I am replacing Tubes on a 1960 RCA stereo, the unit has a total of 14 tubes for the power supply and amplifier. As I test the individual tubes with a tube tester, I am finding the variations one would expect after 45+ years.

I have tubes that have tested "GOOD" at 65% and others at 85%. Also, only 2 that tested "BAD" at 25%-35%

So, one would simply conclude that any test results showing in the tester Green Scale as "GOOD" is acceptable. But we all know any tube less than 100% is showing signs of age and possible performance.

I/m looking for feedback from the experts, what level should be the lower threshold of acceptability. Should tubes below 65% be replaced and those above installed ?

I want to have some level of confidence after replacing all the capicators and bad/questionable Tubes this unit should work correctly as expected.

So, what is "GOOD" enough ?
Comments ?

Bill, much of this is so arbitrary. If you read the book by Alan Douglas on vintage tube testers, it'll show you the relatively poor corelation between different models of tube testers testing the same tube.

I presume that you're using a simple emissions tester, which is fine. But the original tube manufacturers never established a spec value for emssions. And, I don't necessarily think that the difference between, say, 50% and 100% represents a factor of two in life, performance, etc.

Here's how I would interpret your results: the tubes in the "green" should be fine. The tubes in the "red" may be fine, too. Just try them. If you get flakey performance, you can try a different tube to see if it makes a difference.

The most important test is to verify that the heater is OK and that there are no shorts in the tube. I think most tube testers can check for shorts, and if the tube lights, then the filament is good.

Let me say this about "But we all know any tube less than 100% is showing signs of age and possible performance." I didn't know that. What's your tester? Some tubes are oranges and some are apples and whatever else. Some tubes will never read 100% even brand new ones. Your tubes reading 65% may be excellent performers. Tubes reading barely in the green or even in question area could still do ok. If I was testing a tube from a set say a 6EU7 and thought it was reading low I would test another good one and compare them. Testing a number of the same tube, same manufacturer, and known to be good generally results in very close reading for all on the green scale. I like a tester which checks leakage too. The tubes in bad area are to be replaced. You could always sub back in set if not shorted to see the difference. And remember the best test for an oscillator in my opinion is the set. Somtimes you got to swap them out regardless of tester results. For me anything in the green stays in the set for a trial. For me I think the most replaced tube reading in the green after this trial period is the output tube.

Bill VA

:I am replacing Tubes on a 1960 RCA stereo, the unit has a total of 14 tubes for the power supply and amplifier. As I test the individual tubes with a tube tester, I am finding the variations one would expect after 45+ years.
:
:I have tubes that have tested "GOOD" at 65% and others at 85%. Also, only 2 that tested "BAD" at 25%-35%
:
:So, one would simply conclude that any test results showing in the tester Green Scale as "GOOD" is acceptable. But we all know any tube less than 100% is showing signs of age and possible performance.
:
:I/m looking for feedback from the experts, what level should be the lower threshold of acceptability. Should tubes below 65% be replaced and those above installed ?
:
:I want to have some level of confidence after replacing all the capicators and bad/questionable Tubes this unit should work correctly as expected.
:
:So, what is "GOOD" enough ?
:Comments ?

What these guys are saying is right on. A tube tester's reading is only something to give you an idea about the tube's performance. With high current circuits such as the power output section (audio), a weak tube is usually going to put out a bit less power, and may distort more easily. The same weak situation in a pre-amplifier or detector situation may cause no difference. Oscillator sections tend to be picky. RF sections may or may not be picky.

