dsavitsk

They are definitely noisy, and the impedance is surprisingly high -- upward of 300 Ohms. Where I have had OK luck with them is fed by a CCS and used as a bias for a pass transistor like an IRF810 or something. In that case, the impedance does not matter as the current across them is constant. However, they really are all for show as a zener still works more reliably, is quieter, and can be bypassed without creating an oscillator.

In a single feed amp, the point of transformer loading a tube is that it increases efficiency. That is, the power supply voltage represents the midpoint of the tube's possible plate voltage as it can swing above and below this point. This is as opposed to a resistor load where the power supply represents the limit of the tube's swing. This makes sense to do in a speaker amp where you need to squeeze all the power out of a tube you can. For instance, a 300B loaded with a transformer can put out around 15W of power with a 350V supply. In order to do the same with a resistor load would require a power supply over 600V with considerable heat lost across the load. This efficiency benefit comes at a cost which is that single feed transformers are necessarily compromised in quality. They must be gapped to avoid saturation, they must be made from non-exotic materials to avoid bass loss (and saturation), the core needs to be larger and the wire thicker to accommodate the DC both of which lower the fidelity, and they require more windings (to generate the necessary inductance) which increases winding capacitance, increases impedance, and further hurts quality. In a speaker amp where fidelity is not as sensitive as with headphones, these tradeoffs may well be worth it to keep amplifiers reasonable. However, in a headphone amp, this hardly seems to be the case. The power needed is easy to generate, and while they may be wildly inefficient, even inefficient headphone amps don't really use that much electricity. The two primary ways* to transformer couple and avoid compromised single feed iron are via parafeed and with push-pull. Indeed, push-pull actually maintains most of the benefits of the lower more efficient power supply, corrects most of the issues with single feed transformers, and adds the benefit of dropping into class B when necessary. And they sound better, too. So my objection here would be that is it just another amp that is just a scaled down power amp rather than being designed with headphones in mind. All that aside, even within the single feed paradigm, the above referenced amp does everything pretty badly -- poor quality power supply, poor loading of the driver, poor quality biasing methods, showy but noisy regulator, etc. So even if you think single feed amps are better in some way, this one is just not that good. * Intact winds DHT transformers with an additional winding which uses the filament current to counteract the B+ DC.

x2 I miss Chicago.

Happy Birthday!

Happy Birthday!

Oh my goodness. Get better, Ken!

It is not so much that they are discontinued, as that they were not recontinued. The idea is the come up with a design that I like, make a small run, sell them, and move on to something else. There are so many circuits to explore that doing the same thing over and over is just not that interesting. For what it's worth, I just ordered a run of transformers from Cinemag that should be here some time in late January. Hopefully completed amps will follow not too long after that.

Happy Birthdays!

Happy Birthday!

The Torpedo and Crack will teach you wildly different soldering skills. If you see yourself building one-off tube amps using point to point techniques, the Bottlehead is a good starting point. If you want to do primarily PCB based projects, the Torpedo is better. It is probably a good idea to get one project under your belt before jumping into future ones. Different people learn differently -if you are a book learner, Art of Electronics is excellent. If you are a hands on learner, start soldering working on other people's projects, and trying to trace what's going on. It is how a lot of us got into this stuff.

Seemingly interesting but actually poor analysis. It is possible for headphone A to barely pass all categories and be rated A+, while headphone B passes 5 out of 9 with flying colors, barely misses on the other 4, and is rated an F. The cutoffs for each category are arbitrary, with no correlation to how sound is perceived, making this an example of why purely "objective" reviews are 1) subjective and 2) generally useless.

After trying Samsung and Sharp LEDs, we bought the 50" ST60 a couple of months ago. It is really nice. Definitely worth the ~$200 price premium.

Since other tubes work in the amp, build a test rig. You need a high voltage, a heater supply, and a couple of resistors to see if the tubes behave as expected elsewhere.

I assumed it was Iowa and Michigan or something -- the guy coming in from the right has different socks and a different helmet.

Happy Birthday!

And stop in Hartford to pick me up on the way?

Sorry to hear, Larry.

Indeed, we have made a half dozen or so changes that make the amp much quieter.

Happy Birthdays!

Indeed, sometimes a rat's nest amp will work better. Too neat often induces cross-talk from wires running in parallel while proper star grounding can look like a mess. PTP is great for one-offs and simple designs, but there are definitely places where a well designed PCB is superior.

I had one of those once -- Actually, I had an initial root canal where the resin did not fill the cavity completely and I got an infection in the end of it a year later. So they had to do another root canal through the first one. Required 3 3-hour sessions spread over 6 weeks to allow for swelling to recede. To make it worse, the initial root canal was through a crown, which had been put in place when a deep filling cracked. In the initial root canal, the dentist had to do that. At one point the numbness had completely worn off, and he accidentally touched something with the tip of the needle -- I think I jumped 3 feet out of the chair -- hands down the worst thing I have ever felt.

I'm curious how the networking works on yours. For us, with wireless it would not really connect at all (with 3 different APs, one of which is "enterprise class"), and wired, while it said it was connected to the local network, it would claim the connection to the internet failed repeatedly. Samsung claimed that this was evidence that the network was at fault, and not the TV. That seemed plausible, but the Roku worked fine, our computers worked fine, and AT&T spent hours looking for errors and could not find anything suspicious. I don't know that it baffles me, but I do kind of miss it. Useful for keeping a game on in the corner that I only sort of want to see.

Sounds like a job for VMWare ...

To update my stupid story, we bought a Samsung (6300 or something), and the only reason we chose it was that it had all the smart stuff we wanted built in (the usual stuff + HBOGo), which meant less clutter. But the networking never worked, either wireless or wired. After some delightful conversions with Samsung customer service, I sent it back. Truth is, it is a fine TV, and there was no real premium for the smart stuff, but I was just frustrated by it. So we went to BestBuy and the nicest looking LED in our price range that was not a Samsung was a Sharp. And, they had a Sharp dumb TV that was cheaper than the smart one we saw and that we thought was otherwise identical. We took it home, and really didn't like it. It turns out that it is not as nice as the smart one we saw in the store. So we took it back, too, and bought the Panny ST60. It is very nice -- way nicer than we need, so we are pretty happy with it.