NOS versus new production tubes

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Re: NOS versus new production tubes

Post by zhivago » Mon Feb 07, 2011 1:30 am

some more just arrived...RCA 6V6GTAs... :)

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there will be more this week, and then the experimenting will begin! 8)
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Re: NOS versus new production tubes

Post by Jaguar018 » Tue Feb 08, 2011 10:40 am

I'd be willing to take your zhivago seconds... ;)

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Re: NOS versus new production tubes

Post by zhivago » Tue Feb 08, 2011 12:23 pm

Jaguar018 wrote:I'd be willing to take your zhivago seconds... ;)

I'll see what happens after the shootout, and let everyone know how the spares will roll :)
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Re: NOS versus new production tubes

Post by Jaguar018 » Wed Feb 09, 2011 6:31 am

zhivago wrote:I'll see what happens after the shootout, and let everyone know how the spares will roll :)
Cool. Whenever I read stuff on tube comparisons, there tend to be stand outs. Often second or third place is almost as good, or just has a different element to the sound that the tester person subjectively does not enjoy as much as the #1.

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Re: NOS versus new production tubes

Post by zhivago » Wed Feb 09, 2011 6:48 am

very true! :)

this arrived today...

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....and more to come in the next few days... 8)
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Re: NOS versus new production tubes

Post by NoiseAnnoys » Wed Feb 09, 2011 10:41 am

I didn't really buy into the NOS hype until I picked up an old Harmony amp that had the original RCA 6V6's in it. They really do sound amazing. I'm going to have to buy a stash while prices are still reasonable. Yannis, I'm curious to see which ones are your favorites.

I still use JJ's though for things like my Vox AC50, because it just chews up tubes as is and I'd hate to spend the coin on NOS EL34s to keep it going. Plus, I feel this weird kind of ethnic duty to them for having a plant in Slovakia. :D In the end, I suppose I could get NOS for them, but the AC50 was my road amp (and hopefully will be going on tour in the next few years) and I hated the thought of carrying $300+ worth of tubes around as replacements in case something went wrong.

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Re: NOS versus new production tubes

Post by zhivago » Sat Feb 12, 2011 6:58 am

I found this explanation of tube name/designation aliases online on another forum, that I thought we could have here too...
12AX7 numbered variants:

7025 - spiral wound filaments for reduced hum. Most 12AX7s after the mid 50s will have this as a standard feature.

6681 - mobile-rated 12AX7. Filaments perform well with a wider range of voltages.

6057 - Brimar's special quality 12AX7.

7729 - CBS/Raytheon's instrumentation grade 12AX7, with heavily gold plated pins.

CV492, CV4004, M8137 - British Military designators. Typically Mullard or Brimar.

B339 - Another British equivalent, most of these are regular Mullard ECC83s branded Marconi or MWT.

B759 - The Genalex "custom" 12AX7, a selected, tested Mullard ECC83.


12AU7: 5814, 5963, 6067, 6189, 6680, 7316, 7730, CV491, CV4003, M8136, B329, B749

12AT7: 6060, 6201, 7728, CV455, CV4024, M8162, B309, B739

12AY7: 6072
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Re: NOS versus new production tubes

Post by NoiseAnnoys » Wed Feb 16, 2011 8:38 am

I'm going to bump this for a question, primarily directed at Theta or anyone else who knows a bunch about this subject:

So, I have this vintage Vox AC50, right? And it positively chews up EL34s, even biased a little cooler than AC50s typically are. Approximately how much more life could I expect out of a set of NOS EL34s (or any other equivalent) since the amp is running so hot? I've been using JJ's, but if I'm going gain a lot more performance out of it, I might as well consider switching and laying in a stock of NOS while I can.

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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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