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I wanna tube! Please advise

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Posted on October 31, 2001 at 19:00:58
ck42


 
I'm really starting to get an itch for a tube amp. I've NEVER had one, never heard one, never before intended to own one.

But for whatever reason, I now want one ;)

Questions are: How much should I expect to have to pay to get 'into' a *beginner* tube amp? I'm not necessarily looking for audiophile quality material. Heck, I'm not even looking for something new! I've even been rumaging around on ebay looking at old 1950's tube amps...only problem is, I have ZERO clue if it's any good or not.

I don't need something high powered either. I just wanna play with it and listen to something that is not considered a piece of garbage.

I've even looked into a DIY tube project....only thing is, it looks like they can get kinda expensive. Is buying a used one cheaper than building my own new one?

Well...I thing I've given a half decent impression of what my quandry is.

....please advise

 

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Re: I wanna tube! Please advise, posted on October 31, 2001 at 20:17:09
hifitom


 
First, what is your price range? Is there a shop near you where you could audition some tubed pieces? How about a tube linestage kit? Bottlehead's Foreplay is about as inexpensive as you will find and sounds very good. If you decide to tackle the tweaks, there are lots of things that can be done and the Bottlehead forum is very active with folks who will help you along if you run into problems.

The current budget leader in amps seems to be the WAVE AV-8 at $200/pair of pre-built mono blocks. http://www.tubehifi.com/amp/amps.html You can pick up a push-pull EL34 kit from DIY HiFi Supply (there is a link on the opening page of Audio Asylum) for under $500. I have heard nothing but good comments about their 300B kit amps. If you really want to be daring, try a low power (3 watts) Single Ended Triode kit from Bottlehead. There is a distinct difference in the sound of a direct heated SET amp and a PP amp running pentodes tubes (EL34, EL84, etc.)...you should try and experience both before deciding, if you have the opportunity.

Last but not least, if you decide to buy something used, you might try to find one here on the asylum...I don't think it's against the rules to inquire if anyone is SELLING an amp(?). Many of us have perfectly good pieces taking up space and you would be much more likely to get an amp that works well. You might be able to pick up some nice little gem for under $200. They won't be the highest quality around, but they are great for getting your feet wet. Ebay might not be the best place for someone just starting out in tubes, unless you have some electronic knowledge. Having bought a few pieces from auctions, many really need some tuning up and the labor can cost more than the amp is worth. This can be a good way to learn, if that is what you really have in mind. Many folks started out with a Dynaco ST-70 or a Fisher or Scott integrated. When running right, those pieces can deliver very satisfying sound, but even the ST-70s are going for a healthy price nowadays.

And a final word of caution: The voltages inside a piece of tube gear can kill you. It's important to understand what you are dealing with before poking around under the hood!

Hope this helps,
Tom

 

Re: I wanna tube! Please advise, posted on October 31, 2001 at 20:44:54
ck42


 
Tom,

Yes! you've def. given some more to think about and look at. Though, having over 15 years of electronics backround, I've never even fired up a tube circuit before and pretty much all the tube terminology you shot across my bowe totally lost me ;) That's ok tho...

Those Wave AV-8's look pretty sweet. At $99/ea, THAT'S my kinda budget! ;) If it gets me a decent tube amp and let's me hear what I've been seeing so many talk about, I'm all for it. That tube MG Head DT headphone amp really has me going too!!

Do you have a link for that "Single Ended Triode kit from Bottlehead" ? I'd like to check that out as well.


Unfortunately, with my schedule the way it is, I don't have time for projects right now >:(

For right now, I kinda just want something that is plug n chug...no time for refurbing and the like.

Thnx muchos for the info!

 

Re: I wanna tube! Please advise, posted on October 31, 2001 at 21:30:38
hifitom


 
http://www.bottlehead.com/et/et.html will get you to the Bottlehead products page. You might want to consider the Foreplay along with the AV-8s. It's a pretty quick kit to build and then there's the satisfaction of having built your own rig. With your background, the consturction should be a snap and then you have the fun of trying the different flavors of tubes that can be run in this little gem. It's hard to imagine changing the voicing of your entire system for $10-40! Something that's nearly nearly impossible to do with the large scale integration in mass-produced SS gear.

