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Hawk

Valve info

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I've bought thousands of tubes from the states and I think I only ever lost one package and had a few damaged due to crap packaging.

You may or may not get fleeced for duty (almost certainly if sending EMS [express mail] because it comes through Parcel Force).

If shipping via normal USPS, chances are you'll get away with it. But...if it's insured, then the sender has to put the true value on, so it's more likely to get nabbed.

Expect £4 handling fee (PO) or £13 (Parcel Force) + duty + VAT.

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Thanks for that. You don't happen to know what the rate of duty is do you? the valves themselves will cost around £95. Si.

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Not sure, I never managed to work that one out. I'm sure it's some complex formula or other. Way less that the VAT is the main bit...

Cheers,

Pete

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Ok,I can't bugger around any longerwondering if it's going to cost me a few bob more and I need the valves so I've just ordered two sets of Sovtek KT66 matched quads from a sellerin theStates. Si.

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Pete, those valves have arrived from the States straight to my front door, so you can guess that I'm quite pleased. I half expected another slapping. They were packed well and I've already installed one set as you'll probably know from my other posts. Si.

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I recently bought a quad of NOS GE6550A from https://www.tubeworld.com/

Thanks for the help from greg7 (USA based wammer) who gave me the recommendation. The valves were about two thirds of UK price (even factoring in shipping). Well packed and shipped quickly.

Unasked the seller put a value of $60 on the paperwork and I didn't get charged any import duty :D

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Can anyone help me to find Mullard CV 4004 & 4003 without being skinned. I need one of each, unused if possible.

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anubisgrau wrote:

Can anyone help me to find Mullard CV 4004 & 4003 without being skinned. I need one of each, unused if possible.

Any reason for military CV4004/4003's as opposed to the standard Mullards?

Personally, I have to say that unless you can find some box plate (M8137 & M8136 respectively)versions, then I don't think the CV's are any better and in many instances worse - although I know some really think they are the business.

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mrwippy wrote:

anubisgrau wrote:
Can anyone help me to find Mullard CV 4004 & 4003 without being skinned. I need one of each, unused if possible.

Any reason for military CV4004/4003's as opposed to the standard Mullards?

Personally, I have to say that unless you can find some box plate (M8137 & M8136 respectively)versions, then I don't think the CV's are any better and in many instances worse - although I know some really think they are the business.

exactly, it's a personal recommendation so you can consider it to be a mental thing.

i do have ECC83 at present and like it.

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Mr Coco spouted the following wisdom :notworthy:

First came the Triode, invented in 1906. This has three elements (hence Triode): The "Anode" or "Plate", the "Grid" and the "Cathode". Triodes were used in early amplifier and radio sets. Commonly power was a watt, maybe two for the later types. Early triodes were "directly heated" and the cathode was the filament itself. The 300B is an example of a directly heated triode. Because the cathode and heater are the same piece of metal, heating using AC was noisy (DC was not an option as decent rectifiers hadn't been invented). Later on, indirectly heated tubes were invented where the cathode was separated from the filament. This allowed the heater to be run on AC as it was insulated from the cathode, effectively separating the two circuits. (note the directly heated bit can apply to pentodes and tetrodes as well).

Early amps had one output tube and this type of operation was called "single-ended". By it's very nature, single ended amps must operate in class-A because the tubes had to be biased to a point halfway in their operating characteristic, so always drawing (wasting) a lot of current. This is called "singler ended" operation and where the "SE" comes from in "SET", the "T" being for Triode, but could just as well be tetrode or pentode (SEP). Because they were always drawing a lot of current, even at idle, single ended amps are inefficient.

By adding another tube, which was fed a signal which was inverted from the original, one tube would push and one tube would pull. "Push-pull" amps could be biased so that both tubes were of at idle (rather than half on as in single-ended operation). This is called "class-B" and is much more efficient. It's perfectly possible to bias a push pull amp in class-A, so that each tube is half on at idle, or actually at any point in-between (class-AB). One theoretical advantage of push-pull amplifiers is that even-order harmonic distortion is cancelled. However, this leave the odd-order artifacts intact.

