Hi folks, long time reader, new member. Thanks for all the education all these years. Looking for members to rain wisdom upon me

I just acquired my grandfather's old Leak Stereo 50 vacuum tube amp, along with a preamp and tuner. I fired it up... sounded mediocre... one of the tubes starts glowing extra bright... POW! I blew a capacitor. Smoke and paper fragments everywhere. I assume the poor sound quality was related to the imminent disaster.

I plan to fully restore this Amp, maybe replace all the caps and tubes (?)... Or maybe have a pro clean it up for me. Either way, I would appreciate any opinions on anything related. Good Amp? Worth restoring? In over my head? Will the universe implode if I play MP3s on it? Replace tubes/caps outright? Words of wisdom?

Also, once I get this thing going, I think I will need a nice pair of bookshelf speakers in the $500/pair range to go with it. Suggestions welcome.

I am an electronics engineer by trade and give you some advice on this one. I rebuilt a Leak Point one mono amp from scratch and had problems with lots of stuff. Here are some items to watch for:

1) Tubes - replace them all. My amp was based mostly on KT61s which I was able to source from the Soviet Union. When replacing the tubes try to clean up the tube connectors as well. With age they will have oxidized. I lightly used a file on all the tube sockets.

2) Caps - you should replace them all. Old electrolytics will fail just from age alone.

3) Resistors - get a magnifying lens and inspect for cracks. I found two that had cracks and when I removed and checked them they were well off the tolerance levels.

4) Speakers - get something reasonably efficient that has no big impedance dips, these old amps have problems with inefficient speakers, 4 ohm loads and reactive loads.

Let me know if you have any questions. I rebuilt mine just for fun and it's a cool conersation piece to show and amp from the 1950s still functioning. All of the work is dead easy as these are not modern designs. Mine doesn't even have a PCB!!

Ched, you might want to ask the same question on the tube forum at diyaudio.com - there are some very knowledgable people there (and here, judging by exponent's answer).

Actually, in my experience, tube amps sound 'richer' and 'warmer' than solid state amps, which I think is positive in regards listening to any music format including .mp3s. However, an analog source, ie. turntable or cassette, will sound even 'warmer' than a digital source, like a sound card. In this regard, since I spend a great deal of time listening to digitalized audio, buying a great sound card was as important as any other link in my audio reproduction chain. Personally, I'm using an M-Audio Audiophile 24/96, which sounds quite nice.

As well, IMHO, speakers are just like shoes, make sure you buy a pair that still feel comfortable after listening for many continuous hours.

Yes, but it's happened before, so don't panic.

It can be fun to restore, but it will probably cost more than you thought and take 3-5x as long. (been there with other old audio gear)

The Leak Stereo 20 amps were very popular in the 1960s, and with good reason. It's a good implementation of a good circuit. Beware that driving them hard causes the wax in the transformers to melt, drip out, and eventually they will die.

The Stereo 50 is rarer. I've never heard one, but they're supposed to be good. If you decide you don't want it, someone will buy it from you on eBay.


With the stereo 20 at least, it's quite effective to have transistor-fed subs, and the stereo 20 handling the main speakers. You can get sweetness and power without overheating.

You can find everything you want to know about Leak amplifiers here:

http://home.mira.net/~kiewavly/Leak.html


As for the "sound" of valve amps: bad examples (or badly partnered examples) won't give bass that's acceptable to modern ears (though some people love the sound) - most examples suffer from a small amount of microphonics (easily audible if you tap the valves with your finger - you can hear the tapping and ringing out of the speakers!) and self-reverberation (easily audible if you replace the speakers by an 8 ohm resistor and listen carefully to the valves themselves - the music is there!). I believe both can add to the "nice" sound associated with value amps.


It's not just the speakers that matter wrt valve amps (though 50 watts was considered a huge amount of power when that amp was made!) - it's the volume you like to listen at, and the amount (and type) of distortion you find objectionable.

There's also the reliability issue: valve amps won't run for thousands of hours without attention. The valves do wear out.

