Here's one of my creations. This is a prototype that I built nearly 10 years ago. Since acquiring a PC and some good CAD software, I've been refining my circuits and layout to create a rackmount version that can be mounted in a remote location and have Power and Standby control from the listening room. This concept was inspired by a house I saw for sale some years ago that had built-in tube audio along with a 21" round-tube color tv mounted in a wall. It was an interesting setup with a removable panel in an adjoining stairwell to provide rear access for servicing. There was even a tilt-out panel above the tv (with a viewing mirror on the inside) for convergence and other setup tasks. The two large amp chassis were mounted in a wooden rack in the basement with cabling that connected them to the entertainment center upstairs. There were also speakers in several rooms that were mounted behind false cabinet doors with grillecloth panels.

Back to my prototype, it's a 50W stereo EL34-powered unit with regulated B+. My stepson was amazed that omething that looked so ancient could "bump" like one of those weld-busting car systems.

Comments or questions about my amp?

John

The second heater transformer powers the heaters of the regulator control and gate tubes which are elevated to a +150V DC level so their heater-to-cathode voltage specifications won't be exceeded. The main power transformer's two 6.3V windings each power the heaters for one of the amp's channels.

Here are CAD renderings of what this amp will look like when finished. Can't publish the schematic in a public forum.

(front view)

Here are CAD renderings of what this amp will look like when finished. Can't publish the schematic in a public forum.

(back view)

Thanks for sharing you amp design, very interesting indeed. Are you in Ohio? I'm in Columbus. I'm curious of your opinion on a few things that considering your background you may have insight or at the very least, an opinion. What are your thoughts on the importance of the amp's design vs the quality of parts used. Is one more important than the other? And speaking of which what are the particulars regarding the design / choice of parts in your amp?

Seeing that your approach is more on the ground level, what is your opinion of people that take an existing product and then tweak it (replacing resistors, caps, secondary OPT winding, etc...)? Does that approach a "God complex" where one feels superior (let alone qualified) to the designer in the respect of THEIR design? Kits are one thing but this amounts to using an existing component as a starter kit. I understand the upside but is that being disrespectful?

Look forward to your reply.

MikE

Dear Mike,

As to the issue of component quality versus design, I would have to say that the two are closely linked. I've never been one to use anything unusually exotic or expensive in my designs, though. I find that very good, moderately-priced OEM-grade components (like Orange Drop capacitors) are quite sufficient for audio applications. I wouldn't use the cheapest parts on the market for obvious reasons, however, a point of diminishing returns is ultimately reached in the price-versus-quality equation. For example, I read that Carver's "Silver Seven" had silver wire inside, but it had surprisingly poor B+ regulation (the 15th KT88 regulates G2 voltage, remember) because the power transformer was slightly undersized. When designing from the ground up, component selection is an integral part of the design process.
The application for the design is also an important factor in component selection. Guitar amplifier designs allow a higher tolerance for distortion than hi-fi amp designs. Most designs of guitar amps actually incorporate special circuitry designed to introduce controlled amounts of certain types of distortion into the signal path.

As to the question of new designs versus modifications on existing equipment, that's a tough question. Again, we need to consider the application. Hi-fi amplifiers are often designed to operate the output tubes in such a manner as to produce a minimum distortion at rated power output with considerable calculation to determine the circuit's parameters. Many guitar amps are based on somewhat less-critical calculations. Some improvements such as output tube balancing and bias adjustments can be a very good thing, however. It's important to have considerable knowledge of tube characteristics, circuit analysis and design before attempting circuit modifications.

John

You have much more experience on this subject. My current amp, the Moth s45 was my first SET amp and the first component I had some say so with the selection of parts. Sure I'd replaced tubes, cables, cords or footers but never any internal parts. I researched the move to SET for about 9 months and had contact with Moth off-n-on the whole time. Craig was receptive to any custom work that he felt would not adversely effect the amp's performance. All mods were cleared with him first, and relying on his experience and knowledge I presented alternatives from which to choose, asking his opinion of each. Of course, I relied on other sources as well, and based on everyone's input I ultimately decided what I felt would best suit my preferences and my system's needs.

This parts selection process lasted for a few months (remember I was completely ignorant on this subject) but only AFTER I had ordered and delivered the upgrade parts to Craig did I even consider what I was in effect doing; changing the design of the amp. I realized Craig chose the parts he did for a reason but only after working with him did I better understand why. Basically the amp was built to a price point (now $1795 factory direct) therefore the parts I chose were not even a consideration in the design stage. I OTOH was not restricted by this constraint. While I didn't go "hog wild", I chose those parts that we (Craig, myself and "my advisors") felt would have the greatest impact on the amp's performance. The Black Gate caps were not used (much debate here) because of cost and the dreaded burn-in, and re-stabilization issues surrounding them. I also didn't get the silver secondary windings on the OPT. I'd like to look into that down the road.

After all was said and done, Craig called me from his shop after the amp had burned in, and listened to, for three days and he concluded that the changes were an improvement over the stock amp; greater detail retreival and soundstage depth. But that the result was "not significant" or considering the added cost a adoption consideration. Then again, he said he was having a "hard time parting with it". Four months later I'm still tickled.


MikE

Modifications such as silver wire for transformer secondaries and/or hookup wire represent unnecessary expense in my opinion. Unless the silver wire is enclosed in an airtight environment, it will oxidize (tarnish) and lose some, perhaps most, of the advantage over copper wire's slightly-higher resistivity for which it was initially selected. A phenomenon called "skin effect" must be considered, whereby the majority of current flowing through large size solid wire flows near the wire's surface due to electrostatic forces within the wire itself. I find it hard to justify the expense of silver wire when the wire's outer surface will ultimately suffer an increase in its resistivity due to ozidation and "skin effect" will force the majority of current to flow along the oxidized surface of the wire, making it only marginally superior to copper wire if superior at all. Gold-plated connectors, however, provide the advantage of having less susceptibility to oxidation than, for example, nickel-plated connectors. Gold is also a soft metal, however, and surface wear (ultimately exposing the base metal) could become a factor where frequent unplugging and re-inserting of plugs (cable-swapping) is involved.

My background is "Engineering Technology" which is basically a blend of Engineer and Technician training. Engineers work mainly with theory, Techs get more into the practical end of things, while Engineering Technology attempts to strike a balance between the two.

Back to my prototype, it's a 50W stereo EL34-powered unit with regulated B+. My stepson was amazed that omething that looked so ancient could "bump" like one of those weld-busting car systems.

Comments or questions about my amp?

John

Hey John,
Only one question, can I see the schematic please?

pentode@netscape.com
cheers,
Douglas

jshorva65, could you repost your pics? :)