As one person pointed out, some tubes never do test out 100%. This just is how the tester is calibrated. For instance, the high voltage rectifier 1B3, 1G3, 1K3, and all other similar tubes, tends to test out at no better than 400. Often 200 is quite acceptable for this tube. For most tubes, 100% is ideal. Then you have the brand new ones that test out above 100%. So what does this mean? It just means that they are putting out more than the other tubes that run at 100%. It's all arbitrary. The numbers on an emission scale are just that, a scale. With a transconductance tester, they have a bit more meaning, but not much. A tube tester is simply an aid. Never should you replace a tube simply because it doesn't test out well against another tube or against the scale. If it obviously checks out weak, and a better tube improves performance, then go ahead and replace it. If you notice no difference between a new tube and a weak tube, then replacing the weak tube is only wasting a tube. However, in high power situations, a weak tube does not have much life left, so it may need replacement soon. If performance is acceptable, wait until it dies. In other sections like pre-amplifier and detector sections, the weak tube could last you for years. In low power amplifiers, a weak tube in the output section may last you for years as well. So again, if you like performance, leave it alone until it fails.

One reason I change tubes (on occasion) is for balance in push-pull situations, and for tonal characteristics in both push-pull output and non-push-pull output. Using balanced tubes in a push-pull circuit tends to improve tonal characteristics, and certain tube designs, though using unmatched tubes provides different audio characteristics. Sometimes distortion occurs and sometimes a different tonal characteristic occurs that may or may not be pleasing. Different internal construction of tubes with the same number type will lend itself to slight differences in tonal characteristics. Some tubes of a certain number may have more crisp treble, or more sharp mid-range, or more or less bass. These may be reasons for changing audio tubes. However, unless you have a musical ear (not necessarily trained by someone, but one of acute accuracy and pickiness), for everyday use by the average person, such tube selecting is seldom necessary.

Thomas

Most emission testers are calibrated to read 70 to 80 on a scale of 100 for a good tube. This should be in your tester manual. If a tube reads higher than this I would suspect it may be gassy or it may be an exceptional tube. Any tube that reads high is as suspect as a tube that reads low.

Dave

True, true. Still, I've had many a new tube go all the way up to 1000 (my scale is in 100s instead of 10s). I have yet to have a tube read 1000 or over and not function properly, and I always adjust my line adjustment, which puts the 110 volt filament position right at 115 volts if measured with the accurate Simpson 250 meter.

In the end, tube testers are only something to guide you along the way. If your tester in fact has a "gassy" light, then you should keep this light in mind. I've tested tubes on such testers, however, only to find that the so-called gassy tubes function like any other. It all depends upon the circuit. Oscillator circuits, especially those in portable radios (battery), are the most sensitive to slight gas in the tube. Generally a tube will function quite well as an amplifier or output tube unless it glows purple (not blue!). When you see the purple glow, emission will go way down, and the tube may not even light properly for reasons I've explained before.

Actually, come to think of it, gas in a tube shouldn't make the needle go up to 1000. Gas allows current to flow in both directions--alternating current. With an emissions tester, the tube is the rectifier which supplies the meter with DC. If your tube is gassy and starts passing AC, the meter will actually read lower. I think that this is also the principal that the "gassy" light works upon--current flowing in the direction other than normal.

Anyway, in my experience, a gassy tube has never made the needle read higher, but actually made it read lower. As well as that, I have never had a tube not function properly that read 1000.

Thomas

:Most emission testers are calibrated to read 70 to 80 on a scale of 100 for a good tube. This should be in your tester manual. If a tube reads higher than this I would suspect it may be gassy or it may be an exceptional tube. Any tube that reads high is as suspect as a tube that reads low.
:
:Dave

I understand where you are coming from Bill. At this point of your restored project, you have no real way to know if your amp is performing as well as it should. After reading the posts by other members on this forum, you should be getting the idea by now that a tube checker is not a very good way to find out. My comments on this subject will further verify some of what has been said already, and hopefully the additions will also be of use.

The original specifications of your amplifier is the best thing you can go by to verify its performance, but additional equipment is required. If the distortion, frequency response, power output, noise level, etc. is within factory specs, then it makes little difference what a tube tester tells you. If you don’t have this equipment, then your best choice of test equipment is what you hear. If your restored amp pleases you, then “GOOD” is good enough. In the world of audio freaks, this will put you in the “Golden Ear” category instead of a “Meter Reader”.