About the only way I can put the sound of a Directly Heated Triode running in the Single Ended mode, like the Bottlehead amps, into words is to say, organic and immersing. I think there is a common misconception that tube gear, particularly triode amps, sound a little slow compared to their Solid State counterparts. In some cases, yes. There is poorly designed or built tube gear...I know because I have built a few dogs myself. But it most certainly is not always the case. Maybe someone else can shed more light on this than my vocabulary allows...as I am a photographer, not a writer...

Tom

 

Re: I wanna tube! Please advise, posted on November 1, 2001 at 04:21:19
nl


 
With your electronics background I highly suggest building your own amplifier.

You will probably find that it is laughably simple. Some single-ended triode kits have about 25 parts, and they're all really big and easy to work with.

You could build a decent kit in a weekend.

Remember you will almost certainly need new speakers to go with your amp. DIY speakers are also quite easy to build.


 

Re: I wanna tube! Please advise, posted on November 1, 2001 at 09:56:25
ck42


 
Ok! The interesting part of this is the ability to completely change the overall sound of a system....by just changing tubes. That is pretty cool I think. Is this a matter of using the same 'type' of tube but made by a different manufacturer or actually using different 'types' of tubes altogether? The latter seems kinda strange in that it would be the equivalent of throwing in a JFET where a MOSFET was normally used....you can't just do that ;) things have to be changed to accomodate the new type of part.

Another thing...if I'm simply wanting to get the 'sound' of the tubes, should I maybe consider a preamp instead? Wouldn't the tube sound simply be passed through the SS amp? If so, would it be the case that a preamp would be less expensive overall seeing that it is a lower power device? ala Bottlehead Foreplay for $149! btw, that is a really nice looking piece of equipment!

...doncha just love newbies :)

I really appreciate the repsonses guys!

 

Re: I wanna tube! Please advise, posted on November 1, 2001 at 10:29:52
hifitom


 
I am pretty much SS ingnorant, but with tubes the manufacturers sometimes use different metals and configurations in the internal structures of the same tube type. There can be a big difference in the tone of a Amperex tube compared to an RCA in the same family. And then there are the differences in the years that a particular company might have produced the same basic tube. Not sure if there are these kinds of differences in the SS world. There are all kinds of variants for some of the generic identifications, military/computer/low noise. This accounts for the seemingly crazy numbering scheme for tubes. Then there are some that have similar electrical characteristics and can drop in with very minor changes, and sometimes none, in the circuit. I'm guessing there is a parallel in SS stuff.

Check out Joe's Tube Lore in the FAQ section of the Asylum-http://www.audioasylum.com/audio/scripts/d.pl?audio/faq/joes-tubes.html

Gotta run and actually do some work but here's a look at what you might be able to do, given your level of experience, if opt for the Foreplay kit.

 

Re: I wanna tube! Please advise, posted on November 1, 2001 at 11:22:54
ck42


 
Ok...that makes more sense. Yes, in the world of SS, there are analogies. First thing that comes to mind are opamps. There are MANY pin compatible opamps made by different manufacturers of varying quality and characteristics. While each one of them may simply be dropped into a circuit, the individual performance and characteristics of those opamps will vary and thus change the sound characteristics of the circuit.

I'm still interested in hearing what anyone has to say regarding the use of a tube preamp and a SS power amp for the purpose of having a 'lower' cost tube 'sounding' output.

 

Re: I wanna tube! Please advise, posted on November 1, 2001 at 18:09:23
Jenya
Audiophile

Posts: 35
Joined: October 10, 2001
You may want to consider a headphone amp.
1)It is chaeper.
2)It is easier to make one
3)Unless you already have nice speakers, you will be able to achieve a much better sound for money with headphones.

When I was getting into tubes, I got my feet wet with Foreplay and Assemblege 300B SET. After putting together these kits I came to a conclusion that I will never do kits again. Don't get me wrong, I had fun doing that, but not as much as I would have by putting an amp from the scratch. Besides it was quite obviouse, especially with Foreplay, that I can do better with less money.

