Description

The 39 / 44 / VT - 49 is a super-control pentode recommended for use primarily as a radio-frequency amplifier, intermediate-frequency amplifier and superheterodyne first detector in automobile receivers and in sets operated from DC power lines. It has a heater-cathode which is designed for DC operation. This feature together with that of general freedom from microphonic and battery circuit disturbances makes the 39 / 44 / VT-49 well suited to mobile service and other applications where complete DC operation is desirable. It is very effective in reducing cross-modulation and modulation-distortion over the usual range of signal voltages without the use of antenna potentiometers or auxiliary volume control switches. This super-control characteristic makes the tube uniquely adaptable to RF and IF stages of receivers employing automatic volume control. The use of a suppressor is an important feature of the 39 / 44 / VT-49 because it permits variation in tube structure so as to obtain a high plate resistance without impairing other desired characteristics. In comparison with the usual type of screen grid tube operated under similar conditiona, it has a much higher plate resistance and a considerably increased range of voltage swing. Furthermore, a high value of mutual conductance is maintained. The suppressor is connected inside the tube to the cathode. During operation of the tube, the suppressor eliminates the secondary emission effects which limit the voltage swing permissible in the usual screen grid tube at low plate voltage, that is, at a plate voltage approximately equal to thc screen voltage. The suppressor, therefore, makes possible the efficient operation of this tube at a relatively low plate voltage. This may greater than, equal to, or slightly less than the recommended screen voltage. Electrical Data: Heater Voltage ............................. 6.3 DC V Heater Current ................................ 0.3 A Preferred Substitutes .............. 44, 39, VT-49. Tubes test NOS Tv7 tested TUBES All our tubes have been tested for GAS SHORTS TRANSCONDUCTANCE & EMISSIONS If they are listed they have none of the aforementioned and have tested at NOS Test Results are ALWAYS available upon request! Looking for something else and want to save on shipping ? Send me a message! I might have what you need! Tubes will be packaged in white boxes - if the original boxes are not photographed in the listing or stated as “with original box” they are not included. 90 % of our tubes are Tv7 tested, our tv7 is Calibrated and our go to tester. The tv7 tester has been around a long time and zzzis a trusted tester for military, who had high standards for reliable tubes that would not fail in critical conditions. Military standards were tubes needed to meet 60% (minimum value) There isn't a “specific” indicator or result or data set anywhere that universally designates a vacuum tube as "new old stock" when using a tester nor for what test result is given. The best way is to calculate the GM - and check the data sheet for each tube - a nos tube should typically measure between the average and maximum micromhos(GM) Tubes do not give the same reading across testsrs - even the same model tester will give a different reading sometimes. RETURNS ARE NOT ACCEPTED BECAUSE YOUR TESTER SAYS SOMETHING DIFFERENT THAN MINE. If you don’t like the sound of a tube, so long as it is still in the same condition as arrived message me and I’ll work with you A common misconception of tube testing is that every unused tube, new or vintage, should test at 100% of the meter scale of the tester. A tube was considered acceptable/new/ passed standards if it tested between the specified minimum and maximum on a tube data sheet or the minimum value specified on the tester (tv7 is minimum is 65%) Please see my notes on noise tests below ***We have a few different testers available to ensure the quality of the tube***** (as some tubes can not be tested on the tv7) Tv7 testing is tedious and I spend 12-13 hours a day testing tubes and double testing tubes - if you notice a mistake(like a picture doesn’t match the title) please be gracious and let me know. UNLESS PHOTOGRAPHED WITH THE ORIGINAL BOX- tube will come in repackaged white boxes- 50-90 year old cardboard packaging doesn’t hold together well, not in my hands anyways. ***we have over the last 20 years amassed a huge collection of vintage amps/ parts / tubes and have decided to downsize that collection. Every tube has been marked for tracking and security purposes - these marks wipe off easily and without the mark no return will be accepted - Sound quality is tremendously SUBJECTIVE. Please let us know what your intended application is prior to purchase if you have a specific sound in mind and/or just don’t know what you want. NOISE TEST. This is a very marginal test, only for special checking. This test needs sound amplification; hearing listening to noise with headphones would indicate a real disaster inside a tube (THE shorts test WOULD already BE evidence OF THIS) some testers do have noise test jacks that connect to either headphones or to the antenna/ground terminals of an AM radio. There is nothing wrong with performing that noise test. *****this test is not going to tell you whether the tube will be silent in your SET (single ended triode) amp or in anything else. *****Ultimately, the best way of testing a tube for microphonics is in an actual chassis or amplifier similar to one in which it is intended to be used.” Since amps have a wide variety of circuit designs and tube placement, this test is most effective in YOUR AMP or one that is almost identical. Hence, most people advertising tubes as tested for Noise or Microphonics are probably NOT testing them in any meaningful way for you. “Noise” and “Microphonics” are often buzzwords for other issues. (Shorts/ leaks) -there is a small percentage of tubes that have a problem with noise but far less than most people think. *****In properly designed circuits objectionable “tube noise” is seldom found. ******* In other words, it is a rare tube that will be noisy when used in most circuits. Always check the data sheet of the tube you plan to use. 1. RETURNS: I want you completely satisfied with your purchase from me. I will bend over backwards to make sure that you are a happy customer, prior to and after purchase. PLEASE message me BEFORE you open a return. Additionally please not that you can not return a tube for reasons against eBay policy- saying defective or not as described because your different tester reads the tube different is unacceptable. 2. PLEASE NOTE: Tube silkscreen (lettering on the tubes) is VERY fragile. It can be wiped off and destroyed VERY easily. RETURNS ARE NOT ACCEPTED BECAUSE YOUR TESTER SAYS SOMETHING DIFFERENT THAN MINE. If you don?t like the sound of a tube, so long as it is still in the same condition as arrived message me and I?ll work with you