Vacuum tubes are not created equal. Manufacturers have tolerances, and any tube within this range will pass final inspection. If they were all exact, then venders would not be selling matched sets of new tubes for use with high end sound equipment. As you have found out already, your tube tester can indicate some of these differences, so about the only thing you can depend on from it is a comparison between one tube and another. Therefore, it’s not a bad idea to have spare tubes on hand for future use that can also be used to make these comparisons, which brings us to another subject.

It has been said many times in the past that the best tube checker is substitution. If you have another tube that is known to be good, then it can be compared in the actual working circuit, which is what really matters. In some cases, a tube that reads somewhat weak on a tube tester will work just as well as a new one, which leads us to yet another subject.

Vacuum tubes do not usually work at 100% in most circuits. If they did, then every tube in your amplifier would be operating at its maximum voltage, plate current, wattage, or whatever. Since your amp was designed to keep distortion below a certain percentage, just this reason alone is enough for the tubes to be operating well below 100% emission. In other words, distortion usually increases at higher tube outputs, and the designer of the circuit decides where to draw the line. This is usually a point where a somewhat weak tube can sometimes still be within specifications. Since the design perimeter of the circuit determines the operating conditions of a tube, this brings us to even another subject.

Tube testers do not tell you how a tube will be used in a circuit. Your tube tester supplies fixed voltages to the various elements of the tube under test, which may not be anywhere near those in the actual circuit where it will be used. In some cases, just a small difference in the bias voltage can change the characteristics of the tube in actual use. Therefore, a tube tester can tell you that a tube will probably work in a circuit, but it cannot tell you how well it will work.

So, what level should be the lower threshold of acceptability? Only you can be the judge of that.

Also....to add to what Billy said and what the rest of us have said before, tubes aren't often what cause trouble in radios and such. If you are in fact having trouble with your set, replace obvious dud tubes. Then check set performance again. If it improves to perfection (other than slight tonal characteristics associated with that circuit and its components), then the dud tube was likely your problem. If you still experience other trouble, however, such as distortion at all volume levels, or some other strange problem (one channel weaker than the other, thin bass in one channel, muffled treble in one channel), then you have component failure, which is the usual problem within radios.

Leaky or opening condensers (the two terms are diametrically opposit to eachother) cause distortion and other strange audio problems. They can cause crackling and irratic operation. Failing volume controls (bass, treble, and volume) can also cause sound failures within the set. They don't usually cause distortion. Drifting resistors can cause distortion, weak power, and sometimes strange audio changes (low bass or treble). Usually condensers are your first problem.

If you are in fact having trouble with the set, then it is wise to replace dud tubes and then check under the set. Replacing all of the tubes won't likely solve anything, as tubes are not likely your problem in the first place.

I guess, instead of writing all of this, I should simply ask you if you are in fact having trouble with your set, or if you are simply trying to obtain maximum performance from the set by replacing all tubes. As all of our comments suggest, however, replacement of all tubes won't necessarily benefit you in any way.

For some people, especially beginner radio enthusiasts, it is hard to accept the fact that you might actually have to get inside the chassis and replace components. After several tube replacements, however, if you're actually having trouble, you'll find that under the chassis is often where the real trouble lies.

Thomas

I am having slight problems with the stereo. I am actually replacing all the old caps and was checking tubes to correct any questionable components.

The stereo has not been operated for many years. When I turn it on, it took several minutes to begin to operate in a poor state. The left speaker circuit was only static. I switched the R & L wires and the problem also switched to the other channel. Therefore, the speaker circuit were OK.
I suspect many of the larger Capacitors need replaced. I have 8 electrolytics and 15-20 paper base(200-450v) in the circuits. I also have 2 tubes that obviously need replaced.

The tube tester I am using is a "MURCURY" Model 990.

