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 Post subject: Heathkit TT-1A
PostPosted: Aug Sat 30, 2003 9:10 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Well the tester finally came, and it works perfect. No problems. The unit was recently calibrated and came with all documentation, including assembly manual for TT-1 and TT-1A, Operators Manual, 6 extra tube charts, and a bunch of misc papers. It also has the lid assembly for nuvistors ect. which I didn't expect. My question is there is a knob titled "Grid" which has a normal and test selection. How do I use this knob? The rest of the unit is self explanatory except this one knob. <P>Thanks<P>Peter


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 Post subject: Heathkit TT-1A
PostPosted: Aug Sat 30, 2003 11:03 pm 
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Location: Portland, OR USA
It should say "GRID CURRENT" and is a spring return switch. It is used to test for the grid drawing current. Usually from gas.<P>The circuit is shown on page 8<P>See step nine on page 10 of the operational manual. (My OpMan is dated 8-29-69)<P>Hope this helps<P>BTW, I don't put much stock in the LIFE TEST.. But that's me..<P>------------------<BR>Walters


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 Post subject: Heathkit TT-1A
PostPosted: Aug Sun 31, 2003 12:40 am 
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Thanks for the info, I found the page on the Grid Test knob and have but one last question, if the reject point is the number on the charts, how do I determine the test of a good/new tube?<P>Peter


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 Post subject: Heathkit TT-1A
PostPosted: Aug Sun 31, 2003 2:32 am 
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Not sure what you mean, but the reject number is a number generated by Heath. It indicated the MINIMUM gMho. See page 10 of the OpMan. I usually reject a tube if it is 25% below the reject number. I also verify the line test AFTER the tube has warmed a bit.<P>That help?<P><P>------------------<BR>Walters


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 Post subject: Heathkit TT-1A
PostPosted: Aug Sun 31, 2003 10:03 pm 
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Sure, helps. I know that the data states the reject point is 65% of a nos tube. Now what the heck is the math to calculate a nos tube? Been awhile since I fired up the brain cells...


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 Post subject: Heathkit TT-1A
PostPosted: Sep Mon 01, 2003 12:57 am 
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Math? I flunked differential equations forty years ago. I'd use what is in the tube manuals.<P>Acoording to Alan Douglas' "Tube Testers and Classic Electronic Test Gear", the TT1A was adapted from a Weston 981-3 tube tester. The book is available from Antique Electronics<BR>He says and I quote:<BR>"Unfortunatly the 981-3 was fundementally flawed and the TT1 inherited all of it's problems. The meter loads down the plate circuit making it impossible to calibrate, and the plate choke inductance varies widely with changes in the plate current and amplified signal. The half rectified DC plate and screen potentials are sensitive to impedance in the AC supply, unavoidable with the line adjust pot used"<P>He doesn't like the TT1 A!!!!<P>He likes Hickock amd the military TV series. That's nice, but testing 12AX7's on a TV 7 is a PAIN.. Too much setup time. I bought one to test ACORN tubes.<P>I've had one of my TT1 A's since the '60's. I have all the faith in the world in that instrument. Although I have had times when it didn't tell me that a tube was noisy in a phono amp circuit, but I doubt if any tube tester would.<P>One trick I've used. Sometimes (!!!!) the you can't see the filament glow because of silvering on the tube.. Is the filament ok? To keep your wait time from climbing, operate the NORMAL DISCONNECT switch with the LINE TEST switch operated. If the meter goes up a tad, the filament is good.<P>------------------<BR>Walters


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 Post subject: Heathkit TT-1A
PostPosted: Sep Mon 01, 2003 1:43 am 
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Great little trick. Thanks for the heads up on the tester. I had a Hickok 800, and just recently stumbled upon an I-177 for cheap (not sure how often it will get used) and now the TT-1A. If you ever need data I have about 6 supplementary sheets, two assembly manuals and an operators manual. Might try and check the calibration later in the week. Will a dvm do ok?


