🔊 Audio The Vacuum Tube Geeks Thread

[Rudy]

An update of sorts, from our Now Spinning thread:

Verdict: the phono stage has tired tubes, as expected, so I'm comparing a bunch before making the leap. Two 12AX7s, and one each 5751 and 12AU7. (Do I get new issue Genalex Gold Lions? NOS Mullard military CV-series? NOS RCA clear tops? Decisions, decisions.) I'm also checking options for a step-up transformer, since the ART7 has a very low output.

Level Up! Got two Brimar CV4003s coming from Turkey (of all places)--I only need one of them (they are the British military equivalent to the 12AU7), but since these are some of the last ones available, I am keeping an extra on hand. (I also ordered two Mullard CV4058/M8080, a 6C4 equivalent, for the preamp, as he had matched/tested pairs on hand.) For the two 12AX7s, I'm going with the Gold Lions and the 5751 will be the Tung-Sol.

I hate tube shopping! Despite what a few of the vintage guys tell you, there are some very nice vacuum tubes being made today in Russia, many by a company called New Sensor (who makes the reissue tubes using the old brand names like Tung-Sol, Mullard, Electro-Harmonix, Sovtek, JJ/Tesla, etc.). But despite reissues of popular tubes, there are new ones being developed. The Tung-Sol KT-120 is actually a new tube designation, part of the KT-88 family, and is highly regarded (and so far, my favorite in my power amp). The KT-150, which is even newer, is just starting to be used in some power amplifiers and is also becoming well regarded--two of them can easily generate 150 watts of power.

Yet once you look at vintage tubes, this whole pursuit becomes much more involving. It's hard not to consider how long ago many of these tubes were made, and how many different brands were available. But even decades ago, many of the tube "brands" were made by only a handful of manufacturers, so it was common to see tubes labeled and boxed with a particular brand name that were actually made elsewhere. The experts out there can tell by the internal components (the plates, the mica, the getters, even details molded into or etched on the side of the glass) where a tube was manufactured. And like anything, there were both good and not-so-good sounding tubes. Many tubes made for industrial and especially military operations were a lot more rugged, and some of those are highly desirable today.

Once you start visiting a few tube stores, you notice that many sell NOS (new old stock) tubes which were manufactured, boxed up and never sold. Some are sold in individual boxes, yet others were shipped in bulk containers (separated by dividers) for industrial applications--these are boxed individually by the resellers. The good sellers out there will replace a bum tube, but they are few and far between--most of the tubes perform quite well. The better shops will burn in a tube for a short time, then measure it for various parameters to ensure stable operation, low noise, and minimum "microphonics" (which is an actual physical sound of the grid in the tube rattling). They will also grade a tube based on its measurements, like Platinum-, Gold- or Driver/Buffer-Grade; or, A, B, C, with the lower grades being less expensive.

Used tubes can be a crap shoot, but some were not pushed very hard in use and are perfectly acceptable to use. They are a good way to try a particular brand and era of tube without spending for a new old stock tube. eBay purchases are typically a crap shoot unless they are actual well-established tube resellers.

What's to "hate" about all this? So many choices, so little money! It's like walking into a candy store. With each tube having a slightly different sound, it's hard not to create that dream wishlist, or talk yourself up higher in price as you start looking at them on the pages. On a good site, like the one that is run by Kevin Deal of Upscale Audio, you often get his impression of what a tube sounds like, and how it compares to others, so you can make an informed purchase. Like any store, inventory comes and goes. The new issue tubes being made today are always available, but the new old stock tubes are continually in flux. The Brimar CV4003 I ordered from Turkey is his favorite 12AU7, yet he has been unable to find another stash of them. I've made a couple of purchases from Uncle Kevvy so far--he's one of the "good guys" out there. (I will list Upscale and a few other large tube dealers later in a later installment.)

 

[Mike Blakesley]

Once you start visiting a few tube stores

Uh - there are "tube stores??"

We used to have a TV repair department in the back of our store. I think the wall cabinet with tubes in it is still there. I'll have to take a look. Maybe I can retire on tube sales!

 

[Rudy]

Uh - there are "tube stores??"

We used to have a TV repair department in the back of our store. I think the wall cabinet with tubes in it is still there. I'll have to take a look. Maybe I can retire on tube sales!

Seriously, if you have any common audio tubes, there could be interest in those. Let me know! Television tubes were different types, but there are common audio types. Heck, even a photo of the tubes in the cabinet would work--saves typing them. Maybe I could get my pal Mike to scan over the list and let me know what's in there that works in audio circuitry, that would help. Even if you find a box of old used tubes, don't discard any--tubes can still have some life left in them. There might be someone on eBay, for instance, who might take a box of a couple dozen used tubes for maybe $10 or so. At least it's not tossing them away.

