[gibosi]

I have a quartet of Siemens C3Gs, two bought NOS around 2 years ago and used about 200 hours, two used, and these are terrific driver tubes. I do not know about Telefunken or another brand C3Gs, but I suspect there is little difference between them. All were made in the sixties, or early seventies, under a strict West German, mil spec requirement typical of cold war for undeground telephone signal amplifiers that not only will survive a nuclear EMF pulse, but will amplify and forward even the tiniest communication signal, with utmost fidelity, and last a lifetime...cost no object, this class of tubes were designed to perform, with the very best and very expensive exotic metals, a Thorium alloy (I think) to absorb oxygen atoms inside the tube to preserve absolute vacuum...an all out assault to design a super reliable hybrid pentode/triode audio amplification tube. The specs of the C3G are unmatched, transconductance is enormous, something to expect in a tube designed to amplify weak signals reliably...this in itself does not relate necesarily to sound quality, but it does in the C3Gs. And power, dynamics, bandwidth, they will reveal ruthlessly the limitations of your power tubes. For example, 6SN7G double triodes were a clear step ahead over the stock tubes in my LD MKIII, and the C3Gs make them sing clear and loud, the differences just jump out, only a few were up to the task. I went all out to mod my little preamp to accept the mighty 6AS7G big bottles, and after that even the best 6SN7Gs sounded small, limited, restricted. The C3Gs clearly had the power and the amperes to control the big ones solidly, superior dynamics, fast, tight bass and a soundstage to die for... and the little thing is working as a preamp driving 2 mono SS NAD Amps. Extremely powerful as a Pre, I learned to set the NADs at about 1/4 output... Cheers to all !

 
I will grant you that in the LD, the C3g is about as good as it can get. But with all due respect.....
 
First it is important to remember that the LD was designed around the 6AK5, strapped to operate as a triode. If you put a 6SN7 into a circuit designed for a 6AK5, it simply cannot sound its best. The bias is too far from optimal. Fortunately for LD owners, a C3g, strapped to operate as a triode, is a much better fit, and yes, it does sound very good. However, in an amp designed to run 6SN7, I can assure you that the best 6SN7's do not sound "small, limited, restricted." I find them to be just as good as the C3g, but different.
 
Second, there is this myth that the C3g has been engineered to such high specifications that it is virtually transparent and doesn't have it's own sound. In my experience, this is not true. Tubes manufactured in different factories sound different. And further, tubes manufactured in the same factory, but at different times, sound different. I have Lorenz and Siemens C3g, and I assure you that they really do sound significantly different.
 
And third, yes, operated as a pentode, the engineering specifications of the C3g are among the very best of any vacuum tube ever manufactured. However, when it is operated as a strapped triode, the specifications are about the same as a 6SN7. This alone is a major engineering feat. Most pentodes, strapped as triodes, have relatively high levels of distortion and are not very linear, for example, the 6AK5. So again, while this is a major accomplishment, in the end, you have a "C3g triode" that compares well to a 6SN7. But in terms of specifications, if compared to an ultra-linear, low distortion double triode, such as an E80CC, a strapped C3g is really nothing to brag about.
 
I should point out that my amp is designed from the ground up to run either a pair of C3g or a single 6SN7, so it is very easy for me to compare them with everything else being equal.
 
So again, in an LD, the strapped C3g is perhaps among the very best, if not the best. But given that, it is simply not possible to extrapolate beyond the LD and come to any meaningful conclusions.
 
Cheers
 

 

 

[Johnnysound]

Oh yes, G, let me say first that I am not talking about 6SN7Gs as driver tubes, only as power tubes in the MKIII, providing superior sound against the stock power tubes, with the C3Gs in front. In fact, after rolling many 6SN7Gs in this unconventional role, including super nice Sylvanias chrome tops, vintage CBS Hytrons, RCAs and my favorite Tung-Sols, from different vintages, I was hooked with the ITT branded, Hitachi Japan made tubes, of which I bought a quartet. After a good warm up, these 6SN7Gs are magical, in terms of dimension and space. Not a warm or euphonic tube, they can sound very solid state like, dynamic but dry, but after an hour operating, exceptional air and sound comes through. All the opposite from "small, thin and restricted" and I have to agree that these great tubes could not be described that way. They are not, and my comment is valid only in comparative terms with 6AS7Gs as power tubes. I was so happy with my setup, it sounded so good that I doubted that the effort to go all out for the big tubes would offer something better. And my dear G, you, among other experts, concur that the upgrade was worthwile. And it was, of course. So, you get a grand sound, more open, unrestricted, dynamic, dimensional. In contrast, the 6SN7Gs, any of them, even the very best sounded ,well, smaller, if you know what I mean. As power tubes, of course...

 

[gibosi]

Oh, I didn't catch the fact that you were using 6SN7 as output tubes. For sure, while they are superb, small-signal tubes, a pair of 6SN7 simply cannot provide enough current to be effective output tubes. But perhaps 4 or 5, in parallel, per side, might do the trick. lol
 
And I commend you for going the extra mile to mod your LD to handle 6AS7s. The 6AS7 pushes something like 100ma, compared to about 20ma for the stock output tube, or a 6SN7. Being able to push this much current as well as a relatively low plate resistance to gain ratio, makes the 6AS7 a very effective output tube when used in an OTL. And beefing up the associated circuitry in your LD to handle the extra current was very wise and prudent.
 
Cheers 

 

[rosgr63]

Hi Ken,
The SinglePower PPX3-6SN7 uses one 6SN7 as a driver and two 6SN7s for output.
Not a bad amp at all.
I'm side tracking from the LD just for info.

 

[gibosi]

I can only conclude that there must be some very ingenious circuitry in the SinglePower. For sure, two 6SN7s are quite inadequate in more conventional OTLs like the LD and Glenn's OTL.
 
It appears that these amps are not being made anymore... too bad....

 

[rosgr63]

I suppose I'm lucky I got one LOL

 

[vilhelm44]

When you guys mention spacers, where do you buy them from?  My C3Gs arrived today but they don't quite fit with the adaptors I have in the LD IV SE even without the grill, which is a pain.

 

[vilhelm44]

I just found the Leeds Radio site for the spacers but they don't ship to the UK.

 

[vilhelm44]

It's all good now, Richard from Leeds Radio was kind enough to ship to the UK 

 

[dbaker1981]

Are 12AX7 tube compatable with the mk 1+ and mkiii?

 

[gibosi]

Are 12AX7 tube compatable with the mk 1+ and mkiii?

 
Not really. But where there is a will there is a way. For example, an external 9-pin breadboard socket plus a couple of 7-pin test sockets will do the trick.
 

 

[dbaker1981]

Not really. But where there is a will there is a way. For example, an external 9-pin breadboard socket plus a couple of 7-pin test sockets will do the trick.

Im looking for that gold lion sound and it seems that they dont make any in the ef95. Any suggestions on similar sq tubes that fit?

 

[gibosi]

Im looking for that gold lion sound and it seems that they dont make any in the ef95. Any suggestions on similar sq tubes that fit?

 
I've never heard a gold lion, so I have no idea...  Sorry....

 

[Hitogoroshichan]

Just wondering, do 6AS7/6080s have the same problem as 6SN7s have with HE-500s?

 

[gibosi]

  Just wondering, do 6AS7/6080s have the same problem as 6SN7s have with HE-500s?

 
No. The 6AS7/6080 is a much more powerful tube, and it can drive the HE500 better than a 6SN7 or a 6N6PI. However, the LD was not designed to use such a powerful tube and this presents a couple problems. First, the 6AS7 heater draws 2.5 amps, whereas the 6N6PI draws about 1.0 amps, and therefore, it is absolutely necessary to use an external heater power supply.
 
The second problem, alluded to above, is the fact that the plate current of a 6AS7 is about 100 mA, whereas, it is around 30 mA for a 6N6PI. And again, the associated circuitry was not designed to handle 100 mA. As a result, resisters and capacitors in the signal path may well burn out. And therefore, I would encourage anyone wanting to run 6AS7 to follow Johnnysound's example and upgrade their LD to handle this tube.
 
That said, some in this forum have been running the 6AS7 without any circuit modifications, only an external heater power supply, and have not had any problems. Even so, there is still considerable risk that the circuit will eventually fail due to the excessive current. Thus, I cannot recommend the use of the 6AS7 without circuit modifications.