tube fanatic

An integrated amp is nothing more than a power amp with a preamp section. Going to a straight power amp is totally unnecessary. The easiest way to do the connection is to run cables from the "recorder output" jacks of the Fisher to the auxiliary, cd, or tuner inputs of the integrated amp and use its volume control to set your listening level. All of your source components are connected to, and accessed from, the Fisher. Assuming that the integrated amp has a decent preamp section, this should achieve your goal. Thinking back, I don't believe the Fisher allows its preamp to be used as a separate entity from its power amp (I can check the schematic if you want to know for sure). The reverb in/out jacks of the Fisher are probably in the circuit before the Fisher's volume control, so they can not be used as you desire.

No active preamp can equal the sound of a passive line stage, assuming that your source can put out enough voltage to drive the amp to the power levels you desire. In the eighties, when passive line stages were more popular, we built many for audiophiles. Typically, we used a single high quality resistor (such as a Caddock) between the input and output; the volume control was either a high quality Alps pot, or a stepped attenuator with metal film resistors. Assuming the amp was quiet, the sound seemed to emerge from a background of total silence- absolutely no hiss or hum, even with one's ear against the speaker (back than we were using K-horns for the testing prior to delivery). By using short (less than 6 feet long), low capacitance interconnects, there was virtually no high frequency rolloff. Why the passive line stages fell out of popularity is beyond me.

I paid $3600 for a new pair in '88.

Feeding a low level signal from the Fisher to the input of your other amp is fine and will not cause any problems. Disconnect all sources from the integrated amp; even if you remove the jumper between its preamp and power amp sections there could be slight signal bleed-through from internal coupling which could affect the sound quality.

You can't make the comparison based on cost; and comparing a tube to a solid state amp is comparing apples to oranges. Each will have a distinct sound. Then, tube amps can sound differently from one another based on the design- i.e. triode vs. pentode; single ended vs. push-pull. My experience is that any type of tube amp sounds better than any type of solid state amp; but, others may have the opposite view. The only way to know is to listen to different amps through your speakers in your listening room, and then decide for yourself.

" would like to learn more about how khorns respond to tube amps. I don't know if tubes are really "better" or just "different"." The term "better" is in the ears of the beholder, but I can tell you from personal experience (and opinion) that K-horns are simply incredible with tube amps! To my ears the tubes create a smoothness of sound which can not be duplicated with solid state amplifiers. If you're not into extremely potent low bass, a triode amp would be amazing. Given the incredible efficiency of the speakers, even 1 watt per channel is more than enough unless you're into ear shattering sound pressure levels. Perhaps you can locate someone in your area who can bring over some tube amps for demo.

Well, I'm sure you will have no problem getting a decent price for the amps on Ebay. Did you consider listing them also in the Garage Sale section of the forum? I'm sure there are plenty of people on here who would be interested in those amplifiers. Your cabinet work looks great! Do you run into any problems with the cabinets resonating from having all of that low frequency energy in there?

Do you have experience working on this type of electronics? If not, I urge you to refer to a qualified service technician. Testing this unit will expose you to potentially lethal voltages; and if the components are not replaced properly, a hazardous condition could result as well as an improperly working unit.

It's hard to put a value on amps like this, but if it sounds nice, why not keep it? But, if you keep it, it should absolutely have a total restoration- i.e. replacement of all electrolytic caps, all paper/ceramic caps, all out of spec resistors. Amps like this are capable of very nice sound and make great companions for Klipsch speakers. Can you post a large picture of the underside of the chassis? That may be useful in determining if anyone has worked on it in the past.

Great idea captain! Forgot about Niles for switchboxes (senility, you know). It's a bit costly if bought new, but will absolutely do the trick here based on the info sheet: http://www.nilesaudio.com/images/PDF/DPS-1_Cutsheet.pdf

If I understand you correctly, you want to have 2 amps simultaneously connected to the Cornwalls, although only one would be in use at any given time. You don't want to do that!!! The output stages of the 2 amps will interact causing impedance mismatches, among other things. The best way to do it is to build a little switchbox which allows you to connect either amp to the speakers, but will prevent simultaneous connection. All you need is a dpdt (double pole double throw) switch installed in a minibox with the necessary jacks and you'll have a nice, clean arrangement (you need one for each channel, or you can install 2 switches in the same box for convenience).

I think you are mistaking the rationale here. The nice thing about a forum is that is allows not only for information to be exchanged, but also for the classic "point/counterpoint" discussion. I'm not asking anyone to agree with me, and don't care if they do or not! But, sometimes, by looking at a situation through the experiences of others, one may decide to completely change or modify one's own point of view. When I get together with fellow audiophiles we often have very heated discussions about all kinds of things, but we all come away with thoughts and ideas that we may not have considered before (a recent discussion was whether there are audible differences between brands of metal film resistors). So, please don't look at the comments of guys like me as lecturing. We are just offering points of view based on our personal experiences. If that can help someone, great. If not, that's fine too.

The nice thing about this hobby is that everyone is equally correct/incorrect since there's no way to know what the other person is hearing or what their brain is perceiving. Tubes are in the same vein as cables, connectors, AC outlets, power cords, and so on. Does anyone remember, years ago, all the discussions about placing coins or exotic wooden discs on top of your components to greatly improve the sound (I bet the folks who came out with those Mpingo discs laughed all the way to the bank)? Same thing! I just don't like to see people wasting hard earned money chasing something which they probably can't achieve- better to spend it on your favorite music. Discussions about all this have been raging for decades and won't be resolved here..........................

Your friend is right on target!

A solder connection is far superior to any kind of crimp connection. But, for speakers, why not use banana plugs (soldered to your cable) if compatible? Put a little De-Oxit on it and you get an excellent electrical bond.

