The Copper Amps |
- 30 Watt Original Version
The first of this series were thirty-watt and pure class A, as reviewed in Hi Fi Choice in 1998 by Jason Kennedy. They used two kt88s and two 6sn7s in each channel, which were configured as follows; first stage directly coupled to a concertina phase splitter, capacitor coupled to a dedicated driver stage, capacitor coupled to the output stage. Overall feedback was applied, as well as local loops. Power supply HT was via two GZ34's, and large choke for extra smoothing.
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- 60 to 120 Watt Versions
These amps were quite a different breed from the latter. They had four kt88s and three 6sn7s in each channel (later versions had 2 6sn7s and one ecc34). The front-end circuitry was very similar to the 30-watt versions, but the output stage was grid biased and driven by cathode followers. They could be biased to give between 60 and 120 watts! Power supplies HT via solid state, capacitor, choke and capacitor. Time delay circuit for HT, approx. 40 seconds. |
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Stainless Steel Amps
There were only two of these amps, both prototypes; one KT88 single-ended, the other a push-pull EL84 design. Both were integrated and had valve rectification.
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- KT88 Single-Ended
This amp was made with the 'hard to please' customer in mind. It could be switched from tetrode to triode mode with the flick of two switches on the front panel. The screen grids in tetrode mode were regulated with neon stabilizer tubes. It had eight and sixteen ohm taps for the speaker output, which were also switched. It could be used with directly or indirectly heated rectifiers and was fitted with a standby switch, a bass boost control, an amp meter, volt meter, and a pair of feedback switches, so you could switch in full or half feedback. And finally, it looks great too, especially when it's on. I consider this amp to be one of my favorites.
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- Push-Pull EL84
This amp is also one of my favourites...again, it was a bit special. It had a GZ34 for rectification and a voltage regulator tube for the HT on the front-end valves. It could also be switched to pentode or triode mode and had a standby switch for the overall HT, also a pair of feedback switches were included to half the feedback if required.The valve line up in each channel was as follows; first valve (half) ECC82; second EF86; third ECC83; fourth EL84 X2. It also has tone, bass, balance and input controls. |
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Single Ended Amps
There has been a wide variation of single-ended amps made over the years. From real odd-ball triode amps, to the up-to-date sophisticated designs conceived [originaly] in conjunction with Tom Evans of Audio Design and Acoustic Precision fame, although produced soley by Tube Distinctions. As you have probably guessed by now, one of my all time favourite valves is the KT88. I have used these excellent devices extensively in circuits throughout my audio career and have yet to find a better device that combines power, linearity and ease of drive. In my opinion these tubes excel at all three of the above and more. |
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The Next Generation Amps
Over the last three years [2001 to 2004] I have been developing a new breed of amplifiers- the Soul Series power amps and Soul Mate preamp. They are all pure class A, single-ended and come in 15, 30, 60 and 120 watt configurations. These new amplifiers are quite unique in design and performance; they are hyper-linear, ultra quiet and use some of the best technology available from both valve/tube and semiconductors.
Performance Specifications of 15w Version
Input sensitivity: 700 MV peak to peak. Signal configuration: direct coupled throughout. Single ended or balanced line. Non-inverted output. Power output into FR 1 loud speaker: 20 watt. Total noise at speaker terminals: 1mv.
For more info on this design, see the accompanying pages, or contact me, Anthony Matthews, using the email link at the top of the page.
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