Preamp Tubes? - Who, What, When, Where, Why, and How?

[ken361]

I bought a electro harmonix for the hell of it to see how it sounds and it sounds pretty good in the v2 and v3. Not compressed pretty smooth. Also lost a bid on 2 Raytheon baldwin black plates I have 10 bucks on it and thought it would go much higher and forgot about it the other day and saw it go for 20 bucks on ebay! Nice deal!!

 

[core]

Core, the RFTs are great tubes, but the smooth plate Telefunkens are magic. The harmonic content is just unreal compared to other tubes.

I went shopping today with the family and ended up bringing home a little Epiphone Valve Jr. I was playing with it awhile ago and the distortion sounded really buzzy. Guess what was in it? A Sovtek EL84 and Electro Harmonix 12AX7A. I put in a Philips Electrohome 12AX7 that I got from Marty (at a great price!) and an old EL84 I had lying around. Now it's a great little amp. I'm going to pick up a Weber 8" alnico for it to smooth it out a little more, but it's a great little blues box. Just needed a little old glass to help it along. I've heard people rave about that EH12AX7A. Horrible, buzzy tone.

Hmm interesting, if I can find a cheap enough smooth plate maybe I'll give it a try too at some point. Thanks for the input!

 

[MartyStrat54]

I recommend the EH12AX7 in non-critical slots. They are dependable, but not a very good sounding tube. Supposedly a relabeled Sovtek as EH and Sovtek swap spit on several tubes.

 

[ken361]

I recommend the EH12AX7 in non-critical slots. They are dependable, but not a very good sounding tube. Supposedly a relabeled Sovtek as EH and Sovtek swap spit on several tubes.

there not the same i checked my old one

 

[MartyStrat54]

Wow...I put this over here and it disappeared. I will try again. I had some people giving me grief over my numbers regarding tube failure. I put this up as rebuttal. One of the sad things is that amp manufacturer's "want" cheap, shitty tubes. In the past it was good tubes make good amps. Now it's cheap tubes make a higher profit margin on the amps. They are willing to drop the B+ down around 400VDC to get reliability our of the available tubes. That's fine, but some tubes require a certain B+ to work at peak efficiency. Read on.

Here are some excerpts from Vacuum Tube Valley pertaining to current production tubes and how it affects amp manufacturer's.

TQR: In terms of audio quality, durability, and technical performance, how would you rank the various manufacturers previously described?

VTV: I feel that NONE of the current production is exactly as good as genuine premium NOS tubes from Western Europe or the USA. Part of the sound of a really good tube is caused by ultra-pure cathode materials--something Western Electric, M-OV and other firms strove to use whenever possible, for longevity. The chances are, you will NEVER see that done again. The economics of OEM tube sales won't allow it. The largest buyers of tubes are the big guitar-amp makers; Fender, Marshall, Ampeg, Mesa, Peavey and a few others. They drive the market, and they have collectively made it clear that their primary qualification for a tube for use in a guitar amp is low unit cost. They go around shopping for the cheapest tubes which give tolerable reliability in a guitar amp. Many amp companies design their amps around, say super cheap Chinese 6L6GCs and they work just fine. Cathode purity is not important. As far as VTV's editors can tell, very few guitar amp makers pretest tubes to find the longest-lived version or brand. Another issue is with cleanliness and vacuum hardness. This is easily traded off at the factory, and the end-user often can't tell--until the tube out-gasses and its plate current runs away, destroying the amp!

All the current factories are pumping their tubes down for the shortest time they can get away with. Because guitar amps stress the screen grids of output tubes, one can see this as a problem for reliability. When a screen gets red-hot, any absorbed gas in it will be emitted. Enough of it, and the tube runs away. Again, OEMs are demanding low cost and quick delivery schedules, so the tubes are not pumped for 2 or 3 hours, as the best factories once did routinely. This is less of a problem with power triodes like 300Bs, but those are not used in guitar amps. Preamp tubes aren't much affected by gas, except for its tendency to shorten cathode life.

TQR: Are there specific types (not brands) of tubes that seem to be of generally higher quality and consistency today than others? If so, why?

VTV: All of the existing production has improved dramatically in the past few years, thankfully. This was not due to tortured consciences, this was due to competition for the OEM business. SED, for example, really kicked up some trouble for New Sensor, JJ and the Chinese. As far as we know, SED still has most of the EL34 and 6550 OEM business tied up. New Sensor is a very aggressive competitor, and their products have become very good recently. (please note: New Sensor purchased the Svetlana brand name in the USA from the previous Svetlana marketing firm. The "Svetlana" tubes they market, with the "S" logo, are not made at Svetlana.) We also appreciate that they are willing to make low-production types, such as the 7868, 7027A and 7591A, for the vintage hi-fi and guitar amplifier market. JJ and the various Chinese factories are also improving. The Chinese scene is a real mess--we still can't find a totally honest source of information on which tube is made at which factory. As far as quality of a certain type goes, reliability is the major issue.

