New arrivals: Silvercore 833C monoblocks ... not your typical SET
I’ve had a few people query by PM what I have coming to replace my Radford STA100, so beautifully restored last summer by Will of Radford Revival
Well its replacement has actually been here for about three weeks, during which time I’ve done many many swaps back and forth, just to make sure I was doing the right thing.
Enter a pair of Silvercore 833c monoblocks … 20w single ended triodes.
These are not at all what I would have expected to be running with my Tannoys and it just shows how a genuine curve ball can hit you sometime that confounds all expectations and prejudices acquired through past experience. I had had a long term loan of the Thöress Phono Enhancer. This is a very decent phono stage, and indeed is probably the coolest looking phono stage on the planet, but it's not one that fit easily with my bagful of stereo and mono cartridges on swappable headshells, or my two recently acquired multi-adjustable Miyajima ETR-Mono and ETR-Stereo SUTs. It's raison d'etre is flexibility ... but unfortunately not the flexibility I need for my own kind of listening.
When Greg of G-Point came to collect, he dropped off for trial a couple of strange monoblocks that looked a bit like spare parts from a TV transmitter, or a Dr Who set. On plugging them in I half expected my phone to start showing the Test Card. The 833 valve they use is over 9 inches tall, and over 10 inches when the connectors are plugged into the top. But the sound was even more of a shock than the looks. I’ve written before about how Tannoys and single ended amps rarely go together, and opined that it had something to with input impedance/damping factor, which seems to be the general consensus.
Well, here was a SET amp that approached the depth and authority of the Radford in the bass - while at the same time exhibiting the flow and ambience that draws many to live with inevitable compromises single ended amps throw up on most normal speakers. Presentation was very different to the Radford - detail was still there, but a little more diffuse, compared to the Radford’s front seat, pin-point positioning. This was more of a mid hall feel - though I can’t say the soundstage was any narrower, the opposite in many ways as the sound bloomed and extended in a wonderfully free way
For pop, rock and other beat-driven music, or a diet of Wagner or Bruckner symphonies, you’d probably choose the Radford. Possibly certain jazz genres too depending on your specific taste. But on my diet of Lieder, baroque and classical chamber music, Renaissance vocal, solo lute and harpsichord, I was smitten. It even makes a decent fist of classical orchestral, due to its way with flow. At first I resisted. But as a couple of weeks progressed I began to consider seriously that an unexpected, unplanned change might be about to happen. The Radford is a fabulous amp, and after Will’s rebuild, an heirloom quality piece. But I was hearing things anew.
There's not much to be read about these amps in English, even though they've been around since 2013. Digging into the technical specs from pulling up as many of the German reviews and comments as I could find (thank you Google translate) I could see that these were fairly unusual in their construction. The 833 valve had been used previously by Wavac and run in full Class A1, delivering 150w per monoblock of single ended power, consuming 800w each (though this is still modest compared to the valve's original function as a radio transmitter valve, where it outputs up to 2.700w, glows bright red and gets thrown in the bin after a few hundred hours). Nevertheless this still requires a power supply of enormous capacity and complexity, and a resulting price tag of $350,000 a pair (though there is a budget version for $70,000 ...).
Christof Kraus, the engineer behind Silvercore (which I had only heard of as the maker of highly-regarded step-up transformers) took some quite different design decisions. He runs the 833 tube modestly in Class A2, delivering 20w of SET output power, consuming 100w per monoblock. That’s still 10A at the rewired 10V, so to deliver that, he used two 5V switching power supplies, run in series. Obviously switching power needs to be implemented sensitively, but the upshot is a powerful SET amp with a smart but relatively simple, high-capacity power supply that’s essentially silent when not playing music - a rarity in any valve amp let alone a beefy one. To get that bass control, it uses feedback - how much is not clear but it’s clearly used intelligently and does no harm to the amplifiers’s feeling of flow or timing. To get away with a single gain stage, it uses a 1:5 step-up in the input stage (silver wound, in house) and the output transformers are also custom wound in-house. And they are hefty things at 30kg each.
Balanced input only - which is no problem for my EAR 912 - the 833 valve is driven by a pair of EL34 pentodes. An unusual choice for a SET amp driver stage, but highly effective. I’m informed that much fun can be had rolling these with Mullards, Telefunkens etc but my monoblocks came with a quad of TAD EL34s which are the only ones I’ve tried so far. The 833 output valves are RCA NOS - American-made RCA and GE valves seem to be still available, but there are also plentiful supplies of Chinese and Russian made tubes. It seems the transmitters that consume these are still widely used especially in China - Chinese tubes can be had on eBay from £100 or so.
Anyway .. the Radford is an amp that commands attention, unburstable in big orchestral tuttis where it just seems to swell forever without distorting. It’s an utterly class act. The Silvercore 833C's seem to be drawing me in in a different way ... more enveloping, beguiling … it’s certainly a change that’s taking some time to get used to.
I'm sure there will be moments, and specific music, where I will miss the Radford, but it's also interesting to be heading off into uncharted territory, after more than 10 years of feeling constrained essentially to beam pentode or tetrode amps in order to get the best out of the Tannoys - so many single ended amps having disappointed along the way.
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Originally Posted by montesquieu