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 Post subject: Heathkit TT-1A
PostPosted: Sep Mon 01, 2003 6:12 am 
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My TT-1A works much better since Chris took it under his wing. He has seen quite a number of them, where I had only worked on this one, a fairly early example. I could never get it to calibrate following Heath's procedure.<P>I still miss the Gm readout, as I like to mark my tested tubes with Gm and the bogey value (and also mark them with the machine they were tested on). The range multiplier on the TT-1A is just hopeless.<P>------------------<BR>


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 Post subject: Heathkit TT-1A
PostPosted: Sep Mon 01, 2003 10:04 am 
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So how does one calibrate the Heath TT-1A properly? I tested its calibration with the calibration knob and it lined up fine. Is there more I can do? <P>I agree on the gm numbers. Too bad they didn't include the nos value as well as the reject point. C'est la vie!!!


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 Post subject: Heathkit TT-1A
PostPosted: Sep Mon 01, 2003 7:08 pm 
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Location: Grand Blanc, MI USA
The TT1 is an excellent tube tester, and I do not think the numbers thing is a serious issue. It sure is not a problem for me using the tester (although I mainly use a Cardmatic). I really don't care what the actual Gm figure is anyway (anymore than I do on the Cardmatic)--since it is only meaningful in relation to results obtained on other TT1's. Really, it is the reject point that is the thing of value. At least Heath does define how they arrived at their reject point.<P>Hickok is the one that really confused people. Some models, like the 600A list the nominal value for a NOS tube on the chart. Other models, like the 539C, list the reject point value on the chart. They should have just stuck to one system! As it is, people that move from model to model (happened recently with a customer) are constantly confused. If you want a tester with the most complete roll chart data--get a Triplett 3444. They listed the reject point AND the nominal value for each tube.<P>One COULD argue also that the nominal value is not too useful--since new tubes varied so widely. It just seems that people want to know what the "typical" new tube should test. <P>The self-calibrating feature of TT1 is excellent--but there are a number of other things to check beyond what is in the manual. The manual assumes a bunch of new resistors, tubes, caps, and clean switches. Plus--it assumes that the tester was assembled properly in the first place--and not all are! There were even some units with bad switches in them--and that is a real treat to troubleshoot and fix. I am not going to go into all the details of the stuff here. I will tell you that if the machine will calibrate that is a very good sign, but it does not mean the machine is actually working up to spec. There are other testers like this (Sencore MU140/MU150)--it's not just limited to Heath.<P>------------------<BR>


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 12:01 am 
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Another TT1 trick. The tube data in the plastic spiral binder will (!!!) become very frayed with a lot of use.<P>I removed the plastic and placed the pages in clear plastic sheet holders that fit into a three ring binder. The sheets are protected and the holes are reinforced. The plastic alo protects against coffee or adult beverage spills.....<P>Also the date of publication is in the upper left corner. Ergo 1176 or 1-1-74.. <P>------------------<BR>Walters


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 1:59 am 
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<BLOCKQUOTE><font>quote:</font><HR>Originally posted by Chris H:<BR><B>The TT1 is an excellent tube tester, and I do not think the numbers thing is a serious issue. It sure is not a problem for me using the tester (although I mainly use a Cardmatic). I really don't care what the actual Gm figure is anyway (anymore than I do on the Cardmatic)--since it is only meaningful in relation to results obtained on other TT1's. Really, it is the reject point that is the thing of value. At least Heath does define how they arrived at their reject point.<P></B><HR></BLOCKQUOTE><P>In a recent post you stated that all Gm testers should read close if they are properly calibrated and here you say " meaningful in relation to results obtained on other TT1's" Shouldn't the TT1 read Gm the same as any other Gm tester if it is calibrated correctly? Being Gm is a measurement of a tubes ability to amplify a given signal it would stand to reason that a tube with a high Gm would be in better condition than a tube with a lower Gm. Therefore the numbers are important. As far as the reject value I would think this to be be unimportant as this is a arbitrary number usually arrived at by a percentage of the of the average Gm of a new tube. As we all know many tubes will operate properly even when they test below the reject point. A percentage of a average does not give you a real number to work with, just a guideline. I will take a high Gm tube any day over a tube that just makes the reject point. The tube data books list the average Gm for a new tube but list nothing for a reject point.<P>Dave<P>------------------<BR>


