Ty_Bower wrote:This topic was discussed last fall. The thread can be found here:
http://www.diyaudio.com/forums/showthre ... did=131829I offered some of my guesses regarding what is going on in the RM-10. Others pointed out why my theories don't hold up. I do not believe any significant conclusions were drawn. No one has offered any schematics or exact details of the operating points. I suppose someone will need to buy one of the darn things and dissect it to find the answers. I was curious enough to write to Roger and ask a few questions. His response was prompt, polite, and intelligent. He suggested I might be able to purchase a transformer set and schematic from him, but I was not inclined to pay the asking price.
Another one of the many unexplained mysteries of the universe... :?
FYI, Roger posted an explanation of how the amplifier achieves its rated output. Read his post here:
http://www.audioasylum.com/audio/tubes/ ... 61139.html
Thanks for the link. That was so long ago I had forgotten. I'd say the cat has been out of the bag since then. Here's the information that is important to the application taken from the link at the bottom of the link Ty kindly posted.
Let me go through the numbers and tell you how I get more than the specified 35 watts. Actually at the plates of the tubes, where all the tube manuals (bibles) take the data, I am getting about 45 watts. Some of you have misquoted the bias, dissipation and done some poor math, so sharpen your pencils. First the bias is indeed 30 ma. but for the pair of tubes and measured across 10 ohms, hense the 300 mV set point. Though 25 ma will double the tube life, (under light loading or soft playing) it will increase the distortion. Since the tubes are cheap, I let people decide for themselves. At the 700V B+ (yes, 700) the idle dissipation is 21 watts/pair or 10.5 per tube, well within the 12 watt rating. The screens run at 350 V and very cool, further enhansing the tube life. (The opposite of many designs like David Manley and early CJ). It's not the plates that mind the HV, it's the screens.
The only thing missing from the above to make it a complete application is the following. Load: 13,000 ohms PP, max signal current: 100 mA. Fixed bias: -25V (varies widely with tube maker, something that affects the sound of all those cathode biased EL-84 amps).
This is
not a cathode biased amp so stop comparing it to cathode biased amps which make up 99% of the EL-84 amps out there. The main application of the EL-84 was single ended and push-pull amps in phono/radio consoles. The cathode bias and low plate voltages made the circuit simple and the TV Repairman didn't have to adjust anything, just replace the burned-up tubes. So why are we
guilding the lilly of circuits used by Magnavox, Zenith, Motorola and Dynaco when the tube is capable of much more.
If there is enough interest I will look into the pricing of a transformer set or a kit. If I got orders for 100 kits I would do it. Otherwise it takes less time to build one than to kit-up the parts for any fewer. For those who like exotic parts; the hand-wired chassis has plenty of room and substitution is very easy. Gain/damping setting is also easily done.
I love to make things for myself and a great deal of my test equipment is self-made because I sometimes need is not made. I recall something a professor at U of VA told me when I said I like to make my own stuff "If someone manufactures what you need it's less expensive to buy it than make it yourself". To make that statement a bit more appealing I will offer, for a limited time, brand new, fully warranted RM-10 MKII's to this forum at a $500+ discount making the price $1,450 shipping included (that's the +).
http://www.ramlabs-musicreference.com/rm10mk2.html. Also see the design philosophy section listed on the home page.