[braillediver]

My 45 based home amp is dead quiet when driving Altecs that are rated at 100 db at 3 meters.

Dead quiet doesn't really describe the silence- it's like a black hole when you put your ear to the speaker.


Mitch

 

[Roam]

Quote:

Originally Posted by cotdt /img/forum/go_quote.gif People seem to have already solved the hum problem of DHTs with better power supplies.

I'd have to say yes, but not really. Yes they've taken care of hum through DC heating, but this introduces problems of its own which may be worse than hum. The problem is getting from AC to DC, which involves rectifiers, capacitors, and large current spikes as the caps "top up" at the peak of each AC cycle. This current spike is large & fast, and combined with the stored charge from the diodes dumping back into the circuit when they slam shut, it creates a lot of noise & RFI which is exceedingly hard to filter out and finds its way into the rest of the circuit. You can hear some of this as a faint background hiss, other effects may include listening fatigue, lack of tonal fullness, and loss of low-level details. Suffice to say, this is a bad thing.

There are ways to make DC heating work; using a choke input filter combined with RC elements to tame the current spike followed by a CCS to knock out the remainder of the noise as well as providing a gentler filament warmup. As one can imagine, this is not cheap, and I doubt there are many designers with spectrum analyzers and the knowhow to map and chase out all the noise.

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So I still think a 45-based headphone amp would be a great idea!

No doubt, a 45 amp will truly be one of the best amps possible. Realizing its potential though is a long hard journey, and I don't think there are many who can get it right.

 

[Carl]

Quote:

Originally Posted by Roam /img/forum/go_quote.gif I'd have to say yes, but not really. Yes they've taken care of hum through DC heating, but this introduces problems of its own which may be worse than hum. The problem is getting from AC to DC, which involves rectifiers, capacitors, and large current spikes as the caps "top up" at the peak of each AC cycle. This current spike is large & fast, and combined with the stored charge from the diodes dumping back into the circuit when they slam shut, it creates a lot of noise & RFI which is exceedingly hard to filter out and finds its way into the rest of the circuit. You can hear some of this as a faint background hiss, other effects may include listening fatigue, lack of tonal fullness, and loss of low-level details. Suffice to say, this is a bad thing. There are ways to make DC heating work; using a choke input filter combined with RC elements to tame the current spike followed by a CCS to knock out the remainder of the noise as well as providing a gentler filament warmup. As one can imagine, this is not cheap, and I doubt there are many designers with spectrum analyzers and the knowhow to map and chase out all the noise.

There are ways to make AC feeds for DHTs work. Just by sending the cathode a 100Hz/120Hz signal in antiphase to the hum you can take down a good amount of it. There are even some hardcore approaches like this one.

DC supplies don't need to be expensive. A fairly cheap shunt design using a tube rectifier and a LM-family voltage regulator would work fine. And there's always batteries.

 

[Roam]

Quote:

Originally Posted by Carl /img/forum/go_quote.gif There are ways to make AC feeds for DHTs work. Just by sending the cathode a 100Hz/120Hz signal in antiphase to the hum you can take down a good amount of it. There are even some hardcore approaches like this one.

You do realize how far out on the fringe Steve Bench's work is? It's all perfectly sound and it works, but Christ will likely come & go again before much if any of it finds its way into a commercially available amp. There's also the really fun stuff like feeding the filaments alone from an AC regenerator before applying the noise cancelling tweaks.

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DC supplies don't need to be expensive. A fairly cheap shunt design using a tube rectifier and a LM-family voltage regulator would work fine. And there's always batteries.

Are you seriously telling me you can feed the DHT filaments using a tube rectifier supply? Have you recently looked up the current ratings on a rectifier tube? I'll save you the trouble, the current ratings are too low by over an order of magnitude.

As for using an LM-series regulator, no, it does not work fine. In theory it should, in practice it's a disaster, been there, done that, don't ever want to go there again.

 

[Carl]

Quote:

Originally Posted by Roam /img/forum/go_quote.gif Are you seriously telling me you can feed the DHT filaments using a tube rectifier supply? Have you recently looked up the current ratings on a rectifier tube? I'll save you the trouble, the current ratings are too low by over an order of magnitude.