I worked on this stereo as a senior in HS (30 yrs ago) to fix the power supply. It has been many years since I been into the circuits.

I really appreciate your support and information. I have ordered replacement caps and 2 tubes this week. I told my wife 4 weeks ago I would have this up and operating to play an old collection of Christmas records by Thanksgiving. Well, another project I underestimated.

:Also....to add to what Billy said and what the rest of us have said before, tubes aren't often what cause trouble in radios and such. If you are in fact having trouble with your set, replace obvious dud tubes. Then check set performance again. If it improves to perfection (other than slight tonal characteristics associated with that circuit and its components), then the dud tube was likely your problem. If you still experience other trouble, however, such as distortion at all volume levels, or some other strange problem (one channel weaker than the other, thin bass in one channel, muffled treble in one channel), then you have component failure, which is the usual problem within radios.
:
:Leaky or opening condensers (the two terms are diametrically opposit to eachother) cause distortion and other strange audio problems. They can cause crackling and irratic operation. Failing volume controls (bass, treble, and volume) can also cause sound failures within the set. They don't usually cause distortion. Drifting resistors can cause distortion, weak power, and sometimes strange audio changes (low bass or treble). Usually condensers are your first problem.
:
:If you are in fact having trouble with the set, then it is wise to replace dud tubes and then check under the set. Replacing all of the tubes won't likely solve anything, as tubes are not likely your problem in the first place.
:
:I guess, instead of writing all of this, I should simply ask you if you are in fact having trouble with your set, or if you are simply trying to obtain maximum performance from the set by replacing all tubes. As all of our comments suggest, however, replacement of all tubes won't necessarily benefit you in any way.
:
:For some people, especially beginner radio enthusiasts, it is hard to accept the fact that you might actually have to get inside the chassis and replace components. After several tube replacements, however, if you're actually having trouble, you'll find that under the chassis is often where the real trouble lies.
:
:Thomas

Shouldn't be too hard, though. You should have it running by Christmas. Replace all condensers if you can. If you only want to test faulty condensers, then replace those with ANY leakage at all. Of course replace electrolytics if there is hum or something like that. If there isn't hum, though, electrolytics of this time period often last a long time, so you don't necessarily have to replace them all. With a set of this age, I'd hunt for bad components. Again, if you wish to replace all condensers, this is the safest bet that the set will perform flawlessly for years.

A condenser with any leakage is unacceptable. This means that if the needle springs upward to any degree at all, it must fall back to EXACTLY where it started. You are using a resistance check meter, of course (multi-meter). Use the X10,000 scale whenever you test condensers. Condensers smaller than .001 MFD will normally not deflect the meter at all during their charge-up period. They charge up too quickly for the sluggish meter to respond. However, any meter with leakage will cause the meter to jump up, and it won't fall all the way back down. When I say unacceptable leakage, I mean that with the needle zeroed out, it should fall back to exactly where it started. It can't linger above this by even the thickness of the smallest hair. If you remove the condenser from the meter and the needle moves at all downward, then the condenser has unacceptable leakage.

Whenever you test condensers, be sure to remove them from the circuit that they are in. Resistors and other devices wired into the circuit will make you think that condensers are leaky when they really aren't. Also, your hands allow enough current to flow to severely throw off meter readings. Do not touch both condenser or meter leads at the same time with your fingers or you'll think that every condenser is leaky.

It is easier for you to see why any leakage at all is detrimental to a radio when you take into consideration that tubes are EXTREMELY sensitive devices. They are far more sensitive than transistors, though transistors can have trouble with leaky condensers, too. The grid of a radio tube is so sensitive that it can measure incredibly small voltages. I can't think of the exact number, but it is amazingly small. Think radio waves in the sky, and you're probably at least 100 times over the actual figure. Also, very large value resistors are used in supplying bias voltages to the grids and such. By large value I mean high resistance, like in the millions of ohms. If a condenser is leaky in the millions of ohms, it is easy to see how its leaking voltage from one circuit to another will severely affect performance of the successive or even preceeding circuit. Usually the successive circuit is where the grid is concerned, and this is where you have the most trouble in radios (since it is so sensitive).

