Grzegorz "gsmok" Makarewicz,
Interesting tube monoblocks combine a rational approach from the technical point of view with some audiophile's "bells and whistles". The amplifier (produced by American company Cary Audio Design) that came to my hands probably comes from the early stages of production. I do not know when the first copies appeared - probably around 1994, because at that time Stereophile magazine (01/1994) published a detailed review and measurement results.
Monoblocks, whose photos I would like to show are amplifiers "with history". They changed owners. They were repaired (including the repair of the "serious" nature). This was reflected in their outer and inner appearance. They are similar to a long-standing car of good brand, which the owners did care about, but they did not prevent from minor scratches and even bumps. But to the point. Before I go into detail I would like to show you how the monoblock looks in all its splendor - here it is:
It is beautiful - of course in my subjective sense. What I like, besides the power tube used in the output stage are rounded edges of the transformer cans. I know it's a trifle, but I really like it.
The monoblocks that I had the opportunity to view differed from the ones presented in the various tests with one strange feature. So it's a mystery. Here is a photo of a typical monoblock interior (slightly different from described one because of two tubes in voltage stage, but I do not have a one tube version)...
... and here is a photo of the described monoblock:
And the ten points question - what is missing in the presented copy? The question is difficult and the answer is unexpected. Here it is:
Beautiful switch (I marked it with an orange rectangle), to which no wires lead. And it should be because of the fact that a great audiophile knob is attached to the axle of the switch and its functions are described on the front panel.
At first I thought it was a defect of only one monoblock, but it turned out that these dummy switches are mounted in both. So what we have inside? This explains the power amplifier and power supply diagrams.
According to the power amplifier schematic derived from the original operating manual, the feedback loop switch is actually not used. Why, then, on "factory" photos is not just a dummy element?
The amplifier I had the opportunity to watch was modified by typical audiophile technican. What does this mean? Of course the capacitors!!! They are replaced wherever possible. Well, when good capacitors (and such are mounted in amplifiers of higher shelf) are converted for the better. Worse, when inserted are the same or worse. Unfortunately replacement means tampering with the device and is not always done with the right attention. A few examples are shown below. Here are photos of the original design. Please note the capacitors connected in parallel to the large electrolytes in the power supply.
And now a set of photographs documenting the audiophiles cheating:
The mounted polyester capacitors are certainly mentioned with nostalgia by older radio enthusiasts. But in the end the capacitor is a capacitor. However, the issue is of the style in which the factory-installed capacitors have been removed and the "audiophile" ones are "soldered". Here is a detailed photo that is better than a comment:
As you can see the old good capacitors have been cut off or removed together with the soldering lugs and the new ones are attached to the "adopted" solder lugs. Beautiful view, isn't not it? Oh and I'd forget about one more curiosity. Capacitors - the eye in the head of each audiofile - in particular the coupling capacitors were fixed by strips by an unnamed strongman. As a result, the straps caused their visible geometric distortions - they simply "wrung" into the corpus of these delicate elements. See for yourself:
Now it's time for a sad and even very sad piece of description. As I mentioned the presented amplifier is a device with a "history". It came to me because of problems with biasing the 300B tube in one of the channels. Allegedly (deliberately I use presumptive mode, because I have not witnessed these problems, but seem highly likely due to the "defect") in one of the channels the 300B tube burned and with it burned the speaker transformer, which had to be replaced with a new one (made by a well-known transformer manufacturer). After the repair, there was still a problem with the setting of the 300B tube, which even damaged the valuable new tube. Having seen the monoblocks, the first characteristic feature I observed was incorrect fuses, including one "fixed" with a piece of wire. Actually, fuses are not typical (they are not 5x20mm but 6x30mm) but they are available for purchase and installation according to the manufacturer's recommendations. Further observation revealed a combined transformer and current control problem. Please look at the diagram below.
Due to the overwhelming current flowing through the 300B tube, and probably incorrect fuse operation, a portion of the wire connecting the R12/R13 resistors to the large jack for connecting the biasing current milliammeter was blown. This is symbolically shown with a red cross. As a result the cathode of 300B was not connected to the ground. Someone just joined the R12/R13 common point directly to the amplifier ground as seen in the photo below - it's the green-yellow wire.
If someone could not believe in this I showed a detailed photograph:
This "repair" caused the current control circuit to remain active but the milliameter connected to the measuring socket always indicated 0mA. Owner of the amplifier, following the instruction of setting the current of the 300B turned the potentiometer trying to obtain the recommended value of 60mA and exceeded the limit value of the 300B tube by burning it and seeing the millimeter continuously and constantly 0mA. Terrible!!!
And yet such a little curiosity. The burned red cross piece in the diagram consists physically of a wire connected from the R12/R13 resistors to the speaker transformer and the second cable coming from that transformer connected to the test socket to measure the current of the 300B tube. I do not know why this was done. Perhaps in the flooded transformer basin they are the leads of a screen. If anyone knows the details please contact me. Anyway, this burned wire has no effect on the transformer's performance and there was no need to replace it. Has it really been replaced is another matter. I do not think so. The only interference is the latching traces in the flood at the transformer leads as shown below. But maybe I'm too inquisitive.
If you have been through the reader so far, then I invite you to familiarize yourself with the detailed photographs of the exterior and interior. The amplifier is still in my hands. I will try to add additional information. Have a nice watch.
The amplifier after some "repair" has been stripped of the screws fixing the bottom to the chassis. The repairer thought that the owner could not see it. True, monoblocks are heavy, but no one knows who and when will turn and what will make the photos worse. I do not know if the visible deficiencies are related to the repairs done.
Grzegorz "gsmok" Makarewicz,