[Puddleglum]

So with me thinking about getting a singlepower PPX3, I want to know more about the tubes themselves.

1. What are power, rectifier, and driver tubes?

2. Is any tube compatible with any amp. More specifically, what works with the PPX3 and how can I tell if it works?

3. Why are matched tubes better?

4. Is there any website that would be a guide or a source of info more specific to the tubes themselves.

If anyone can answer any of these questions or anything else that I'm forgetting that would be great.

 

[Len]

1. Power/output tubes provide usable, amplified signal to your speakers and are the final stage of an amp's circuitry. Driver/gain tubes feed the power tubes low level signal from your source, providing gain to make the power tubes function nominally (some power tubes need more gain then others). Rectifier tubes are used to convert AC to DC. Most tube amps use solid state rectifiers nowadays, but there are some that still use vacuum tubes for this function.

2. A tube amp can only use tubes that its circuitry is designed for. You can't substitute any tube you want, only tubes that are equivalent to the tube type your amp uses. For example, a PPX-6CG7 can only take 6CG7 while a PPX-6SN7 can only accept 6SN7 tubes. There are some equivalents, as mentioned, but don't plug in a tube without checking if it's suitable first. Also, a lot of tubes have different designations which confuses the matter for tube newcomers. For example, 6SN7 is sometimes referred to as VT-231, its military designation. Any tube with the prefix 6SN7 (e.g. 6SN7W, 6SN7GT, 6SN7GTA, 6SN7GTB, 6SN7WGT, 6SN7WGTA, etc.) are variations of the 6SN7. Some have minor electrical specification differences, but they will all work in 6SN7 applications. So will 5692 tubes. Another example of multiple designations: 6DJ8, ECC88, E88CC, 6922, etc. are all variations of the same type of tube. Yes, it's confusing.

3. Matched tubes are only critical in some push-pull circuitries, but matching is recommended for output tube applications when possible. It helps to make sure both channels are on par with one another, but more importantly, that the two channels are sharing the load equally instead of one side overtaxing your amp's components. Most tube experts will tell you matching pre/driver/signal tubes isn't a major issue. In robust designs like Singlepower, matching any of the tubes probably isn't a serious concern at all.

4. There's info scattered all over the place with some decent general tube FAQs (nothing specific), but I don't recall the URLs. Keep in mind there are thousands of different tubes, so getting info is a chore in and of itself. You won't find a one-stop place for all your tube info. Just ask questions here and in Audio Asylum and you'll likely get the answers you're looking for.

 

[sacd lover]

Quote:

Originally Posted by Puddleglum So with me thinking about getting a singlepower PPX3, I want to know more about the tubes themselves. 1. What are power, rectifier, and driver tubes? 2. Is any tube compatible with any amp. More specifically, what works with the PPX3 and how can I tell if it works? 3. Why are matched tubes better? 4. Is there any website that would be a guide or a source of info more specific to the tubes themselves. If anyone can answer any of these questions or anything else that I'm forgetting that would be great.

First, the power tubes or output tubes are what drives the load be it headphones or speakers. The driver tube is a voltage gain tube which drives the output tubes. A rectifier tube is a tube used in power supplies to convert AC to DC, and the ppx3 doesnt use one. The ppx3 uses three tubes, all the same type, one driver tube and the two output tubes.

Tubes are specific to a particular design and absolutely cannot be interchanged. For example you cant use a large 6as7 tube in a small 6cg7 socket or vis versa. Tubes come in a huge number of different sizes and types with different pin configurations, voltage requirement etc. and they plain wont fit each others tube sockets(like the big 6as7/ small 6cg7 example) most of the time. In cases where a tube will fit into the same tube socket that doesnt mean the tube will work in the amp.You need to know what type tube an amp uses and use only that tube or a direct substitute that has the same or nearly the same characteristics. Now different brands of the same tube can be interchanged, for example, RCA and Tung Sol brand 6sn7 types will both work in an amp that uses 6sn7 tube types.

The ppx3 has auto biasing so you dont need to worry about the tubes being closely matched in the ppx3; or any singlepower amp for that matter. The auto bias matches the tubes for you.

The ppx3 uses 3x 6cg7 tubes or 3x 6sn7 tubes depending on the version. You know it will work because tubes are marked as to their type and you simply use the type specified by the manufacturer. The tubes have a pin guide which shows you how to line up the pins. You push the tube in the socket once you have it aligned correctly and your ready to go. Never turn on a tube amp without tubes in the sockets. Most tube amps need connected to a load(headphone or speaker etc.) if they are turned on or you will damage the amp. Common sense here, dont change tubes with moisture on your hands or immediately after you turn off the amp and they are HOT. I know this seems stupid to mention but you appear to be completely new to tubes. I think I hit all the high points. If you have some more questions give me a pm.

