The SAM-A1: A fully configurable Stereo Valve Amplifier.
Pictures of the SAM-A1 in its soft black anodised, custom designed enclosure.
A brief introduction to valve amplifiers:
The reproduction of sound has been one of man's pursuits for over 100 years and long before transistors were invented, there were valves, thermionic emission vacuum tubes. We are not going to go in to a massive history lesson here – there is plenty of reference material on the web. But as a brief introduction:
To enjoy music in your home, reproduced though loudspeakers, regardless of the source, be it vinyl, tape, CD, MP3 etc. the small signal produced by the player needs to be amplified to be a large enough and with enough power to move the cones in the speakers to make the sound. The equipment that does this is called an amplifier. (Some of these players produce such a small signal that they need another amplifier, called a pre-amplifier, before the main amplifier driving the speakers – Record players using vinyl as the source is one of these!)
Modern HiFi or stereo equipment uses amplifiers that are designed and built using transistors in one form or another.
Just about all technology in the early 1900s through to the late 1960s (and later in some applications) was based on valves. This all changed with the invention of the transistor.
Vacuum tubes or valves are made from glass, use quite a lot of power, get hot and use high voltages at low currents to operate (they are also large compared with transistors). This in turn means that more often than not, a transformer is used both to isolate the user from the high voltages and to convert the high voltage, low current to lower voltages at higher currents required to make the loud speakers work. Transformers are large, heavy and expensive.
Transistors are smaller, encapsulated in plastic (mostly), use lower voltages, are capable of delivering higher currents and more often than not, drive the speaker directly, without the need for a transformer. Transistors are also a lot cheaper to make. This makes it easier and cheaper (smaller and lighter!) to design an amplifier using transistors.
Unsurprisingly, the use of transistors rapidly overtook valves almost everywhere- except in electric guitar amplifiers and in some high end HiFi music reproduction (there are other places where valves are still in use).
The pursuit of cheaper more convenient products however, left something behind - decades of development that had gone in to valves and their use in radios, televisions and music reproduction systems.
There are many who would argue that there is something special about valve amplifiers and that they sound different from solid state amplifiers. While it is true that there are some very fundamental differences between how energy is transferred from the amplifier to the speaker in a valve amplifier compared with an amplifier using transistors, there are differences between one transistor amplifier and the next.
We have researched the technology and looked at how it was done by the best and then gone back to first principles in electronics engineering and physics to design our own. Of course there have also been huge advances in all of the other components that are needed to make the valves work since the 1950s and 1960s and we have used modern components to develop a great sounding amplifier making valve technology available for you to enjoy.
All we know is that the SAM-A1 is the first in a family of valve-based, stereo audio amplifiers that have been designed to make the best of the vintage valve technology.
They sound amazing.
Not only do they sound amazing but we believe they look good too and whether or not you believe that valves are somehow special compared with transistors; we like the way our amplifiers sound and there is definitely something special about seeing the valves glowing as they work, seeing them light up as they get hot, something ‘alive’ about them which definitely sets them apart from transistors – which only glow when there is something very, very wrong!
We hope you enjoy our amplifiers as much as we do.
The SAM-A1 stereo valve or tube amplifier from Fireworks Solutions Limited is a fully configurable stereo valve amplifier, designed from scratch, from first principles, using modern components to get the best from vintage vacuum tubes or valves. The amplifier uses bespoke power and output toroidal transformers to achieve the unique, clean and pure sound that is achievable with valve amplifiers. The enclosure is designed to be sleek, supplied in soft black anodised aluminium, with a flat top, no transformers or capacitors sticking up or boxed in on top of the enclosure, so just the valves you have chosen to use are on display. All the design and custom build is done in the UK, supporting small UK businesses.
The Output Stage
The SAM-A1 can be configured to use triodes or pentodes or pentodes as triodes.
With triodes the SAM-A1 will deliver between 1Wrms and 7Wrms*1 in to 8Ohms in:
Pure Class A all the way - Class A input, Class A output push-pull,
Class A input, Class A to AB output push-pull, or
Class A input, Class AB output push-pull.
With pentodes, the SAM-A1 will deliver between 8Wrms and 12Wrms in to 8Ohms depending on configuration; Class A, Class A to AB or Class AB Push-Pull all in Ultra-Linear mode. With pentodes as triodes the SAM-A1 will deliver between 6Wrms and 10Wrms in to 8Ohms depending on configuration; as pure Class A, Class A to AB, or Class AB output push-pull.
The output valves are all controlled by fixed bias (the correct way to set up an output stage!). The bias is easily adjusted (with the cover on) to allow you to set how your output valves are driven. This means that absolute matching of the quad of output valves is not critical and we match our quads on what is important for achieving the best results in our amplifiers, using our own automated, computer-controlled valve tester.
All of the output valves listed in the Compatible Valves List have been tried and validated against the design and can be interchanged. The bias will need to be reset each time a new set of valves is fitted.
*1 These figures depend on the configuration of the output tubes, their bias setting, the specific quad of valves used and its age. As valves age they lose emission capability and require lower grid voltages to achieve a given bias point this limits how hard they can be driven before the onset of distortion.
The Input Stage
The input stage is open-loop so the two triodes used for the left and right channels should be similar in terms of their gain in the circuit; this does not mean that they are required to be perfectly matched, as both channels are adjustable (and you can chose to use adjustable, overall feedback). We match our input valves accordingly in our in-house computer-controlled valve tester. The second half of each triode is also not important from a matching point of view, since this is used as a unity gain inverter.
The inverter stage can be configured as a Paraphase inverter or a Cathodyne inverter and both are adjustable to ensure both halves of the output drives are perfectly matched. The input stage can be traditionally biased, known as automatic bias, using a cathode resistor, or use LEDs to set the bias.
The input stage is designed to allow a range of double triodes to be used, depending on what you want in terms of input sensitivity and on your preference for sound (and how it looks!). All of the double triodes listed in the Compatible Valves List have been tried and validated against the design and can be interchanged, allowing you to experiment and try different valve types.
If a type of valve is not in the list and you want to know if it can be used, let us know and we will investigate. If we think it will work, with or without modification, we will let you know; send us the valves and we’ll test them against the design!
Please note that valves should always be replaced as a set i.e. both input valves and/or all four output valves. Whenever valves are replaced we would always recommend that the amplifier is re-calibrated or 'tuned' to ensure the best performance from your valve selection.
Without entering in to a debate on whether or not it is beneficial, it is configurable. We chose to use overall feedback and this can be adjusted allowing the ‘brightness’ of the sound to be altered but also lowering overall harmonic distortion, reducing hum and making it very unlikely that powering your amplifier without a speaker connected will lead to oscillation, runaway and the destruction of your output transformers and output valves; but you can chose to remove the link and not have it!
|Valve type||Cyrillic||Brand/type Stocked - click to see our valve page|
|6N1P||6H1П||Voskhod: NOS The classic 6N1P tube from Voskhod (Kaluga) great sound.|
|6N1P-EV||6H1ПEB||Voskhod and Nevz (Novosibirsk) NOS, Military ruggedised, extended life, version.|
|6N1P-VI||6H1ПBИ||Nevz: NOS NIB, Military Ruggedised version. Optimised for Peak/pulse current; great for punchy bass and for use in an output stage.|
|6922||e.g. Electro-Harmonics 6922EH and 6922EH Gold (not stocked but tested; sound great; identical construction to the 6N23P-EV triodes)|
|E88CC||Tesla, JJ etc. (not stocked but all tested)|
|ECC88||Philips, Siemens etc. (not stocked but tested)|
|6N23P||6H23П||Reflektor (Saratov) and Voskhod: NOS standard and Military ruggedised versions. Fantastic sound, really clear highs and firm solid bass.|
|6N23P-EV||6H23ПEB||Reflektor: NOS & NIB: Best of the bunch! Military ruggedised, extended life version of this fanstasic sounding triode.|
|6N6P||6H6П||Nevz: Taller tube, higher power, double triode, designed for audio. Lower i/p gain. Sounds similar to the 6N23P-EV i.e. excellent; Two versions stocked, both NOS.|
|6N2P-EV||6H2ПEB||Voskhod: NIB & NOS: Provides higher i/p gain, for lower input signal applications. Impeccable sound, Military ruggedised, extended life version stocked.|
NOS (New Old Stock) valves are new, unused valves from old stock, not modern, remade valves. A NIB valve is a NOS valve in its original manufacturer's box. All are tested rigorously by us before being used in any of our audio equipment. Note: all of these valves can be ‘rolled’ in to the input stages without modification, ideally the amplifier will need to be calibrated or tuned whenever valves are swapped or replaced.
