How good is the sound of amps based on 6BM8 tubes? I know they were used in some Allied, Pioneer, Knight and other amplifiers in late '60s-early '70s. Are these nice sounding units worth to have or "dogs" to avoid?
In a fairly standard power amplifier circuit, I used a pair of well- made output transformers taken from an older Sansui amplifier. While the original Sansui design left something to be desired (too many unnecessary features and gizmotronics), the transformers were excellent quality; and from the resulting amplifier I have built, which uses a pair of 6BM8s in PP, though producing only about 7-8 watts maximum power, the sound is wonderful, and as good as any EL84 amplifier I have owned.
They are very dynamic and transparent.
These things are so hot that I am ready to join a cult, and have already located an ornate metal box into which I plan to rebuild the amplifier.
as good as el84's but with less power.
IME more chunky from the mid bass through lower mids, surprisingly linear even in pentode.
Just a pair in SE with a slow start rectifier tube, or NTC thermistor's, would make an ideal bedroom amp, just IMO.
I wouldn't use more than 2 in PP or PSE per channel though.
They also make great headphone amps, I am told.
The sonics of the tube (ecl82/6bm8 and it's slightly more powerful cousin ecl86/6gw8) is considered to be dense and focused. The triode section is similar to a 12ax7 and the pentode section is similar to a 6v6. Both tubes in one bottle allowed compact amps for TV's and portable record players, which didn't have much in the way of transformers or speakers, thus the bad rap. Properly implemented it is an excellent tube choice, as witness Raver's Heathkit AA-32, but the tube itself is not the qualifing factor. Higher filament voltage tubes in the same eclxx family are also popular. The 6bm8 is still in production, the 6gw8 is not, thus the current preference for 6bm8.
It is hard to say how good a tube sound without referring to specific amp. Even a 1930 NOS WE300B might sound terrible in some circuits.
And some of the most well regarded tube amps use tubes which are NOT designed for audio application.
So it is really depending on the amp and its designer/maker.
The 6BM8 club was founded in Japan. And Hong Kong is in China instead of Japan.
The 6BM8 is "one of the good ones" IMHO. I don't know about the specific circuits you mention, but it could well be that they were held back by the quality of their OPT's, particularly if they were SE designs.
FWIW, the 6BM8 is one of the faves of Japanese DIYers.
I think that this group is based in Tokyo.I saw pictures of various 6BM8 amps housed in the most unbelievable housings(candy boxes and the like).
Hmmm, I'll have to hunt around and do some websearches. I know that I've seen the "candy box" 6BM8 before, and I used to have some Japanese language DIY sites bookmarked. Unfortunately I lost a lot of my bookmarks the last time my system crashed.
Very interesting! Hmmm, have they got a webpage? I'd love to see some of their efforts online.
See the link below for a pic of my 6BM8. One of these days I'm going to upgrade the iron on it and see how much better it can sound - very good now but the $9 OPT's limit bass response a bit too much....
All the best,
Yes it is in Tokyo.... Here's one that use those 6BM8 amps (In cookie aluminum cans) to drive very small Fostex backloaded horns (dorm room speakers!) Another similar tube I like is the ECL86. Here's a Japanese link in English btw.
The infamous 6BM8 cookie can amp.
6BM8 has gained popularity amongst Japanese DIY'ers who use it in the so-called "super-triode" configuration. The circuit uses the triode section of 6BM8 in the feedback loop of pentode section. The theory is that the whole thing then looks like a triode with very low Rp - hence the name Super Triode.
At least that's what is claimed by the guy who started it:
And the link below is the example of 6BM8 super triode amp. Scroll down for schematics:
The 6BM8 is used in many "low-end" tuner/amplifiers. The sound is not that good. You will be better off looking for an amplifier that uses the 6BQ5/EL84/7189 instead.
IMO they sound more lively and three dimensional than EL84's even if it has lower outpur power, especially in a very good circuit... Another one I really like is the ECL86.
The 6BM8 has a triode driver section and a pentode output section in a single tube. The idea behind this construction is that you can build an amplifier with just one tube per channel. It saves costs because the tube doesn't require a complicated multiple-tube circuit design, so many "budget-class" tuner/amplifiers and portable record players used this tube in the 1960's (Many of these sets were made in Japan and exported to the U.S.). Of course, you can use this tube in a more sophisticated modern circult design like the "Ultra-Triode" design that some people have tried in Japan (I see some mention of this in the posts below.). I agree that the 6BM8 is very easy to use because it has good sensitivity, and more importantly, it is highly stable if negative feedback is applied. In that sense, it is a good tube for sure.
I have just received shipment of the Eastern Electric MiniMax Amplifier and believe that the 6BM8 circuit we employ in push-pull configuration with our own transformers would possibly make you retract your statement.It's as musical an amplifier albeit 8 watts as any SET or EL84 amp.
Morningstar Audio Imports
The 6BM8 itself is good but can sound sucky in these vintage circuits.Most of these models were the "budget"models.Your better off building a 6BM8 amplifier yourself or buying the ASL Waves.
I am getting a bit sick of you put downs of vintage stuff. You do realize that besides the use of CCS and the Ultrapath circuit, there has not been new circuit designs. Right? They are all a variation of the old ones. A vintage amp with beefed up power supply is as good, if not better than most of the new stuff. Now, if you don't like the vintage integrated b/c they pass the signal through tone control circuits, then that's debatable.
The wave 8 uses a pretty simple vintage design as well, iirc.
By circuit I mean all the extra crap the signal must pass through and most of the time the shitty design parts.Remember that the 6BM8 was thought of as a budget tube.Not a lot of attention went into these designs.
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