 

[gundam91]

I'm not an expert in anyway, more like the opposite, but I'll try to explain.
Quote:

Originally Posted by Puddleglum 1. What are power, rectifier, and driver tubes?

Tubes are used in many different applications. Signal tubes (ususally smaller) are used to "process" the signals. Power tubes (usually big) are used to amplify the signals. Some other tubes, like the rectifiers, are used in the power supply. In a solid state equipment, these tasks would be carried out by transistors instead.

Quote:

Originally Posted by Puddleglum 2. Is any tube compatible with any amp. More specifically, what works with the PPX3 and how can I tell if it works?

There are literally thousands of different tubes designed for different applications. If I understand your question correctly. The answer is no, you cannot just find any old tube and plug it into your PPX3. There are two versions of PPX3. One uses 3 6CG7 tubes, the other one uses 3 6SN7 tubes. I am not familiar with these two tube types. But most of the tube have other substitutes, and Europeans uses different designations for every tubes. There are tube substitution websites to find out, or just ask around.

For example, 6DJ8 is a very popular preamp tubes. You can substitute it with 6922, or 7308. European designation for 6DJ8 is ECC88, for 6922 is E88CC, and for 7308 is E188CC. You can also substitute with Russian 6H23N, 6H23N-EB. (These are Russian military designations). Confused enough? No? There are also British military tubes (CV2493) we can use as substitutes.

Currently, only Chinese, Russians, and some other former Eastern Block countries still manufactures tubes. Most people prefer old production tubes from the '50s, '60s, '70s. These are call New Old Stock (NOS) if they are unused. Of course, the quantity is limited, so you have to pay premium for them. But they do sound better in most cases. Different brands of the same tube will sound differently. Your best bet is to buy them from reputable dealers as they will have them tested for you already. Otherwise, you need to buy a tube tester to test for yourself.

Quote:

Originally Posted by Puddleglum 3. Why are matched tubes better?

It is not better per se. It depends on the application. Let's look at the PPX3, the audio signal probably travels through the first 6CG7, then split into right channel and left channel. (I'm guessing here) Let's look at the first case where one tube is "processing" both the right and left channel signals. This probably means the tube has two sections and each section is processing one signal. In this case, you would want to make sure the measurement of those two sections are nearly identical, so the signals will be "identical" or "balanced" going to both channels. The signal is then split into right and left channel. There is a 6CG7 "processing" or "amplifying" the signal in each channel. So, again, you want to make sure that the two tubes measured identical (matched) to each other. In some applications, this is not critical as you can adjust the bias for each channel to compensate.

4. Is there any website that would be a guide or a source of info more specific to the tubes themselves.

Check out the FAQ section on Audio Asylum, there are a lot of information on tubes in general. The Tube forum there is also a great place to browse to gain knowledge. I also have some websites that have specific tube substitution info and tube measurement information if you are interested. PM me if you are interested.

I have written mostly in generic terms. In many cases, I've simplified things for the purpose of this discussion. I am sure others will chime in if you want to have a more technical discussion, which I am not qualified to do so.....

 

[Rob N]

Quote:

Originally Posted by Len Rectifier tubes are used to convert AC to DC. Most tube amps use solid state rectifiers nowadays, but there are some that still use vacuum tubes for this function.

Some say tube rectifiers sound better

 

[sacd lover]

Quote:

Originally Posted by Rob N Some say tube rectifiers sound better

I do.

 

[go_vtec]

Quote:

Originally Posted by sacd lover I do.

I knew you gonna say that

 

[Len]

Quote:

Originally Posted by gundam91 Currently, only Chinese, Russians, and some other former Eastern Block countries still manufactures tubes.

There are American and Japanese companies churning out tubes as well. A lot of great new production tubes are currently being made, especially KR and Emissions Labs. Westrex is getting going again, and hopefully Alessa will find his way back into production of his very fine AVVT line of tubes. A lot of the modern small signal tubes, unfortunately, aren't up to snuff with NOS productions.

Quote:

It is not better per se. It depends on the application. Let's look at the PPX3, the audio signal probably travels through the first 6CG7, then split into right channel and left channel. (I'm guessing here) Let's look at the first case where one tube is "processing" both the right and left channel signals. This probably means the tube has two sections and each section is processing one signal. In this case, you would want to make sure the measurement of those two sections are nearly identical, so the signals will be "identical" or "balanced" going to both channels. The signal is then split into right and left channel. There is a 6CG7 "processing" or "amplifying" the signal in each channel. So, again, you want to make sure that the two tubes measured identical (matched) to each other. In some applications, this is not critical as you can adjust the bias for each channel to compensate.