Anything that is bought by OEMs in huge numbers is likely to be usable, in MODERN amps. Please note that the screen-grid overheating problem is worse in older amps that run the tube screens at higher voltages. This is a major reason why many guitar amps run only 400v plate supplies; it's not the plate that causes the problem, it's the screen grid--which is always run at the full plate voltage in guitar amps. Audiophile tube amps are mostly triode nowadays, but even they are running lower voltages today--even if they don't have to. More than that, I don't dare say. A few major tube dealers in the US and England are some for the most aggressive businessmen we've ever seen. Because tubes are easy to relabel, government oversight has vanished, and consumers are ignorant, the pirates are having the time of their lives right now.

TQR: Do any of these manufacturers do a decent job of screening their own products prior to shipping? We know of tube retailers who screen and match tubes, but not manufacturers.

VTV: As I said, the low-cost OEM market drives manufacturing. Svetlana does their own factory matching of output tubes, which has caused JJ to follow suit (just recently). New Sensor has spent a lot of money recently on two huge power tube matching machines. Magic Parts, in Petaluma, CA does a great job on power tube matching and screening of certain small signal tubes. I doubt if their factories are performing any extra testing. In most cases we have noted that small signal tubes such as 12AX7s, 12AT7s, etc. are not routinely tested for noise or microphonics by manufacturers. With some modern 12AX7s, we have noted up to a 70% reject rate because of excessive noise and/or microphonics.

Additional resources: Groove Tube Reject Rates

***Preamp Tubes***

Please note that the tests on tubes was done on raw factory samples. Some tube vendors test and/or select or grade, and some do not. Many rely on the end user’s reluctance to return a single tube such as a preamp tube for problems, so they just send their tubes out with no testing or minimal testing.

A preamp tube that is not microphonic when first installed, can become microphonic in short order after a few heat up and cool down cycles with expansion and contraction. This is one reason to know and trust your vendor.

Some companies such as Groove Tubes have a very long warranty on tubes, in the case of preamp tubes, six months. Some reasons for the cost of GT premium tubes are due to the labor intensive testing process (each tube, one at a time, in place in high gain amps and tested for various attributes), and their cost for the tubes initially when buying from the major tube factories. In many cases, the GT reject rate is in excess of 60%. The data below, are for the raw factory samples, not GT tested examples. This is the way they come from the factory, and the sort of performance you can expect if your vendor does not test for gain, output, noise and microphonics. In the case of power tubes, gas leakage, grid leakage, and low vacuum are also test parameters that require expensive and complex test equipment which very few vendors have in house.

Note: I'm not a big fan of JJ or Groove Tubes. However, there have been several people asking whether all of the testing is done at the factory level, the vendor level, or both. My research has shown that the factories have been skimping on testing until "pressed" into doing so. If you go to Euro Tubes you would get the impression that a JJ tube has never failed and it sounds better than anything else. Well, I guess that is what is going to happen when you only sell one line. Bob doesn't say how many tubes are rejected during his "in house" testing.

Another thing that I have stated has found its way into amp design. This involves lower plate voltage. All the amp manufacturer's have dropped their amps B+ to 400VDC or less. So here is a situation where cheap, unreliable tubes have changed the designs of dozens of amps. Even though they tests the power tubes at 400VDC they still have massive failures.

There are other articles, but I don't want to make a novel out of this. My point that I stand behind is that current production tubes, although better now than say five years ago, are still problematic and "still have a very high failure rate." I have said that competition has made for "slightly" better tubes. The fact is, why improve a product if you already have a willing market (see Guitar Amp Manufacturer's)?

There are many articles that involve the quality of the raw materials used and the "clean process" techniques that are not followed by the current manufactures. Even so, I will say there are a handful of decent CP tubes that are being made and I openly recommend them.

 

[MartyStrat54]

Yeah, let's see if we can hit "Page 100" today. I did my part with the long article. You guys can list your shoe sizes or something like that.

 

[RiverRatt]

Ok i have found a little mystery valve, can anyone help me out here. The getter is unsual, and the micas seem to be totally round with no points on at all. The plates have center holes that go all the way through the plate, its a real mixture and i cant find any pics of anything like it on the internet. HELP!

Spirit, I don't know. The plates look a lot like Philips parts, but the getter looks Chinese or maybe Tesla. Can you get a better shot of the getter and the top of the tube? The logo is cool looking. I'll keep a look out for something similar. Are these yours are were you thinking about buying them?

 

[RiverRatt]

I made a comment last night and apparently it got lost. I've been rolling PI tubes for lack of anything better to do. Has anyone tried using an Ei ECC83? This tube really seems suited for the task. My amp seems a lot more open and dynamic with it.

 

[MartyStrat54]

My 1999 DSL401 came with all Ei tubes (Ei Elites). That was the best sounding stock amp I had ever heard and that's why I bought it. I think any Ei tube from 2000 on back is solid. The last runs were done with no QC and that's why they have so many bad tubes.