Even greedy tubes like GM70s can be. High current thyratrons do exist, even if they can get pricey.

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As for using an LM-series regulator, no, it does not work fine. In theory it should, in practice it's a disaster, been there, done that, don't ever want to go there again.

Care to share your experiences?

 

[Chops]

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Originally Posted by Roam /img/forum/go_quote.gif The other thing is the 45 isn't as well known as say, the 300B or 6SN7, at least not here in North America, it's not widespread enough for a company to capitalize on the market.

I have news for you, my father has a 2-car garage (converted over to his work shop) full of old tube radios, many of which use one or two 45 tubes each, some SE and some PP, depending on the radio. These are RCA, Airline, Zenith, Silvertone, Philco, Emerson, Motorola, etc, etc... And they are all American made radios. There's probably over 2 dozen 45 tubes sitting out there right now, and all test good!

In short, 45 tubes are very well known in North America.

 

[recstar24]

Quote:

Originally Posted by Chops /img/forum/go_quote.gif I have news for you, my father has a 2-car garage (converted over to his work shop) full of old tube radios, many of which use one or two 45 tubes each, some SE and some PP, depending on the radio. These are RCA, Airline, Zenith, Silvertone, Philco, Emerson, Motorola, etc, etc... And they are all American made radios. There's probably over 2 dozen 45 tubes sitting out there right now, and all test good! In short, 45 tubes are very well known in North America.

I concur - a more accurate statement is that current american manufacturers may not be totally aware of the 45 tube and its merits, but from the 30's to late 50's the 45 tube was very popular and well known. The current manufacturers that do use them are simply the smarter ones who have done their research and have concluded that despite its low power, has fantastic linearity, with a sound that to my ears is utterly "immediate" with tons of presence. Great tube.

What I would like to see is a properly designed push pull 45 amp that gives a bit more grunt with 95 ish db speakers, while still sounding as sweet as a single 45 tube run in SET. Right now at 1.8 W you are looking at high 90's/100's for speakers, push pull should bring it to at least 3 watts which allows the user to go to 95/96 db efficiency in a relatively moderate sized room.

 

[Chops]

Quote:

Originally Posted by recstar24 /img/forum/go_quote.gif What I would like to see is a properly designed push pull 45 amp that gives a bit more grunt with 95 ish db speakers, while still sounding as sweet as a single 45 tube run in SET. Right now at 1.8 W you are looking at high 90's/100's for speakers, push pull should bring it to at least 3 watts which allows the user to go to 95/96 db efficiency in a relatively moderate sized room.

Hmm... A 45 SET amp would go perfectly with my hybrid Klipsch Cornwall (bass bin only) and Altec 511B/902-8B combo at a humble 105dB @ 1W.

 

[Carl]

Quote:

Originally Posted by recstar24 /img/forum/go_quote.gif What I would like to see is a properly designed push pull 45 amp that gives a bit more grunt with 95 ish db speakers, while still sounding as sweet as a single 45 tube run in SET. Right now at 1.8 W you are looking at high 90's/100's for speakers, push pull should bring it to at least 3 watts which allows the user to go to 95/96 db efficiency in a relatively moderate sized room.

PX4s have a different tone to 45s, but to me the sound fairly comparable in musical and technical quality (a slight edge to the 45). A well designed PX4 SET could drive 95dB speakers fine.

Another option would be to try 50s.

 

[Roam]

Quote:

Originally Posted by Carl /img/forum/go_quote.gif Even greedy tubes like GM70s can be. High current thyratrons do exist, even if they can get pricey.

Unfortunately they share some of the same problems as mercury or xenon vapour rectifiers, they tend to throw off a fair bit of RF hash. It trades off the problem of dumping noise into the powerlines with the problem of radiating RF into the air from the tube itself, one can of worms for another.

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Care to share your experiences?