(And BTW, if you happen to have a tube tester left over from the old days, those are worth something also.)

The tube stores are mostly online, although Upscale is a retail store in California, and Uncle Kevvy doesn't mind if a customer stops by. Aside from the audiophiles, tube guitar amplifiers have made a huge comeback. My buddy is still kicking himself. He had a tubed Fender guitar amp when we were all in high school. He sold it for a pittance back in the mid 80s. Had he held on, they're worth hundreds if not over $1,000 each. Despite all the solid state electronics and digital processing, there is just something about a tube sound that can't be reproduced any other way, and the guitar amp users even know which tubes have the sound they are looking for. An RCA blackplate 12AX7 sounds different from a Raytheon, both of which differ from a Mullard or Telefunken.

 

[Carpe diem]

I'm sorry if I am a little off topic Rudy, but when I saw the "Vacuum Tube" referenced in your thread, it reminded me of my dad back in the 60s when I would accompany him to the local "Save-On" drug store. After he would pluck the suspect tubes out of our B&W TV set and take them down to be "tested" after our set "went on the fritz". My dad was about the most non-technical guy ever, but I remember him plugging tubes into the slots and reading the meter. I thought he was a genius! It seemed every hardware, drug, and music store had a "tube tester". Seems to be a Baby Boomer rite-of-passage about our dads...That, and home movies, but that is another thread at another time!

 

[Mike Blakesley]

if you happen to have a tube tester left over from the old days, those are worth something also.

We used to have a floor-standing tester in the store but I have no idea what ever happened to it. I'll get a photo of the tubes in the cabinet (if they're still in there) and shoot it your way.

 

[Rudy]

@Carpe diem You are right--the testers were in very many stores back then, almost as ubiquitous as light bulbs it seems. The testers in the stores were fairly simple as testers go--they might have conducted only one test, maybe two, but they also had to cover a lot of different tubes back then.

What's sad is that if any of had known how valuable these tubes would have been today, we would have stored cases of them in the garage to resell decades later.

 

[Murray]

Aside from the audiophiles, tube guitar amplifiers have made a huge comeback. My buddy is still kicking himself. He had a tubed Fender guitar amp when we were all in high school. He sold it for a pittance back in the mid 80s. Had he held on, they're worth hundreds if not over $1,000 each. Despite all the solid state electronics and digital processing, there is just something about a tube sound that can't be reproduced any other way, and the guitar amp users even know which tubes have the sound they are looking for. An RCA blackplate 12AX7 sounds different from a Raytheon, both of which differ from a Mullard or Telefunken.

Rudy, I just kicked myself so hard that it’s going to hurt to sit down! After my dad passed away in 2005, I went through his stuff, and found a Peavey tube amp in a basement closet. I don’t think it had been used in years (he had to give up playing guitar due to declining health). I plugged it in to see if it worked, but all I could get out of it was a hum. I took the back off, and noticed that a couple of the tubes barely glowed at all, and would likely need to be replaced. I had no idea that tubes were still available anywhere on earth, so I donated the amp to the Salvation Army thrift store! I even felt badly about sticking them with it, because I thought that they’d never be able to sell an old amp that needed repair. Ouch! (I kicked myself again!)

 

[Rudy]

After my dad passed away in 2005, I went through his stuff, and found a Peavey tube amp in a basement closet. I don’t think it had been used in years (he had to give up playing guitar due to declining health). I plugged it in to see if it worked, but all I could get out of it was a hum. I took the back off, and noticed that a couple of the tubes barely glowed at all, and would likely need to be replaced.

The hum? Depending on the age, I am guessing some of the capacitors went bad. If it was more than 25-30 years old, that is most likely the case. Electrolytic capacitors tend to break down with age (they are somewhat chemical based, without getting too technical).

Tubes do get noisy or weak over time, so that also could have been an issue, but many tubes will last quite a while. Some tubes do not glow too brightly--the newer Mullard (New Sensor) 12AX7 I have in my desktop tube amp barely glows at all--it does glow inside (it is actually a filament heater for the cathode inside), but the way the plates are made, just about all of the glow is not visible outside the plates. In the same amp, though, the EL84s (the power output tubes) have more of the heater visible and therefore, more orange glow.

The EL84s are the two outside tubes. The 12AX7 in the middle is lit more by the orange reflections from the EL84s than by its own filament glowing! Other manufacturers' tubes will glow differently.



