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It's like there is some sort of competition to see who can use the valve that is the least suited to audio applications.

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2 hours ago, rabski said:

It's like there is some sort of competition to see who can use the valve that is the least suited to audio applications.

What are those giant valves originally meant for?

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Radio transmitters Wilson. The majority of large, directly-heated triodes were designed for RF transmitters and many are capable of handling massive power at very high frequency. There are some medium-power valves designed originally for telephone systems (300B is one), but few few requirements for big power at audio frequencies in the past, apart from public address systems and cinemas. However, there were lots of radio transmitters. And of course radar, especially in WWII. Out of all the big directly-heated triodes, I think only the 845 and 211 were actually designed for use down to audio frequencies.

Every valve will work down to very low frequencies, but not necessarily work well. There are lots of issues, but many types are not particularly linear across the audio range and a lot have quite complex requirements in the best way to drive them or have particularly unhelpful characteristics. There is a tendency for designers to come across a valve, discover one property that looks good, and then try to design a circuit. Sometimes the results are surprisingly decent, but often they aren't.

The same thing applies to all valves of course, not just big triodes. Valves designed for military or aviation use need to be physically and mechanically very robust. Valves designed for computer use need to be reliable over many cycles and able to run in a down state for extended periods without cathode degeneration. Valves designed for medical equipment need to be reliable and accurate, etc. Sometimes those requirements align well with audio use, but often they don't.

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RF transmission valves mostly, for radio and communications gear. Some others are for pulse work (radar and similar).

Very beautiful, seriously high voltages are the norm (1500-3000V) and often complex bases and cooling requirements. As a rule of thumb they are very dangerous and were never 'consumer' items, they are often quite rare although not necessarily pricey, and the bases are often made of unobtainium.

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EDIT: Hah! Richard's about, crossed posts

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Most enlightening guy ... Thanks ... I’ll stick to my itty bitty valves 😬

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Morning James!

Very good point about the bases. Even some fairly standard types are getting a bit thin on the ground.

Very beautiful and potentially very dangerous indeed. Mind you, as I've said before, the person signing the post mortem won't care whether it was 200 volts or 2000. I actually like working with much higher voltages. It's sometimes a bit too easy to get blase with a couple of hundred volts.

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Afternoon Richard!

Another point worth mentioning respecting high voltage valve bases (sockets if I'm using correct terminology) is that the Chinese clones, whilst often made of ceramic and nice looking, often use cheap metals for the contact with a micron thick smear of gold over the top. This can rub off after a couple of valves have been inserted/removed exposing the oxidisable metal underneath which now creates the contact, with likelihood of higher resistance at the connection, and a heat/fire risk. There is talk as well that some of the newer variants of old high anode voltage valves which are now made using non-original octal bases rather than the original bases, or higher voltage modern variants of old octal valves, can create a serious hazard when inserted into a poor quality phenolic or plastic octal socket, which are common. The voltages that these sockets accommodate can be as low as 450V and above this voltage carbon tracks may start to form, leading to arcing between the (typically anode and heater) pins which are set rather close together for the 800V+ encountered. In the original mil-spec bases the pin contacts are slightly recessed and ridges are employed to increase the distance the track has to cover to reduce this possibility.

As ever, prudence is king. And yes, I totally agree that it is slightly too easy to get blase about the 'low' voltages found in eg. valve pre-amps. I am currently working in the 90-250V range and need to step away from time to time to prevent myself from becoming a visual facsimile of, but in no other way resembling, Albert Einstein.

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27 minutes ago, Jazid said:

Afternoon Richard!

