Sniffyduke, yes I built the Zwreck very nice amp I like my tele through it, the LP really punches through.
Ryan (KT66) a TAG member posted this nice layout and schematic which would get the job done Michael.
Mark
Oh thanks Mark. Is that Close?
you can use that layout but add in the 220k summing resistors like in a normal layout, ground the one that would have come from the normal ch., hang a 47k resistor to ground off the front of the reverb channel 220k summer (where it meets the .1uf from the previous stage), and that's it. i believe the top of the p.i. tail may be 100ohms instead of 47 ohms. leaving out the trem load makes it a louder, more broken up amp----hence the idea about making it switchable. i've got some gut pics somewhere.
here's a couple. you can also see he's added the tone control to the reverb (from dave funk's book) and the big parallel/switchable treble cap for the whopping mid boost (ala diaz and others). rh
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Whose in for the x10 build? I'm getting parts all sourced up. Edcor stuff looks good but not sure if I want to wait 4 weeks for my pt...maybe I will just put it in last. Ordering all mf resistors, sozo caps, not sure about the filter caps but I can get the TADs dirt cheap spragues too. Good times can't wait to get started. I think this amp is gonna be a cool one
Anyone have an idea on the wiring for the led circuit in this amp?
I use leds on my builds a bit, and have recently been trying to get them to dim slowly on shutdown.
I see Michael has been looking at this idea too, that .47 200V cap next to the cathode R/C is connected to the hot side of the led by the look. Im assuming the led side of that cap is connected under the turret to the power source.
What i read on these lamps is that a cap by itself does bugger all without a resistor in series to ground with it, basically in series with the led, then the cathode grounds via its current limiting resistor.
Ive been having trouble making it work well, but i think its cos i didnt have enough current in the first place. hmm
You want the LED to dim slowly? When you build the amp, put the anode to the hot side and the cathode into a resistor going to ground (I think I got that right, damn diodes!). In parallel with the resistor, put in a large electrolytic cap, minus side to ground. I'd say a good start for a long decay is in the 470uF range for a pretty small current limiting resistor (a 4.7k resistor and a 470uF cap is only ~0.5 seconds before it's not making light anymore, a 4700uF cap makes this 5 seconds). Formula is just 1/(RC) which gives you the time constant in seconds.
Im taking a pair of diodes off of the heaters, so rectified should be 4-4.4V there abouts. The led drops about 2V, and needs about 50ma or so, roughly.
Calc says 47R. Now thats all good, works cool. And i think prolly doesnt need the dual taps at all, could run one side of the heaters at a bit over 3V and use around 22R instead.
I was dicking around with this the other night, and tried a 330uf cap, all i had, that and the 22R made things too damn fast. I tried a higher resistor, and that slowed it heaps, but also limited the current to where the light was dropping out like Tom Hanks piss in the green mile.
So i guess i need a higher voltage to start with to get a higher resistor value and slowthings back?
I'm already receiving stuff. I did order two 400v solens to use instead of the bigger 630v. They are the last two in the chain and rated at 250vac so they should be plenty.
I just need the iron, circuitboard, and turrets/eyelets and i'm ready to build.
surfsup wrote:I'm already receiving stuff. I did order two 400v solens to use instead of the bigger 630v. They are the last two in the chain and rated at 250vac so they should be plenty.
I just need the iron, circuitboard, and turrets/eyelets and i'm ready to build.
I'm ordering up everything now. I have chassis on the way (thanks V). How are we all feeling about the schematic? Do you think we've got a good handle on the amp? It looks good to me with the exception of a couple unknown values.
What about the dropping resistor from B1 to B2...does 1k 10watt work? ANd then the Fixed cut circuit...120k and the .0047cap? Everything else looks like it's pretty well sorted out.
Let me know what you guys think I'm about to pull the trigger...gonna try to build two of these at once.
Had a look at these newly emerged pics from Fat sounds root dir. Looking at the master volume, i cant tell for sure, but the resistors on the MV are definitely not 2M2. They appear to my eyes to be 1megs. Looks like brown black black, im guessing its brown black green. If they are 1megs, and its a 1meg pot, then thats 500K, over the 220K gives about 150K grid leak value.
I just wish someone could confirm the pots values. Theres been so many little tweaks to this amp from the one we heard and fell in love with, when Greg V played the demos. Wonder why the changes, and more importantly, is if its as sweet...
***EDIT: SCHEMATIC REVISED AND MOVED TO PAGE 16***
Here is an updated schematic which I'm calling version 2 to reflect the design changes in the latest gut shots. Changes which Azatplayer pointed out include:
1) The removal of the 470k/470k voltage divider between V1a and V1b.
2) The removal of the 56k grid leak resistor (no longer visible in the v2 photo on the valve socket).
3) Changed the PI output coupling caps to 0.022uF from 0.047uF.
4) Addition of what is presumably an 0.1uF orange drop cap across the output tube cathode resistor and bypass cap. This mod is noted in 18W circles and is used to add a bit of sparkle back to the power amp [if this is indeed what this cap is being used for...].
5) Changed Master Volume pot and paralleled resistors to 1M respectively to agree with the idea that the sum grid leak value is 150k/150k.
6) Added the most current gut shot to the bottom of the schematic for reference.
Unknown/unconfirmed part values are still shown in red. If anyone sees anything they disagree with or have comments on, please post and I will revise the drawing. Please adjust your BOMs accordingly.
Thanks.
Last edited by Colossal on Sat Apr 16, 2011 12:35 pm, edited 1 time in total.
The 12AU7 Dave
Oh and that cap by the power tubes cathode R/C is a .47uf OD. It has a wire coming from the led lamp to the front side of it. I was wondering if it had something to do with a fading circuit for the lamp?
Love your work Dave!
