Head-Fi.org › Forums › Equipment Forums › Headphone Amps (full-size) › 6SN7 Tube Addicts
New Posts  All Forums:Forum Nav:

6SN7 Tube Addicts - Page 247

post #3691 of 4437
Thread Starter 

Some ECC32's have been wrongly marked as ECC33's too check the photos here:

 

http://www.head-fi.org/t/536785/ecc32-tube-addicts

post #3692 of 4437

Sorry to bring this up again but

Quote:
Originally Posted by khaine1711 View Post

Hmm, are these CBS/Zenith actually the same as the famed Hytron black plate? 

Processed By eBay with ImageMagick, R1.1.1.M1

 

And

 

 

Are the pair above the same as the famous Hytron 6sn7 black plate I've often heard about or are they different?

 

I think I'll jump the Raytheon, Tung-sol and maybe the CBS/Zenith (from the same seller actually). He only gives test result and doesn't guarantee anything so I'm a bit wary, but not much choice for 6sn7 in the UK or EU.

post #3693 of 4437
Thread Starter 

There are some great 6SN7's made in Europe, you need to research a bit more.

 

As for guarantee what exactly are you looking for?

post #3694 of 4437
As far as I can see the CBS tubes in the photo are hytron. Two things to look for are the top mica having no "teeth" which press against the glass, and the etched logo on top of their tube with the circle drawn around it. The circle is pretty unique to hytron.

Since your Sylvania's are GTA tubes you could look into the vt231 Sylvania's or the gt tubes with the very heavy top gettrer flash. The w tubes are nice too but there's are half a dozen different kinds just within the Sylvania brand alone so it can be tough to choose.
post #3695 of 4437
Thread Starter 

The Zenith is also made by CBS/Hytron, the makers code confirms that.

post #3696 of 4437
Quote:
Originally Posted by rosgr63 View Post

There are some great 6SN7's made in Europe, you need to research a bit more.

 

As for guarantee what exactly are you looking for?

Microphonic mostly, aside from not dead on arrival of course.

 

Also regarding the CBS/Hytron/Zenith, the seller said the test results were

 

Quote:

Tested on our old but trusty taylor 45C tester.

                                            [New is 3.00 megohms]

 

 #1  CBS Code  TC [No date code]                    T1= 3.1     T2= 3.4

 #2  Zenith Date Code 5530 [1955 week 30]        T1= 2.7     T2= 2.2

I actually have no idea what these number means. How close to a matched pair are these?

 

I'll get channel imbalanced if they're not matched, although I do not know how tightly matched a pair should be to avoid that.

post #3697 of 4437
Quote:
Originally Posted by rosgr63 View Post

The Zenith is also made by CBS/Hytron, the makers code confirms that.

I meant to imply that but didn't, thanks for clarifying it.

post #3698 of 4437
Quote:
Originally Posted by khaine1711 View Post

Microphonic mostly, aside from not dead on arrival of course.

 

Also regarding the CBS/Hytron/Zenith, the seller said the test results were

 

I actually have no idea what these number means. How close to a matched pair are these?

 

I'll get channel imbalanced if they're not matched, although I do not know how tightly matched a pair should be to avoid that.


I wonder if the seller is testing correctly, or using the correct values.  New Gm (transconductance) on a 6SN7GT is 2,600 uMHOS at 250 volts. Some tester will read this value and some will not, instead testing the emission and displaying it using an arbitrary scale.  Generally if you know the New and Minimum Good values for that specific tester then the test results have some meaning, but the strength of the tube is always secondary to whether or not the tube has been properly tested for shorts and leakage.  He might be confusing the emission/transconductance read out with the leakage test read out too.  The words "trusty old tester" also brings into question how many years it has been since that seller has had his tester calibrated.  An old tester which is out of calibration is no different than having no tester at all.

 

You can find some good deals or rare finds on eBay but caveat emptor are the words that carry the day there.

 

FWIW tube matching is pretty overrated, they would have to be pretty far apart to make a real difference.  Matching can mean different things too, emission, transconductance, plate current, these are all different ways a tube can be matched.  For a tube that is used as output the last of those three is probably the most important I think.  Also, most amps are self-bias and will make up for small differences between the two tubes. 


Edited by Xcalibur255 - 8/26/13 at 4:54pm
post #3699 of 4437
Thread Starter 

The Taylor 45 is a British mutual conductance tester.

 

The seller has used the wording at the bottom of the scale but his results are in mA/V and has two scales 0 to 3 mA/V and  0-15mA/V.

 

It tests for shorts at 10MOhm which is excellent much better than Hickok at 0.25MOhm.

 

Assuming it's accurate the first tube tests better than New and the sections are 10% apart.

The second is 90% and 73% of a new tube, and the sections are 20% apart.

 

The strongest section of the first tube is 35% more than the weakest section of the second tube.

More than 10% variation is too much.

 

In conclusion the 1st tube has sections within 10%, but the 2nd has sections 23% apart.

 

The plate current is one of the best methods but that again says very little as it tests for one point on the curve.

You have to have the full curves matching to be sure the tubes will match at the amp's operating conditions.

 

Testing for microphonics is also amp dependent, unless the problem is severe a slightly microphonic tube can be used. Besides low microphonics are part of a tube's magic.

 

Finally because a tube doesn't test new doesn't mean it's not good.

Test values are a sales tool nothing more.

post #3700 of 4437

As I posted on the -rebuilding an old tube amp thread. Mutual conductance=gm=mu times 1000 over Ra=ma/volt. The US uses the term trans conductance but gives the same resultant gain in micromhoms  which equals ma/volt. I have the Taylor 45c as well as an avo vcm Mk4 . The only things to watch are testing very high gain tubes which weren't reckoned with you might find it hard to zero the balance using the 2 controls[A+B] I inserted a small value variable resistance in series with the -A -control via a micro switch [to switch it off when not needed ] when trying for zero balance  with a high gain tube switch the resistor in  leaving it at mid point then using the control set it up as near as you can and finally use the small value pot. to finalize the adjustment. The one thing that goes wrong with them is the mains primary windings sometimes overheats and becomes  s/c  totally changing the tester into a paperweight. Transformers are hard to find.I also made several tube bases to plug into the IO-1- tube socket. But you need a commercial tube manual for checking which socket pin goes where. - A lot of time involved also using the book that  comes with it for the pin codes .  

post #3701 of 4437

good read on tube amp

post #3702 of 4437
Thread Starter 
post #3703 of 4437
I have never been that brave biggrin.gif
post #3704 of 4437
Thread Starter 

They don't even have Chelmer original boxes but bulk boxes.

post #3705 of 4437

The boxes are available in another auction for $300 each. k701smile.gif

New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Headphone Amps (full-size)
Head-Fi.org › Forums › Equipment Forums › Headphone Amps (full-size) › 6SN7 Tube Addicts