Regarding LM-series regulators. Yes it's quiet and there's no hum nor buzz, but I found it flattened out the sound. The soundstage loses a fair bit of depth and the tone becomes washed out. It sounds bleached and unnatural.

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Originally Posted by Chops /img/forum/go_quote.gif In short, 45 tubes are very well known in North America.

Perhaps I should rephrase that: not well known in the North American high-end audio mainstream. Mention 12AX7, 6SN7, or 300B and most hi-fi guys will know what they are and be able to rattle off a bunch of trivia, ask them about a 45, 10Y, or 50 and many will go "a what?" At least that's been my experience to date.

 

[Carl]

Quote:

Originally Posted by Roam /img/forum/go_quote.gif Unfortunately they share some of the same problems as mercury or xenon vapour rectifiers, they tend to throw off a fair bit of RF hash. It trades off the problem of dumping noise into the powerlines with the problem of radiating RF into the air from the tube itself, one can of worms for another.

Agreed, they certainly don't make things easy in that respect. That said, I really do love the sound of well executed mercury, so it can be very worthwhile if you get it to work. It also gives you an excuse for playing around with capacitorless power supplies and other fun toys.

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Regarding LM-series regulators. Yes it's quiet and there's no hum nor buzz, but I found it flattened out the sound. The soundstage loses a fair bit of depth and the tone becomes washed out. It sounds bleached and unnatural.

Have you tried isolating them from the current pathways in the amplifier? If you keep them "hidden" their nasty sound doesn't end up at the cathode, well at least most of it. The same goes for all solid state devices, really. Of course spotting when it sneaks back in is hair pulling stuff even with a scope.

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ask them about a 45, 10Y, or 50 and many will go "a what?" At least that's been my experience to date.

The boutique market barely touches tubes like the 26 and 10, either. Even those brave enough to try them usually put them straight into the 'too hard' basket and then move back to chartered waters.

 

[Roam]

Quote:

Originally Posted by Carl /img/forum/go_quote.gif Have you tried isolating them from the current pathways in the amplifier? If you keep them "hidden" their nasty sound doesn't end up at the cathode, well at least most of it. The same goes for all solid state devices, really. Of course spotting when it sneaks back in is hair pulling stuff even with a scope.

I tried that too, fed the filaments from a CCS following the regulator, it's better but there was still a bit of the "whitening" effect which never went away. I then went back to an LCRC filter followed by a CCS which almost got me back to where I was with AC heating but with a slightly lower noise floor, a lot of work for not much gain. After that I went back to AC power for the filaments, but fed it through an AC regenerator instead of having the power come straight from the wall. Much better, lower noise floor and better tone, everything is bigger, faster, cleaner, and more complete.

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The boutique market barely touches tubes like the 26 and 10, either. Even those brave enough to try them usually put them straight into the 'too hard' basket and then move back to chartered waters.

True enough. Only experience lunatics will mess around with those tubes, but when they're made to work right it's something truly special.

 

[cotdt]

How is the bass of 45-based tube amps?

 

[Roam]

Quote:

Originally Posted by cotdt /img/forum/go_quote.gif How is the bass of 45-based tube amps?

If you're familiar with the bass from a Grado HP-1000, that's pretty much what a good 45 amp is like. Fast, clean, clear, and incisive, no bloat, no overhang, no colourations. If you expect warm tubey fullness, it's not there unless you put it in with the input tubes. Going back to the Grado HP-2 analogy, like the Grados, the 45 doesn't really have a signature, but it will brutally expose the signatures & colourations of every upstream component.

 

[cotdt]

Quote:

Originally Posted by Roam /img/forum/go_quote.gif If you're familiar with the bass from a Grado HP-1000, that's pretty much what a good 45 amp is like. Fast, clean, clear, and incisive, no bloat, no overhang, no colourations. If you expect warm tubey fullness, it's not there unless you put it in with the input tubes. Going back to the Grado HP-2 analogy, like the Grados, the 45 doesn't really have a signature, but it will brutally expose the signatures & colourations of every upstream component.

So are you saying that the 45 doesn't sound like a tube amp at all? Does it have a warm midrange?