I completely agree about the EL38. Great sounding valve in triode. I used it for about a year, and because it has more gain it's just about possible to use a DHT driver tube like a 10Y on a more sensitive system, giving what I call an "Inverse DHT Amp" where the DHT is in the input. Second to the EL38 in triode is the EL12, also a very good valve.
But my favourite right now is the 6C4C or 6S4S - the Russian 6B4G. I prefer the sound to all the cheaper 300b valves I have - I don't have boutique ones to compare. But on the cheaper end, 6C4C is king. As good as, and in fact modelled on, the older 2a3 valves. It sounds great as a preamp tube as well.
But my favourite right now is the 6C4C or 6S4S - the Russian 6B4G. I prefer the sound to all the cheaper 300b valves I have - I don't have boutique ones to compare. But on the cheaper end, 6C4C is king. As good as, and in fact modelled on, the older 2a3 valves. It sounds great as a preamp tube as well.
The first amp I built was a PP 6BQ5, with Karlson cabinets and 12" RE speakers. I remember they sounded great, but we already know that's not a valid argument, listening memory...it was more than 50 years ago.. .
I'm curious why " history showed that it was one of the best tubes " and a link to it would be interesting....
Question:
Favorite output tube for:
Push Pull
With no negative feedback, and using a proper design, the 2nd harmonic distortion will be mostly cancelled, and the 3rd harmonic is most often dominant. With negative feedback, your mileage may vary.
Some tubes that have plenty of 2nd harmonic distortion actually work real good, and the 2nd harmonic distortion is mostly cancelled, plus the circuit may also have less early 3rd harmonic distortion as well.
Single Ended
With no negative feedback, and using a proper design, the 2nd harmonic is most often dominant, typically 15dB higher than the 3rd harmonic.
However, consider when some 2nd harmonic distortion comes from the driver stage (regardless of what stage in the driver and earlier stages in the chain is producing that 2nd harmonic distortion).
In that case, there will be some cancellation of the 2nd harmonic distortion from the driver with the 2nd harmonic distortion of the output tube (serial stage cancellation effect).
With negative feedback, your mileage may vary.
In addition, favorite for what reason . . .
Best sound?
Best measurements?
Or what other reason?
This hobby is meant to be fun and enjoyable.
Favorite output tube for:
Push Pull
With no negative feedback, and using a proper design, the 2nd harmonic distortion will be mostly cancelled, and the 3rd harmonic is most often dominant. With negative feedback, your mileage may vary.
Some tubes that have plenty of 2nd harmonic distortion actually work real good, and the 2nd harmonic distortion is mostly cancelled, plus the circuit may also have less early 3rd harmonic distortion as well.
Single Ended
With no negative feedback, and using a proper design, the 2nd harmonic is most often dominant, typically 15dB higher than the 3rd harmonic.
However, consider when some 2nd harmonic distortion comes from the driver stage (regardless of what stage in the driver and earlier stages in the chain is producing that 2nd harmonic distortion).
In that case, there will be some cancellation of the 2nd harmonic distortion from the driver with the 2nd harmonic distortion of the output tube (serial stage cancellation effect).
With negative feedback, your mileage may vary.
In addition, favorite for what reason . . .
Best sound?
Best measurements?
Or what other reason?
This hobby is meant to be fun and enjoyable.
EL506, the last iteration of the 7868 (7591, 6GM5). Basically an beefed up EL84 and instead a beam power tube. At 300V it models very similar to the EL84 but it has a Pa of 19 watts and the screen can in music handle 6 watts. I strongly belief the Electro Harmonix 7868 has more in common with the EL506 than with the US 7868.
$3 EL506 ?? Sure looks close. 19 Watt Vertical Amp tube, linear. (uses a lower V screen grid)
https://frank.pocnet.net/sheets/123/1/10JA5.pdf
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The curves do look darn near identical - I am playing with them now. Even wound up a special transformer to give me the screen voltage tap without a ridiculous drop in the regulator, the 10.5 volt heater as well as 6.3 and 12.6 for everything else, and give me the full 400 V B+ under load not just idle. And they look exactly like the same pentode curves from 6LR8/6LU8, which are yet still another project. Looks like they copied the graph and pasted in.
Not every amp I’m playing with has a bunch of zeroes following the first digit and causes neighborhood brownouts. I had some 25-ish watt UL-tap-less output iron laying around….
Not every amp I’m playing with has a bunch of zeroes following the first digit and causes neighborhood brownouts. I had some 25-ish watt UL-tap-less output iron laying around….
6L6GC and/or their cousins, just for practical reasons: they fit my MC240 for Hifi, and my G60VR for guitar.
