NOS versus new production tubes

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Re: NOS versus new production tubes

Post by øøøøøøø » Wed Feb 16, 2011 8:59 am

I don't have any experience with the AC50 first-hand.

But here's some stuff to weigh out in your mind.

First is that NOS EL34 of high quality are expensive. VERY expensive. Marshall guys want them, Vox guys want them, McIntosh and Dynaco and tons of other Hi Fi guys want them (maybe even more than the guitar guys). The really nice ones are Mullards. Siemens are OK, too. Those (especially the Mullards) will break you. I absolutely would not buy a set unless I was absolutely sure the amp was not going to destroy them.

Second is that in addition to sound and longevity, a big difference between NOS and new production is that, very often, the NOS tubes are drastically over-engineered. Voltages and currents listed on the data sheet as "design maximum" can be handled without a sweat, and very often can be exceeded by a great deal with little consequence. Manufacturers of old gear knew this (in the back of their minds) and would often push the tubes in their gear well beyond the "limits" set forth by the manufacturers. Old Fender amps that use 6V6s and 5881s will often push the tubes well beyond maximum plate voltages, sometimes by 50 or even 100 volts (or even more). The old tubes handled it fine, because they were over-engineered.

New production tubes are very often built to "barely meet" the numbers in the data sheets, and sometimes they fall short even of that. Until the JJ 6V6 came along (probably the only decent tube that company makes), there was not a single current-production 6V6 that would run reliably in a Deluxe Reverb.

In the old days, in addition to just good old-fashioned over-engineering of all products, they'd often produce one tube type and all similar, lower-rated types would just get the same tube with a different pinout (if necessary) and labeling. For example, after the 7027A came out, the lower-rated 6L6GC became the same as the 7027A internally. The data sheet had lower numbers, but to make production easier, they just made one tube... some got 7027 bases and labeling, some got 6L6GC bases and labeling... and those were some robust-ass 6L6GCs. Similarly, the JAN/Philips 5881 is actually a 6L6GC inside.

So it's possible that your AC50 (which I know nothing about) was designed with the assumption of over-built tubes, just like many older amps (Deluxe Reverb, tweed bassman) were. Perhaps it pushes them beyond what's on the data sheet. Perhaps this is why it eats new EL34s (Try something other than JJs, as well, which don't necessarily have the best rep for reliability or sound in an EL34. I've bought 4 pairs of them for various "repair and flip" projects, and was underwhelmed).

Thirdly, consider that modern wall voltages have crept up and up over the years. When the voltage gets transformed upward for plate voltage, the difference of 5 or 10 volts at the wall can be very significant... it can become 30 or 50 volts different on the secondary side of the transformer. If tubes were already being run "at the edge," this can prematurely put them under in some cases. Stick a meter in your wall and find out what you're getting out. If it's significantly higher than what's printed on the back of the amp as the input voltage (usually 117 in the USA, probably something close to 220 or 240 in Europe), then consider getting a source of regulated, steady power.

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Re: NOS versus new production tubes

Post by jetset » Wed Feb 16, 2011 9:14 am

øøøøøøø wrote: Thirdly, consider that modern wall voltages have crept up and up over the years. When the voltage gets transformed upward for plate voltage, the difference of 5 or 10 volts at the wall can be very significant... it can become 30 or 50 volts different on the secondary side of the transformer. If tubes were already being run "at the edge," this can prematurely put them under in some cases. Stick a meter in your wall and find out what you're getting out. If it's significantly higher than what's printed on the back of the amp as the input voltage (usually 117 in the USA, probably something close to 220 or 240 in Europe), then consider getting a source of regulated, steady power.
+1 on this. I have an old Vox AC15, and I had the guy who restored it (Matt @ JMJ amps) include power scaling to be able to dial in the right voltage. A lot of guys also get a step up transformer and run their Vox or other British amps that have voltage selectors on the 245V (UK) setting. Some say they sound better that way. If you have a tube rectifier (which most ac50's don't) you may also be able to adjust things with a tube substitution. Not sure about that.

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Re: NOS versus new production tubes

Post by NoiseAnnoys » Fri Feb 18, 2011 7:59 am

Thanks Theta and Jetset. I'll have to look into the line-voltage. The amp has been frankensteined a bit, so that the voltage selector isn't easily accessible anymore (the previous owner took its big-box AC50 chassis and transplanted it into a narrow-box AC100 shell), but it's still there. I'll ask my tech about it next time I take it in.

