Another fun build. Driver and phase splitter.

[Tubeglow]

Originally Posted by G8HQP Dave

Not offended. Amused.

Ah yes.
Been there done that.

Tubeglow.

[Sideband]

Originally Posted by G8HQP Dave

where is the circuit diagram? That is what really matters.

Can you post the circuit? I've never come across those valves before and I'm always interested in other people's builds.


Cheers

[Tubeglow]

Just posting the circuit is not a good idea, I know what your thinking but this is not as straight forward as you might think. Mr Miller is the driving force so to speak.

The circuit is not complicated however read this first. The power supply has enough power to probably make your first contact your last.

This is a very good OTL.
http://www.mellowacoustics.com/artic..._amplifier.pdf

The power consumption of these amps is a real eye opener. just look at the heater currents for a start.
The nature of OTL is as it says no output transformer..ie no direct isolation between the output valves and the speaker.
My amp is based upon the futterman circuit so no further explanation is really necessary.
http://www.audiodesignguide.com/otl/
However this is an audiophile design and my amplifier is designed with some strange ideas.
I know this is not a good exercise to continue on this site.
The heat is a major issue with these designs..not to be taken lightly it will destroy electronics and cause thermal runaway.
A red plate 6C33C has to be seen to understand this as the glass tube melts.
How you wire the heaters has an effect on how long the tube sockets last is another example. However for someone who knows what they are doing its one step away from something like a 211 SE triode design. However you have current to deal with as opposed to HV b+.

Tubeglow.

[G8HQP Dave]

I can never see the point of OTL valve amps, except for headphones, when there is a perfectly good appropriate technology available: semiconductors. Each to their own.

[Tubeglow]

I know what you mean,

however its a challenge maybe to far for some. A bit like 211 SE like Ongaku.
I have listened to these amps. A bit like a krell with Magnepan.

The point of posting was really with the idea of people building valve amps and not having any starting ideas for a build (how you can build). Rather than to pursue audiophile design. (Which posting the circuits will possibly cause a conflict with the site) That was the idea of lots of pictures to inspire more simple builds.

The technical problems are a great challenge..and source of hours of redesign.
I really like my RH amp its really good fun! The Mozart type is very good.

Tubeglow.

[Tubeglow]

For interest,

6C33C data.

http://www.jogis-roehrenbude.de/Russ...atasheetMB.pdf

NB the switchable heater power is good in OTL in SE the output transformer needs to match the valve due to the effect on THD.

Another thing to remember is how old the OTL circuits are..and its nice to have a piece of a MIG fighter playing music.

6C33C in a MIG fighter radar unit and military background..as you can see it provokes some very diverse ideas.
http://www.goodsoundclub.com/Forums/...px?postID=6140
Once you start researching this kind of thing it can get quite interesting (Mu stage.)


Tubeglow.

[G8HQP Dave]

Originally Posted by Tubeglow

That was the idea of lots of pictures to inspire more simple builds.

Pictures do not inspire us, unless they are of vintage wireless sets. Circuits may interest us, especially combined with discussion about circuit operation and design issues such as component values. You need to understand that words like Krell, Ongaku and Magnepan have no meaning for us - some of us may vaguely recognise them as words used on US audio sites, but there is no cultural affinity.

People here have plenty of starting ideas. We generally start from Mullard or Leak designs, as you will see with a little searching.

[Sideband]

Originally Posted by Tubeglow

Just posting the circuit is not a good idea, I know what your thinking but this is not as straight forward as you might think. Mr miller is the driving force so to speak. The circuit is not complicated however read this first. The power supply has enough power to probably make your first contact your last.

Just as background.....I and many other here are familiar with high voltage high current circuits. I work with high voltage circuits a lot in my capacity as a test engineer. There are also people here who have had the dubious pleasure on working with pre-war TV's that have mains derived EHT....that is lethal in the wrong hands...thousands of volts at some milliamps deserves great respect. We're also aware of what happens to power valves when drive is wrong or missing....any TV engineer will know what a melted line output valve looks like!

As engineers, we are more interested in the circuit rather than the make of resistors...it's the circuit that produces the sound so it's just out of interest that's all.

Anyway it's up to you....I'd still like to see the circuit though!


Cheers

[Tubeglow]

Ok,

I get your point. I won't post anymore information.
As you say its not inspiring anyone.

I also see why Dave found it amusing.
I thought it might be interesting, but I now realise it was an embarrassing waste of effort.

Moderators please delete this thread thank's.

Tubeglow.

[Radio Wrangler]

I've come across Krell, Magnepan, and Ongaku before, but I'm more likely to mention Bruel & Kjaer, Audio Precision, Tektronix and Hewlett-Packard.

They too are reassuringly expensive. The interesting thing is that several brands of equipment operating by different principles tend to offer results in agreement with each other. As blind coincidence becomes progressively more improbable, then there emerges the simple solution that they are most probably right.

Building a few valve amps is a sort of rite of passage, but few move on to the more difficult challenge: Designing a good and original semiconductor amplifier.

It isn't the restoration of vintage equipment, but a thorough understanding of all the techniques used in the past along with their strengths and weaknesses is a good starting point.