There's also the safety issue: if you have kids, a valve amp needs to be well out of the way - especially vintage model like this - they were designed for hiding away in cabinets, though most people now have them on display. When switched on, there's enough voltage in each of those valves to kill you, so be careful. Don't let anyone fall on it or stand on it!


It'll be fine fed from a good lossy source. You could probably run it directly from an iPod and a simple passive pre-amp.

The Leak power amps work very well (IMO: best!) with a line-level source and a basic/passive pre-amp. Good valve pre-amps are much rarer than good valve power amps. The contemporary Leak pre-amps were terrible - avoid. Some modern ones are better, but with a line level output from a CD player etc you don't need one.

Cheers,
David.

When enclosing a tube amp in a cabinet you must be very aware of air circulation issues. They give off a lot of heat and this needs to be disposed of properly. The tubes themselves will probably not be damaged, but electrolytic capacitors in particular will dry out very quickly and fail if overheated. The heat could also damage the cabinet.

Wheres the TOS#8 police when you need them? The font police must also have the day off...

Although I find the post disturbing and tending to cut against the grain of common wisdom at this forum, it is not a clear-cut violation.

I think there's plenty of information available that demonstrate how tube amps, turntables and cassette players color sound more than solid state amps and digital sources. Furthermore, it's the poster's prerogative to decide which sounds better to him, provided he can distinguish a difference.

Are you suggesting he can't distinguish a difference?

Uhrm what?

How can people moan about TOS#8 in this context?

The rules are fine to be there but throwing them against a statement like that is just bull.

And, Greynol, thanks for not playing along that game.

Folks, thanks for all the helpful information so far. I am taking in everything from everybody, and slowly digesting it. I also started reading "Amateur Radio Theory Course" to review the basics before I electrocute myself. Again, I REALLY appreciate all the great advice and opinions.


I do have a couple of rugrats. Is the risk only if the tubes are broken? Or might there be some other surfaces that could zap you? Presumably the caps on the bottom could kill you, but thankfully its too heavy for the kids to lift.


I have the Leak Varislope Stereo preamp. Does that fall into the "terrible" category? It sure does look nice sitting on my shelf... What problems do they have? Perhaps I don't need to utilize the "terrible" functionalities. :-)

Glowing tubes are nearly irresistible to children; sadly, said tubes are also blazing hot and a quick touch can produce second degree burns.

Even when enclosed, there seems to be a temptation to poke at them through the grill - followed by breakage and shocks.

If there are exposed or visible tubes, make sure they are caged behind a wire mesh.

Cats also seem to have a remarkable affinity for caged or enclosed tube amps - they like to sleep on them. So if you have one be prepared to vacuum from time to time or put up with the smell of the shed fur burning.

Lastly, very few things seem heavy enough to prevent determined children from moving them, and if they are on a shelf, toppling them over. You may want to strap the amp down.

I once had a tube amplifier (Dynaco) that had a pair of octal sockets on the front panel, not to plug tubes into but to plug in some kind of add-on (preamp? I can't remeber). The tubes were well protected by a perforated metal cover, but my little girl discovered that she could insert pencils into the center hole of the octal sockets. Eventually she shorted it out and caused a lot of damage.

That's the one I have. It's just 100% terrible, except the turntable input, which is 200% terrible.

Yes it looks nice, so leave it on the shelf, but don't use it!


Keep it all well away from kids. It's not like the power amp needs to be anywhere accessible. Yes, ventilated - but if you must look at it, put it on a high shelf.

Cheers,
David.

Doh! That's my favorite input!

I apologize for my statements. My gripe was mainly about the parts involving MP3s, but after careful rereading, it seems you are right: he did not claim that it would make it sound any more transparent or closer to the original, only that it would sound 'warmer' (which can only objectively be described as different) which it probably does.
I have been in situations where I was unable to distinguish between a solid-state and a tube amp, but this is probably more of a rarity than a common occurrence, so I won't ask him to prove his claims.

Hello. I restored a roland tube amp and have always enjoyed its sound.

The issue was dried out capacitors, so I simply replaced every last one and it was less than 50$ Canadian but a lot of work.

The amp uses mostly 12AX7's in the pre-amp and drivers, and 6BQ5 outputs. Repalcement tubes are a bit more expensive. I find the Russian ones leak less and are fairly cheap.

