mcrracer wrote:Hey RJ
This looks very interesting We may very well end up with several different workable takes on a DLM type amp. Without verification from an actual owner we just have to build until we are happy with the result.. B+1...should it really be before the standby switch? Exxcuse my question but I just don't understand this part. Also what do you think about it having a NFB control? If so should it come in on pin 8 of V1a? Do you have estimates of what you think the B+ voltages should be? I am sure your design skills far outpace mine so please excuse my noob type questions. Thanks for starting the ball rolling.
If I had drawn it right the B+ would be on the other side of the standby switch , the same as the Trainwreck Rocket. Schematic is now updated to reflect this correctly. This allows for those first two caps to charge up by themselves and not hammer the GZ34 rectifier with all the filter caps charging at at once... kinda like what Ron had mentioned.... good catch and it's fixed now.
I haven't gotten as far as NFB but I'm sure we need to experiment with it at the very least...
The correct B+ voltages for a DLM? I can only guess. There are claims that you can get from 8-12 watts out of this amp so that gives us a clue. KF seemed to prefer moderate B+ voltages in his other builds so that will flavor my guess as well. What power transformer voltages would make sense? My guess is not less than 235V and not more than 300V. Those are transformer voltages but I know everybody can sort out the approximate B+ from that. How's that for non committal. I threw in a somewhat random value on my schematic because I happen to have a 280-0-280 custom wound transformer from Edcor and I'm thinking that is a good middle of the road starting place.
Speaking of transformers, one other feature common to most Trainwreck amps was the use of heavy iron. That flavored my choice of the 25 watt output tranny as well as the 250mA power tranny. I'm not familiar with a lot of hefty Single ended output trannies and I read something somewhere about a prototype SE wreck that used a PP output tranny with the center tap lifted.... it's more guess work and speculation than fact until the official answers make their way to us.
I would try to avoid splitting up the tubes for the cathode follower, it is a much cleaner build if it is on one tube. So, how about removing the stage that is now marked V2b? the wiper of the treble pot could go either to a voltage divider or a 250K pot and then feed the grid of V3. Then, for a presence control, a 47K to 100K resistor to the 820 ohm cathode resistor of the cathode follower. This makes the NFB. For the Presence a .1uf cap to a 5k pot to ground.
If it was left as a plexi style circuit with the one gain stage before the CF, I would do a simple resistance divider from the treble to V3. A 220k to ground and whatever value is needed on the top side.
If two gain stages were before the CF, such as a 2204 style circuit, then I would probably put a master volume (250K) from the treble to V3.
Also, maybe a bleeder resistor from C18/C19 to ground so that the caps don't charge to a high voltage when in standby?
From looking at Wreckboy's photo, it appears to have 2 inputs, 6 knobs (guessing that it's VTMB Pres. MV). There is no standby switch on the front panel, but it may be on back? Or not have one at all.
I nearly snagged one of these a year or so ago but just missed it.
It has a sweepable mid control (sweep and mid), bass, treble, volume and slope.
If this DLM preamp does indeed resemble a JCM800 then the sweepable mid may have been left out to get the gain up and the master and presence controls added back in.
It may be some food for thought at least as an alternative JCM800-style preamp.
There's no documentation in English, but my first built was a 12 W SE (TT66, documented on tubetown.de) amp with a toroidal 2x300V and the Hammond 125 ESE. Auto/cathode bias. If you use the larger tubes (6550) at higher voltages (400+) you might prefer even a bigger output iron. 125 ESE is larger than Fenders 35 W PP OT iirc. Some use 125 FSE.
The schematic is like a CHAMP. Just for fun I've put a cascode (see firefly AX84) in front of it.
Not a Dumble, not a Plexi, just different. Similar to pentode front ends. Gain enuff.
Just if in case you like your CHAMP on the slightly FATTER side.
Ciao
Martin
PS: my latest built: Princeton derivative "der kleine TonPrinz", not documented here, see tubetown.de or ask me w. 15" Eminence and solid mahogany cabinet.
Looks like I'm not only into the skinny ones...
My production amp, the Absinthe is parallel singled ended octals, but I have been using EL34s. I need to try some other tubes in it just to see how they sound. The OT is good 35-40W SE, so it can handle just about anything.
It's an interesting amp for sure, and really sounds mean.
Hey Dart, can you tell us what iron you are using? It may have an application here. I for one am not stuck on using a PP tranny for my SE build. Thanks
I use a SE 35 watt ot in the Beast II.. I think Dana has the numbers on it,or i can look and see if i can find the info.. made by heyboer.
The Beast II runs a 5979 preamp,and a 12ax7 channel,which also the 5879 feeds into the 12AX7.. dual octals,with option of flipping one out with a switch..
We are already hitting the third page of the thread and many are starting to iterate on previous posts. I am getting a lil' frustrated by the good intentions that seem to be swamping the forward motion.
Forward - in all directions!
What kind of iron would we need for a 100w SE amp? Anyone got some spare arc welder parts?
For output iron, I'd use a Fender Deluxe Reverb OT with the center tap lifted. If sourcing new SE iron, I'd go with iron rated at 15 watts or greater.[/quote]
Zippy or anyone who can answer...Ok on using a PP OT lift ct BUT how do we figure or know what our primary impedance is when using PP trannies. They are quite a bit cheaper over using SE OT iron of similar wattage.? Do you think KF tried a PP OT in a SE design because he just happened to have one handy? From what I have read he seemed to be very good at using what he had available.
w. 15" Eminence and solid mahogany cabinet. 