Low Power pure triode output
|Valve type||Cyrillic||Brand/type Stocked - click to see our valve page|
|6N1P-VI||6H1П-BИ||Nevz (see above)|
|6N1P||6H1П||Voskhod (see above)|
|6N6P||6H6П||Nevz (see above)|
|Valve type||Cyrillic||Brand/type Stocked - click to see our valve page|
|6BQ5/EL84||The classic 6BQ5 and EL84 Pentodes e.g. Mullard, Philips, GEC, JJ, Electro-Harmonics, Bugera, RFT, Sovtek, TAD, Tung-Sol etc. (not stocked, some tested)|
|6P14P||6П14П||Reflektor: NOS. The 6P14P is a great equivalent to the 6BQ5/EL84 pentode but with higher power capability, (14W not 12W anode power). .|
|6P14P-EV||6П14ПEB||Reflektor: NOS & NIB. Military ruggedised, extended life version of the 6P14P.|
|6P14P-ER||6П14ПEP||Reflektor: NOS & NIB. The ultimate Military version of the 6P14P; specifically selected for stable characteristics over its life.|
|For the SAM-A2/A3|
|6P3S||6П3C||Reflektor: NOS & NIB Military. Output Beam Tetrode; Octal base. 375/300V (anode/2nd grid) 20W. Near Equivalents; 6L6, 6L6GT, 6L6GC, 5881|
|6P3P-J||Guigang: Chinese classic (from the factory allegedly bought by PSVANE). NOS, NIB Output Beam Tetrode, Octal base. These are a big bottle valve looking like the 6L6GC, very similar to the 6P3S- 400/330V 20.5W. A great sounding, great looking valve!|
Notes: Replacing or swapping output valves will always require the bias to be reset and ideally the amplifier should be calibrated or tuned. All valves/tubes supplied with the SAM-A1, or for use with any of our amplifiers will be provided with the test results for each tube. Different grades are available for most of the tube type we stock and they are available with different grades of matching. We will never supply a set of valves that cannot be used with your amplifier and that do not sound right for their type; having matched a set appropriately, we will test them in our own amplifier before supplying them.
About the Power Supply
The Power supply; the heart of any good amplifier! The Mains Transformer is designed and rated to cover all variations of the SAM-A1 amplifier; it has been wound and screened to minimise magnetic fields and hum: even driving very sensitive speakers, you will be hard pushed to hear ANY hum (measured output at idle less than 3mV).
The input voltage is compatible with BS7671, requiring a range of 230Vac +10% -6%, 207V to 253V. The SAM-A1 mains transformer has multiple primary windings allowing it to operate from 205 to 255Vac; the input range being selectable for the following supply ranges: 210 ±5V, 220 ±5V, 230 ±5V, 240 ±5V and 250 ±5V (with significant overlap between each range). In its simplest terms, this will allow you to choose the most appropriate winding to match your mains supply. The Output windings provide AC power to the Power Supply Unit (PSU) and to the valve heaters (yes we use ac heater supplies and no, in the SAM-A1 valve amplifier design, this does not cause hum!). Changing your Mains Transformer input winding choice also allows you to decide how hard to drive the heaters on your valves with our preference being simply to stick as close as we can to the mid specification for the valves. We can go in to more detail on the truth about, advantages and disadvantages of varying heater voltage/current/power if you wish!
Yes, it might be a bit of an over-kill, but the SAM-A1 PSU provides fully regulated DC supplies to the valve anodes of the input stages, fully regulated DC to the anodes of the output stage (yes regulated output stage supply!) and fully regulated negative dc for the fixed bias on the output stages.
What this means is that the amplifier can be configured for many different options, to use many different valve types to allow you to set up the amplifier to your preferences and try different valves to achieve the sound you are looking for!