Last count, I have 58 of them, from NOS to Shuguang. I know, it's overkill, since my 1st set of RCA's from the McIntosh Clinic lasted 1978-2012, even though I ran them hard at 65mA instead of the original wimpy 20mA or so. RIP. My 2nd set, Philips/ECG 7027A was not so brilliant: 1 of them shorted after only 8 months. Replaced them with Winged-C: they sound different but good nonetheless, and they're still going strong 10 years after.
Also worthy of note: the Chinese 6L6's that came with my guitar amp look cheap, but they don't sound bad at all, after some mod's. I've got some NOS stashed away for a possible "upgrade", but they stay in the vault.
Last count, I have 58 of them, from NOS to Shuguang. I know, it's overkill, since my 1st set of RCA's from the McIntosh Clinic lasted 1978-2012, even though I ran them hard at 65mA instead of the original wimpy 20mA or so. RIP. My 2nd set, Philips/ECG 7027A was not so brilliant: 1 of them shorted after only 8 months. Replaced them with Winged-C: they sound different but good nonetheless, and they're still going strong 10 years after.
Also worthy of note: the Chinese 6L6's that came with my guitar amp look cheap, but they don't sound bad at all, after some mod's. I've got some NOS stashed away for a possible "upgrade", but they stay in the vault.
All good suggestions. It is always great to hear what people like and why. With Covid, the local audio show has been canceled for the last two years. Not sure on this year yet. And I miss hearing other peoples gear and being able to ask questions and learn.
That is why I bumped this thread. I have no particular build in mind. This is like visiting the local audio show and seeing what people like and why. Sound? Cost? Availability? Power rating? Coolness factor? Esoteric? Esthetics?
That is why I bumped this thread. I have no particular build in mind. This is like visiting the local audio show and seeing what people like and why. Sound? Cost? Availability? Power rating? Coolness factor? Esoteric? Esthetics?
Smoking Amp,
I happen to have some 6336’s and I have some 12HG7’s which look similar to the 12HL7’s. So to clarify. Use a trioded 12HL7 as the driver tube and then run feedback from the output tube plate to the driver tube G2? I am familiar with the the plate to plate feedback commonly called “Schade”, but I have not seen this suggestion. A variation of it?
thanks
Thanks, I'm aware of it, but I only list tubes that I have personally used in an amplifier. Single ended is my next project, and it's almost 100% it will use a GU-29B.
This is a little different. This is very similar to an old scheme called UL driver Fdbk. The driver is run as a pentode, but use is made of it's internal g2/g1 triode. If Vg2/Vg1 stays constant at the internal Mu ratio, then the pentode driver puts out constant current. g1 is driven by the input signal from the front end as usual, and g2 is driven by an attenuator (and possibly a Mosfet follower to handle g2 current) from the output tube plate (or possibly from the OT UL tap, if stable).
So the output tube is controlled by the driver to maintain the output V at Mu times the input signal. Mu for the triode is not quite constant of course, but approximately constant. The pentode driver acts as a high gain Op Amp essentially, controlling the output tube to maintain that Mu ratio. So whatever internal triode curves that driver has, will be impressed on the output tube effectively. Hence the "emulation" name. For P-P the Fdbks need to be crossed to get phasing correct. For SE, one needs a full LTP driver stage (over CCS) to control the output tube (so correct phasing for N Fdbk can be set up). So a driver LTP is needed for either P-P or SE.
The scheme can be taken further using a -separate- -actual- triode, run in reverse. Call it the "model" or "emulant". That is, the N Fdbk goes to that triode's plate and the triode's cathode then drives the LTP driver grid with correct phase for N Fdbk. ( the model triode's grid held constant, or sometimes used as the signal input, YMMV) This version has been around for a while too. Some Japanese schemes. The main issue with all of them is maintaining stability due to an inherent high gain control loop, so some grid stoppers and possible LP limit filter can be used.
Since there are a number of driver type pentodes around, with good quality triode curves, the simpler scheme can be used with say 12HL7, 4P1L, 6J11P, E280L, .... as drivers.
Since the output is being controlled by a strong control loop, the output Z will be low for all these schemes too. Generally a good thing, especially for SE where output Z is often an issue.
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Smoking Amp,
Thanks for the explanation. I have to think that through. I will try and draw it up to see if I understand.
I have an existing 6336 SET but I have never been totally happy with the driver stage. My OPT’s are edcor with the UL taps. So I have most of the required parts but it sounds like I would have to add the LTP.
thanks again
That PX4 in super triode configuration for 50 plus watts may be unreal.
I have a 6922 supertriode setup that is awesome.