 25W for original 6L6GC and KT-66. Technically...
  15. Bauhausler

    Schematic bleg: Knight KA-55

    I have 2 of these in great cosmetic condition that need some work. The PCBs are hard to figure out so I need the schematic. Does anyone know of a source? Thanx Bau
  16. Bauhausler

    Heathkit W-5M First Tube Amp Rebuild

    The PT secondary is 900v CT so to load that at 100ma you'll need a resistor of 8000 - 10,000 Ohms with dissipation rating of around 100w. I use cheap aluminum bodied 50w power resistors bolted to heat sinks from dead SS receivers and wire them in series with clipleads to get the value I need...
  17. Bauhausler

    Stupid question: setting AR XA stylus overhang

    I find alignment pretty simple for an excellent elliptical like the Shure M91ED. Grado's too. I bought a M91ED a few years ago and really wanted to love it. Tried several combinations of loading, and higher R/lower C seemed best. But that cart just seems to have a greyness overlaying the...
  18. Bauhausler

    Stupid question: setting AR XA stylus overhang

    Maybe damping, though the Mayware Formula 4, if that's the one you're referring to, has fluid damping at the pivot. I haven't looked into the mechanics of the AR arm pivot but I think there's some damping via lubricant viscosity going on there. My experience with Grados is that they act...
  19. Bauhausler

    Stupid question: setting AR XA stylus overhang

    But I will have to look into one of those auto lifts. This table is so quiet it's quite easy to fall asleep to sometimes. I use the Pahmer Q-up on two of my manual 'tables. It's a breeze to set up and works faultlessly. About $60 directly from Pahmer or through eBay. I worked out a way to...
  20. Bauhausler

    Stupid question: setting AR XA stylus overhang

    Well, you're right about basic setup being pretty simple. When this table was new styli were conical or maybe a simple elliptical. Those are pretty tolerant of overhang and angle, and don't benefit from higher precision in alignment. But when you get to more complex tip shapes like a line...
  21. Bauhausler

    Stupid question: setting AR XA stylus overhang

    When I fix the headshell leads and get a cart installed in it I'll line it up to the overhang gauge that I have (with the cart centered on the headshell screw posts as much as possible to duplicate the intended angle), then check the angle against the arc template to see if it matches. This...
  22. Bauhausler

    Stupid question: setting AR XA stylus overhang

    But this is important. Because the stakes are so low!
  23. Bauhausler

    Stupid question: setting AR XA stylus overhang

    They could have changed the bend angle of the arm tube, but if not, to be perfectly scrupulous they'd have to change the position of one screw post in the headshell to conform to the new offset angle dictated by the overhang change. That would mean that not all AR headshells that look identical...
  24. Bauhausler

    Stupid question: setting AR XA stylus overhang

    Looks like the one pictured with these differences; Is not yellowish Does not have printing '15MM' Hole is visibly nearer to the lettering 'SPINDLE', which correlates with the measurement that I get. This overhang gauge and the plastic stylus force balance came in the turntable box and I...
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