Another point worth mentioning respecting high voltage valve bases (sockets if I'm using correct terminology) is that the Chinese clones, whilst often made of ceramic and nice looking, often use cheap metals for the contact with a micron thick smear of gold over the top. This can rub off after a couple of valves have been inserted/removed exposing the oxidisable metal underneath which now creates the contact, with likelihood of higher resistance at the connection, and a heat/fire risk. There is talk as well that some of the newer variants of old high anode voltage valves which are now made using non-original octal bases rather than the original bases, or higher voltage modern variants of old octal valves, can create a serious hazard when inserted into a poor quality phenolic or plastic octal socket, which are common. The voltages that these sockets accommodate can be as low as 450V and above this voltage carbon tracks may start to form, leading to arcing between the (typically anode and heater) pins which are set rather close together for the 800V+ encountered. In the original mil-spec bases the pin contacts are slightly recessed and ridges are employed to increase the distance the track has to cover to reduce this possibility.

As ever, prudence is king. And yes, I totally agree that it is slightly too easy to get blase about the 'low' voltages found in eg. valve pre-amps. I am currently working in the 90-250V range and need to step away from time to time to prevent myself from becoming a visual facsimile of, but in no other way resembling, Albert Einstein.

Full of good points there. I've always used ceramic sockets, even for small signal valves. And preferably, older ones. Plating looks pretty, but beauty is often surface deep. As much as anything, constant tinkering inevitably involves soldering, desoldering and resoldering on a regular basis, so anything with the possibility of heat softening or poor contacts is a bad idea.

Stepping back and thinking is always best. Think first, check second, measure last. Always with one probe terminal clipped to something, one hand kept in the pocket and clear elbow space behind. The last one was taught to me many years ago, because no matter how careful you are, the body's automatic reaction is to jerk backwards in response to unexpected stimulus. Not necessarily electric shock, but just something flashing or making a noise is enough. Bang your elbow on something, and the reaction in turn is to jerk forwards again, which might make a bad job worse.

Anyway, 'safety first' out of the way, what are you playing with?

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56 minutes ago, awkwardbydesign said:

hqdefault.jpg&f=1&nofb=1

:nerves:

Makes the haircut easier when it's all standing on end :D

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Currently fighting the noise on a 2P29L Moglia build. And the instability. Got the latter under control but its not the placid valve I believed, more of a tetchy b*stard. Through the noise it sounds good though!
Currently I've a 'loaner' pair of Rullit field coils filling up the 0.2m2 remaining space in the man cave, listening through them... I can't afford corona virus, if I cough the t/t, pre-amp PSU, stuff will fall off the shelf!


Sent from my BLA-L09 using Tapatalk

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15 hours ago, Jazid said:

Currently fighting the noise on a 2P29L Moglia build. And the instability. Got the latter under control but its not the placid valve I believed, more of a tetchy b*stard. Through the noise it sounds good though!
Currently I've a 'loaner' pair of Rullit field coils filling up the 0.2m2 remaining space in the man cave, listening through them... I can't afford corona virus, if I cough the t/t, pre-amp PSU, stuff will fall off the shelf!


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Field coils :love:

I've still not got round to trying the 2P29Ls, but I've got a pile of them. That was down to Ale and Geoff banging on about how good they are, and one of the Russian sellers I've used had a 'buy ten' price I couldn't resist. I know Geoff has had success with them on a headphone amp, but also suggested they can be very prone to oscillation. PSRR and power supply impedance are apparently crucial issues.

I really need to clear some of the other stuff first, but it looks as though we might have more 'spare' time available than any of us would have normally anticipated so I might get an opportunity to try them. I did contemplate using them in a first gain stage for the 'new' 845, but it's probably unnecessary complication and grief. Headphoen amp looks sensible though. I don't have one at the moment...

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Hi all..

Need some advise regarding tube amps for treble duties for my 3 way active build. I have the good fortune of getting tube mono blocks custom built for me from a very local company called anode acoustics. But I really don't know what to get. 

I do understand as sir @rabski always says, it is always the circuit and not just the tube :)

So was wondering if any particular tube I should go for from the outset. 

By the way , I was previously getting some SET 300B's mono blocks, as already shared here. But the seller, sadly has developed cold feet, looking at the prices of new output transformers as he will need to build a new one for himself. So Iam sadly back to square one :)

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