DIY Audio Projects Forum

Hi everybody,

a few words on heating. I tend to use AC heating now, too. My OddBlock has now AC on the KT88 and rectified and regulated dc on the pre tubes. The 25 ampere bridge rectifier I used to rectify the 6,3 volts for the KT88 is so slow, the it's reverse ripple voltage poisoned my whole system with some background noise ( hum). Now, that I got rid of the bridge, my amp is hum free. As for polarization, I don't know about that. I definitely need DC heating of highest quality to construct a noise free RIAA pre amp. But for power amps, AC heating is alright, if you twist the wires good and make sure they don't run parallel to any signal wires to avoid inductive and capacitive coupling (ghost capacitors, oh yes they do exist).If you decide for DC heating, do it right and use also high quality diodes for the rectifier and a voltage regulator. The regulator really does the trick, it improves the quality of the DC signal so much, it is a must in all my amps, especially, because it removes high frequency noise, the kind of that is otherwise so hard to get rid of. Success.

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Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project

You won't regret it. This amp is about as far from a SS amp as you can get. I can now understand why the 300B SET is a popular amp. Don't expect thunderous volume levels, but expect a very "open, airy, detailed, silky" sound that brings out the detail in recordings.

Funny thing, some recordings sound distorted through this amp, but it's not the amp distorting. The amp just brings out the detail in the music including distortion that's on the sound source. If the source is distortion free, so is the amp. But if there's a little bit of distortion present on a recording, the amp will faithfully reproduce it instead of smearing it or smoothing it over.

Vocals, strings, guitars, and percussion "jump out of the speakers". I would add the word "lively" to describe the sound.

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Stephen

Interesting what Benny said about the rectifier puting noise into the ccts. Just another reason to stay with AC on the heaters. Bloody SS stuf!!! With a lot of wire twisting, earthing the heater's center tap and careful wiring most of the time AC induction can be controlled. My latest KT88 SE UL has AC heaters only in both stages and it is dead quiet.

Just supporting the comments made about the sound of the 300B SET. I think you can almost make the same comments about any tube SE. OK the 300B may just do it a bit better. Even when I built my first 6T9 SE I new from the first minutes of play that there is a transparency and quality that few other configurations can match. But you do take a power hit.

And now with my latest JJ Blue Glass KT88 SE UL, with remote driver stage and Russian paper and foil caps, all those initial qualities I heard in my first 6T9 and other KT88 SE's I have built recently have been amplified (excuse the pun) to produce a truly spectacular sound amp.

Long live the SE!!

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Projects: "Precision" - 300W Class AB Holton power amp | "retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp |

I just raised B+ to 380 volts and this amp is singing!!! It's noticably louder before distortion. It was designed to properly self bias at 380 but I needed the right voltage tranny to boost the voltage.

I'm amazed, I really am. Thinking of how complicated my SS amps are, and then thinking about the fact there are only two active devices in the signal path to amplify in this 300B amp, and no negative feedback, yet it sounds so damn good. I guess the simplicity is exactly why it sounds so good, that and the class A bias with no crossover distortion and the preponderance of lower even harmonic distortion when it does distort (very gracefully) at higher power levels.

I also put sine waves through it at full power and checked the traces. Above 30 Hz the waveforms look perfect. At 20 Hz there is a slight tilting of the waveform, but when the power is reduced slightly the waveform returns to its normal shape.

I'll use a function generator to try some square waves through the amp as soon as it arrives. My old one died.

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Stephen

Slight tilt at 20Hz????? You don't need no other test'n honey!!

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Projects: "Precision" - 300W Class AB Holton power amp | "retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp |

May I ask how many output watts (clean) you get from a KT88 in SE ultra linear?

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Stephen

About 7.5W into 8ohm resistive load. I'm running 9mA into each tube at 365V Plate to cathode.

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Projects: "Precision" - 300W Class AB Holton power amp | "retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp |

Hi.

Yes, no amp can sound as musical as 300BSE, IME. But if you want more power & more dynamic, go 300B PP.

When you settle down with yr new amp. Replace yr 300Bs with Western Electric. You will be amazed !! I bet.

"Just like an old bag dragging her feet magically transformed to a Cinderella spinning ballets in her dancing shoes" So much more elegant, silky & effortless. WE 300B worths every buck spent on it.

c-J

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"If the facts don't fit the theory, change the facts" quoted Albert Einstein.

That's a point of dissension on which I have no opinion (yet) for lack of experience. Some say the PP won't sound as good, just more power at the expense of sound, others say the 300B shines in a single ended class A amp and that PP is inferior. I simply don't know.

Once my KT88 oddwatt is complete I'll have something to compare my SET with.

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Stephen

You should have a good example of what a well designed PP valve amp can do in the oddwatts. I know Bruce has put a ton of effort into their design to get the best out of them in all ways possible. He helped my tweak-up my latest KT88 SE UL. And with his guidance l increased the amps performance ten fold. Only one draw back: I cannot plug and play tubes as I did before we tweaked the amp. But I'm extremely happy with JJ Blue Glass matched KT88s.

Bruce will probably disagree but my (big) GUT still tells me the SE is the way to go. If you wnat more power from an SE amp use bloody big tubes like 211s. A friend has a single tube SE guitar amp which delivers 60W!!. But the tubes are a grand each.

There are many ways to skin the audio cat. At this point my pussy is SE.

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Projects: "Precision" - 300W Class AB Holton power amp | "retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp |