tony sayer wrote:
which leads you
to directly heated triodes, then you have to consider the fillament
supply, DC hums less, but AC sounds better.


Do they still make directly heated valves and surely AC would hum like
no ones bizz, or was this some wind up?....

Yes, it can do depends on design, no it wasn't

For eample of current production...

http://www.westernelectric.com/300B/specs300Bindex.html

--
Nick

Ian Bell wrote:
Nick Gorham wrote:


Fleetie wrote:

I am VERY interested in learning about how to design valve amps,
but before I do that, I want one for my hi-fi, that just works.
Then I'll worry about how to design them myself. I guess the
simplest design to start off with is a Single-Ended Triode
amp - would that be right? Only one grid to worry about, and
only one power valve. Might as well walk before one tries to
run!

But for now, I just want a working valve amp for my hi-fi.


Ok,

First up, Single ended anything is simple on paper. BUT. to actually
make it sound as you might wish, its not quite that simple. As SE is
simple everything is important. Its very dependent on the regulation of
the power supply, so either you have a complex regulated supply, or you
use choke regulation, which means big (as possible) chokes, Then the
last cap in the power supply is in parallel with the output transformer,
so you can't just use any old electrolytic and expect good results. Most
SE designes are limited in gain, so feedback is not used


I don't know of anything that inherently means an SE design is gain limited.
The very first one I built back in the 60's used feedback from the output
transformer. It consisted if a 6J7 and a 6V6.

Ian

Agreed, but what I said was most designs are gain limited, not that they
had to be.

--
Nick

"Nick Gorham" wrote
tony sayer wrote:
which leads you
to directly heated triodes, then you have to consider the fillament
supply, DC hums less, but AC sounds better.


Do they still make directly heated valves and surely AC would hum like
no ones bizz, or was this some wind up?....

What I don't understand was someone's earlier assertion
(I paraphrase): "DC heaters hum less but AC sound better."

HUH?! Why would an AC heater supply make the amp sound better
than a DC?


Martin - easily confused sometimes
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

"Trevor Wilson" wrote

"Fleetie" wrote in message
...
Hi.

As subject.

I bid twice tonight on Ebay UK for different valve amps.
I left it near the last minute.

I was totally outbid bith times. Prices are outta sight
recently on there, it seems.

Anyone have a cheap, but _modern_ (manufacturing date)
one. I've done the QUAD II thing, and now I wanna try
a shiny new modern one - even if it will be an old
design in a shiny new case.

I will be interested in a power amp (or pair of monoblocs),
or a full integrated amp.

Only interested in fully working ones, with plenty of
valve life left, and in very good cosmetic condition.


I realise it's a long shot, but I thought I'd try.

**Why would you bother buying any piece of audio equipment, without first
listening to it? You don't mention what speakers you have, so I fail to see
how anyone can provide meaningful advice, since tube amps have restricted
impedance operating ranges. Why would you just not go an buy a nice Rotel?
They make some nice products well within your price range. They'll be more
reliable, work with a wider range of speakers and provide far better sound
quality than any cheap tube amp.

If I don't like it, I can flog it on.

Also, you may gain some insight into the reasoning by reading
some of my earlier posts.

Also, I flogged my QUAD II set in about 1993, and now it's 11
years later, and I totally have the "valve itch" again.

Also, one of the cheapest ways of getting hold of a ready-built
valve amp seems to be Ebay. With Ebay, you don't usually
get a chance to listen before buying.

Plus I don't have like mega-high-end speakers so there's currently
little point getting a super-mega-golden-sample-TdP valve amp, to
play through Mission 752Fs.

So I'm willing to take the risk. As I say, if I don't like it,
I'll flog it on.

As for why I don't "go buy a nice Rotel": Cos I already have a
Cyrus II.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

"Fleetie" wrote in message
news:O36wc.1157$Oc1.196@newsfe4-gui...
"Trevor Wilson" wrote

"Fleetie" wrote in message
...
Hi.

As subject.

I bid twice tonight on Ebay UK for different valve amps.
I left it near the last minute.

I was totally outbid bith times. Prices are outta sight
recently on there, it seems.

Anyone have a cheap, but _modern_ (manufacturing date)
one. I've done the QUAD II thing, and now I wanna try
a shiny new modern one - even if it will be an old
design in a shiny new case.

I will be interested in a power amp (or pair of monoblocs),
or a full integrated amp.

Only interested in fully working ones, with plenty of
valve life left, and in very good cosmetic condition.


I realise it's a long shot, but I thought I'd try.

**Why would you bother buying any piece of audio equipment, without
first
listening to it? You don't mention what speakers you have, so I fail to
see
how anyone can provide meaningful advice, since tube amps have
restricted
impedance operating ranges. Why would you just not go an buy a nice
Rotel?
They make some nice products well within your price range. They'll be
more
reliable, work with a wider range of speakers and provide far better
sound
quality than any cheap tube amp.

If I don't like it, I can flog it on.

**Yes, you could, but that does not answer my question/s. Seems like a great
deal of hassle to go through, for a possible gain of zero. Or worse.


Also, you may gain some insight into the reasoning by reading
some of my earlier posts.

**I might. I would gain more insight if you could answer my simple
questions.


Also, I flogged my QUAD II set in about 1993, and now it's 11
years later, and I totally have the "valve itch" again.

