Is this a fake Telefunken?

[brokenbones]

I picked this up this little mysterious tube today. Frankly, i'm not even sure of the type. There are no markings besides inside the diamond. The Y getter looks legit but what about the diamond? Can anyone spot a fake?



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[Silverface]

The square and numbers in the base look exactly like the codes...with different numbers..in my Telefunken 12AT7's. The construction looks moralize a 12Ax7, but it's hard for me to tell without a full-length shot.

Telefunken - yes. Which tube, hopefully somebody else can pin it down.

 

[brokenbones]

free photo website hosting

 

[Armo]

Ticks all the boxes for me. That diamond I would imagine would be difficult to copy. That's a real nice score. I have some Ei's which used the same tooling or so I'm led to believe and they are excellent, my fav tubes. The Telefunkens are real pricey.

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[mgreene]

My understanding was always that fake telefunkens do not have the diamond.

You can probably google pics of real telefunken markers.

Mike

 

[D'tar]

Now You can tele funken real one from a faken!

 

[mRtINY]

...groan...

 

[cabra velha]

score!

 

[Silverface]

Once it's ID'd (the specific tube type) if you want to use it you should use a calibrated tube tester to make sure it's not bad (tube testers are lousy at testing quality - they don't put out enough plate voltage) - you don't want to plug in a shorted tube - and then test it in an amp for balance and microphonics.

At least a quarter of the "high end" preamp tubes I've bought used I ended up tossing halfway through the screening process, and another 25% don't make it through microphonics or balance testing.

 

[protein]

I have two smooth and one ribbed plate....all of them have diamond bottom and some numbers in it...

 

[protein]

Your looks like mine...

 

[brokenbones]

I did a short test with just a dmm last night and it was fine. I'm actually in the middle of restoring/recalibrating my Knight (non-mutual conductance) tester. Once completed i'll give it a run through it. That tester tests for shorts and leakage. The nearest repair guy that I trust is 40 minutes away but he has a good mutual conductance tester.

I came across this video on youtube on how to determine the gain factor. I may try doing this (with other known tubes first) to determine this 12a's value.

 

[protein]

A friend of mine has Amplitrex tube tester and it is best as far as I know...there was a pdf online guide about gain,volume,noise factors...

 

[Silverface]

A mutual conductance tester will not do much more good than an emissions tester as far as guitar amp use goes - and there's no way to test for gain other than in a guitar amp or with a specialty tester that costs thousands of $$$.

Mutual conductance testers - no matter how "good" - run octal power tubes at a maximum of 185 plate volts - and 9-pin tubes, especially preamp types, are run *far* lower.

Without hitting the tube with voltage similar to the plate voltage of a guitar amps - some run in the 200V +/- range - the tests are completely invalid. You simply can't use low-voltage comparisons as tests for a tube that will be running at 2 or 3 times the voltage.

The additional stress of higher voltage changes the operating properties of the tube.

The "mutual conductance" tester is not even useful at lower voltages unless it's been calibrated in the last 3-5 years or so. Over 90% of the ones in use are either used by radio/TV repair people or ham radio buffs and I've encountered a handful out of several dozen over the years that were properly calibrated.

Virtually every one sold on eBay *not* sold as "fully calibrated" (with the paperwork to back it up) is a boat anchor - and there are very, very few people in the U.S. who calibrate them (and it's an expensive job).

I have a calibrated Hickok 6000A. I use it only to screen tubes as "good/bad" - NOT "how" good. All power tubes are tested and the bias checked (whether fixed or cathode bias) in an appropriate, fully-serviced guitar amp; preamp tubes are tested for gain, microphonics/other noise and (very important for driver tubes) balance, again in a serviced guitar amp.

Without a high-voltage tube tester it's the only way tubes *can* be tested. using just a tube tester is a complete waste of time, and for guitar amp purposes "mutual conductance"/"transconductance" testers are a waste of money. They - and emission testers - can be useful, but *only* to test tubes for shorts and other complete failures.

(I actually had a high-voltage military tester about 20 years ago, but was offered $2500 for it and sold it.)

 

[jazzguitar]

Can anyone spot a fake?

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It is a real Telefunken. A smooth plate one.

All the signs are there. The getter ring shape, the hint of blueish rim on the glass bottom, the shape of the filament connecting posts and where the filaments are welded, and also the shape of the evacuation tip on top of the tube (different from GE and Philips, slightly similar to typical RCA), all match perfectly.

I don't really need the diamond but it is there as well.

 

[cyberpunk409]

I think the bottom diamond and the labelling are things that are external and can be faked. What can't be faked is what's INSIDE the glass.

The only way to do that would be to break the glass, modify the internal structure, create new glass, reseal, etc. At that point, you may as well just produce a fake from ground up, which I don't think anyone is doing right now given the complexity.

Having said all that, here is another clear sign of a real Telefunken:

The getter is not a round circle. The bit where it's welded to the supporting rod is indented. Now that CAN'T be faked.