That's a bummer that there's no EL34s even remotely close to old specs around. :'(

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Re: NOS versus new production tubes

Post by jetset » Fri Feb 18, 2011 8:51 am

NoiseAnnoys wrote:the voltage selector isn't easily accessible anymore but it's still there. I'll ask my tech about it next time I take it in.(
If you want to go the step up transformer route, you could have him wire up the 245 tap directly, and bypass the selector. Those vox voltage selector gizmos are kind of sketchy anyway.
-J

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Re: NOS versus new production tubes

Post by NoiseAnnoys » Fri Feb 18, 2011 9:15 am

NoiseAnnoys wrote:the voltage selector isn't easily accessible anymore but it's still there. I'll ask my tech about it next time I take it in.(
If you want to go the step up transformer route, you could have him wire up the 245 tap directly, and bypass the selector. Those vox voltage selector gizmos are kind of sketchy anyway.
-J
Yeah. I haven't read anything good about them. I was kind of idly thinking about having him just set it permanently to 115, but that's starting to sound like a better option in some ways. :D

Vintage correct, stock AC50s are kind of death traps, apparently. :derp:

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Re: NOS versus new production tubes

Post by jimboyogi » Fri Feb 18, 2011 3:05 pm

NoiseAnnoys wrote: That's a bummer that there's no EL34s even remotely close to old specs around. :'(
Have you thought about/tried the JJ KT77?

http://www.vintageamps.com/plexiboard// ... 65&start=0" onclick="window.open(this.href);return false;

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Re: NOS versus new production tubes

Post by øøøøøøø » Wed Feb 23, 2011 12:51 am

Ominous words from Oliver Archut today:
Hello guys,
the situation will get even get worse in the next couple of years, since the crumbling of the CRT market, the companies in Russia that made the raw materials are stopped production due the fact that nobody wants CRT based monitors anymore and that was the last big domain for inexpensive vacuum materials.

Every year I buy a bunch of in production valves and sorry to say, none of the current EL34, 6L6 variation or EL84 are even close to a NOS tube of western origin.
The lifetime is the first problem, the best EL34 I tested works for about 3 month, that they go either deaf of die in a light of glory and melt down. I recently retubed the first amplifier ever sold commercially (28 years by now) with EH 6V6 and from the 6 I bought two where bad, and two did a melt down. Ended up and bought a bunch of EMI made 6V6 type tubes and they work great.

From the last batch of EL84 I bought for Oahu amps, half of them were bad right out of the suppose to be computer tested batch.

Regarding NOS tubes, every month good batches of GE, Sylvania and Mullard lots show up, the question is just the price. $120 for a genuine 6L6GB that will last without a problem for 10 years? I think it is a fair price given the fact the pain of replacing junky in production tubes.
It is getting harder with Telefunken or RCA tubes.

Best regards,

Oliver

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Re: NOS versus new production tubes

Post by sookwinder » Fri Apr 22, 2011 8:41 am

We were discussing where to buy NOS valves a month or so back in this thread and I made the comment that bargains can still be had on ebay if you watch and watch and do your homework.

Well I ahve been "stocking up" on EL34s / 6CA7s for a project I have planned for 2012 (while the aussie $ is worth 1.07 US$ ) and managed to win two NIB/NOS Mullard EL34s branded as RCAs ... they are the XF2 variant , probably late 60s to early 70s ... for $100 for the pair .. that's $50 each ... they go for anywhere from $100 - 150 for a single valve on ebay normally , sometimes even higher ...

get this ... then the seller asks if I want two more of the same, but with the boxes slightly eaten by mice... for $45 per valve ... as I said bargains can be found

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relaxing alternative to doing actual work ...

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Re: NOS versus new production tubes

Post by OffYourFace » Fri Apr 22, 2011 9:04 am

excellent score David!
synth tech at www.rosensound.com

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Re: NOS versus new production tubes

Post by øøøøøøø » Fri Apr 22, 2011 9:08 am

nice find!!!