Now, overall I've spent quite a lot of time and money to get to where I am, but the final version of an amp is fairly inexpensive and provides great results.

Just a thought.

jenya

 

Re: I wanna tube! Please advise, posted on November 1, 2001 at 20:27:49
ck42


 
Jenya:

Thanks for the response. Speaking of headphones, my primary listening is in fact done with cans. This is also the reason I've expressed interest is building a tube preamp vs. a tube poweramp...I can use the preamp as a headphone amp ;) ...well, that and thinking maybe it would be cheaper for whatever reason.

What you say about designing your own for less than kits...this is kinda the reason I was asking some of my questions; I don't want to buy a kit that sux.

I've been pouring over everything that I can find online regarding tube amp operation (and tube operation itself!) and have come to an early conclusion that I want to start off with a SET amp. The weird thing I seem to be seeing is that they all are basically the same circuit. It's doesn't appear that there are too many ways of designing an SET. And if this is indeed the case, then it would be a no brainer to just make one and then tweak it via better componetry and minor circuit mods. I mention this because it seems to contradict the idea of 'designing a better one' vs. the kits. If there are few ways to design it, then improving on the kits would be hard to do.........I feel like I'm just repeating myself at this poin t so I'll stop with that idea.

The one thing I haven't been able to figure out yet is the multiple tube stages that I see in most schematics. I understand the input stage, but then the plate goes right into the grid of the next stage on so on. What exactly is the purpose of this?

Oh, I've got a copy of "Beginners Guide To Tube Audio Design" from OCSL on its way to me now ;) Hoping it will shed some more light on things.

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 00:19:00
A.L.C


 
Hello,
If you want the tube sound and are on a budget you should get a vintage Eico integrated amp with a tube rectifier. Most newer products in your price range use solid state rectifiers and nothing is ever overbuilt. With the Eico you will have quality OPT's, tubes and a nice chassis.

To sum it up. Don't bother with newer "budget" kits. You will not get that tube sound you are interested in. I've been there already. The expensive stuff is good, but its expensive :-) Otherwise, DIY and make a SET combo, but you said you are short on extra time. I'd get the Eico!

Good Luck,
-Mark

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 10:51:25
Jenya
Audiophile

Posts: 35
Joined: October 10, 2001
"early conclusion that I want to start off with a SET amp. The weird thing I seem to be seeing is that they all are basically the same circuit. It's doesn't appear that there are too many ways of designing an SET. "

I think it is good that you decided on SET. It will give you a very good reference baseline. As far as number of different topologies for SET, I think in a crude way you are right. There are few tricks that you can play with though. Ultrapath for example. Some people would also tell you that there are 11 ways of implementing parafeed, which is another variation of SE. Power supply designes can vary from two $0.05 diodes, couple caps and resistor to a heavily regulated one. CCS loading is another trick worth of playing with. I am sure there are more.

"And if this is indeed the case, then it would be a no brainer to just make one and then tweak it via better componetry and minor circuit mods. I mention this because it seems to contradict the idea of 'designing a better one' vs. the kits."

I don't know if 'designing' a better amp would be an objective. Afterall, as far as I understand, all tube circuitry theory was pretty much complete by 1950-60. Not much you can invent there. However, ending up with a better amp than you would get by assembling a kit is a very achievable goal. As I mentioned above, there are few variable that you can play with to end up with a better sounding design.

"The one thing I haven't been able to figure out yet is the multiple tube stages that I see in most schematics. I understand the input stage, but then the plate goes right into the grid of the next stage on so on. What exactly is the purpose of this?"

After you finish reading your book, you will get a better idea how this works. In the nutshell, tube is a voltage amplifying device. When current passes through a first stage tube there will be a voltage drop across it. This voltage is applied to the grid of the next stage just like the one that was applied to the grid of the firts tube from your CD player. You are describing a dirrect coupling. Some circuits use a decoupling capacitor between stages.

By the way, if you decide on making headphone amp, you may not need multiple stages. My current version consists of only only stage that serves both for amplification and output, all thanks to a remarkable qualities of 6C45 tube. The simplest SE disign that can exist.