I have an RCA 45-EY-3 record player in the basement with really weak sound output and a loud hum. That is a classic case of the capacitors needing replacement, as I'm told that much of the time, the tubes in these are still strong.

 

[Murray]

Thanks Rudy. Yes, the amp had a loud hum, and it crackled when I turned the volume knob.

I don’t feel so badly about giving it away now. Replacing capacitors is something that I wouldn’t be comfortable attempting myself, and getting a professional technician to do the job could easily have cost hundreds, if I could have found somebody local to do the job. Both of the repair shops that I used in the past have gone out of business.

 

[Rudy]

Depending on how old it is, those tube amps were a lot simpler than newer ones, and a good tech would probably not have taken too long to repair it.

What's sad today is that the way electronics are made, they are pretty much disposable when they're done. Even back in the 70s and 80s, components were still large enough to work with. Today, it is all done with subminiature components called surface mount devices. They require special equipment to assemble, and only those with really sharp eyesight, a high-powered magnifier and some very tiny tools could even attempt to work on them. Rather than older components (resistors, capacitors, transistors and diodes, etc.) which had wire leads to solder, these are placed on the board and then "wave soldered".

This is point-to-point wiring on a tube amp chassis (which is still done today):



Discrete components on a circuit board:



Even tube components have circuit boards these days (this one's inside my own preamp, a pair of CV4058/M8080 Mullards with silicone damping rings):




Computer chips and many tiny surface mount devices:

 

[Rudy]

Fresh off the FedEx truck...shipment from Upscale:



They burn in and measure each new tube, and provide the measurements on their sticker on the side. They perform matching on the pairs or quads of tubes they ship out at no extra cost. (Matching the specs means the equipment will not have a volume or performance bias towards one side or the other.) ECC83 is the 12AX7 equivalent. The Tung-Sol is the 5751, which is a low-gain 12AX7.

These are brand new tubes. The remaining tube I need was only available from the seller in Turkey that I mentioned, and those will arrive Wednesday (one tube for the phono stage, one extra, and two spare Mullard M8080s for the preamp since I have to order those from overseas also). They will be new old stock, so they are decades old but unused, often in their original packaging.

 

[Rudy]

I've had an uphill battle with the phono stage but I think I'm on the road to getting it licked. It didn't sound so great with the tubes it came with, which the previous owner said were the factory originals. So they were probably 15-20 years old. The new set of tubes...didn't sound much better. Still kind of dull. But I let the component run over a long weekend (from a Friday morning to the following Monday) and it sounded better. After using it a few more times and giving it a couple of overnight burn-ins, it is now sounding about where it should be. It could be that the old Brimar tubes needed to burn in for quite a while. My M8080 tubes never had that issue, but, they are also military-grade tubes, so they may not need so much burn-in. Sometimes different types and brands of tubes need a little time to break in.

I still have a slight hum, but I think the cable from the turntable to the step-up transformer needs an upgrade. I may try something shorter. The cable I have now is way too long anyways.

 

[DeeInKY]

Would you say it’s “warmer” sounding after some break in time? (I’m not sure how else to describe it.)

My brother used to repair stereos and TVs (among his several careers) when that was a thing.

 

[Rudy]

Would you say it’s “warmer” sounding after some break in time? (I’m not sure how else to describe it.)

I might say "smoother" or "cleaner." Some have said the sound "opens up" when some tubes break in. The problem I was having was the phono stage was sounding quite dead and dull, and running it for a while seemed to get things breaking in.

I know that warming up some components can help--all the parts inside can shift slightly in value as the temperature changes, so things sort of lock in once all the bits and pieces get up to operating temperature. As for break-in of solid state components, well...that's a tough one. I know that capacitors can exhibit some break-in due to their chemical composition, but anything else, I'm skeptical of.

Mechanical items like speakers and phono cartridges do clearly exhibit break-in--it is often rubber, plastic, etc. softening up as it is used. Kind of how shoes can break in after an initial few wearings.

Tubes are sometimes said to have a "warm" sound, but that is not always true. I've heard some modern tube amplifiers that were almost a little too clinical sounding, very similar to solid state. It all depends on the type of tube and the circuit it is used in. (For instance, an EL34-family tube tends to sound more lush and the 6550/KT88/KT120/KT150 family more clean and analytical.) The components I have are sort of on the cusp of when this particular company moved from an older design that was a bit warmer and less analytical to the opposite, so it is like having the best of both worlds. Some tubes can also have different operating modes (triode vs. pentode) that affect their sound--supposedly the triode is that more lush sound but it also produces half the power output, and on a few amplifiers, this is switchable.

