tube fanatic

I like the SE sound and it is certainly a simpler design...the only gotcha is the power envelop....hard to get high WPC's using a SE approach unless you do what Cary does on their V12's and parallel's the SE's and drives them with el-84's. about your track record question....I have in my possession 3 Manley MB-350's which came out of a recording studio. They were in use every business day for the last 19 years. Each amp has 8 KT-90's. 350WPC capable but probally never really driven above 50WPC. Well one of the amps failed after 19 years and 1 power tube flamed out and took out two resistors and two capacitors. Tube life has many factors....how much you beat them towards their max WPC.....heat....high bias......excessive plate voltage....lack of soft start....etc You are absolutely right about the power limitations of SE designs and the factors which control tube life. I have always preferred that route for up to 10-12 watts out (easily obtainable with 2 tubes in parallel) after which I've had to go to p-p due to lack of availability of affordable output transformers which could handle the current. And then there's the issue of the size and weight of the single ended output transformers too. Some argue that the distortion of SE pentodes is way too high; but, that is easily managed/reduced with some negative feedback at the ouput stage. The resulting smoothness, to my ears, is unbeatable. Regarding the tube life, one of my favorite amps is a triode strapped Philips 6BG6GA which has a 30 watt plate dissipation (basically a 6L6GC which was packaged for horizontal output service in a TV). With 250V on the plate, and idling at only 40ma, this tube doesn't even know that it's doing anything. I wouldn't be surprised to see a life span of 25000 hours or more on this one.

I can see driver tubes lasting 10,000+ hours...but common audio output tubes? It all depends on how the output stage is set up. With carefully controlled filament voltage (i.e. does not exceed its rating under any line voltage condition), selection of its operating point, and proper ventilation, it's easy to achieve (I'm speaking about US made tubes as I have no familiarity with those of current manufacture). I've worked on numerous communications receivers from the 40s and 50s which used a 6AQ5, 6V6, or 6K6 in the audio output stage, which were operated 24/7, and had no failure of those tubes after 1-2 years! Similarly, in the past 15 years I have had no output tube failures in any of the single ended amps that I've designed and built for local audiophiles and family members who average 2 or more hours of use/day. I'm curious as to how modern tubes stack up against that kind of track record. So, if anyone has experience with that, please post!

Makes a nice case for single ended, cathode biased amps! Put in the tube, measure the circuit parameters to see if they're within spec, and forget about it for the next 10,000+ hours!!!

Agree! I posted it because the presentation is funny. It was sent to me by a relative who is an eye doctor.......................

A fix which "may" work is to remove the buttons from the switch shafts, stand the receiver up vertically on its back, and let some Deoxit (using the bottle version with the long tube attached) run down the shafts into the switch housings. Doing that, and working the switches multiple times, may restore operation. Certainly worth a try.

If the economy is getting you down, visit your local optometrist or optician- hopefully they carry these:

Keep in mind that every piece of electronics which you add to the signal path has the potential to introduce degrading factors such as noise. Also, the additional interconnects needed can have a sonic influence as well. I've always favored dealing with room acoustics with mechanical means whenever possible; and since you are going to rely on your ears to make the changes, that may be a better and more cost effective way of dealing with the acoustics.

You are certainly correct about not being able to buy the parts to build an amp like this for your asking price! Why are you "giving it away" for so little???

Bottlehead makes some nice, relatively inexpensive tube amp kits. As long as you can solder well you should be able to try one of their simple offerings: http://www.bottlehead.com/store.php

If anyone has an emergency before Craig resurfaces, drop me an email and I'll try to help you out. Maynard

Check out the offerings from Decware. Their prices are reasonable, and their stuff has an excellent reputation. http://www.decware.com/newsite/homepage.html

Hey Gregg! My wife has used one of the Gold's Gym recumbent bikes for a number of years (I didn't check the model as it's probably discontinued by now). We got it on sale at Walmart and it wasn't too expensive as I recall. She's 6 feet tall and doesn't have the frame extended to nearly what it's capable of (I'm your height and can easily use it too; but I prefer walking). Pedal tension can be selected, and at the highest level the effort is significant. The seat isn't overly padded, but an additional cushion can always be used. Lumbar support isn't wonderful though, and isn't adjustable on this model, so if you have stenosis it may get a bit uncomfortable without that capability. Hope this info helps. Regards- Maynard

Thanks tube fanatic!!!!! Another PM should be waiting for you!

PM sent in reply to yours.

Anything in particular I am looking for with the wires? Solid connection? Yes, look for a solid connection to the center pin of the jack in particular. If you have an old, crappy, speaker you can connect it to, power it up (being extremely careful not to touch any exposed 120 volt wiring from the power cord), and use a straw or piece of dowel to move some of the leads around to see if you hear anything in the speaker. In fact, if you can feed a signal into the amp from a tuner or cd player, you can use this method to determine if moving any wiring results in sound being heard.

Unplug it, open it up, and take a look at the wires to the input jack (assuming that it isn't circuit board mounted). The problem "may" be there, although there is much else that could cause the symptom you describe.

Thanks for the advice!!! I think I will have a tube tech rework the pre and amp before I turn it on! Definitely a good idea. Lots of capacitors need to be replaced before you put it into regular use. It's a great amp, with lots of power, so I'm sure you will enjoy it tremendously! Post or email if you need any info or advice........

Looks like two of the 6CA7s have lost their vacuum. Replace those before powering up!

Glad you guys enjoyed the article. Another really interesting area to explore is the use of space charge tubes which were actually designed to work with very low plate voltages. Check this out also: http://www.junkbox.com/electronics/lowvoltagetubes.shtml For me, the bottom line is that tubes are truly amazing devices which I'll never get tired of!!!

Since you're interested in starved circuit applications, you may find this article informative: http://www.freewebs.com/valvewizard2/Triodes_at_low_voltages_Blencowe.pdf

There are all kinds of designs which have been used for vacuum tube buffers. However, as Erik pointed out, everything that is introduced into the signal chain has the potential to degrade, not improve the sound. Back in the 80s, passive line stages were quite popular because many believed that every component, solder joint, plug, jack, etc. in the signal path has the potential to decrease sound quality. And there is merit to that belief. If you build/use a buffer you will be introducing additional power supply hum (even with the stiffest designs, if AC operated, there will be some degree of ripple which is passed through), tube noise, microphonics to some degree, and so on. Then there's the issue of an additional set of interconnects which can possibly alter the resultant sound. Given how high the input impedance of your preamp is, there is really no need to bother with a buffer, as I mentioned previously. Your best bet is to find someone who can bring one over, or loan you one, so you can try it without spending any money. I seriously doubt that you will find that it improves the sound at all!

There's no way that the CD player output impedance can be that high! Typically, the values are a few hundred ohms. Even if the output impedance of the CD player is very high, say 1k, there is not going to be any interface problem when driving the 47k load at the preamp's input.

Dan Gibson's Illumination works for me! http://www.solitudes.com/Shopping/ViewProductDetails.aspx?productID=INDY_0096741144127_MP3

What are you hoping to accomplish by using the buffer? Also, please clarify what you mean by "integrated" tube buffer. The goals you have stated are technically possible, but I question whether it's worth the trouble.

As you mentioned, the Cayin amps have received very good reviews. Do you have a dealer who would let you bring one home for an audition before you commit to purchase? That's the only way you will know if the sound is to your liking.