Marvel

Jim, You can't fool me. That's a Japanese fellow at home with his horns. How about these Goldmund Apologues?

I was seriously interested in their ST70 amp. Mostly because of my real ST-70 I suppose. Erik, I know that Shawn has a current limiter in his spec for his DIY 35 amp, but it has a solid state PS. He also had comments on his forums about the use if a switch on the center tap being dangerous. Maybe because of the ss power supply. Here are a couple of ways to get around the spike they were having (from the DIY tube forum - I make no claim to these ideas): 1. I tried wiring the 1M resistor across the standby switch today. So far, so good. I do not have a scope so I wouldn't see any really fast transients, but what I do see - is that the voltage at B+ rises from 0 to 6V in about 15 seconds after power switch is turned on and stays there. Each leg of the transformer secodary measured to ground is about 340 VAC - the ground reference is there. 2. Cathode Switching The most common "new" stand-by method is called "cathode switching". This is simply a ground-interrupt switch in series with the cathode circuit of the output stage. To reduce the switch transient, and more importantly, to avoid the risk of cathode stripping, a resistance is wired across the switch contact. Any value from 4K7-2W to 10K-2W is suitable. This is equally applicable to both cathode bias and fixed bias amplifiers, with any type of output tube. O'Connor, K. 1996 Principles of Power.Power Press Publishing. p3-25. Later, Bruce

That would depend on your sound card. If it is an SB, they are notoriously fragile. A bummer anyway. I had to feed my soundcard (one of them anyway) into a line level mixer, just to buffer it to feed the inputs on my ST-70. Otherwise it sounded awful. Bruce

How much for the Ives? Am I on the right track or am I just loco? [] I think I sold all my Ampex gear.

I agree. You wouldn't know he's a Phd. would you? Although, Jeff does a good job too. [] Bruce

Picky, A decent used tube pre should work well with the NAD 2200. And a tube pre would require almost zero upkeep, where you would have to keep an eye on a tube power section. Sorta. I don't pay much attention to the ST-70, but I do check it now and then. Also, I think the HIIs listed around $1100 U.S. Bruce

I have gathered different material over the past couple of years, and wanted to pass this one on. It was written by a PhD guy, who is working in digital high tech stuff, but who also works on tube equipment designs. He has the attached pdf on his website, so I don't feel awkward about posting it. Please note that he works more on guitar amps, but this is still very useful. He had a company called Engineering Musician Design, but it is defunct as he has moved on to other work. I have some other material he published where he was stepping through the design of a guitar amp, a section at a time. His current site is here: http://www.eecs.umich.edu/~mmccorq/ This and another tube paper are listed under research. Hope some of you may find it useful. Bruce Intro_to_tubes.pdf

He should send them to me. They would go great with my Merlin I'm sure.

D-Man, For a while Sound Valves had the surplus parts for the Dynacos. Then they rolled their own. Their ST-70 was a nice looking amp, and not too highly priced. But they are now defunct. Bruce

Never get rid of amps. You are just supposed to get more! []

I can't believe how huge those output transformers are on the SA100. Those are all sweet looking pieces of gear. Bruce

Jon, I understand your concern with upping the wattage rating on the resistors. The problem is the originals are too small so they tend to break down quicker over time. Replacing them shouldn't be too hard at all. If the traces on the board are still good, you can clean them off and replace the resistors as mentioned above, leaving the leads a bit longer so they mount away from the board. If there is room and you are careful, you could mount the resistors on a heatsink, to cool them even more. Believe me, it will work wonders. Bruce

Here's the pic. I forgot to scale it down.

I also used the Curcio under chassis ps board. I did replace the power tranny with one from Ned at Triode Electronics. The attached pic shows how massive it is compared to the original. Ned's is on the left, original on the right. It still gets pretty hot, but we have TVA power here and the voltage pretty much stays at 125 VAC. Bruce

tpg, So, does your mom understand now, that there was something wrong with it? Looks nice. His designs are great. Bruce

Craig can probably (make that definitely!) give you more info on the biasing of the KT88s. The plate current rating and the bias current aren't the same. The .02 mfd cap can stay the same value. The heaters on the KT88s pull a bit more current than the EL34. If you are using the original PS tranny, you may find it warms up even more than before. I would think it would be quite a stress on the PS to use KT88s. Whose upgrade driver board did you go with? I am tempted to replace the Curcio board I put in last spring, mostly to see what difference there would be. It sounds okay. Way better than the original, but there are better designs around. Bruce

Terry, Does that mean you aren't enjoying that little rascal yet? Sounds so sweet. Bruce

Many of them are made with a silicone rubber compound, which will resist the high heat of the tubes. I had one of the 7199s in my old Dynaco that would start to whine at me every so often. I would tweak the chassis and it would stop for another hour or so. But they were going on 25+ years. Bruce

skonopa, I do the same thing all the time. btw, I love the Wright designs. Bruce

Michael, It was the certainlywood website that I got the wood examples from for the 3D drawings. Just wanted to let you lnow I hadn't forgotten ya. The program acts up every once in awhile. I want to render a higher res image than the ones I had already done. Bruce

Anyway, my parents really love seeing Frank Lloyd Wright's Joseph and the Technicolor Dreamcoat. They have that DVD with Donnie Osmond playing Joseph. ... I think you mean Andrew Lloyd Webber. Frank Lloyd Wright designed houses. [] Bruce

Michael, I believe it would be possible, once the poly is off the wood, to steam out some of the Titebond II. Then again, you might end up havign to do the whole side again. Looks nice though. Bruce

D-Man, That second pic can be found on Bert Doppenberg's website. The purple horns are his, and the bottoms are one of the earlier Pi Speakers cabinets on their sides with the excess cut away. Other than the colors I find them pretty cool. They don't look that big until you compare them to the chair in the photo. If you go to his site and click on the showroom link you can see lots more with his horns. One guy is a dentist and has a pair in his office pointing at the patient's chair. The sweet spot! http://www.diy-systems.com/ Bruce

The lasers on older generation CD players actually tracked right on the surface of CDs. They were especially susceptible to skipping when the CD had the least amount of warping (or experienced external vibration, I guess). Not true. It had to do with the beam splitter technology. I worked on CD players. They all had a mechanism that when a CD was inserted, the lens would track up and down (towards and away from the disc) until it could focus the laser properly. It constantly tracked the disc that way. Some were just better than others. I just recently threw out the repair literature I used, or I would scan it and post it.

A Zobel is a series resistor-capacitor (R-C) network that is connected in parallel with a loudspeaker driver in order to neutralize the effects of the drivers voice coil inductance L(e). I found this on the web. Is that accurate, in a nutshell, the straight poop?