I was curious to know how closely matched the stock KT88s in my R8 were so I asked Tube Labs if there was a method to roughly check this when you don't have access to a tube tester. This is the method they suggested. A) Let the amp warm up then set the bias on V1. B) Switch off the amp and switch V1 & V2. C) Switch amp back on then check the bias on V1 and note its position. D) Repeat steps B & C but with V3 then V4 in the V1 socket. Here are the results I got as displayed on the R8s bias meter. I also purchased a matched quad set of TAD KT88-STR tubes and their results are also displayed below:

Just stumbled across this archive of older electronics and tube related publications with associated PDF files: http://www.tubebooks.org/ Here is a sample of the type of things you will find in this archive ($10.86 for an output transformer and only $7.95 for the power transformer - where is a time machine when you need one?):

I guess this explains why there are no Chinese clone amplifiers based on Bob Carver's designs: (Note: This schematic is for the 1988 'Silver Seven' that used 14 KT88 tubes and was rated at 375 watts into 8 ohms. The specs and photo are for the 2014 'Silver Seven 700' that uses 20 KT120 tubes): Carver Silver Seven 700 Monoblock Rated Power (8 ohms): 900 watts RMS continuous - 900 watts RMS with vocal and music Frequency Response: 2 Hz to 85 kHz (-3 dB) Distortion: Less than 0.5% Power Bandwidth: 18 Hz to 28 kHz Line Inputs: 2 (RCA); Normal (AC coupled) or Lab Direct (DC coupled) Input impedance: 100 K ohms Gain: 36 dB Tube complement: One 12BY7A, one 12AL5, three 12BY7A, and twenty KT-120s Hum and Noise: Better than 120 dB, referred to 700 watts, (A-weighted) Bias: Rear panel potentiometer adjustment Source Impedance: 1.7 ohms Speaker Output Taps: 2, 4, and 8 ohms. (Designed to drive any load 0.75-ohm and higher) Color: Deep burgundy with gloss black, natural aluminum, and bright chrome highlights Dimensions: Amplifier Chassis: 9” (228.6mm) x 13” (330mm) x 20” (508mm) x 2 - Power Supply Chassis: 9” (228.6mm) x 11” (279.4) x 20” (508mm) x 2 Weight: Amplifier Chassis: 55 lbs. x 2 - Power Supply Chassis: 45 lbs. x 2 Warranty: Lifetime warranty including the tubes.(DC restorer circuit means that the tubes will last as long as 50 years)

Although I am new to the world of tube amps, even I can see the issue with this amp. Is it designed to deceive people or is there a legitimate purpose?

I have started my next project, a bucking transformer. I initially had problems finding a suitable transformer until I remembered an old 13.8v power supply I had for powering an AM CB radio back in the late 90s. I dug it out of the garage and tested it's output, 19 volts, which would make it ideal for use with 220v devices. However, quite a lot of these Chinese tube amps are 230v and I also worried that I would suddenly have a use for that power supply so I opted to search for another transformer. This is what I found: "Custom audio 64W multi-purpose power transformer Multi-voltage input secondary multi-winding output voltage adjustable" https://www.aliexpress.com/item/32982855405.html The 'B' version seems to have all the right specs to reduce the voltage to 220v and 230v except for the 2 amps output. I would have thought that the amperage would vary across the output voltages so if 32v is 2A, then the 20v and 10v output I need would be 3.2A and 6.4A respectively? I went ahead and ordered the transformer anyway and plan to use this schematic that I modified from here https://sound-au.com/articles/buck-xfmr.htm

While there are a multitude of Chinese made tube amps available online, there are also a number of small scale manufacturers around the world producing quality gear. Share links to these tube amp makers here. To start off: Eric Chan based in Sydney, Australia who makes McChanson amplifiers: https://www.mcchanson.com/

I found this interesting video where they make the tubes for their build: https://www.youtube.com/watch?v=-UEfqAWb3fE

Due mainly to a lack of availability of the Hammond choke used in the R8 upgrade in my part of the world, I threw caution to the wind and got a 250mA 4H choke from Aliexpress (https://www.aliexpress.com/item/1005004221303875.html). It cost me about half of what the Hammond choke would cost if it had been available to me. As my test equipment is limited to a digital multimeter, a capacitance meter and ESR meter, are there any measurements I can make to ensure its specs are what is claimed? Its physical specs are: Dimensions: (H) 50mm (W) 60mm (L) 60mm (mounting hole spacing) (70-75mm) Weight: 644grams (1.4lb) (Note: The Hammond 194G is 570grams (1.25lb) The label text translates to: EI573018 Copper Wire Inductor Zhongshan Lime Electronics Co., Ltd.

As Stephe is soon to build some speaker kits, I thought I would share my experience of doing the same. Back in 2001, I purchased five kit speakers from the Australian company VAF (www.vaf.com.au) for my home theatre. At the time, VAF offered their affordable DC range in kit form as well as fully assembled. They no longer do this. My brother recently gifted me a pair of DC-1 speakers that I use as Atmos front speakers. Unlike the kit Stephe is looking forward to building, VAF sent fully assembled cabinets and crossovers with wiring attached. I think this was due to the complex nature of the speakers internal structure. For example, their largest DC-X speakers have a large internal brace that doubles as a transmission wave guide. The cabinets are made from painted 20mm MDF and use a full length stocking and vinyl covered caps to finish off the top and bottom of the speakers. It was more of a component assembly rather than a complete build. The DC-X uses a minimal component crossover, just a single resistor and capacitor due to close driver matching and tuning. The smaller DC speakers have more complex crossovers. The DC-X and early DC-2 speakers have a D'appolito array and the tweeter on the DC-X is recessed into the cabinet for improved time alignment with the woofers. The DC-Xs sound excellent for the money and are still in perfect condition after all these years (likely due to my cities dry climate). They produce a really nice soundstage and go down to the 30hz region. Their only fault is that they can be too revealing so you hear every little flaw in the recording process You can read more about the DC-X Series 1 here (mine are Series 2 and the crossover resistor is the only difference as far as I am aware): https://archive.org/details/EA1997/EA%201997-01%20January/ VAF DC-X showing the D'appolito driver array and the use of felt pads to dampen driver resonances in the woofers and absorb sound diffraction from the tweeter: The VAF DC-X Crossover. Note, I ordered the cable upgrade for these speakers: The more complex crossover and standard wiring of the small VAF DC-1 speaker:

Last night I began my journey into building tube amps by ordering a kit from (play horror music) Aliexpress. I opted for the non-Bluetooth model to simplify things and it cost me $438AU (incl. postage and sales tax). I will report back once it arrives and I start building it. SPECS: Tubes: 6J8P x 2 / FU50B x 2 / 5U4G x 1 Output Power: 8W+8W Frequency Response: 20hz-20khz Output Impedance: 4 ohms and 8 ohms SNR: 90db Input Sensitivity: 500mv-1000mv Input Impedance: 100kΩ Harmonic Distortion: 1%(1khz) Size: 320mm(L) 210mm(D) 160(H) Caution: Product options are kits, not finished products, you need to assemble yourself, the package includes circuit diagrams and wiring diagrams. Please install it correctly according to the drawing. Please contact me if you have any technical problems. The kit does not come with a power cord. UPDATE: I just found this useful video series showing construction of this amp 😀 https://www.youtube.com/watch?v=nUK4sOOE7WQ&list=PLnyQFHUSljIpCy0KD6aTbms7K0Mb5Krhx