Good condensers do not pass current ever, but hold charges and allow circuits to influence eachother. This is why a condenser only "passes" alternating current. Once a condenser charges up, it cannot influence a circuit anymore, so if you supply it with direct current, it'll charge up and then stop. They are used to pass and bypass alternating currents like radio signals and audio signals, and are used to block the direct currents that are used in each stage of a radio.

I do not mean to get too detailed. I can go into more detail, but I assume that you already know something about radio. If you want more detail, I'll give it. I just want you to understand the importance of perfect condenser operation. This is probably the biggest reason for radio failure (along with dirty switches and drifted resistors). It cannot be overstressed. Once you're done replacing bad condensers, you'll probably find that many of the weak tubes which you replaced actually work quite well. A radio must perform perfectly once you are done working on it. Too many people have this idea that old radios are inferior and have inferior sound quality. There were inferior circuits back then just as there are now (some modern radios sound like junk). For the most part, however, the only thing lending to bad sound quality with a properly working old radio is the speaker, and in some cases bad circuit design. Poor quality sound has nothing to do with tube technology. With most AM radios of the 1930s and early 1940s, speakers, not necessarily capable of full range, but of rich tonal quality, were used, so most of these radios should be able to put the poor quality assumption to shame, especially since most modern AM radios cannot in any way compare to the tonal quality of these old radios. Modern ones sound grainy and raspy. The old radios make up for the missing highs and high fidelity with a mid and low range that is very pleasing. With your stereo, I'll assume that high quality speakers were used. If they were balanced properly for natural tone reproduction, you should be able to place the needle upon a Toscanini record and be held in breathless suspension (assuming that the record has been cared for). Danse Macabre is a perfect example of his fine work.

Thomas

Thomas, I must confess, I am an EE from the 80's so I have very limited experience with condensers and tubes. I had not considered testing or replacing any condensers until I received your follow-up. Looks like I need a condenser class 101. Where can these components be purchased ?
Are you interested in seeing the schematic ? If so, send me your email.

