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KT120 and KT150 tubes not up to spec
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Author:  gofar99 [ 08 Feb 2017, 16:07 ]
Post subject:  KT120 and KT150 tubes not up to spec

Hi Everyone, What many of us have feared is apparently taking place. QC on Tungsol power tubes seems to be inadequate. A UK licensee of some of the Oddwatt designs has been having KT120s red plate and been getting defective KT150s from a previously trusted source. The red plating occurs at around 60-70% of rating. Not good. Worse there is a thread on that others are having the same issues. So if you build something and the tubes seem to be misbehaving send them back as often as needed to get good ones. So sad.

Good listening

Edit: ... ost4975833

Above is the link

Author:  Geek [ 08 Feb 2017, 18:43 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

I'm a Rogue Audio dealer and they're sending back a lot of bum T-S before passing the good ones on to us :(

Author:  Gio [ 08 Feb 2017, 21:27 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

So are the problem tubes random, QC as Bruce suggested? Because if the tubes are not being called back by lot numbers from the retailers, it could take years to flush the bad tubes out of the stores.

Author:  Geek [ 09 Feb 2017, 02:46 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

Gio wrote:
So are the problem tubes random, QC as Bruce suggested?

Not sure. The amps arrive with good, tested, biased-and-holding tubes. I just heard they have to go through a few at the testing phase before sending them out with good ones. Will ask our rep for more info when I see him.


Author:  gofar99 [ 09 Feb 2017, 14:48 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

Hi, Our folks in the UK are getting them more or less randomly. Some good some bad within the same lots. They are burning them in now. In the US so far we have been ok. But when we run out of the current stock we (Oddwatt Audio) are likely to have to burn in all of them to send with the kits and amps. Thank you very much Tungsol. :mad:

Good listening

Author:  Peter W. [ 10 Feb 2017, 08:17 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

Why is this a surprise to anyone? Modern-day tube manufacturing is a sad and sorry shadow of a once great industry. Once upon a time, perhaps as late as 1960, the cost of excellent QC and extremely careful manufacturing processes was divided amongst tens of thousands of tube produced in any given week. There was actual competition between material suppliers to the tube industry and between tube manufacturers and OEM equipment manufacturers *AND* the service industry also would hate to have a free come-back for a defective tube.

Today, manufacturers could sell DIY tube kits (supply your own vacuum) find buyers. Not only that, but I would suspect that the entire annual production from any given maker would be dwarfed by a day's (probably hour's) worth of production from the Sylvania plant in Emporium, PA, or even their skunk works in Philadelphia which was a very modest 200,000 s.f. and dedicated to short-run specialty tubes.

Guys and gals - the only way this will change is that if the price of tubes more-or-less doubles, those revenues becoming entirely dedicated to QC and materials improvements, as well as machinery maintenance and repair. Right now, consider the supply chain and costs involved. Legitimate sellers who stand behind their products understand that they need to purchase 50% more tubes than the actual demand so as to cover defects. If each tube costs them $5 to obtain, and then need 100 items per quarter, they must purchase 150. The raw cost of each viable tube is now $7.50. Then shipping, handling, bad will. Overhead including labor, rent, heat, light... Only after all that profit. No wonder such a tube at $5 from the factory might run $50 or more at retail.

And the manufacturers see no advantage to making really good tubes as far too many buyers are fooled by the printing on the box. Tung-Sol was once a top-level maker. The box reads Tung-Sol - it must be good. Mullard.... . Gershwin had it right: It ain't necessarily so.

I see no easy solution other than infinitely patient and demanding users. And middleman retailers willing to take up the slack in the process (not very likely) by holding their suppliers' collective and several feet to the fire. Sadly, the brute fact of the matter is that there is simply not enough demand worldwide for this to happen in any meaningful way as there is always *somebody* who will buy this crap at any price.

Author:  gofar99 [ 03 May 2017, 18:03 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

Hi everyone, The issue is now on a sister site ( I am hopeful that if there is enough public fall out on it that perhaps NewSensor and TS will get back on the program. The alternative tubes (Psvane...not recommended and Treasure ....probably OK) are not as common and in the second case quite a bit more costly. I would like to hear if anyone has used the Treasure tubes in a class A amp either PP or SE and how well they worked at higher power dissipations.

Good listening

Author:  Geek [ 03 May 2017, 22:45 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

Shuguang Treasure I've had no problems with, even right at max Pd and Va.

Author:  M. Gregg [ 07 May 2017, 05:23 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

Here is my take on it,

Tubes and quality are going to be an ongoing issue, so we can throw the doll out of the pram and have a hissy fit or:

Accept that tubes are variable in quality, try to discover what "out of spec actually means"
Is it the plate size, cathode size, cooling, heating or leakage.

Then if possible make the design cope with the "modern tubes".
If its leakage deal with the leakage heater cathode or other.
if its the physical size of the tubes de-rate the tubes or have a switch to do the job or some auto design.
Etc, etc.

Yes we know the tubes should be perfect but this isn't unusual just look at 6c33c as an example.

I don't believe that tube production is going in an upward trend.
Think of it as a challenge is one way. The other is keep using burn't in tubes until they all fail at burn in.
Then look at the smashed pile of out of spec tubes and wish they were still in one piece.

Just my thoughts YMMV.
Just one more thought, I don't think leakage is a reason to scrap tubes. A difference in potential between heater or cathode is an issue but only if you let it be. Under size plate or cathode is a different issue.
I know for a fact that in the past a company made 6L6 tubes which could not carry the current so they repackaged as a "super 6V6"
they sounded great.

You will see ECC83 re-labelled as 12ax7 and substitutes repackaged etc etc, this is not new its been going on since tubes were invented. OH look my tube heater flashes does it :eek: , chuck it in the bin..but they work fine well do we stop manufacture or fit a timing get the point.

Perhaps the manufacturer should grade the tubes..and you flick a switch to use the B grade..etc

M. Gregg

Author:  M. Gregg [ 07 May 2017, 06:01 ]
Post subject:  Re: KT120 and KT150 tubes not up to spec

The other side of the coin,

Only my thoughts and YMMV.
My amp uses KT150 and it has pre-burned in tubes..its a great amp..then in the future every tube I fit red plates and I can't get a burned in set.

In my book at KT150 is a designer tube, perhaps a new tube that will sound great for a limited period.
Its like having parts for a vintage car that has mass appeal, or a one off special. Which one has the parts to keep it on the road longest.

Car parts>> EL34/KT88 or a KT150?
That's why I like amps that are "universal" a bit like Mad Maxes car use any fuel available while the desert expands.. :|

M. Gregg

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