I've thought about finding plans to build my own smaller tube amp for my desktop. It's kind of fun to play with this stuff.

 

[Rudy]

Update on the phono stage--the tubes have pretty much broken in now, and it is sounding as it should. I need to do a needle drop one of these days. I had an issue where a loud bass drum or kick drum would make it sound like it was overloading the phono stage--kind of "flubbed" in a way. I had bought a used Morrow Audio PH4 phono cable to go to the tonearm to try and deal with the hum. I still have a little hum, but...who knew the original cable had that anomaly? I haven't heard it since putting in the new cable! I have two more interconnects ordered from Morrow so it will complete the path to the preamp with all Morrow cables. Once they are installed and broken in, I need to do a needle drop and share here.

---------------------

My youngest is doing some sort of video project for the end of the semester, and needed an "old radio" for it. I offered up my Grundig 2420 that I posted in this forum last summer. It was noisy--I tried cleaning the tube sockets and re-inserting all of the tubes but it only got worse--the sound was sputtering. I did not like the loose fit on the EL84 audio power tube. Turns out the loose socket was the issue. I got one of my old Chinese tubes from my desktop amp, slightly bent the pins outward, and the sound came back to life. It is still noisy, however. I am thinking that I will need to pull the chassis and replace all the capacitors in the audio circuit at some point.

The EL84 from the Grundig had its pins very slightly deflected to one side. I am thinking this tube should be original, since it is a desirable Telefunken (which was made in W. Germany). Since my desktop amp has a noisy Mullard, I pulled it and replaced it with the Telefunken for now. And guess what? That 55 year old Telefunken is dead quiet and sounds quite good! It does glow brighter than the Mullard, but that doesn't mean anything. I am afraid to clean off the decades of dust, since it can also wipe off the lettering.

The old Telefunken lives:

 

[Rudy]

Here is something different--a nuvistor. It is a small vacuum "device" (I hate to say "tube") enclosed in metal rather than glass. Because vacuum can't be drawn from the enclosure like it can with glass, nuvistors were assembled and sealed in a vacuum chamber using simple robotics. The metal shielding was necessary since nuvistors were originally made for RF (radio frequency) electronics, and needed the shielding to keep out stray signals and noise. The basic operation is the same as a vacuum tube since it has heaters, grid, cathode and plate. Since it is a triode, it can also be used for audio amplification.

 

[DeeInKY]

I find this amazingly interesting.

 

[Rudy]

I'd heard of nuvistors before, but a couple of days ago, a rare item came up that uses them, and I couldn't help but look into what a nuvistor was. The old electronic components from decades past are interesting, especially seeing how everything today has moved to SMTs.

 

[Rudy]

Another vacuum tube of interest is the subminiature tube. They run on a lower voltage, and were used in portable equipment.

One interesting audio company out there is...ummm...Schiit. Yes, it's pronounced exactly as you'd think it would be. It was founded by two audio industry veterans (Jason Stoddard, formerly of Sumo; and Mike Moffat, founder of Theta Digital, and also co-developer of the GAIN analog-to-digital chain that Mobile Fidelity uses for mastering their CDs), and they specialize in making Schiit that greatly outperforms its modest price, with a wee dose of humor. They started by specializing in "personal audio" products, meaning, headphone amplifiers and DACs (a DAC is a digital-to-analog converter), but have expanded a little into home audio. I saw the prototype of their upcoming Sol turntable at AXPONA, along with the Aegir power amps.

This product on their site caught my eye. You can buy these "drink coasters" (pictured below) at Schiit at $12 for a set of four.

Looking for the quintessential Schiit schwag? Look no further. Here’s a set of four PC board coasters, perfect for resting your drink on. Well, at least if you don’t mind maybe still ruining the nice wood finish underneath the coaster, because these things have holes in them.

Yes, that’s right—these coasters are made out of PC board material. And yes, that’s right, they have a PC board pattern etched on them. It’s even plated in gold (technically, Electroless Nickel Immersion Gold, or ENIG.)

Aaaannnddd…you can build these coasters into a working hybrid headphone amp if you’re a super-mega-geek like us. The docs are available at schiit.com/coaster. Have fun!

Here is where a vacuum tube comes in. The Schiit Vali was one of their earlier headphone amps that used vacuum tubes, but for a kit, they did not want to create something that had the typical high voltages that tubes use (often 300V+). This coaster DIY project is called the Vali Mini. In the finished photo below, you can see the small vacuum tube laying down on the circuit board directly adjacent to the big volume control, and there is another on the far side of it. These tubes are soldered into place, as opposed to using sockets. They are no longer being made, but there is such a large number of them left in the world that there is little chance they'll run out of a supply of them in our lifetime.