 

[MartyStrat54]

Spirit-I looked in all of my valve files and couldn't find a thing on these tubes. What are all of the numbers? Also, look real close around the base of the tube for microscopic print in a very light ink. And what does the logo look like to you?

 

[MartyStrat54]

This is some good info for you Matsushita lovers.

Amperex tubes were originally produced in Holland (The Netherlands) and are very high quality tubes. Many prefer these to the Telefunken and are probably the second most sought after brand of 12AX7. There are many versions of this tube. The earliest versions from the 1950's have a "treble clef" logo or just the name Amperex (looks like the lettering above).. 1960's versions have the famous "Bugle Boy" logo. 1970's versions have the "World" logo in orange printing. All sound very good and will last a long time. Be careful of the orange printed ones. Some of them say "Made in Holland" and in fact are Japanese. The easiest way to tell the difference is to look at the side of the plate in the center. There will be a half circular hole on one side of the plate and not on the other if the tube was made in Holland. If there two holes forming a complete circle, then the tube was made by Matsushita Japan. The Japanese made tubes will also have a dark colored getter. Actually, the Japanese made tubes are nice tubes, too as the Matsushita plant was set up by Mullard. They just aren't Amperex Holland. Amperex tubes made in Holland have a curious characteristic. When the filament is first energized, it flashes very bright for a second and then dulls down to the normal soft orange glow. Other tubes do this as well such as Mullard, Matsushita and Ei Yugosolvia.

 

[MartyStrat54]

I figure that if three more people post, we can get this thread on page 100.

Anyone out there with an interesting tube story to tell? Any organs found by forum members? Did Joe ever get his amp back yet? There has to be something that you can post about.

Here's one for you. A 12AX7 has nine pins. You know why it doesn't have ten?

It wouldn't fit in the socket.

 

[solarburn]

I may have to try some EI tubes. I never have and from the sounds of it they are good...

 

[solarburn]

No amp yet. Maybe by the end of the week.

 

[RiverRatt]

I may have to try some EI tubes. I never have and from the sounds of it they are good...

To me, they sound similar to a real Tele with more aggressive mids. They are a very musical tube, but like Marty said they had some bad ones. They can be noisy and microphonic. My Marshall had two of them in it when I bought it, and they sound really nice. You can still find them in the $20 range, I think.

I need to pick up a few more, too. I may have to sell some of my Japanese stock. I'd like to have a few more Ei and definitely some Raytheons.

My Blackheart has a single Ei ECC83 in it and it thinks it's an AC15. I've been getting into my smaller amps lately. I had the DSL, the Blackheart Little Giant and the Epi Valve Jr. all going at once this afternoon. It was a wicked tone.

 

[solarburn]

To me, they sound similar to a real Tele with more aggressive mids. They are a very musical tube, but like Marty said they had some bad ones. They can be noisy and microphonic. My Marshall had two of them in it when I bought it, and they sound really nice. You can still find them in the $20 range, I think.

I need to pick up a few more, too. I may have to sell some of my Japanese stock. I'd like to have a few more Ei and definitely some Raytheons.

My Blackheart has a single Ei ECC83 in it and it thinks it's an AC15. I've been getting into my smaller amps lately. I had the DSL, the Blackheart Little Giant and the Epi Valve Jr. all going at once this afternoon. It was a wicked tone.

I bet that was awesome hehe.

 

[el zilcho]

My 1999 DSL401 came with all Ei tubes (Ei Elites). That was the best sounding stock amp I had ever heard and that's why I bought it. I think any Ei tube from 2000 on back is solid. The last runs were done with no QC and that's why they have some many bad tubes.

My 2000 DSL100 came with Ei tubes in V3 and V4 and unlabled Chinese tubes in V1 and V2. The Chinese tubes went microphonic after about 2 years. I still have the original Ei's in a drawer, and they're still good!

 

[SpiritOfTheAge]

Spirit, I don't know. The plates look a lot like Philips parts, but the getter looks Chinese or maybe Tesla. Can you get a better shot of the getter and the top of the tube? The logo is cool looking. I'll keep a look out for something similar. Are these yours are were you thinking about buying them?

Its an ebay auction and thats the only picture, they are going for about £10 at the moment, i was wondering fo they were worth it.

 

[Landshark]

So I opened up the back of my Vox today because I was interested to see what brand of tubes were used in the amp. I was kinda ticked when I saw Ruby tubes in it. Any ideas Marty on where to start with rolling new tubes in this head?

 

[guitarmartin416]

So I'm runnin in the BBRI V1 Tele smooth, V2 RCA Black Plate
and in my Bandmaster V1 Mullard, V2 Sylvania

what a nice colaboration between both amps!

Gonna try some new power tubes for both this week.... but thats a whole nother thread!

p.s. hope this takes us to page 100!!!!!!!