Regards,
Jenya

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 12:06:31
ck42


 
Jenya:

"I don't know if 'designing' a better amp would be an objective. Afterall, as far as I understand, all tube circuitry theory was pretty much complete by 1950-60. Not much you can invent there. However, ending up with a better amp than you would get by assembling a kit is a very achievable goal. As I mentioned above, there are few variable that you can play with to end up with a better sounding design."

Hehe....this is really was I was trying to say :)

"When current passes through a first stage tube there will be a voltage drop across it. This voltage is applied to the grid of the next stage just like the one that was applied to the grid of the firts tube from your CD player."

This still seems weird to me, though I'm sure it will all make sense very soon. For right now, it seems like I'm amplifying a signal, and then using an AMPed signal just to run a grid on another amp...it doesn't seem doing this would server much purpose...that book better get here soon! This is driving me nuts.

As for the headphone amp, my original goal was indeed to build an amp for the cans....but, I started to think maybe I should just go ahead and do a preamp since there didn't seem like there'd be much more to it. The preamp would give me the added ability to hear the 'tube amp' through some speakers. Only thing is, pretty much all the preamp circuits I see don't accomodate a headphone output. I *think* it should simply be a matter of finding the right OPT with a secondary to run the cans. Or is there another (better) way of doing it?

BTW, your answers to my other questions were terrific...thank you VERY much.

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 12:44:09
Jenya
Audiophile

Posts: 35
Joined: October 10, 2001
"This still seems weird to me, though I'm sure it will all make sense very soon. For right now, it seems like I'm amplifying a signal, and then using an AMPed signal just to run a grid on another amp...it doesn't seem doing this would server much purpose..."

It seems that you are understanding perfectly what is going on but not seeing the purpose in doing that. You can imagine that if you drive a second tube with an amplified signal, you will even further amplify that signal. Another thing is that not all tubes are designed for amplification. For example, output tubes usually don't have great amplification factor but are capable of conducting fairly high current that can be routed through an OPT. Therefore, all amplification has to be done before that stage. I am sorry, if I keep confusing you.

"I *think* it should simply be a matter of finding the right OPT with a secondary to run the cans. Or is there another (better) way of doing it?"

You could put together an SRPP preamp and use fairly big size decoupling capacitor for driving headphones. Personally, I don't like OTL (Output Transformerless) amps as much as the ones with OPTs. Nevertheless, it can sound quite well. Take a look at www.headwize.com
They have a fairly big library of hadphone amp projects. I may be wrong, but the problem that you may encounter with using preamp for driving cans is an output impedance of an amp. Generally, you want to use output tubes with fairly low plate resistance. However, it is not necceserely the case with preamp, since you are just trying to raise the voltage. To be honest, I am in the guess land right now and hopefully somebody else would be able to comment on this issue.

"BTW, your answers to my other questions were terrific...thank you VERY much."
Anytime.

Jenya


 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 13:35:06
ck42


 
"You can imagine that if you drive a second tube with an amplified signal, you will even further amplify that signal."

I can see this being the case. It just seems that the first stage APM'd signal should go to the cathode and not the grid....the grid input just seems to be a modulation signal (thereby not needing to be a strong signal). This is what confuses me.


"Another thing is that not all tubes are designed for amplification. For example, output tubes usually don't have great amplification factor but are capable of conducting fairly high current that can be routed through an OPT. Therefore, all amplification has to be done before that stage."

Now this sheds a LOT of light on things! This is something I can wrap my mind around. Is this what is happening with so many of the SET designs where there are only two tubes in the circuit?

"I am sorry, if I keep confusing you."

NO! hehe...you're doing great! I seem to be the one confusing myself, if anyone :)

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 14:45:38
Jenya
Audiophile

Posts: 35
Joined: October 10, 2001
"I can see this being the case. It just seems that the first stage APM'd signal should go to the cathode and not the grid....the grid input just seems to be a modulation signal (thereby not needing to be a strong signal). This is what confuses me."