Well, I certainly don't agree with you based on my experience back then with folks who used K-horns, among other great speakers, coupled to some very fine electronics (I'm talking about Macs, Marantz, etc.). But, that being a matter aside, one has to consider the fact that auditory memory is extremely short. In the time it takes to listen to a song, shut the amp, remove the tube in question, replace it with another, turn it back on and let it warm up, your brain no longer remembers "exactly" what it heard previously (lots of studies on that over the years). In addition, you have to consider the aspect of psychoacoustics- how often do people listen to their systems and think that there could be no possible improvement, only to listen again 2 days later and feel that it sounds like crap? Back in the late fifties/early sixties the audiophiles I knew seemed to have much more of a sense of the realities of those factors and didn't obsess over minute nuances as they do today. It's too easy to convince yourself that the tube that you just paid $200 for sounds better than the NOS GE which it replaced.

Yes, "tube rolling" is definitely a modern phenomenon!!! Keeping in mind that tubes can sound slightly different from one another (one may have a bit more noise, or be more microphonic), it was far less of a concern 40-50 years ago than it is currently. And if one did replace a tube, and found it was a bit too noisy for example, they just went out and bought another and popped that in. Most folks, even those who were into "hi-fi", didn't get overly taxed over such minor issues. I know audiophiles who lose sleep at night agonizing whether the black plate tube they bought was really worth the money, instead of just going with the regular gray plate version. The bottom line is your satisfaction with the sound. If it's pleasing, why bother trying to extract that extra quarter percent of "whatever" from the sound? As a tube amp designer/builder, I advise people to just sit back and listen. If they like what they hear, they are done!

The Scott 299 specifies that 3 mv into the mag 1 and 2 low setting will produce the rated output. Sensitivity of mag 2 high for rated output is 9 mv.

It might be worth contacting Jef Larson of Abraxasaudio (http://amps.abraxasaudio.net/index.html). He's a custom tube amp designer with a good reputation, and reasonable prices.

With all the apparent interest in vintage solid state receivers among forum contributors, I haven't seen any discussion of checking the DC offset before hooking them up in your system. Often, for a variety of reasons, the DC offset (the DC voltage mesured between the (+) and (-) speaker terminals, with speakers disconnected, the volume control all the way down, and no signal input) can be very high. This not only results in greatly increased distortion, but if high enough, is potentially speaker damaging. I'd start to get concerned if the offset is greater than 50 millivolts, and would recommend that the units be serviced by a qualified technician who can set it for you. Ideally, the DC offset should not exceed single digits. Turn on the receiver and wait about 10 minutes for things to warm up and stabilize before measuring.

The negative lead is clearly marked, usually with a series of minus signs.

Do you know anyone with a good single ended triode amp? Cornwalls sound great with them- nothing provides a lush sound better than that kind of amp. Any dealers nearby who would let you bring one home for audition?

My computer speakers aren't exactly "hifi," but your sound clip sounds very silky (if you have access to a digital camera, please post pictures of your amp). Ultimately, regardless of what test instruments show, the ears are the final arbiter of good sound (some well respected amps look positively awful on the 'scope). You can often find decent oscilloscopes very inexpensively, so it might be worth picking one up. With that, and an inexpensive sine/square wave generator, you can really learn a great deal about amplifier performance. As you discovered, star grounding can make a huge difference in eliminating hum. If you're going to the trouble to re-cap, I'd replace the mylar caps as well. Over time they can have leakage problems. It seems like you have become a definite convert to "tube sound," something which I agree with totally!!! If you can find a dealer, or someone who has Klipsch speakers, listen to them with tube electronics and you will have a whole new area in which to spend money! The combination is truly unbeatable (and, no, I do not work for the company!)..................

I'm not familiar with the German replacement caps that you mentioned and, yes, Telefunken and Mullard tubes are definitely becoming more scarce and expensive. Congratulations on building your guitar amp! That's a wonderful way to learn, especially if you have access to an ocilloscope with which to evaluate the amp. By making small changes in bias and other voltages you can then look at the resulting waveform and try to correlate that with what you are hearing. Regarding wearout of rectifier tubes, generally you will see a decreased voltage. As tubes age the emission of electrons from the cathode (or filament, if a filament-type tube) decreases which will result in more of a voltage drop within the tube. You can always, if a replacement is not available or affordable, replace it with a solid state rectifier (keeping in mind that the B+ will greatly increase and necessitate changing the value of the filter resistors accordingly). Anyway, keep up the good work! It sounds like you are well on your way to some great listening experiences with the tube equipment..............

Well, as far as the tubes are concerned, you don't need to have Mullard or Telefunken tubes for the amp to sound great. In fact, if one were to replace the tubes with NOS Sylvania tubes for example, it may not be possible to tell the difference when listening. Often, the differences are extremely subtle (such as putting your ear near the tweeter and hearing a bit more hiss with one tube vs. another). Regarding the transformers, they are not overly delicate and were generally rated for much more current than the circuit uses. You have already checked and adjusted the bias which is great. Something you can do which can greatly increase the longevity of a tube amp is to keep it on an open shelf and place a small, quiet running muffin fan over the heat vents to draw heat out of the cabinet. If you want to develop a good understanding of amplifier circuitry go to: www.pmillett.com He has a vast library of books on the site, which you can download, covering just about every aspect of audio amplifier operation and design imaginable. As far as replacements for the electrolytic caps, you can either leave them in place and install modern, very small replacements under the chassis, or remove the inside of the cans and place the modern replacements inside. This site has links which can point you in the right direction for doing that: http://www.dslreports.com/forum/r23472078-Rebuilding-Old-CanType-Electrolytic-Capacitors So, I hope this will be of help to you. You can private message me any time if you have other questions which you don't wish to post on the site.