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tube fanatic

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  1. Try to find a dealer who will allow you to audition a tube amp in your system. The only way to know how it will sound is to do an actual listening test. The spl calculator mentioned above is a a great way to get some idea as to your power needs, but you also need to consider the room itself- does it have lots of carpeting, drapes, curtains, and other sound absorbing materials, or is it sparsely furnished with hardwood floors, etc? That will also affect your power needs significantly.

  2. Power conditioners, in addition to providing surge protection, also "clean" the AC which powers connected equipment. The AC lines in our homes have all kinds of noise which can be generated by fluorescent lights, light dimmers, motors, poor outlet connections, etc. The conditioners have various kinds of filters which can potentially block this stuff from getting into sensitive equipment like amps/preamps and so on. Some also isolate the outlets from one another to eliminate possible interaction between the devices which are plugged into it. As to whether it's necessary to use such a device is debatable. Some people claim that they hear a huge difference from their audio systems with conditioners; others say that the picture on their TV is better with it. Personally, I don't use them, but I do use good quality surge suppressors (some of which also contain filtering). Powerline surges are well documented, and solid state equipment can certainly be damaged by overvoltage conditions. So, I'd recommend going that route to protect your investment.

  3. All antique radios are potentially restorable. What you are showing is probably from the late 1930s. Unknown, of course, is what is doing under the chassis. I seriously doubt that it's capable of 5 watts of clean output, however. In addition, the amplifier of such radios is not capable of audiophile quality reproduction as its circuit was probably designed for a frequency response of maybe 200 Hz to 5 khz give or take. It would not be worth the trouble to rearrange the circuitry, install an audio quality output transformer, etc. in order to make it usable in your system (and, of course, it would be mono). If you can provide information of the manufacturer, model #, tube complement, etc, I can probably give you lots more information if it was made by a US manufacturer. These radios, when restored, can provide enormous listening pleasure; so, if the owner decides to part with it at a reasonable price, buy it! I speak from experience, having restored many hundreds of such radios over the years.

  4. Before modifying any speaker which is under warranty, I'd check with the manufacturer to verify that doing so will not void it. It would be a shame to install a different crossover, for example, and then blow a tweeter which you now have to pay for. Crossover modifications sometimes involve changes in the frequency at which the drivers operate which, of course, can affect the sound. Others involve switching to "audiophile grade" capacitors or changing to different drivers. Whether that makes any difference is in the ears of the listener. In the shop we very rarely were asked to do crossover or driver changes for any in-warranty speaker. Usually, it was for speakers which had been sitting unused for 20-30 years. Whether modifying a speaker will affect its value depends on what the modifications were. Some people consider the changes as a value enhancement, and others consider them detrimental. You have to decide for yourself.

  5. Anyone know of a good tech in the Maryland, Virginia, Pennsylvania , new jersey area. I have aquifer a pair of Rowland model 7 monos that I would like to have checked over. Joe

    Be sure to find a tech who is very well versed in working on this type of equipment as it's too easy to mess up such a fine instrument! You may want to contact Rowland to find out if there's an authorized repair tech in your area:


  6. I've used either a razor knife or pliers to get most of the coating off, then coarse sandpaper to get the rest off and smooth the conductor surface. That was only to get bare wire ends to connect to terminal strips though, I never soldered.

    For #26 or heavier wire, coarse followed by fine sandpaper does a great job of removing enamel, formvar, and other coatings. If you spend a few minutes doing it, so that there is no residual coating left, it solders beautifully.

  7. How large is the room itself? Also, what kind of speaker placement are you using, and where is your listening position? Bass response can be greatly altered by something as simple as moving the speakers a few inches or less, or changing your listening position by the same amount. Any possibility of posting a picture of the room showing the layout, etc?

  8. How loudly are you listening that the 50 wpc Luxmans aren't enough? In my experience, 5 wpc into a pair of Cornwalls produces sound pressure levels which drive most people out of the room. Can you describe your listening room in terms of size, carpeting, drapes, book cases, etc? That may help to clarify your power needs.

  9. The difference in bias voltage between the 2 schematics remains a mystery. It would have been helpful if they printed a serial # range for each one, and even more helpful if they specified the plate voltages of the el34s. It certainly is possible that they decided, at a later date, to run the tubes cooler to increase longevity. As far as sound quality with the two bias voltages, why not reset it to -37 and take a listen? You certainly won't hurt anything by running the tubes at a lower plate current. The chances are, even if it does increase the distortion a bit, you may not even notice a difference when playing music. As far as output power, measure it at 1 kHz at the onset of clipping on the 'scope and compare with the two bias values. It might be a fun experiment! And you can certainly measure the plate current/voltage/screen voltage at each bias value, and graph it at the two bias voltages (I still do it the old fashioned way on paper, with a ruler, etc. If you know someone with a CAD program it sure will save you a bunch of time). You would then need to measure the transformer impedance (easy to do with your signal generator) to see which provides the closest match. Who knows, you may find that the "correct" bias voltage based on the graph is in between the two values printed! If you have, or can borrow, a copy of the Radiotron Designer's Handbook it will give you everything you need to graph virtually anything. It's been my "bible" for longer than I can remember. In any event, you certainly have a good handle on what's needed here to answer the bias question. Also, in case you are not familiar with it, check out www.tubedata.org which has the most extensive database of tube characteristics anywhere in the world. Please post your results after doing the experimentation. I have lived and breathed tubes for the past 50 years and still marvel at the amazing things that they can do! Your last name is definitely a credit to your interest in the subject!!!

  10. Sounds like you want to have some "fun" with this! By chance, is your 'scope a dual trace type with which you can superimpose the waveforms? That would make it easier to compare your sine/square wave input with what is coming out. But, in any event, you can connect your 8 or 4 ohm resistive load (assuming it's rated for the power needed) and look at the sine wave appearance at the point just before the onset of visible clipping (a flattening of either the top or bottom rounded portion of the waveform. In most amps, the clipping will not be symmetrical). Of course, don't leave it running like that for too long. Compare that to the appearance of the input signal from your generator. There are some nice articles online which show how to interpret deviations in the waveform appearance and form some correlation with distortion. You can try that for multiple frequencies to get some appreciation of what's happening across the audio band. Do the same with a square wave input to see how things behave with a more "complex" signal that effectively encompasses a range from around 1/10 the input freq. to 10X the input frequency. With this, however, I wouldn't go beyond about 1 watt output (keep your multimeter, set to an AC range, across the dummy load to monitor the voltage- keep it to 2.83 V maximum). Again, check out the online articles on that- it's much easier to explain with pix than in words. I suspect that you're not going to see a huge difference. Considering that tube characteristics can change quite a bit as they age, a 7 volt bias variation could occur with normal use over time. Most users of tube equipment, unless they're really into the technical side, never check tube bias anyway. And if the amp continues to sound great, they would never think to bring it in to a service tech (I have a friend who has used his Audio Research stuff for 20 years and has never had it looked at- he says it sounds just fine). And, yes, if you allow the tubes to draw too much current by biasing very low, life span will definitely be reduced as you might exceed the maximum plate/screen dissipation rating of the tubes. So, I hope this helps you a little bit. Post or PM if I can help any further.

  11. Didn't have time to study the schematics, but a quick glance suggests that your interpretation is correct. By lowering the current a bit, the plate/screen voltages will run a bit higher. This, of course, will affect the required load impedance somewhat. Since Altec used the same output xfmr in both units, it apparently isn't of much concern. But, if all is well with the -30 volt bias, why mess with it? You could always put a 'scope on the output (with a proper load connected) and see what effect the altered bias has..................