I think I understand the way you think about it. Amplifier doesn't produces power, it takes a power from a power supply and, as you point that out, modulates it with the signal. Try to think of a tube as a kitchen faucet valve. One end of it is connected to a high pressure water line (B+), another points out to the sink (ground). Now, you are putting your hand on the twisty part of the faucet (grid) and while listening to your favorite music, keep opening and closing faucet. There you got it, an amplified signal in the shape of the water stream. The same happens with electron stream. Valve is sitting between high potential (B+) and the ground and by adjusting the grid voltage more or less current goes through it. All the power, however, comes from the power supply. In multistage circuit, the last valve is the one that controls the output power of an amplifier. For it to conduct a lot of power, its grid voltage has to be swung over a very wide range. In order to achieve that range, the previous stages are used.

"Now this sheds a LOT of light on things! This is something I can wrap my mind around. Is this what is happening with so many of the SET designs where there are only two tubes in the circuit?"

I'd say yes.

Jenya

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 16:25:03
ck42


 
"In multistage circuit, the last valve is the one that controls the output power of an amplifier. For it to conduct a lot of power, its grid voltage has to be swung over a very wide range. In order to achieve that range, the previous stages are used."

Ok...so would I be correct in saying: The higher B+ is (greater Voltage), the higher the modulating voltage MUST be on the grid?

If this is the case, then it would seem that it would be VERY near impossible to have a line level input modulating a SINGLE high(er) power amp (no in between stages)...you kinda have build up the modulated signal until it's big enuf to actually properly 'feed' the main power amp tube.

Groovy...I think I'm finally getting this!

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 17:33:02
Jenya
Audiophile

Posts: 35
Joined: October 10, 2001
"Ok...so would I be correct in saying: The higher B+ is (greater Voltage), the higher the modulating voltage MUST be on the grid?"

Even though I understand your logic, I wouldn't call that assumption a rule. It depends on the bias voltage and limiting factors of the valve. So, let's say your tube's bias is set to -70V. Roughly speaking, you can swing grid plus-minus 70volts. You see, you can't allow grid to go positive, otherwise it will start sucking electrons on it and you'll get grid current. Anyways, I am pretty sure you can find two setups at which one of them may have lower B+, but use wider grid swing. The important thing is that you are getting the idea how this work. If you think of the kitchen faucet example, you can imagine that if you have a faucet open for a certain idle current, the amplitude of the swing around that point is determined by either the distance from idle current to a complete shutdown or the maximum available current. Beyond any of these points you will get what's called 'clipping'. This is a fairly loose analogy, but similar boundaries exist for valve. One is grid going positive, another is complete current shutdown with grid being very negative.

"...you kinda have build up the modulated signal until it's big enuf to actually properly 'feed' the main power amp tube."
Exactly!

Jenya

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 21:25:01
ck42


 
I see where my logic was too generalized now.

One thing that I've been pondering over recently is power supplies....

Am I mistaken or is NOT the purpose of a PS, in this case, to supply a clean DC signal? Some of the PS's I've been seeing are SO esoteric and EXPENSIVE to build! more than the amp itself many times!

I almost get the impression that different circuit topologies actually require a special type of PS. Please tell me this isn't the case ;)

 

Re: I wanna tube! Please advise, posted on November 2, 2001 at 23:19:33
Jenya


 
I don't think you need to worry about esoteric power supplies right now. A power transformer, tube rectifier, a filter choke or two, few capacitors will do fine. Of course, you could go with SS rectifiers. Cheap, easy to make. Personally I have a strong preference towards tube rectifiers.

Jenya

 

Re: I wanna tube! Please advise, posted on November 9, 2001 at 15:21:26
My my ... so many responses I don't have time to go through them all, so this may be repetitive.

Good stuff cheap: Dynaco Stereo 70 and Stereo 35.

Good stuff reasonable: Mac MC-60s (one of the most innovative circuits of all time) hard to find and worth it, Quad tube amps (low power); conrad-johnson MV-75 (can be superb with slight mods); Dyna/GSI Stereo 70 (check that components glued to the underside of the chassis are held firmly in place -- when they fall and short stuff out it can be spectacular) which is one of the best amps I've ever heard; early VTL monoblocks, especially the Compact 100s.

 

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