tube fanatic
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Posts posted by tube fanatic
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The schematic shows two 250 ohm resistors in parallel to give a net value of 125 ohms. So, if you're absolutely sure about your 125 ohm resistors being connected in parallel, giving you a net 62.5 ohms, that would account for an approximate 10 volt higher reading at C1, the input filter cap for the power supply, based on the assumed current draw of around 160 ma. Since the efficiency of tubes is so variable, measuring 20 volts high is very typical. Sometimes it's impossible to tell if parts are "factory," or just well installed by someone else. You can't always tell by looking at the solder joints..............BTW, where do you live?
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Well, firstly, be extremely careful when working in there as the voltages can be lethal! The small variations in voltages that you are noting are normal. These amps were designed to operate over a fairly wide range of line voltages. I don't have the schematic handy, but it will probably state the line voltage at which the specified DC voltages were measured. Also, take note that they may have been measured with a VOM having a fairly low input resistance (as compared with modern meters) which can result in a lower DC voltage reading. In addition, if they measured everything at 110 VAC, and your line voltage is 120, of course the DC voltages you get will be higher as well. Tubes of the same type can draw varying amounts of current which will affect the voltages which you measure. Has this amp been restored? If not, at the very least, the electrolytic caps should be replaced as they are often prone to failure after a long period of time. If you decide to do this yourself, be sure to put your meter across them before you stick your fingers in there. These caps may not be fully discharged and can store quite a wallop if you get your fingers across them. Regarding the 125 ohm resistors, they are no doubt wired in series to get the needed 250 ohms and also to double the wattage.
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The tube chart may be more difficult, but I'll make some inquiries and will post if I can get it for you.
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My buddy just picked up a 600A and is looking for a calibration manual and the most up to date tube chart available.
Anybody have some suggestions?
Tom
http://www.radiolaguy.com/PDF_Files/Hickok600-600Acalibration.pdf
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Using the extension cables is fine (I am assuming that you're only talking about a few feet) and should not affect the sound at all.
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Perhaps an antenna in the attic can collect a nearby static discharge but if it takes a direct strike you got bigger problems.
That's quite correct. Even a nearby thunderstorm (or snowstorm) can induce charges of hundreds of volts in antennas regardless of where they are mounted. To think of having any kind of antenna installation which is not protected is a mistake. A properly designed discharge unit constantly drains all induced voltages to ground (as opposed to those which don't discharge until a predetermined voltage is present) which makes the antenna less "attractive" to the step leader which preceeds the lightning strike itself. These units are not only grounded, but also bonded to the ground system of the building's electrical service, telephone service, and if copper plumbing is present to that as well. There are many sites which discuss the correct way to install lightning protection for antennas including Polyphaser's and ICE's.
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Lightning just burns out the braid on the co-ax, whether or not it's grounded.
_Sometimes_ what it was hooked to can be repaired.
djk is quite correct. A direct hit to the antenna would vaporize the antenna and the connected coax. But, in the process, many kilovolts would pass through the coax into any connected equipment, and possibly into the house wiring. The devices by Polyphaser and ICE are designed to prevent such connected equipment from that event when installed correctly. That is why the coax needs to be brought outside the house to ground level for connection to the protective device. A number of ham operators I know have taken direct hits to their tower mounted antennas (in some cases at 75-100 feet above ground), but the connected equipment remained intact!
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Grounding is not necessary to protect from lightning simply because it will not protect anything if you get a direct lightning strike. The only thing that would protect against something so catestrophic is a home lightning rod system. You are better off not grounding so it does not introduce a ground loop into your system.
The correct way to do it, if you want lightning protection, is to bring the coax outside the house (possibly through the gable vent, or a small hole) and take it to ground level where it can be attached to a properly designed and installed lightning arrestor (such as available from Polyphaser or Industrial Communications Engineers). The coax coming out of the arrestor can then be routed back into the house as desired. As stated above, attic mounting does not offer protection from a direct hit, so if you are in a high lightning area you are taking a big chance. Additionally, if the grounding of the antenna is properly executed, you will have no ground loop problems.
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You guys are going to throw daggers at me for saying this, but the differences in the sound of interconnects is usually related to the capacitance of the cables- it's not the fancy gold-plated plugs, or the silver plated copper wire, etc. This can be easily tested yourself if you are handy with a soldering iron by buying lengths of various coaxial cables, putting on your own RCA plugs, and then sitting down to listen. The chart found on the site below shows the capacitance of various coaxial cables which you can use as a guide. They are available from the major electronics suppliers like Allied, Newark, and Mouser (Radio Shack even has some). Some local audiophiles and I have tried many blind listening tests in which we compared the sound of some very expensive cables with our home-made cables, and the results were not what one would have expected (the megabuck cables often came in last)! Try it and post your results........
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For that price I'd grab it! But, bear in mind that it may be way out of calibration in spite of the claim that it works perfectly. The calibration info for it is readily available, so you can always bring it to a technician to have it brought up to spec.