:Shouldn't be too hard, though. You should have it running by Christmas. Replace all condensers if you can. If you only want to test faulty condensers, then replace those with ANY leakage at all. Of course replace electrolytics if there is hum or something like that. If there isn't hum, though, electrolytics of this time period often last a long time, so you don't necessarily have to replace them all. With a set of this age, I'd hunt for bad components. Again, if you wish to replace all condensers, this is the safest bet that the set will perform flawlessly for years.
:
:A condenser with any leakage is unacceptable. This means that if the needle springs upward to any degree at all, it must fall back to EXACTLY where it started. You are using a resistance check meter, of course (multi-meter). Use the X10,000 scale whenever you test condensers. Condensers smaller than .001 MFD will normally not deflect the meter at all during their charge-up period. They charge up too quickly for the sluggish meter to respond. However, any meter with leakage will cause the meter to jump up, and it won't fall all the way back down. When I say unacceptable leakage, I mean that with the needle zeroed out, it should fall back to exactly where it started. It can't linger above this by even the thickness of the smallest hair. If you remove the condenser from the meter and the needle moves at all downward, then the condenser has unacceptable leakage.
:
:Whenever you test condensers, be sure to remove them from the circuit that they are in. Resistors and other devices wired into the circuit will make you think that condensers are leaky when they really aren't. Also, your hands allow enough current to flow to severely throw off meter readings. Do not touch both condenser or meter leads at the same time with your fingers or you'll think that every condenser is leaky.
:
:It is easier for you to see why any leakage at all is detrimental to a radio when you take into consideration that tubes are EXTREMELY sensitive devices. They are far more sensitive than transistors, though transistors can have trouble with leaky condensers, too. The grid of a radio tube is so sensitive that it can measure incredibly small voltages. I can't think of the exact number, but it is amazingly small. Think radio waves in the sky, and you're probably at least 100 times over the actual figure. Also, very large value resistors are used in supplying bias voltages to the grids and such. By large value I mean high resistance, like in the millions of ohms. If a condenser is leaky in the millions of ohms, it is easy to see how its leaking voltage from one circuit to another will severely affect performance of the successive or even preceeding circuit. Usually the successive circuit is where the grid is concerned, and this is where you have the most trouble in radios (since it is so sensitive).
:
:Good condensers do not pass current ever, but hold charges and allow circuits to influence eachother. This is why a condenser only "passes" alternating current. Once a condenser charges up, it cannot influence a circuit anymore, so if you supply it with direct current, it'll charge up and then stop. They are used to pass and bypass alternating currents like radio signals and audio signals, and are used to block the direct currents that are used in each stage of a radio.
:
:I do not mean to get too detailed. I can go into more detail, but I assume that you already know something about radio. If you want more detail, I'll give it. I just want you to understand the importance of perfect condenser operation. This is probably the biggest reason for radio failure (along with dirty switches and drifted resistors). It cannot be overstressed. Once you're done replacing bad condensers, you'll probably find that many of the weak tubes which you replaced actually work quite well. A radio must perform perfectly once you are done working on it. Too many people have this idea that old radios are inferior and have inferior sound quality. There were inferior circuits back then just as there are now (some modern radios sound like junk). For the most part, however, the only thing lending to bad sound quality with a properly working old radio is the speaker, and in some cases bad circuit design. Poor quality sound has nothing to do with tube technology. With most AM radios of the 1930s and early 1940s, speakers, not necessarily capable of full range, but of rich tonal quality, were used, so most of these radios should be able to put the poor quality assumption to shame, especially since most modern AM radios cannot in any way compare to the tonal quality of these old radios. Modern ones sound grainy and raspy. The old radios make up for the missing highs and high fidelity with a mid and low range that is very pleasing. With your stereo, I'll assume that high quality speakers were used. If they were balanced properly for natural tone reproduction, you should be able to place the needle upon a Toscanini record and be held in breathless suspension (assuming that the record has been cared for). Danse Macabre is a perfect example of his fine work.
:
:Thomas

They can be found at www.tubesandmore.com. Replace with exact same values +/- 15%. A .01 MFD condenser may be replaced with a .015 MFD condenser. A .05 MFD condenser may be replaced with a .047 MFD condenser. Use same or higher working voltages. If originally 400 WVDC, then any condenser rated at this voltage or higher may be used. A condenser is a capacitor. Condenser is the older word which I use for some odd reason. It's all the same stuff that they use in modern radios, though.

You may find a limited variety of condensers at Radio Shack. They have .01 MFD, .0047 MFD, and .001 MFD condensers rated for 500 volts. In an emergency these may be used. If you need .05 MFD, just wire five .01 MFD condensers in parallel. These are ceramic condensers of modern design, which are extremely reliable. All of the other condensers which they sell are usually rated under 100 WVDC. You can't use these in your set.

www.tubesandmore.com is an excellent source for many things that you'll need for your set. I recommend ordering their catologue, as it's a bit easier to read than their web site, though you'll find the most up-to-date information on their web site.

Thomas

Radio Shack also sells 1.0mf metal film caps at 250 volts that can be used in series to yield other combinations. I don’t remember seeing these a while back, so maybe they are a recent addition. They are more expensive though, so I doubt if I will keep them in stock. I got caught short a few days ago while building up a 1924 superhet and had my wife pick up a few. A single one is perfect for installing inside the metal can types used in these older radios.

Yeah, I’ll agree that you'll find the most up-to-date information on the AES web site. A few weeks ago we were talking here about one of their audio transformers and soon after that it was removed from their list. Now I see that it is back, so who knows? Maybe we had something to do with that.

Caps are readily available from www.tubesandmore.com www.radiodaze.com and www.justradios.com

For film caps, it's probably best to buy all 600V. For electrolytics, get 450V. This is overkill for an AC/DC set, but it's easier to just buy caps with sufficient voltage rating for virtually any set you might run across.

Most run-of-the-mill places, like RadioShack and internet surplus pedlers, typically stock caps for use with solid-state ckts, which have too low a voltage rating for tube-type ckts.

Doug, as I just wrote, Radio Shack has a limited supply of condensers that will work fine in his stereo. They are all rated for 500 WVDC. If you are in a bind and need a quick fix, this limited variety can be a large help. I recommend www.tubesandmore.com for a full variety of condensers suited for tube work.

Thomas

Thomas,

I did not remember the term condenser and capacitor were one-in-the-same. I have ordered replacement Capacitors this week. I ordered the ones that I believe are questionable, these were all the paper type, most ranged in voltage from 200-450v. I replaced with 650V rating. I did not replace ceramic or Mica type. Everything I have read says these are very reliable and should not be replaced unless there is a specific reason. I also replaced all electrolytics, these are probably the most unreliable due to the fact the stereo was not used much (Sometimes turned on 1/year in the past 20 yrs), It was not worth the risk and the cost was limitd.

Thomas - If you have any other tips to direct my restoration, I would really appreciate your input.
I am hopefull my parts arrive this week so I can get this put together and test the system.

:Doug, as I just wrote, Radio Shack has a limited supply of condensers that will work fine in his stereo. They are all rated for 500 WVDC. If you are in a bind and need a quick fix, this limited variety can be a large help. I recommend www.tubesandmore.com for a full variety of condensers suited for tube work.
:
:Thomas

Ceramic and mica condensers should be tested just the same. They do occasionally short out. It is rare.

Thomas

Check all resistors as well. Each must be unsoldered in order to be tested accurately. A resistor or two may have drifted or may have opened up somewhat, causing static sounds. A condenser is more likely the problem, but resistors fail, too.

Also check volume and tone controls as well as the selector switch. Spray the selector switch with tuner/contact cleaner. If you are good with disassembly, disassemble the potentiometers (volume and tone controls). Wipe the carbon elements with a very thin film of di-electric grease, found at your automotive parts supply shop. If you noticed no improvement in audio when the controls were moved around when you first tested the set, save this until after all other faulty components have been replaced and the radio has been tested again. The volume controls and tone controls may be at fault, but disassembly is a big job and is not necessary unless they have been found to be at fault.

Thomas

Bill,
While some tube tester only offer a "Good" or "Bad" indication, there are higher quality testers that actually lets you see how far from normal emission the tube really is.

When a tube is tested, the tester usually has you set up the tester for a standard bias (by setting all the controls as stated in the setup for the tester). This will only tell you if the tube had emission or not. Others, like most of the Hickock testers tell you what the mutual conductance should be for that particular tube. If the bias control on the tube is lowered to the range specified on the chart, and the tube does not have meet the mutual conductance as a minimum, then it's performance will be less than the purpose of its design. Most manufacturers will play with bias to set the tubes class of operation, where is operated on it's particular design curve, etc. With my tube collection, if it doesn't meet the minimum mutual conductance, I throw it out.

Donnie

:I am replacing Tubes on a 1960 RCA stereo, the unit has a total of 14 tubes for the power supply and amplifier. As I test the individual tubes with a tube tester, I am finding the variations one would expect after 45+ years.
:
:I have tubes that have tested "GOOD" at 65% and others at 85%. Also, only 2 that tested "BAD" at 25%-35%
:
:So, one would simply conclude that any test results showing in the tester Green Scale as "GOOD" is acceptable. But we all know any tube less than 100% is showing signs of age and possible performance.
:
:I/m looking for feedback from the experts, what level should be the lower threshold of acceptability. Should tubes below 65% be replaced and those above installed ?
:
:I want to have some level of confidence after replacing all the capicators and bad/questionable Tubes this unit should work correctly as expected.
:
:So, what is "GOOD" enough ?
:Comments ?