David

[Sideband]

What's the problem with posting the circuit? It's not the first time that high power amps have been shown on these pages with accompanying circuits. Very often they invoke lively discussion which is what it's all about. In fact it's more likely to inspire someone else to build. Just seems odd that's all. Most people who build something different, which this is, are happy to share information.


Rich

[turretslug]

It could be argued that, by having a fascination with valves, many of us on this site are slightly barmy when transistors and their follow-on integrated circuits have proved themselves thoroughly capable for decades and to offer hugely sophisticated features as a knock-on of component density.

In the end, it's a harmless diversion that most of us could take or leave. For some of us, the particular fascination might be oscilloscopes or signal generators, others get a thing for communications receivers or pre-war domestic radios. I think, though, that we each have a broad interest in what everyone else here does and there are a few members whose acknowledged speciality is the painstaking and quality restoration of the classic valve amps. I've no doubt that they would agree that it's a good thing to use high quality components to ensure good performance, reliability and long life of associated parts. Where they would differ from the so-called "audiophile" camp is on the necessity of spending 10x or even 100x the money on components bearing brands that seem to be conspicuously absent from unambiguously respected masters of their trade, say Tektronix 'scopes or Hewlett-Packard signal generators.

I'd also be interested to see the circuit- I'm prepared to be open-minded about anything a bit "different" and I'm encouraged to see that, by using the hefty 6C33 regulator triode, it's not depleting a valve that's useful for other purposes. It doesn't have a huge voltage rating or a top cap, so it won't pass muster for RF PA or line output use, say, and even for the down-and-dirty business of series regulation, we have plenty of HV power semiconductors to take its place, so why not make a slightly off-the-wall audio power amp with it. (And I really don't believe all the obscurantist stuff about MiG fighters etc. that the net is awash with. Sorry.) There are folk here with genuinely outstanding knowledge and understanding of all sorts of circuitry (not me!) and they may be able to offer useful advice on simple improvements that will be effective. And it won't involve sandalwood capacitors, bamboo charcoal resistors or directional interconnects with depleted uranium pins.

[ScopeMonkey]

Originally Posted by Tubeglow

This amp uses High current drive and the PSU can deliver high current at 400V B+.

Nice build! I second the "slow down" comments though, you put the rest of us to shame

One thing I am curious about - why the US name for HT?

Ed.

[cmjones01]

Originally Posted by Tubeglow

NB the switchable heater power is good in OTL in SE the output transformer needs to match the valve due to the effect on THD.

With respect, you're preaching to the choir here. We know that output transformers have to be matched to their valves. I'm going to second what others have said: what we're interested in here is the technical details. I admire the craft of your construction, but if there's some subtlety of the circuit design of an OTL amplifier, we're interested in it. And I'm not talking about who made the resistors. That doesn't matter at all.

Show us the circuit diagram. Show us the measurements. Then you'll get an interesting discussion. We're not frightened of high voltages - everyone's read the disclaimer.

Chris

[Tubeglow]

Originally Posted by ScopeMonkey

One thing I am curious about - why the US name for HT?

The reason is linked to the definitions of low voltage and high voltage as defined under regulations. In days gone by there was low/medium and high.

The voltages used in some valve /tube gear will fall in the low voltage category and could not really be termed HT. This can be misleading so I use the term B+ also because it gives a reminder that the amount of current released is linked not to the supply but the amount of capacitance in the supply.

Tubeglow.

[Station X]

This is a UK forum. The terms LT, HT, EHT and valve are well understood in the UK.

I see no reason for giving them American names. My car has a bonnet and a boot, not a hood and a trunk.

[Tubeglow]

Then its low voltage.

http://www.conformance.co.uk/adirect...?id=lowvoltage

NB tension is not English. ie HT.
https://www.google.co.uk/#q=what+is+...ch+for+voltage

Tubeglow.

[Station X]

I'd better relabel my reproduction batteries to make sure I'm not breaking the law then.

[Tubeglow]

Originally Posted by Station X

I'd better relabel my reproduction batteries to make sure I'm not breaking the law then.

I know, I don't like it either its the same under BS7671 17th regulations.
Perhaps the batteries are French..but the CE still applies.
Perhaps B+ batteries LOL


Tubeglow.

[cmjones01]

Originally Posted by Tubeglow

The reason is linked to the definitions of low voltage and high voltage as defined under regulations. In days gone by there was low/medium and high.
The voltages used in some valve /tube gear will fall in the low voltage category and could not really be termed HT.

For the better part of a century, the US terms 'A', 'B' and 'C' have been directly equivalent to the UK terms 'LT', 'HT' and 'GB'. They probably existed before the regulations you're talking about were even thought of. Nothing has changed which makes them any less relevant today, especially given that this forum deals mostly with older equipment and its documentation which uses the older terms.

The electrical safety regulations may have changed, but nobody is going to go back and re-write all the existing documentation in order to warn technicians about 'medium voltage'. Just because it's not formally called 'high' doesn't mean we don't have to be careful with it.

This can be misleading so I use the term B+ also because it gives a reminder that the amount of current released is linked not to the supply but the amount of capacitance in the supply.

It does nothing of the sort. How on earth does 'B+' indicate to anyone that the amount of current available is related to some capacitance somewhere? That's a dangerous notion in itself, and only true in very limited circumstances. It's easy to make a power supply with no capacitance but enormous current capability, or large capacitance and very limited current.

Chris