🔊 Audio The Vacuum Tube Geeks Thread

Rudy

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I had a bit of an issue here almost three weeks ago--it sounded like the stylus was mistracking on the records. (Jumping ahead for a second, it's like there's a fuzziness and weakness in the highs.) Tried another phono stage and removed an attenuator with no change, and then I tried digital and got a similar result. After some deduction, I figured since I had a lot of hours on them, the tubes in the power amp were getting old. Swapped in a pair of GE JAN 5751s, and I thought it might have improved things a bit, so I bit the bullet and got two new Tung-Sol 5751s and a quad of KT120s from Uncle Kevvy.

Those arrived, got them installed. Went to bias the KT120s and noticed the bias LEDs aren't illuminating, even if I turn the adjustment pots briefly through the entire range. So, there's something internal going on here. Contacted Music Technology in Virginia and it looks like I'll send it down to them for a repair. The president was the technical director at C-J, and worked there over 20 years, so he's the go-to guy for repairs. C-J can also repair directly, but they tend to want to push their teflon capacitor upgrade, which costs more than I paid for the amp, and I'd never get that out of it if I tried to sell it. (I've seen others try to sell similar models and try to recover the capacitor upgrade, and they sit unsold.)

I'll miss it while it's gone, but have the PA-7 to shlep out of the basement and drag into my system. (It's a heavy beast.) The site shows a 10-12 week turnaround time. While it's there, I'm having him address the very slight channel imbalance, check on doing the upgrade to the 11A (from the 11, which is the addition of a diode), and add an IEC socket so I can use my own power cord, as the original was nicked and taped up by the prior owner, and I have a couple of spare power cords here.
 

Rudy

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Temporarily, I may move the new-ish amp from my desktop into my main system. (The other tube amp did not work out, and is mothballed for now.) I may do a little write-up here of that piece, as it's impressive for its size and is a good go-to for some looking for a small but flexible component to build a system around.
 

Rudy

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I'll miss it while it's gone, but have the PA-7 to shlep out of the basement and drag into my system. (It's a heavy beast.)
And I did that this afternoon. It's a nice amp, but right away I could hear the (not good) change in sound. Back to that metallic, "steely" sound that I've heard with McIntosh solid state amps (which I do not like, and never have). So this will do, but it's no tube amp. Granted the PA-7 needs a refresh also, as the electrolytic capacitors are at or near end of life, and Nelson Pass (who designed it) mentions that they can stand to be recapped when they are this old. But my choice there is to do it myself and figure out how to adjust the bias when I'm done, or send it off, 2/3 of the way across the country and hope that UPS or FedEx don't destroy it along the way.
 

DeeInKY

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We once got a shipment of reel tapes at work that FedEx had not only dropped off the truck but had run over. :cussing:
 

JOv2

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Back to that metallic, "steely" sound that I've heard with McIntosh solid state amps (which I do not like, and never have)
I know what you mean. I remember my father switched out his Scott 340A for some solid state affair in the late '70s...The new receiver punched harder -- as a teenager I thought it was great. As an adult I've been on tubes for over 20 years now. I've had two vintage amps from the early '60s but now run a nice little Luxman (with those sweeeet EL84s). I could never return to solid state.
But my choice there is to do it myself and figure out how to adjust the bias when I'm done
Lo! The other side of the coin with tube amps. Everyone I know (except me) maintains their amps -- particularly the '50s/'60s equipment, which in all cases is refurbished or even rebuilt. I've just never developed an interest in EE (much to dad's chagrin I studied chemistry). In any event, it is fascinating when my friends start talking all that well your rectifier isn't syncing with your floating parahprase inverter producing the capacitance required to... business. Once the music conversations switch gears into electrical engineering, I go to the ice box and grab a Schlitz...
 

Rudy

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I've had two vintage amps from the early '60s but now run a nice little Luxman (with those sweeeet EL84s). I could never return to solid state.
I know of some who run those old H.H. Scott or Fisher integrated amps or receivers that are tube powered, and love 'em to bits. The only thing is, now that the secret is out, finding a clean, refurbished example of either one will run several hundred dollars. That is something I'd use in a second system (in a den or other small room)--it'd be perfect size-wise, and sound really nice. It's one of those things where I hope to luck across an old one at an estate sale, pick it up for $50, and freshen it up to keep as a spare, or hand it down.

Lo! The other side of the coin with tube amps. Everyone I know (except me) maintains their amps -- particularly the '50s/'60s equipment, which in all cases is refurbished or even rebuilt.
Some of the newer amps today (like those by PrimaLuna, and others) are self biasing. But with mine, it's a simple process, and you only have to attend to it when you replace the tubes, and maybe tweak it a week or so after the tubes settle in, then once or twice a year. Essentially, you turn the potentiometer for each tube in one direction until the LED illuminates, then back it off until it juuust extinguishes. Since I run mine with the tube cage off (as most C-J owners do), the pots are accessible right on top of the panel for easy access. No opening up the case, and no multimeter needed. The biasing in this case promotes longer tube life, and ensures the channels are balanced.

