Tubes Asylum: REVIEW: Transcendent Sound Tube Analyzer Accessory by Tom §. Questions about tubes and gear that glows. FAQ

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Model:	Tube Analyzer
Category:	Accessory
Suggested Retail Price:	$579-1099
Description:	Vacuum tube tester/analyzer
Manufacturer URL:	Transcendent Sound
Model Picture:	View

Review by Tom §. ( B ) on November 26, 2002 at 08:30:21 IP Address: 205.175.225.22

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Vacuum tubes are dynamic devices. Their AC electrical characteristics change over their DC operating range. Going further, for the same tube type the AC electrical characteristics at the same DC operating point change from manufacturer to manufacturer and even from tube to tube (and even section to section) even in the same production run. They’re all snowflakes in a sense, not one alike. Sure they will still function similarly within a given range but none will function exactly the same way. Naturally, this would tend to create favoritism towards certain brands and vintages because people would tend to prefer how brand X consistently screws up the process as compared to brand Y.

Most every designer out there has a different idea as to which method is best to operate a vacuum tube. This leads to the notion that not every amp sounds the same even when using the same vacuum tube type and general circuit topology. Some manufactures go to great lengths to weed out the tubes that don’t function in the manner that they want them to function. Ever wonder why a few manufacturers get a bit antsy when a customer proclaims their amps don’t sound right when they slap in their teleumptysquatperex NOS 12AX7? Uncontrolled variables at play…..

So we have two wild cards playing against each other producing a mish-mash of sonic results: variability in tube manufacturing and difference in utilization from the manufacturers.

How do we make sense in this tempest-in-a-teapot chaos? The end user has control of the tube swapping aspect so……….test the tubes and make sure they’re the same, damnit!

Sounds simple, right? Well, the great majority of tube testers just test emission which isn’t an indicator of how the tube performs dynamically. Another kind of tube tester is the mutual conductance tester. This gives a result more meaningful for AC performance but it doesn’t test the tubes under the conditions of *your* gears operation of the tube. Two tubes can test exactly the same in the static mutual conductance measuring system but will not perform exactly the same in your amplifier (music isn’t static, remember?). Your amp doesn’t use the tubes like the mutual conductance tester uses tubes. It’s not much of a meaningful comparison but it is better than emission testing or inspecting the tubes structure to see if it’s “good.”

“But wait a minute Mr. Dumbass squiggly S person, just stick them in the amp and use what sounds good. “

I completely agree. However, knowledge is precious and saves time, effort, and resources. Wouldn’t you want to know why certain tubes sound good to you while other tubes that are supposed to be the same don’t sound the same? Don’t you want to know what will reliably work for *your* situation? Wouldn’t you like to test the 50 tubes you just picked up at the repair shop (or cleaned out of antique elec. supply’s stock…..selfish bastards) and see which ones will tend to give you satisfactory performance without sticking them all in and out of your amp? If you’re a basement designer, wouldn’t you like to find out the ‘best’ operating condition for a tube in your design without creating a high voltage briar patch of electrical wire and clips on a wooden plank? Wouldn’t you like to slap a tube in a socket and have the knowledge by pressing a button?

Meet Mr. Transcendent Tube Analyzer. Now, before I go any further, I have to point something out. There is another device in a similar vein to the transcendent tube analyzer. It’s the RAT tube tester designed by Steve Bench . The RAT tester is strictly a scratch build DIY project. Both the RAT tester and the transcendent tester have very similar voltage and current capabilities with which to test tubes. I’m willing to bet Bruce started out building Bench’s design and decided to make some changes of his own. The similarities are striking. However, the two testers *are not* the same so don’t go off assuming that Bruce copied the RAT design. There is significant power supply configuration and measuring method differences between the two so it would be like saying that porsche copied ferrari’s automobile designs. Both accomplish similar tasks but do it very differently in implementation.

So which one should you go for? If you want to track down tiddlywink resistors and capacitors and scrape out holes in an aluminum chassis then go for the RAT tester. If you want a fully packaged kit with instructions, parts, PCB, and fully finished chassis then go for the transcendent analyzer.

So what is it? Basically the transcendent analyzer is a 0-300V 0-50mA variable power supply with separate adjustable bias, fixed filament supplies, and a fixed audio oscillator with a true RMS meter strapped on the end. It can achieve higher currents at lower voltage settings (up to 150mA) but 50mA is the rated top end if you’re running at the max voltage. Although, I was able to squeeze out 80mA at 290V while testing a 300B. I wondered why the limitation was there but I soon found out the reasoning in Bench’s description of the RAT tester: to limit thermal stress (flaming parts) from high power usage in the case of tube shorts. Sounds reasonable. However, it does limit the tester to small signal tubes and lower powered pentodes and triodes. No 845 or 6C33C testing here, folks.

Don’t let the power supply limitations lead you into thinking this isn’t a useful tool. The great majority of small signal tubes range of operation falls within the capability of the tester. You “can” test higher powered triodes and pentodes (in either pentode or triode mode) albeit at levels that usually are not what power amps put the tubes through. Although it *is* a lot better than a kick in the ass or emission and static mutual conductance testers.