Specifications for the SAM-A1 stereo valve amplifier
382 x 341 x 77mm W x D x H(mm)*
Supply Voltage input:
The input voltage is compatible with BS7671, requiring a range of 230Vac +10% -6%, 207V to 253V. The device will operate from 205 to 255Vac:
Input Signal, impedance and voltage:
98-110KOhms impedance, 200-500mVrms for full power output depending on configuration and valve choice. (This will not work with a vinyl turntable without a pre-amplifier).
Bluetooth connectivity; if you wish to connect your device to the SAM-A1 via Bluetooth, there is a large range of bluetooth receivers available on-line, see the owner's manual, link below.
Output, impedance and power:
8Ohms impedance; Power Out is entirely dependent on valve choice and configuration, please read text.
Frequency response ('more than adequate!'):
To a lesser degree dependent on the valves, as measured with 6N23P i/p, cathodyne splitter and 6N6P triodes o/p:
-3dB response better than 5Hz to 50kHz at maximum power.
*Note the depth excludes the connectors at the rear:
The sockets add 20mm - it then depends what you plug in to them and the depth of your mains inlet plug, the one provided is a right angled type for minimum depeth at the rear.
The knob on the front adds another 20mm to the front (depending on the knob fitted).
The standard feet add another 3.4mm to the height, the dominating factor is the choice and height of the valves fitted.
Remember that sufficient clearance is required above the valves; they get hot!
Refer to the Owner's Manual for more details:
Click on this icon to download the User's Manual: .
How to buy the SAM-A1 stereo valve amplifier
The SAM-A1 is available as a CE marked, fully assembled and set up amplifier, ready to plug in, switch on and enjoy! All you have to do is decide how you would like us to configure your amplifier and which valves you would like to start with. Please contact us for further details.
Prices start from £2,400 including VAT (at 20%) for our recommended base configuration, which is: LED biased input, a balanced Cathodyne phase splitter feeding pentodes in ultra-linear push-pull, set to a mid bias point, allowing pure class A at lower listening volumes and a lower quiescent energy use - migrating seamlessly to AB push pull at higher volumes. As for valves; our starting point is Voskhod 6N1P or 6N1P-VI triodes and Reflektor 6P14P pentodes. Please let us know if you would prefer to upgrade your input or your output valves, or if you would prefer a higher or lower gain input stage; please see our valves page for more information (link below).
Upgrades available to the base configuration include: Higher specification valve choices, Higher or lower gain input stage valves, Power Supply Upgrade, Premium valve selection and matching, Premium calibration.
Custom configurations are built to order with a 10 working day build and test time.
For Optimal performance the SAM-A1 needs to be set up for your mains supply voltage. If you know what this is, we can configure the power supply accordingly; if not we will set the SAM-A1 to its default 240Vac (230-250Vac in) please see the Owner's Manual for details..
WARNING! The voltages and currents required inside valve amplifiers can be LETHAL.
Disclaimer: Building and modifying valve amplifiers is DANGEROUS. Valve amplifiers invariably use high voltages, both Direct Current (DC) and Alternating Current (AC) which are also available at high currents: the combination can kill you. The amplifiers are supplied with full instructions but it is your responsibility to operate in a safe manner at all times to avoid electrocution of you and others and to use the products safely. The equipment must never be operated with the enclosure opened or with any of the valves removed. FSL accept no liability for your negligence.
Our audio equipment is assembled to the highest standards and tested thoroughly before despatch/delivery. All equipment supplied is CE marked and all aspects of the design relating to user safety are detailed in the owner's manual supplied with the equipment and in our Technical Construction Files supporting the CE mark declaration of conformity. FSL accept no liability for any damage or injury sustained through or as a result of either the modification of the equipment or use of the equipment in any way other than for its stated internded purpose.
Valves get HOT! Up to 220C. Do not touch the valves when they are on or until they have cooled down.
(Please note: the introductory offer price of £1900 for the base configuration expired on the 1st September 2020)
[You may well be wondering what a page on Valve Amplifiers is doing here!? Well, it's another passion and if you know what valve amplifiers are and you're interested in buying one of the most configurable and elegant valve amplifiers around, please contact us to find out more! Our amplifiers sound amazing, look really elegant and can be set up in lots of different ways allowing you to exploring this wonderful vintage technology].