I know a few who build their own tube amps, and I'm envious of the skills they have acquired in being able to tune those things, and know exactly which values to change to affect the sound in the way they desire. They also seem to have encyclopedic knowledge of dozens of tubes and how they act in a circuit.

I'm great with soldering, and could easily build a tube amp kit but my electronics years were in the solid state era, and our textbooks never covered vacuum tube circuits. For me, I'd have to relate how a tube functions to its solid state equivalent, to get a grasp on it. For tube amp kits, I was for a while considering the Bob Latino M-125 kits, which are basically higher-powered monoblock variations on the old Dynaco Stereo 70 amps.

But I can't complain--I got my amp four years ago from a seller who was facing some dental bills and wanted to get rid of it, and it's worked fine. But it's almost 30 years old, so it was destined for a look-over anyways. And I've wanted the IEC socket so I could replace the power cord, and the repair shop can do that for me.
 

Rudy

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We once got a shipment of reel tapes at work that FedEx had not only dropped off the truck but had run over. :cussing:
I think they were a better company back before they got into ground-based delivery. They took on ground delivery when the Roadway freight company sold off their RPS spin-off, basically a UPS clone, to Federal Express a long time ago.

I've had good luck with our drivers at the house--they deliver to an area that isn't easily accessible, vs. leaving things on the front porch in full view of the street. But I've heard of others who have careless delivery drivers, who would toss packages from a distance, leave them in poor areas, or deliver to the wrong address. Not to mention problems at the distribution centers where boxes are tossed around, or allowed to fall off the conveyors. Not pretty!

I did have that happen once with a set of struts for one of the cars here. I had gotten a delivery notification when I was leaving a local audio club meetup (which was more about drinking and eating than listening to music 😁). Got home...nothing. Looked at a couple of neighbors' houses, nothing there either. Got a text message the following day--a neighbor one street over with the same street address number had gotten my two heavy boxes. I thanked her and picked them up. As these things go, not too long after, I got a package for her, and we had to arrange a similar pickup.

We keep meeting like this, and people are gonna talk. 😁
 

lj

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Wow--what a great hobby to have dealing with audio electronics, vacuum tubes and the like. My uncle in the 1960s, in his opinion, felt that the Mac Intosh tubes were the top of the heap for his audio system.
 

lj

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As a follow up--I just read that tubes in their heyday were very powerful and not vulnerable to electromagnetic pulses. Also today some musicians still prefer tube amps over their solid state counterparts.
 

Rudy

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Tubes are kind of a tradeoff. They burn a lot of energy that does not directly translate into power that eventually ends up going to the speakers. They aren't really "powerful" per se--the most powerful audio tube made today is the new production Tung-Sol KT170, a pair of which could probably put out 160-175 watts. But there's power in numbers. Three classic Conrad-Johnson amplifiers have the same basic circuitry but have different outputs based on the number of output tubes. The Premier 11 gets 70 watts out of a pair of 6550s (or equivalents like the KT88 or KT120) per channel. Premier 12, same circuit but in a monoblock configuration, puts out 140 watts from four 6550s and the Premier 8 is at 275 watts with eight 6550s. (For reference--at idle, a single Premier 8 I believe draws over 500 watts. So it's over 1,000 watts to run a stereo pair.) So theoretically you can (putting this really simply, without getting into electronics theory) chain many tubes together to get more output. Taken to an extreme, the Carver Silver Seven uses twenty (!) KT120 tubes per channel to output 900 watts RMS.

Silver Seven | bobcarvercorp.com

The other thing with tubes is that even today, you still see some lower powered tube amps driving high-efficiency speakers, which are often horns. One watt into a pair of Klipschorns would be louder than we can stand it, and it's not uncommon to see some horn speakers driven by 10-15 watt amplifiers. (The opposite would be an old pair of Advent speakers--they were very inefficient in comparison, and would need hundreds of watts to theoretically play as loud....only, the drivers would burn up before they could ever play as loud as Klipschorns!)

For uses beyond audio, there were more powerful vacuum tubes for things like radio transmitters. Such as this 100 kilowatt tube that was introduced almost 100 years ago.


For guitar amplifiers? My buddy had a Fender from the 70s and sold it in the mid 80s for under $100. I saw a larger version of that same amp, in somewhat ratty condition, for sale at Guitar Center for $1,100. Where a new, similar-sized solid state amp probably would have cost $250. There are also new production tube guitar/bass amplifiers. One of the characteristics of tubes is how they overload--they have a smoother distortion than a solid state amp when overdriven, so they are more in demand.

Today's polar opposite are Class D (switching) amplifiers. What's amazing is that the better Class D modules sound excellent, yet they are very small, and run cool. I have a 50W RMS x 4 Class D power amp in the car that I can fit in the palm of my hand; in the past, I need a huge "plate" amp mounted in the trunk for the same amount of power.
 
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