The amp has an interesting way of softening the bass a bit. It sounds nice somehow. It is incredibly powerful as a headphone amp.

Scout the price of the caps and tubes before proceeding. An old TV repair shop should have a tube tester so you can check the ones you still have.

It was a fun project and all.The amp sounds pretty good. The highs roll off at about 15Khz. The bass is a warm and wooly sounding. Max power is about 15 watts but it absolutely rocks on headphones.

That's surprising - valves themselves are capable of very high frequencies - though when they were in common use, almost no one had speakers that could reproduce above 15kHz.

There's a note in the Leak pre-amp instruction manual that reads (from memory)...

Note regarding faulty treble control. We have received a number of returned units from owners who believed that the treble control on the pre-amp was faulty, as turning it produced no change in the sound. Upon testing the units in our lab, we found them to be fully functional. Many speakers sold today are not capable of reproducing the region of high frequencies that are boosted and attenuated by this control. If you believe your amplifier is faulty in this regard, please use a full range source, and listen to the output on full range speakers capable of reproducing frequencies over 10kHz.


I have a Rogers HG88 integrated amplifier with a variable frequency cut off, 5kHz-20kHz, which works as advertised with modern partnering equipment (CD input, modern speaker on output). My Dad said he didn't think that control ever did much when he used it in the 1960s!

Cheers,
David.

That's probably a limitation of the output transformers. A good amount of feedback could help to overcome it, but the transformers themselves had to be designed to cover a 3-decade frequency range, which is not easy.

They would respond well up over 25Khz if you increased the input signal amplitude. But observing it on the scope with a constant amplitude, variable frequency sweep, the rolloff point was 15 and change for a 3db drop.

This was measured on the speaker outputs. The pre-amp may have better performance.

Ouch. That's pretty poor.

Certainly in my 20s I wouldn't have been at all happy with such an amp. I guess when the only available domestic sources were FM radio, tape, and LP, it wasn't quite such a limitation.

Cheers,
David.

But can you state for sure that you could have distinguished a 20kHz tone when taking into account the masking effects of the other tones in a complex waveform?

I'm not saying that you couldn't, but spot-frequency testing and complex waveform (ie, music) testing are two very different animals. If it wasn't for these masking effects then MP3 wouldn't work for the human ear.

It's also worth bearing in mind that distortion produced by all simple single-ended valve amplifier designs consists predominantly of even harmonics. Even harmonics sound chordant rather than dissonant so behave in a similar way to the harmonic-enhancement method sometimes used to extend the apparent frequency response of original audio signals of limited bandwidth. In short, as far as the human ear is concerned, it sharpens up the waveform in a pleasant manner.

When it comes to the way that valve amplifiers behave, there's a lot more that meets the ear than immediately meets the eye, if you get my meaning.

Cheers, Slipstreem.

PS I sincerely hope that I haven't broken the TOS#8 reg. Independent and certifiable evidence to support the "benefits" of even harmonic distortion are readily available to those interested enough to Google.

I'd say that David is quite familiar with masking effects and has taken this into account.


Most likely the amplifier under discussion here is a class AB push-pull design, but I don't know what effect that has on your argument.

Even an A-B push-pull design generates a higher degree of even than odd harmonics in valve design, although the overall level of distortion is likely to be lower as a higher level of negative feedback is usually used to overcome the slight amount of crossover-distortion generated in almost any push-pull design. This will reduce all forms of distortion throughout the waveform to a degree dependent upon the feedback factor(ish).

I'm not saying that David isn't aware of these things already. I'm just trying to flesh-out the valve amplifier theory for passers-by who may not be so familiar with them.

Cheers, Slipstreem.

I did not listen your amp, but I can say that there are a lot of audiophiles very proud to have a Leak.....

I couldn't agree more! As the owner of number of different amplifier designs, personally, I simply like the sound of class A valve amps. It's not something I really need or want to prove. I am simply very happy with what I listen to music with.

As for my original post, I was careful not to say tube amps sound better, simply that they sound different, which I hope is not at all controversial. As for the font thing, well, that was maybe a little too subtle.