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The most important question before considering the S-5000 is whether it has been restored or not. Amps of that vintage usually need to have many capacitors replaced, the output stage bias checked and readjusted, controls checked/cleaned/lubricated, and lots more! Also, what is the condition of the tubes? If memory serves, some of the S-5000s used 7868s in the output stage- real expensive if they need replacement. Are you considering buying it from a reputable dealer/restorer who will give you some kind of warranty? The bottom line is if it is working properly it should sound terrific. But frankly, with K-horns you would probably be better off with a nice, new low powered triode amp. Unless you are into extremely high sound pressure levels, 3-5 watts is more than enough with those speakers.
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Be careful if you purchase a used player as you have no idea how much abuse the transport has taken. We had many come through the shop which were supposedly "minimally used," only to develop transport problems shortly after. To me, it isn't worth taking the chance unless you know the person you are purchasing from.
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If your dad doesn't mind a changer, the Sony SCD-CE595 is an incredible value for a street price of around $125. The sound of this unit is beyond phenomenal and approaches that of my friend's Wadia Model 6, one of the best sounding CD players ever made. Buy from a place like J & R music and you can return it if not satisfied. I've used one as a source when designing and restoring tube amps and it has never taken me in the wrong direction!
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This may interest you. Came across it during my daily Ebay scan for vintage equipment. Not a bad deal if you are not interested in sourcing your own replacement parts:
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I haven't worked on a 500C in too many years to recall if the numbers, etc, are baked on enamel or decals. If it's enamel you can just wipe it with a paper towel moistened with some Windex or similar. If decals, you need to lightly moisten a q-tip with some Windex and clean around them without getting the decals overly wet. It's painstaking work, and you will need a few dozen q-tips, but it can be done. I've used these methods to clean the dial glasses of a few hundred antique radios and it works out quite well.
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And combining magnificent speakers of vintage design with equally vintage tube electronics designs completes the wondrous experience!!!
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Well, the Isoblok above is rated for 600j. I live in a very high lightning strike area and have never had one fail, nor has anything plugged into one failed either. You can buy spike suppressors that go up into the thousands of joules; whether you need that much protection is hard to say. But, for a few dollars more you can get a similar plug-in unit which is rated for around 1400j:
http://www.tripplite.com/en/products/model.cfm?txtSeriesID=74&EID=345&txtModelID=3980
You also need to consider the clamping voltage, or the voltage at which suppression becomes effective. Some units out there clamp at over 300 volts whereas these clamp at 140 volts. You want the clamping voltage to be as low as possible.
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For the money you can't beat the Tripp Lite Isoblok- it plugs directly into your duplex wall outlet. Inexpensive, very effective (I've been using them for years), and ot of the way:
http://www.tripplite.com/en/products/model.cfm?txtModelID=3974 -
Thebes is right: #16 zip (lamp) cord for runs up to 20 feet- 25-30 cents/foot is a much better idea!
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Transformers are made with different types of insulation- some can safely run at hotter temperatures than others. Do you know the manufacturer of this particular transformer? If so, you can contact them to obtain the necessary info. If you are concerned, why not use a small and quiet running muffin fan to dissipate the heat somewhat. All the components will be grateful for that.
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Be careful if you buy an Eico as many were sold as kits and may not have been well constructed (i.e. poor solder joints, overheated components, etc.). Also, depending on age, many will need to be restored by replacing out of spec resistors, replacing all the capacitors, and then being recalibrated..............
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With tube amps, due to the relatively high output impedance, you need to use short connections to the speakers or you will notice definite frequency response differences. Given the 30 foot run from the amps to your source components in the studio, be sure to use very heavily shielded cables to avoid hum and noise pickup.
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Well, if you really want one, definitely follow the advice above from dbspl and get a Hickok. But, be absolutely sure you can get hold of the calibration info for it to verify its accuracy. If it isn't properly set you may think that the tubes you are testing are great when in fact they aren't.
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Look at Dope from Hope, Vol. 16, #1. It will tell you how much power you need for a given spl with Cornwalls.
http://forums.klipsch.com/forums/storage/3/740089/DOPE%20from%20HOPE!!!.pdf
The Fisher X-100 Rectifiertube problem?
in Technical/Restorations
Posted
You are worrying far too much!!! Having slightly low filament voltages is fine and will result in longer tube life. But, at the same time, the cathode emission may be slightly lower (from the reduced filament emission) resulting in higher plate/screen voltage readings (not a problem either). In addition, tube to tube variations are often large- if your 7189s happen to be drawing a bit less current, the voltages you measure can be higher. Back in the sixties voltages were measured either with a VOM (generally having a fairly low input resistance), or VTVM (vacuum tube voltmeter). The latter often had an input resistance, on some ranges, as high as 10 megohms which tended to load circuits far less than VOMs. Many modern multimeters maintain a constant input resistance on all ranges. So, the only way to have a "true" idea of your operating voltages is to use the same kind of equipment as the manufacturer did. The following site will give you a good understanding of how the typical 60's VOMs and VTVMs worked and will, I hope, set your mind at ease about the amplifier. Why not just sit back, put on your favorite music, and enjoy it? But, as mentioned in my previous post, if the electrolytic caps are original, they absolutely should be replaced. The most common cause of amplifier failure, in vintage equipment, is a bad electrolytic capacitor.
http://www.allaboutcircuits.com/vol_1/chpt_8/3.html