**And here is where I have MAJOR problems. Here is why I have major problems
with your approach. REALLY good valve amps and really good SS amps sound
very, very similar, provided the load impedance is reasonable (to the valve
amp). So similar, in fact, that I have been caught out, several times, in
blind trials. Reasonably priced SS amps sound VERY close to quite expensive
SS amps. Really cheap tube amps sound VERY different to both cheap and
expensive SS amps and really good tube amps.

What does this tell you?

It tells me that cheap tube amps distort the audio signal. Distortion is the
antithesis of 'high fidelity'.

I believe that by restricting yourself to valve amps only, is silly.


Also, one of the cheapest ways of getting hold of a ready-built
valve amp seems to be Ebay. With Ebay, you don't usually
get a chance to listen before buying.

**Bingo! Caveat Emptor.


Plus I don't have like mega-high-end speakers so there's currently
little point getting a super-mega-golden-sample-TdP valve amp, to
play through Mission 752Fs.

So I'm willing to take the risk. As I say, if I don't like it,
I'll flog it on.

As for why I don't "go buy a nice Rotel": Cos I already have a
Cyrus II.

**I did say "Rotel". I did not say "Mission Cyrus II".


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote
[stuff]

Oh. I stand corrected.

Fleetie wrote:
"Nick Gorham" wrote

tony sayer wrote:

which leads you
to directly heated triodes, then you have to consider the fillament
supply, DC hums less, but AC sounds better.


Do they still make directly heated valves and surely AC would hum like
no ones bizz, or was this some wind up?....


What I don't understand was someone's earlier assertion
(I paraphrase): "DC heaters hum less but AC sound better."

HUH?! Why would an AC heater supply make the amp sound better
than a DC?

Well, first thing, this is with directly heated valves, secondly it just
does seem to do that in practise, and thirdly I will see if I can
explain my theory about this, but its just that my theory.

If you look at a typical output stage using a DHT, where the fillament
is also the cathode, you will see the power to heat it applied, then a
couple of resistors to create a center point, and this is then taken
down to ground or through a cathode resistor.

Now firstly you can see from this that the fillament supply is directly
connected to the output stage of the amp, so any components in the power
supply to the filament can play a part in the amp sound. AC supplies are
normally just a transformer secondary connected to the fillament, but DC
supplies are normally a TX, maybe some plain slow diodes, and a big old
electrolytic, maybe better diodes and maybe a PI filter or matbe a
regulator. but whatever is used its connected to the output stage, so
any switching noise or inductances of the caps all can get into the act.

Secondly, if you look at the voltages on the fillament, one side will be
at a higher voltage than the other, by the heater voltage, no this means
that there is uneven bias along the length of the fillament, so I would
expect a uneven electron flow. Now I don;t know if thats actually taking
part in the difference, but I can't see how it can help. If you take a
extream example, of GM70 running at 100ma current, and the fillament
being connected via the normal two 100R resistors, the 20v filament
supply seemd to me to mean that o current flows in one leg, and 200ma in
the other.

This is not to say that you can't have a DC supply that doesn't suffer
from the first problem, just that it will take a bit more care.

Another interesting area thats being investigated is to use hi frequency
(20k) ac to driver the heater.

--
Nick

In article ,
Nick Gorham wrote:
Secondly, if you look at the voltages on the fillament, one side will be
at a higher voltage than the other, by the heater voltage, no this means
that there is uneven bias along the length of the fillament, so I would
expect a uneven electron flow. Now I don;t know if thats actually taking
part in the difference, but I can't see how it can help. If you take a
extream example, of GM70 running at 100ma current, and the fillament
being connected via the normal two 100R resistors, the 20v filament
supply seemd to me to mean that o current flows in one leg, and 200ma in
the other.

The same applies to an AC heater. Only at 100 times a second. Nicely
inside the audio band. Be interesting to use HF AC - outside the audio
band - and see how it compares.

--
*If you don't pay your exorcist you get repossessed.*

Dave Plowman London SW 12
RIP Acorn

Dave Plowman wrote:
In article ,
Nick Gorham wrote:

Secondly, if you look at the voltages on the fillament, one side will be
at a higher voltage than the other, by the heater voltage, no this means
that there is uneven bias along the length of the fillament, so I would
expect a uneven electron flow. Now I don;t know if thats actually taking
part in the difference, but I can't see how it can help. If you take a
extream example, of GM70 running at 100ma current, and the fillament
being connected via the normal two 100R resistors, the 20v filament
supply seemd to me to mean that o current flows in one leg, and 200ma in
the other.


The same applies to an AC heater. Only at 100 times a second. Nicely
inside the audio band. Be interesting to use HF AC - outside the audio
band - and see how it compares.


Yes agreed, but while I can't prove anything, it just worries me being
constantly one sided.

There are a couple of us intending to investigate the hf ac heating, so
we will see...

--
Nick

Yes agreed, but while I can't prove anything, it just worries me being
constantly one sided.

There are a couple of us intending to investigate the hf ac heating, so
we will see...

Course, you could circumvent all these worries by just heating a
plate of suitably-coated metal from outside the glass, with a big
****-off laser.

Just a BIT inefficient, but hey, you gotta pay to have the best!



Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk