Johan, I think my point is pretty clear. It is the same point you yourself previously made: let's stick to discussing favorite output tubes and not circuits.
On topic:
I notice your output tubes are very close to one other. Don't they overheat? I mean, your amp does put out 100W, which is an awful lot.
Regards,
Milan
On topic:
I notice your output tubes are very close to one other. Don't they overheat? I mean, your amp does put out 100W, which is an awful lot.
Regards,
Milan
On the first point: Accepted Milan!
On the second:
I hoped nobody noticed! Yes, I ran into trouble. I thought air naturally rising would do it; it didn't. There the temperature reached 62 degrees on the chassis in the middle of the 4 tubes. The picture was taken then.
I then drilled a cross of holes in the chassis between each 4 power tubes, and mounted a small fan underneath on each side. Mercifully not audible. The temperature in the space between 6L6s then went down to about 70 degrees (summer day, room temperature 28 degrees). The amplifier is also mounted on a baseplate (not showed) about 15mm above it. The next one will be larger; I must also take South-African temperatures into account! I could perhaps have the choke (smaller "bin" in front) underneath; will have to re-look at the whole thing temperature-wise.
Appropriate to the thread then: Folks do need to pay attention to arrangement of power tubes - one knows that, but ...... It is unfortunately a little difficult to test, unless one assembles a collection of small 27W (in my case) heaters. Should be practical. (I operate each 6L6GC at Va-c of 550V, Ia of 50 mA, thus quite class AB.)
Regards.
On the second:
I hoped nobody noticed! Yes, I ran into trouble. I thought air naturally rising would do it; it didn't. There the temperature reached 62 degrees on the chassis in the middle of the 4 tubes. The picture was taken then.
I then drilled a cross of holes in the chassis between each 4 power tubes, and mounted a small fan underneath on each side. Mercifully not audible. The temperature in the space between 6L6s then went down to about 70 degrees (summer day, room temperature 28 degrees). The amplifier is also mounted on a baseplate (not showed) about 15mm above it. The next one will be larger; I must also take South-African temperatures into account! I could perhaps have the choke (smaller "bin" in front) underneath; will have to re-look at the whole thing temperature-wise.
Appropriate to the thread then: Folks do need to pay attention to arrangement of power tubes - one knows that, but ...... It is unfortunately a little difficult to test, unless one assembles a collection of small 27W (in my case) heaters. Should be practical. (I operate each 6L6GC at Va-c of 550V, Ia of 50 mA, thus quite class AB.)
Regards.
I currently have no one favorite output tube, however the ones I prefer would all be DHT and the topology in which they are used SE.
Currently my daily listener is the 300B. I like WE and older JJ. I'd like to try KR and TJ sometime soon.
Next by dint of (my) longest term use would be the UX-245 (RCA Radiotron) and its variants. I've never heard a bad one, something I can't say for the 300B! Reliable and long lived too.
Finally the 2A3, I like the old dual box plate Kenrad. Some are great and some aren't.
In past lives the 6550, EL34, and 6BQ5 made the list.
Next I'm going to look at 211/845/GM70 - who knows perhaps one of those will unseat the 300B as the king of my heap..
Currently my daily listener is the 300B. I like WE and older JJ. I'd like to try KR and TJ sometime soon.
Next by dint of (my) longest term use would be the UX-245 (RCA Radiotron) and its variants. I've never heard a bad one, something I can't say for the 300B! Reliable and long lived too.
Finally the 2A3, I like the old dual box plate Kenrad. Some are great and some aren't.
In past lives the 6550, EL34, and 6BQ5 made the list.
Next I'm going to look at 211/845/GM70 - who knows perhaps one of those will unseat the 300B as the king of my heap..
well, he said it's on eBay, but no link to it though. promoting? I don't really think there was any deviciveness (sic) ... just pride showing through IMO.EC8010 said:
On topic, I'm really dig'n something lately I doubt many have ever heard. A Directly Heated Pentode, 4P1S [ 4N1N is an equiv ]. It's used in my headamps in OTL Triode form ; switchable in one of them to pentode mode. Dramatic differance.
For speaker driving, 6550 gets kudos from me.
I mentioned the EL38 in the past -
I have a few of them in my stash, so I took a picture of a few of the bizarre versions I have.
first is just your normal run of the mill Mullard EL38
second is a really early late 40s/very early 50s - no Mica, came in a grey rough (looked like recycled paper) box
third is a real mystery - H&K EL38 - it looks like a KT77 with a plate cap!
and the last is labelled RSD, but it doesn't look like any Mullard I've ever seen before. Almost every other EL38 I have is definitely from the Blackburn plant - this?
I have a few of them in my stash, so I took a picture of a few of the bizarre versions I have.
An externally hosted image should be here but it was not working when we last tested it.
first is just your normal run of the mill Mullard EL38
second is a really early late 40s/very early 50s - no Mica, came in a grey rough (looked like recycled paper) box
third is a real mystery - H&K EL38 - it looks like a KT77 with a plate cap!
and the last is labelled RSD, but it doesn't look like any Mullard I've ever seen before. Almost every other EL38 I have is definitely from the Blackburn plant - this?
).Esoteric tubes were always out for me. Too rich for my blood. Also out: tubes that require voltages that i’m not comfortable with and/or require big, expensive and maybe custom iron. Best yet no iron and in that case EL509. If transformer-coupled it was between EL34 and 6L6. For me, no contest: the 6L6 has lots of electrical equivalents, the EL34 none.
Having only Noval experience so far... my pick is the 6GM5. I like the fat bottle look, and they're easy to drive. Using single ECC832 for preamp/invertor duty each channel- beefy output into 12" subs; clear mid's and hi's into modd'ed Polk T50's.
I've read here they were a popular tube back in 60's, just before SS arrived. Someday I may try the Octal stuff, but I'm happy w/ current design that started as PP ChiFi kit.
Jim
I've read here they were a popular tube back in 60's, just before SS arrived. Someday I may try the Octal stuff, but I'm happy w/ current design that started as PP ChiFi kit.
Jim
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The answer to this question depends on how much power you want or need.
For a 1 watt SE guitar amp that fits inside a guitar body and runs for hours on a 7.2 volt NiCad from an RC car its a 6AK6 being driven by a 6AK5 in a circuit similar to a Fender 5C1 Champ with a switching supply making about 175 volts.
For a 25 watt SE amp or a 200 watt P-P amp is the 26/36LW6 or the 26HU5.
There are lots of tubes in between these extremes, but I tend to favor TV tubes and other oddballs that can still be found cheap.
If building an amp for a musician, you are usually restricted to tubes that can be found at a music store. This makes the output tube a 6V6GT, EL84, 6L6GC, EL34, KT88, or 6550. I have made HiFi and MI amps with all of them. For "chick singer with a guitar" music an EL34 or 6V6GT in triode is my favorite. For Pink Floyd cranked to the edge of clipping, its KT88's or big fat TV sweep tubes!
Cheap tubes with great triode curves.
Since all the exotics are extinct or priced into orbit by now, I would look to Tube Emulation now. Take some small tube with great curves and use N Fdbk to make a big output tube act exactly the same way, relatively. You can make any big tube look like a 12HL7 or say 4P1L or 6J11P.... in triode, for example:
Attenuated N Fdbk from the output plate back to the 12HL7 driver screen grid. Could make a 6336 or 6528 or 26LW6 ..... into a great LV triode -without- 1000s of Volts B+ for some transmitting tube. Could even be done for OTL output.
????? There is the KT77 that is interchangeable with EL34. It's got better triode curves, besides being specially designed for UL mode too.
JJ makes a variety of EL34 variants besides.
I think the same, to listen to solo singers accompanied by acoustic instruments, EL34.
Rock or classical music that requires some extra "weight", KT88.
For operas, either, but in triode mode and I have the best of both worlds.
They are also widely available tubes with affordable prices, although I recognize that some NOS tubes have an "extra", I am not willing to pay the astronomical figures they ask for them. A friend lent me vintage Phillips EL34 "Made in Holland" and it had that "plus" compared to my JJ Electronics made in Slovakia - tested and paired in the USA with computer programs. (At the time, I corroborated it with a web address, which I did not remember now)
I think EL34 was used by The Beatles in their early days in their Vox amps. They have a plus of nostalgia too.
Unfortunately my friend didn't want to sell them, so I didn't ask him how much they would cost in the local market...
The appearance was identical to the first photo of this link, there is a little history of this tube there...I'm sorry, I can't correct the "quote " with the link .... it's not a tubelab post ....
https://www.radiomuseum.org/tubes/tube_el34.html