  12. I think I'm a tube nerd. 4 tube testers, 14 tube amps, 2 tube pre amps, a few dozen extra 8417's, kt-88's, 6l6's, 12A*7's, el-34's, 62**'s, etc, couple of variac's, a 300v and 500v tube power supply, 2000va line regulator. Where did all this SH&*%T come from?

    Well, you are almost a rival for my title, although my amp stock is down at the moment- only a dozen (that will change though with some new prototypes in the early stages)!

  13. I'm looking for a 12 inch metal stand to put a large bookshelf speaker on and I'm comin' up with nuthin'. Something I could fill with sand/shot to keep resonance to a minimum. Ideas?...

    You can make great speaker stands out of a piece of steel sewer pipe which is available in different diameters. Between their weight, and filling them with sand or shot, they are extremely stable (and heavy!!!) and resonance free.

  14. To rule out whether it's the speakers which are kicking out some nasty distortion products at a certain power level or higher, you need to connect another amp/preamp, receiver, etc, and increase the volume to produce the same sound pressure level at your listening position as the Parasound equipment. Alternatively, if you have a peak reading/storing multimeter, you can connect it (AC range) across your speaker terminals (each can be tested individually) and measure the voltage at which they start sounding poorly to you. Then, connect the other equipment and listen at the same voltage or higher. If the speakers still sound find, you at least will know that it's the Parasound amplification which is causing the problem.

  15. You mention having problems with the volume control at 9 o/c or higher. Because of the way much equipment is designed, with the volume control at that position you could be driving your amp into clipping (it would be worth knowing the input sensitivity of the amp). More details about your amp and preamp would be helpful. Also, if you happen to have, or can borrow, a sound pressure level meter with which to take a reading at your listening position when the sound isn't to your liking, some potentially useful information may be gleaned. Where are you located? There may be folks nearby who can come over with other equipment to form the basis of comparison.

  16. I've taken some temperature readings. So far today.....after two hours of testing the hottest reading was 123 degrees Farenheit. That was after one hour of warm up time at 75db and a maximum output of 105db for 15 minutes at a time. (2 hours total)

    I'm gonna monitor this for the next couple hours at different spl's but then gotta leave the house. I guess I'm somewhat surprised that the highest temp reading was only 123 degrees. Just going by sense of touch I thought it would have been slightly higher.

    It should not be surprising to find that kind of temperature. If your hot water is typical, it is set at 120 deg. F; you certainly know what that feels like if you stick your hand under the tap!

  17. Remember that power transformers are designed to run extremely hot without failure. This does not necessarily indicate that it's undersized for the job. Most are designed to allow an operating temperature of 105 deg. C (around 220 deg. F) minimum. If the transformer is delivering 400 volts at 200 ma (not unusual in a stereo amp), we're talking 80 watts of dissipation. Add to that 4 or 5 amps of filament draw at 6.3 volts, and now we have another approx. 24-30 watts. Now add the radiated heat from the tubes themselves and it's easy to see why the amp can seem so hot if you touch the transformer housings. So, as mentioned by others above, at the very least keep the amp on an open shelf if at all possible to allow maximum air circulation (and never put it on anything which can block uptake of air from the underside of the chassis where vents are typically located).

  18. Do any of you use a fan to cool your tube amp? If so, what type? Is it quiet enough?



    Tube amps are generally designed to operate at the expected high temperatures. However, if your amp is within an enclosure, it certainly can't hurt to put a small muffin fan on top of the vents to draw heat out. Some fans can be extremely quiet and won't interfere with your listening, even at low volume levels. Excessive heat is a definite cause of tube and electrolytic capacitor failure. The other factor to consider is the temperature of your listening room. For example, I don't use air conditioning, and my listening room is often in the 90's during the summer months. My amps run quite hot during those times. In the winter, when the room is in the mid sixties, the amps only get warm. Bottom line- if you're concerned about how hot your amp is running, use the muffin fan.


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