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Re: NOS versus new production tubes

Post by jimboyogi » Fri Apr 22, 2011 1:01 pm

Bingo David! This project is getting closer and closer :)

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Re: NOS versus new production tubes

Post by Jay » Sun Apr 24, 2011 4:21 pm

Nice deal there! I have a pair of the exact same XF2 Mullards (though Mullard labeled) and one is fantastic in the Champ I modded so I imagine you'll be pleased as well. I'd also recommend looking for an old Tung-Sol 5881 for your build. I find one of those to sound the coolest in mine—albeit by a slim margin over a 6V6 or EL34.

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Re: NOS versus new production tubes

Post by sookwinder » Sun Apr 24, 2011 6:25 pm

I really enjoy this amp design/building thing...

Here I am looking (and finding parts) for the project for next year (PR with 2 x EL34) and realising that I need to do a lot of reading and underatnding of designs that have gone before, when the current project (Champ Reverb with EL34) is still half way finished ...
relaxing alternative to doing actual work ...

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Re: NOS versus new production tubes

Post by idiotbear » Thu Jan 24, 2013 11:12 pm

The '69 Pro Reverb I have my eye on has a lot missing: it's trashed. But it's also cheap, so I'm going to try my hand at restoring it.

It seems that theampdoctor's TAD tubes get good reviews - but it'd be great to know if anyone has any experience of using them? I'd like to avoid the cost of NOS if at all possible, but then I also want to avoid false economy. If I'm going to have to replace a bunch of early blown tubes, then maybe NOS is more cost effective.

Anyway. TAD opinions?

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Re: NOS versus new production tubes

Post by ludobag1 » Thu Dec 24, 2015 6:26 am

i have read all and it is really interresting
i would like just to tell me a story between nos and brand new tube
i trust in nos but you must know what you buy or you will be not happy

beguin of the story
i have buy this fender reverb reissue from 93 us model 110 v with the 220 110 v transformateur
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the guy give with this spare tube
Image

in it i have a 12at7 rca ,a fender 12ax7 and a 6v6 tad

it sound good but i have a hiss coming from the verb ,when the mix was at 3 and you push the volume on amp a larsen appears ,i swap with the tube in my deluxe and found it is the 12at 7 rca was the trouble
then i go to buy some tube for spare and i find some groove tube (12ax7 and 12at7 )at a musical store and the store work with a tech then i visit him and buy also tube 12ax7 EH and 12at7 syvania (nos) for sure
result the groove tube works don't know for how much time but my trouble is solved i can reput the tube in my deluxe that i have swap to try
the 12at 7 don't work ,i call the guy and (it is an asshole to be short) cause he explain me no refund on tube i could have make lot of thing with ,bla bla then i go to him and tell him that i have swap with other tube and it is his tube that doesn't work (the trouble is no reverb on my unit ,the 12at 7 is the tube for the tank then it is the culprit)
then he give me another 12at7 syvania (same looking ) and you know what ,it doesn't work too ,then i have visit another technicien to make repair my bass amp and ask him to test this tube
answers he have try in his head(he repair and build amp) and the tube don't work too

all of this to say ,if i can i will buy totally new tube cause i think it is rare to have one not working ,for the nos it is really risky cause lot of guys sale old tube ,not tested ,or maybe worst old tube out of life they have find in a box that come from an old technicien and this box was the box where not working tube where stock

don't know for you guys but for me in France there is not lot of good tech who can test tube ,and if you put a dead tube in a good working amp the damage could be grave for the amp ,shortcircuit ect...
i have seen lot of auction for tube but i haven't the knowledge to look at ?
for exemple
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on this 6k6 the sylavania have a label writen on 38- 45 like the RCA ,but the third is Ge but no marking and more over no 6k6 marking on it then i don't know what it is ?

i have swap the 6v6 tad for the sylvania 6k6 to my taste the sound is better ,more hot

i see lot of auction for nos ,full tested ,90 % of life , or result in ma but where do you find chart to knew if the tube is good enought to be use ?
for exemple a 12at7
it is a rare saler who tell the caracteristics
fil= 13v
polard = -2,v
anode =250 v
10 mA-10 mA correspond à = 100%
résultats
10,8mA - 9,8 mA
10,0mA - 10,0 mA

cause lot said tested and you buy something you don't know if it is nos or uos or worst ready to dead

sorry for the book :fp:

also i have an old EL84 Mazda in a old radio can i try it in my little vox ac4 without too much risk ? ,if it work it is ok ,if it is not working will it blow something in the amp?

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