Well, Donnie, those settings in your tester cannot possibly meet all of the operating conditions found in every radio ever made. A tube tester should be used as a guide, showing you where possible trouble lies. If you are absolutely sure that there is no other trouble, and the tester shows a tube to be weak, and the trouble goes away after you have replaced the tube, then the tube was in deed at fault. The tester led you to this. If, on the other hand, you are simply throwing out tubes because they test poorly in your tester, regardless of how they perform in an actual radio, then you are wasting tubes.

As I have said before, an extremely weak tube may work poorly or not at all in a power output or rectifier situation. The same tube may work just fine as a detector diode, even with it registering at the very bottom of the scale. The tester should show you where the weak and suspect tubes are. Substitution should give you your final answer (whether the new tube does better or not). I realize that I cannot change everyone's opinion to match my own, but you really cannot rely on a tube tester as your only decision maker, regardless of how well it is built.

Thomas

And yes, I know that your tester is not an emission tester. Regardless of how infinite your bias selection is, your tester probably does not have the capability to run a tube under all current load conditions. Your tester is probably usually right, but I discourage using it as the last word.

Thomas

Thomas,
Thanks for your remarks. Not all engineers use the same tactics or approach to a repair, but if the outcome is the same, that's what matters. Six to one, half dozen to the other as they say. I choose to trust my tester, it has never failed me in 20 years of service. If you want to plug every tube of a certain type into the socket of a radio to find the one that works well enough, that is your choice. I trust that when I plug a tube into a socket, it will operate to anyones satisfaction. This approach has always worked well for me, and the way I prefer to do it.

Donnie

:And yes, I know that your tester is not an emission tester. Regardless of how infinite your bias selection is, your tester probably does not have the capability to run a tube under all current load conditions. Your tester is probably usually right, but I discourage using it as the last word.
:
:Thomas

Hi

Regardless of what a tester shows don't throw away 01A's or other very old tubes. Some can have emission brought back and even duds have value.

Norm

:Thomas,
:Thanks for your remarks. Not all engineers use the same tactics or approach to a repair, but if the outcome is the same, that's what matters. Six to one, half dozen to the other as they say. I choose to trust my tester, it has never failed me in 20 years of service. If you want to plug every tube of a certain type into the socket of a radio to find the one that works well enough, that is your choice. I trust that when I plug a tube into a socket, it will operate to anyones satisfaction. This approach has always worked well for me, and the way I prefer to do it.
:
:Donnie
:
:
::And yes, I know that your tester is not an emission tester. Regardless of how infinite your bias selection is, your tester probably does not have the capability to run a tube under all current load conditions. Your tester is probably usually right, but I discourage using it as the last word.
::
::Thomas

Norm,
I don't throw away all the tubes that check weak. I just don't waist a lot of time trying fifteen tubes when there is one that I know will work, the first time.

Donnie

:Hi
:
: Regardless of what a tester shows don't throw away 01A's or other very old tubes. Some can have emission brought back and even duds have value.
:
: Norm
:
::Thomas,
::Thanks for your remarks. Not all engineers use the same tactics or approach to a repair, but if the outcome is the same, that's what matters. Six to one, half dozen to the other as they say. I choose to trust my tester, it has never failed me in 20 years of service. If you want to plug every tube of a certain type into the socket of a radio to find the one that works well enough, that is your choice. I trust that when I plug a tube into a socket, it will operate to anyones satisfaction. This approach has always worked well for me, and the way I prefer to do it.
::
::Donnie
::
::
:::And yes, I know that your tester is not an emission tester. Regardless of how infinite your bias selection is, your tester probably does not have the capability to run a tube under all current load conditions. Your tester is probably usually right, but I discourage using it as the last word.
:::
:::Thomas