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 3:10 am 
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Hi Dave<P> A data book gives Gm values under specific conditions. I don't know of any popular tube tester that duplicates this? Testers like Hickok 539 only have single plate & screen voltage. Even these aren't filtered. <P> Chris will calibrate testers to manufactures specifications. Two Hickok 539C's will give similar readings. You can't expect a Heath & Hickok to give the same readings.<P> Relative readings have a meaning. A tube reading higher is usually better. Speed of getting to the reading is an indication of emission. <P> There are very few testers out there that can duplicate data book conditions. Maybe Chris has one?<P>------------------<BR>Norm


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 3:29 am 
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Dave--this is an excellent post. When I say that mutual conductance testers agree-I mean that they agree based upon what they consider to be a good or bad tube. What is good or bad depends upon the roll chart data for that particular tester. This is because a tube's amplification figure depends upon the conditions under which it is tested--and testers vary a great deal in this regard. The actual Gm figure a tester delivers will most certainly NOT agree with all other testers. It will also NOT agree with the tube manual--unless the tester provides conditions the same as the tube manual describes (only a few do). What WILL tend to agree is how high a tube tests above the reject value for each tester. I covered this topic in depth in the article that I wrote on testing the 12AU7 tube.<P>Consider the 6DJ8 as tested on the 600A series of Hickok testers. There are about three different set ups given for the tube and they provide very different figures for the expected mutual conductance. As the bias for the tube is varied the expected mutual conductance goes up or down. Now this is just for one model of one brand of tester--but it illustrates how the absolute Gm number is only of value in the context of the roll chart data for a particular tester. Or consider that the same 12AU7 tube will test about 2400 on a Hickok 600A--but test over 3000 on a Hickok 539C. This is again normal and shows that we have to look at the roll chart for each tester to interpret Gm figure obtained. A 12AU7 that tested 2400 on a 539C would not be that good--but would be very good on a 600A.<P>Now--if tube testers provided tube manual conditions--then the average Gm value for a tube provided in the manuals could be compared with the results obtained on the tester. But--this is just not usually the case. What we depend upon in roll chart data is that the manufacturer of the tester determined how a certain tube would test on that model of tester. The reject point thing was probably somewhat arbritrary, and manufacturers differed on the determination of this figure. Some companies(Triplett) used more stringent standards for voltage amplifiers than current amplifiers. Some treated both types of tubes the same(Hickok & others). The reject point is an attempt to predict a performance minimum where a tube meeting this minimum will perform in most all circuits designed for that tube. This does not mean that the tube will not work in some circuits. <P>Tube testers(lab types excepted) are designed to find BAD tubes, not really to evaluate the merit of good ones. That is why the reject point is the figure of interest. Virtually all of the better testers provide the reject point--because the question the tester is designed to answer is: should I consider replacing this tube?<P>Now you may prefer a tube that tests higher in mutual conductance to one that tests lower. But--what If I said: would you prefer a 12AU7 tube that tested 2300 on my 600A, or one that tested 2500 on my 539C? If you picked the higher number you would pick the weaker tube! <P>------------------<BR>


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 3:58 am 
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Norm--really only lab testers like the RCA WT-100A come close to duplicating tube manual conditions--I don't have one of these. The Triplett 3444's and the Heath TT1's probably come the closest of testers in the service grade gear category. They have variable plate, screen and signal voltages, and the voltages are filtered (rather than pulsating DC). But--the service grade gear is subject to complex voltage sags depending upon the current demands of the tube under test. So you might set up for 200 volts and actually get much less. Testers like the WT100A have regulated voltages--so what you see is what you get. <P>When you start to try to figure out what voltages are going to the tube on the typical Hickok it's pretty confusing. The plate and screens sag with current, as does the filament. The screen voltage goes down as the bias is increased. The grid signal goes up as the bias is increased. But--the important thing is that it all works pretty darn well. Bad tubes get found--and equipment gets repaired. Tube testers are full of compromises, born out of the need to test thousands of tube types. The better testers do a darn good job, and reflect clever solutions to a most difficult problem.<P>------------------<BR>


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 6:08 am 
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Well said. Just a quick note: Gm is dependent mostly on plate current, and *in theory* different testers should read the same Gm if the bias is set to give the same plate current in each. However plate and screen voltage also affect the readings, and in any tester with rectified AC on the plate, rather than filtered DC, a DC milliammeter won't read quite right (about 10% off, depending on the shape of the tube's characteristic curve). So it can be difficult to reconcile the different readings on various testers.<P>------------------<BR>


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 2:42 pm 
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I have stressed the value of tube tester roll chart data. A person on another newsgroup asked how Hickok created the roll charts. Just how did they determine the reject points for all of those tubes? I did not know the answer and spoke with Wendell Hall about this. Wendell has worked on Hickok gear for decades, he knows the history and lived it. Even Wendell did not know how the roll chart data was created. He stressed just what an unusual company Hickok was, and that they were very secretive. Wendell suggested that the method used in the creation of roll charts may have been considered a trade secret by Hickok. The people that knew about roll chart creation are probably long gone now. Anyone with additional knowledge--please speak up. Hard to imagine that such recent history may be lost forever.<P>Alan is probably correct about the theoretical aspects of making tube testers read the same by manipulating the plate current. The problem is, that with many testers, adjusting the plate current (by changing the bias) changes the grid signal voltage, and the screen voltage. Plus--the plate current causes complex voltage sags in the rest of the tester. So--it is pretty much impossible to change one voltage or current in a tester without affecting all the others. If you want to see this first hand--spend and hour testing a tube on a TV2! Of course, the various voltage sags are not the same for all tester designs--they are not even the same for all testers of the same model due to variations in the power transformers. So--I guess what I am saying is that theory cannot be realized in practice. <P>------------------<BR>


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 9:06 pm 
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Wow, great info guys. Thanks for the idea regarding the roll chart, although I have several updated photocopies of the tube data and don't use the roll chart. The operators manual states that the reject point for the Heath TT-1A is 65% of what a nos tube would test in gm. Given this fact what I've done is divided the the reject point value by 65 and multiply it by 100 and I get an approximate of what Heath dtermined what the tube would test at nos. <P>ie: 6CA7 reject point is 1430gm/65=22 multiply by 100 and 2200 is an approximate nos tube. I could be wrong on this but its really only a referance point anyhow. I use the tester to match tubes and filter out bad ones. <P>Thanks for the info guys. I cleaned up the machine (polished with Silvo, came out gleaming), cleaned the switches and calibrated the unit and all is well.<P>How often do you replace the tubes inside?


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 10:02 pm 
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<P>How often do you replace the tubes inside? <P>The tubes in my first TT1 A (purchased 1968 or 69) are the original tubes. I think it's one of those: 'if it ain't broke, don't fix it' things. I do have a couple of tubes that I use as test bench marks to verify the unit reads today what it read when I calibrated it. And also to verify my other TT1-A is 'about' the same.<P>I thought about the Heath charts too. I wondered how they determined the values. Wouldn't be too hard today, but the charts were created before computers were really used.. Unless they used a IBM 650 or 1401..<P>Valvo, you REALLY started an interesting string. now when are you gonna register????<P>------------------<BR>Walters


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 Post subject: Heathkit TT-1A
PostPosted: Sep Thu 04, 2003 11:23 pm 
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Just did!!! Great forum. First one I've seen for test gear. <P>------------------<BR>


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