My contention is it is not critical to match tubes except for a few extenuating circumstances (such as in some PP and SET amps). Tube matching is far more then just matching up gm values. You need to plot the curve for plate voltage as well, and these types of testing devices are uncommon and expensive. I'd only bother "true" matching big power tubes (especially SETs) and tubes intended for PP amps. I try to use similiar vintages and gm values for smaller signal tubes in order to keep the sonics consistent between the channels, but IME it is not a critical as it doesn't make a whole lot of difference .... even with variation upwards of 20% (vintage is more important then anything else, IME). Most importantly, you aren't going to damage your headamp with mismatched sections as you would in PP or SET amps.

It should be noted that tubes that are initially matched (say a 6SN7 pair that reads 3000/3000 and 3000/3000 with curves almost identical) will not necessarily depreciate over time in the same manner. That is, just because they're matched from day one does not mean they'll stay matched on day 365.

 

[petery83]

Quote:

Originally Posted by gundam91 Most people prefer old production tubes from the '50s, '60s, '70s. These are call New Old Stock (NOS) if they are unused.

...and to think that for the last 2 months I thought NOS tubes were tubes filled with nitrous oxide instead of a vacuum...

 

[ReDVsion]

Quote:

Originally Posted by petery83 ...and to think that for the last 2 months I thought NOS tubes were tubes filled with nitrous oxide instead of a vacuum...

Don't feel bad (unless that was a COMPLETE joke), it took me a while to figure that out as well...

 

[PhilS]

Why is it that currently manufactured tubes don't sound as good as NOS tubes? Just generally, one would think that advances in technology would make it easy to meet or improve upon something that was manufactured 40 or 50 years ago. What's the explanation for this?

 

[AuroraProject]

Not to hijack the thread, but I have a few basic tube questions as well. I have an ASL MG Head DT OTL on it's way to me with various tubes included.

1. Are tubes keyed? (ie do they only fit in the socket one way?)

2. How long do they need to warm up before you can listen?

 

[Len]

Simply put, today's manufacturers don't care. Tubes manufacturered in the hayday of vacuum tube technology were built with pride and care because many things (including the military) depended on their reliability and performance. From careful selection of raw materials, metallurgy and chemistry processes, glasswork skill, and the actual skills involved in hand-assembling vacuum tubes, the old boys simply knew how to make better tubes. Tubes these days are a fringe market delegated for less critical applications (although we audiophiles would vehemently disagree with it being less critical

). Consider vacuum tube manufacturering a lost art. Well, mostly (there are some modern manufacturers that are doing tubes justice).

 

[Len]

Quote:

Originally Posted by AuroraProject Not to hijack the thread, but I have a few basic tube questions as well. I have an ASL MG Head DT OTL on it's way to me with various tubes included. 1. Are tubes keyed? (ie do they only fit in the socket one way?) 2. How long do they need to warm up before you can listen?

Tube pins are fashioned so they'll only go in one way.

I warm up my tubes for at least 10 minutes before I listen to it. Some amps have a "soft start" feature, in which case the amp is unusable in the first 2-5 minutes. I find the sound evens out about an hour after warm up, but this will depend on the tube and on the amp.

 

[dd3mon]

Quote:

Originally Posted by PhilS Why is it that currently manufactured tubes don't sound as good as NOS tubes? Just generally, one would think that advances in technology would make it easy to meet or improve upon something that was manufactured 40 or 50 years ago. What's the explanation for this?

40-50 years ago was before transistors. This meant that ALL consumer electronics (radios, TVs, organs, anything with an audio signal, even power stations and phone companies used them for everything) were based on tubes. Millions upon millions were being made by the biggest names in electronics. Now, only a super-tiny fraction of new devices are being made with tubes in mind. Transistors have all but replaced them in every application. Specialty audio is about the only place people still use them, and new products are still being made to use them.

It's like say.. oil lamps.. Before electric lights I bet there were far higher quality oil lamps on the market than there is today. Simply because there was a market for them, and that drives innovation. No market for oil lamps? Someone might still make them, but it's not exactly a cutting edge field with lots of research going into it.

The phrase "they don't make 'em like they used to" applies perfectly in this situation. Modern day tubes are manufactured probably mostly for replacements in very old electronics where the "quality" of the tube doesn't really matter. They are made to be cheap - and they are cheap. The market for a brand new, very expensive tube (but very high quality) would be very small indeed. I'd love someone to do it, reinvent the tube with some modern ideas and materials - but the money to fund that kinda research and manufacturing just isn't there (or if it is, no one's tapped it yet!).

EDIT: I believe possibly the 300B tube is the exception to this rule? But in general what I said holds.

-dd3mon