The triode was not the most efficient thing and in search of more output power for less input, the designers added another element between the plate and grid called the "Screen Grid". This device was called the Tetrode. Tetrodes were more efficient, but higher in distortion than triodes and suffered from an effect called secondary emission, thus the tetrode as an amplifying element was fairly short lived. To solve the secondary emission problem another grid was added between screen grid and plate, called the suppressor grid to solve the secondary emission problem. EL34s are pentode tubes. A variation of this is the "Beam Tetrode" which for all intents and purposes behaves exactly like a pentode. Examples of beam tetrodes include the KT66 and KT88.

Pentodes are more efficient, but suffer from higher distortion than triodes, and a higher output impedance when used in pure pentode mode. The advent of feedback allowed the pentode to be used by lowering the output impedance and distortion produced by the pentode.

Interestingly, a pentode or tetrode can be made into a triode (and is electrically indistinguishable from a true triode) by connecting the Screen Grid to the Anode or plate. The designers of the day thought about this and wondered what would happen if the screen grid was connected in such a fashion as to behave like something between a pentode and a triode. Thus was born "ultra-linear" and the screen grid of the pentode is connected to a tap on the output transformer at some point between the ppwer supply connection and plate connection. In theory this gives the best of both worlds, lower distortion like a triode, but with some of the higher efficiency of a pentode.

In it's day this topology was very popular and many, many, ultra-linear amps were made. This was pretty much the golden age of tubes, where ultra-linear circuits using feedback ruled. By this time, the triode had more or less died out as a power amplifier device, though small triode were used in the low level stages of amplifiers, i.e. as voltage amplifiers and drivers, due to their lower distortion vs pentode. Commonly tubes such as the ECC83, ECC82, ECC88 & 6SN7 were used. These are all indirectly heated tubes with a cathode separate from the heater for better noise performance.

This was the status quo for quite a while and eventually the transistor came along offering cheap power and tubes began to die out.

Recently, people have realised that tubes still have something to offer, and there has been a bit of a resurgence. Some mad audiophiles in Japan and France looked back to the really old days and rediscovered the triode as an amplifying device. The triode is really very linear and can therefore be used in simple circuits without feedback. On the principle of "KISS" They tried some of these old and primitive circuits using these antiquated devices and were amazed by the results. The idea of going back to a single device (i.e. SET) is the purest form, the theory being that no two tubes can be perfectly matched, therefore causing distortion as the tubes slightly different characteristics combine. The term "SET" is now commonly used to describe such amplifiers. They require *very* careful speaker and system matching if they are to sound good, but with efficient speakers can offer amazing sound quality.

Valves are high impedance (high voltage, low current) devices, whereas loudspeakers are the opposite. Some way to match these two different paradigms was required. The device that its used to do this is the transformer - nearly all valve amps use a transformer to step down the high-voltage low-current operation of a tube to something suitable for driving a loudspeaker. The output transformer is the single most critical part of a valve amp and is also going to be to be the most expensive. With the resurgence of valves, there are now many manufacturers today offering some excellent designs.

Single-ended amplifiers place greater demands on the output transformer because of the idle current that the tube must constantly pass and which flows through the transformer. This uses up some of the headroom and power handling that the transformer possesses and in turn means that the core of the transformer must be bigger and heavier, and so more expensive. In a push pull circuit, even if it is class-A the idle currents flow in opposite directions in the transformer and so cancel out. This allows the transformer to be smaller, lighter and cheaper. All things being equal, it's much easier to wind a smaller transformer and so the transformers for single-ended use require more care to prevent problems with leakage. They also require an air-gap to tolerate the DC idle current, thus compromising them even further. Theory tells us that SE amps are horribly compromised, but in practice... well it's not that simple.

Yikes! Did I write all that! :shock::shock::shock:

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Here's a link to Anthony Mathews who builds the Soul and Soul Mate amplifiers.

He's also a good source for NOS valves.

http://www.tubedistinctions.co.uk/first.htm

Ian.

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anubisgrau wrote:

Can anyone help me to find Mullard CV 4004 & 4003 without being skinned. I need one of each, unused if possible.

I think I have an unused one of those. Need to check.

I've obviously bought it for a reason tho', maybe a spare for my phono stage.... can't remember it is some years since I upgraded it.

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Purchased a quad of Winged C 6550s from http://www.tubedepot.com on Tuesday at 3pm, arrived here with me at 12.26pm today - pretty good delivery time from TN, USA, especially as they very kindly declared them as a 'Sample' so no duty to pay.

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