So what does it do? It determines transconductance and mu at any operating point within the capability of the tube and tester by injecting an audio frequency on the tube grid while measuring the output on the plate. Why is that important? Because those characteristics determine the overall dynamic electrical nature of the vacuum tube which affects the overall musical performance. Now, this doesn’t mean that if a tube tests higher in transconductance than another one of the same type under the same conditions that it will sound better. It just tells you how the tube is performing dynamically under those conditions. You may prefer the tube that has the lower transconductance and you can now weed out the tubes for those that meet these characteristics. Isn’t that just neat-o spiffy?

There are other factors that come in to play in regards to determining overall sound quality that um…..transcend simple mu and transconductance tube characteristics. Circuitry plays a big part in sound quality. Since the circuitry in an amp stays the same, culling out tubes that don’t perform consistently in these parameters will engender consistency in the end result: music quality. The vacuum tube is the independent variable that needs to be nailed down.

So what else can you do with it? Trying to describe the tube analyzer is like trying to describe duct tape. There are numerous applications one could think of for this tool for casual tubers and for techy tube geeks alike. You can use it to manually plot curve traces as long as you have a multimeter to measure plate voltage (using a pin socket intended for the EL-509 top cap wiring). You can use the tester to find the “sweet spots” of operation of a tube for a future design. You use it just to test for bad tubes or verifying how NOS your NOS labeled tube really is. You can use it to find out if the dual sections of your 12A_7 or 6S_7 are matched under the conditions provided by your phono/pre/power amp. You can use it to test tubes under starved plate conditions (wanna guess which popular DIY preamp uses this kind of operation?). The possibilities are too numerous to mention in one writing especially when you can change tube sockets and socket wiring for oddball tubes.

Speaking of tube sockets, there are quite a few tube types this tester can test. 8 pin pentodes, 8 pin dual triodes, 9 pin 12A_7 triodes, magnoval 9-pin tubes i.e. EL509, 9 pin 6.3V small signal triodes, 9 pin pentodes, 4-pin DHT’s like the 2A3 and 300B (I modified mine to accommodate 101D’s). More detailed information on tube types tested is available on transcendent’s site.

There are limits though. The power supply range isn’t the only annoying hangnail in this units overall capability. The filament voltage is limited to 6.3V max. The 12.6V tubes the tester can measure are wired for the heaters in parallel so that 6.3V can be used. 300B’s use a separate 5V winding and 2A3’s use drop down resistors attached to the 5V winding to drop the voltage down to 2.5V (which means you’d have to change the resistor values to test 45’s). The great majority of small signal 12.6V tubes can get by using the heaters in parallel but there are quality variants of popular audio tubes that use a single heater @ 12.6V. Plus, there are audio tubes that use 7v and 10v heaters. An adjustable filament supply would go far in extending the capabilities of the tester. Only having 6.3V max for a filament supply was almost a deal-breaker for me. It might be a deal-breaker for those who need to evaluate tubes with filament requirements that exceed the tube analyzer’s voltage and/or current capability.

Hangnails aside, the unit does offer quite a bit of usefulness for nearly all the popular audio tubes used in today’s tube amplifiers. The analyzer and the RAT tester have the potential for becoming a well-used tool for designers and techs much like the multi-meter and O-scope have become. Is it necessary for all people using tubes to have one? Not quite. A mutual conductance tester is probably all some people will really need to just to test for used or dud tubes. If you want to delve a little deeper, the RAT and the analyzer are the way to go. The RAT and the tube analyzer go a few steps further and give the end user the ability to see how the tube performs dynamically under most practical conditions. Granted, a curve tracer can provide dynamic data but there are a few things the RAT/analyzer can do better than a tracer. I think Bench put it nicely in one response on the newsgroup list in a thread discussing the RAT and curve tracers: “I would second or third the comments that a tube tester is not the same animal as a curve tracer. Each has different qualities. I use both.”

Notes for kit builders:

Most of the parts used in the kit are pretty common so finding replacements down at radio shack or the local radio supply store is pretty easy. As with any large electronics kit there is the chance you’ll have a missing resistor or two.

Despite the inclusion of a circuit board for the power supply and manual with illustrative color pictures, the kit is not for beginners due to the wiring complexity in and around the tube sockets and switches. The switch circuit alone is a tedious endeavor. If you have some PCB soldering and sufficient hard wiring soldering experience then you can tackle this kit. Be prepared for long sessions of hard wiring.

For the initial test and calibration procedure the instructions have the installation of the fan after the calibration of the AC source. I think it’s better to install the fan first and then let the unit reach a thermal equilibrium with the fan running for calibration because that’s the condition the unit will be in operation.

The sine wave/audio oscillator in this circuit is a type of op-amp based phase-shift oscillator which is coined “the bubba oscillator” by a Texas Instruments paper. The oscillator has a very low distortion output as well as very tight frequency drift control. However, it is very sensitive to tolerances of part values. There is a ratio between two resistor values in the circuit that needs to be adjusted if the circuit does not oscillate on start up. I ended up changing one resistor value by 2% in order to get the circuit working. Manufacturing tolerances on resistors could cause this circuit not to function on startup so be prepared for that possibility.

Tom §.

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Product Weakness:	It's in the review
Product Strengths:	It's in the review

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Associated Equipment for this Review:
Amplifier:	na
Preamplifier (or None if Integrated):	na
Sources (CDP/Turntable):	na
Speakers:	na
Cables/Interconnects:	na
Music Used (Genre/Selections):	na
Type of Audition/Review:	Product Owner

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