Here is the 6418 tube used in the kit:




The 6088 is another subminiature which will work in the same application:




(There's a bit of tech-speak in this video, but it's interesting to hear about their approach to what they build. Moffat had experience working in video/home theater as well as digital audio...and has the best t-shirt in the room. NSFW, BTW.)

 

[Rudy]

I've updated the desktop amp, as the TubeCube | 7 wasn't the best in clarity. This amp was recommended by Steve Guttenberg (columnist with CNN, formerly of Stereophile, and on YouTube as The Audiophiliac). Unlike the version he bought that came with mediocre tubes, I found this version of it with point-to-point wiring vs. a circuit board (just like the old days, which will make future upgrades and repairs very simple), and sold without tubes. I did not get the cage, but probably should have.

Tube complement: ElectroHarmonix 6CA7 power tubes (rear, EL34 equivalent), Voshkod Rocket 6N2P preamp tubes (front), Tung-Sol 5AR4 rectifier (middle). Amp runs in single-ended class A. So, not very powerful in the grand scheme of things, but plenty for near-field desktop use with the KEF LS50s. (Kind of a coincidence how, in the still photo above, right above Jason's shoulder is a KEF LS50. )



The Voshkod Rocket tubes sound really good and are well regarded, but aren't the easiest to find. By rewiring those two sockets I can use the 12AX7 in its place. (Basically it's rewiring the pins for the heaters--remove the ground from pin 9, move the 6.3V wire to pin 9, and then wire pins 4 and 5 together.)



I also had a bit of a "situation" with the rectifier tube. The amp was designed with a 5Z4G rectifier tube. I had a Mullard on order from the UK but, thanks to all the postal service and customs problems, the 1-2 week delivery took almost seven weeks. I'd given up after about five weeks, ordering one in the US that arrived in two days. I dug around on the Internet, found some old data sheets, and discovered that a 5AR4 rectifier would work in its place, the only difference being a slight difference in voltage drop that wouldn't affect the circuit at all. Sure enough, it's working fine.

I'd considered a PS Audio Sprout100, or a NAD D3020 or D7020 for the desktop, but really didn't want to give up the non-fatiguing sound of the tubes.

 

[KentTeffeteller]

My present favorite A&M Ochre era playback device happens to be a 1966 Fisher Custom Electra console with Dual 1010 record changer (original cartridge, Pickering V 15F, now has a Shure M 44-7 installed with LP and 78 styli). All tube save for the output transistors. Italian Provincial. 20 real watts/channel, 3 way speakers.

 

[Stevenj]

My current rig is a Mac Mini music server feeding a MHDT Pagoda NOS DAC. Pre amp is Musical Fidelity M3B and amp is Conrad Johnson MV55. I'm running Winged C el34s in the CJ (well one of the winged bit the dust, just went dark, so on mullard new issue). My preamp has Kevin's Stash Tungstram 6922. I wasn't pleased with my maggies, so got some TDL monitor transmission line speakers and it's now my reference. Gotta love the tubes.

 

[Rudy]

C-J Premier 11 here, with a PV14L preamp and EV1 phono stage. Got hooked on the C-J sound. 😊 I found the Premier 11 on our local Craigslist, of all places--I think it was in Livonia or Westland. Seller ended up needing to pay some dental bills and it sat on CL at a low price for months. (Knowing the flippers around here, he probably got offered a small percentage of what it was worth.)

I wasn't sure how the 11 would work with stats in terms of power but since they are more efficient than the Vandersteen 2CEs, they play louder than I can handle it. I replaced the tired stock GE 6550s with the Tung-Sol KT120s and along with the other new tubes, it really brought the amp to life. (It was a bit dull and lifeless, but was on the original tubes after decades.) I got all of those tubes from Uncle Kevvy myself--don't we all, at some point? 😁

BTW, are you over at AudioKarma or HiFi Haven?

 

[Stevenj]

Yes, live and learn. I still have two sonographe sa250s, but needed to get back to tubes. I would never pay dental bills while a hot audio purchase was pending.😉

 

[Rudy]

I'm still hanging onto a Nakamichi PA-7, which was the Nelson Pass-designed Stasis amplifier--I got it from an audiophile up in Clarkston. The C-J were my first "real" tube components but I have to admit that Pass's designs come really close. Ideally I'd like a nice pair of Premier 12s but it's not in the budget at the moment...