Colossal wrote:Great to hear you got it sorted out Taylor. Which OT primary did you end up using for four triodes (2 6SN7s)?
Dave is there more than one primary on this OT? I have the one from Chappelle amps, as you probably remember. I know he made one with dual taps, but I don't think this is it.
Then that would be the OT you got from me and it is 22.5k (single pair of primaries). That's one of Cliff's custom OTs as well.
I used 2R resistors for the bias points to account for the paralleled tubes, and I have the NFB loop coming off the 16 ohm tap vs the 8 ohm tap. Is there anything else I can do?
Nah, probably no right or wrong...only what sounds good to you.
amplifiednation wrote:Turns out I had my plate wires switched from V1a and V1b so essentially I had taken the entire tone stack/volume/gain stage out of the circuit.
So I was having a lot of hum with the amp...I wasn't sure what it was, but I had a lot of wires criss-crossing because of the parralleled tubes, and my not-so-nifty idea of hiding my tube leads just didn't seem to be working out.
Yesterday I ripped out all of that really bulky PVC pre-tinned wire from mojo I had used. Man, I do NOT like that wire. I'm sure it's good in some instances, but it's really bulky, melts so easily and I don't even like the way it looks.
I replaced all the wire with the solid core AWG I bought for my Express build...the amp is DEAD QUIET!! Very cool...it even sounds better. I'm very happy with the changes.
edit, added before/after pic
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Last edited by amplifiednation on Mon Jan 23, 2012 2:08 pm, edited 2 times in total.
awesome man. Did you listen in stages during the rewiring to see what made a difference? I am wondering, the biggest change I see in layout was the grid lead into the PI (light blue wire) used to run with the heaters and other leads and now it is run under the board against the chassis away from stuff. Longer but separated.
surfsup wrote:awesome man. Did you listen in stages during the rewiring to see what made a difference? I am wondering, the biggest change I see in layout was the grid lead into the PI (light blue wire) used to run with the heaters and other leads and now it is run under the board against the chassis away from stuff. Longer but separated.
No I didn't, but I have a feeling that the hum was coming from those leads being bunched together - exactly what you noticed. I also had jumpers going across the sockets of the power tubes, the wires were literally touching.
Omited R2 from the circuit, I have a 9H choke, so I don't need a choke resistor!! Not sure why I didn't realize that before. That brought my operating volts up to where they should be.
Also, pulled the DC filament elevation lead entirely, the artificial CT has the amp running dead quiet
Les Paul -> 440 Spider Amp -> EVM12 -> SM57 -> Computer
I added a tad of reverb to warm it up a little. The bass could be tighter, but i'm not sure if that's the speaker or not
Main does this thing cook for 3.5 watts!!
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amplifiednation wrote:The bass could be tighter, but i'm not sure if that's the speaker or not
If you want, try reducing the value of the coupling cap(s) before V2a - Looks like you have the 2n2 poly in parallel with the 1n0 ceramic. I just took the ceramic out and it tightened up the bass. (Maybe I should try 1n0 ceramic in parallel with 1n0 poly sometime). I eventually went further and changed the treble pot for 250k which killed a bit more bass and made the tone controls much more responsive IMHO. (Note I've chopped the Ax84 PI design around a bit, which may have a bearing on the relevance of these comments).
Hi,
I built sucsessfully a mini Express with PP 12AU7. Sounds great.
I´ve the Hammond 125E in and wired it at primary to around 8k. Sounds good, but what would be the right Raa for this tube? 22k? Is´nt this too much?
Its a Kathodyn PI, 470 Ohm on the common Kathode and I have there 11,4 VDC above this Rk. On the plate 316 V.
The Amp is death quiet. When I fired him up ( no Input) I heard nothing. I thought I made a mistake and switched off. This moment I heard a "plopp", so I switched on, guitar in the input and BANG, here it was.
I never thought a Trainwreck can be so noisless. When the git. is on but I dont play - I m afraid, there is something wrong. No Hum, no hiss, nothing, only pure guitar sound. I put it in a small cab with 2x8" speakers to be independant, but on the 1x12" or 2x12" its an absolut adoult amp.
Beautifult tone, late brake up and this is also very nice.
The only extra switch is in the tone stack where I can change the treble cup between 120p and 500p. There could be a 3 way Slope/Trebe Cup switch interesting. But more this circuit dont needs.
Never the less there is only a 12AU in the power amp its very loud on a 1x12". But very fine to clear up by guitar vol.
In this box you see below its in. Its an old picture, therfore you dont see the Express in.
Best
Hans-Jörg
Last edited by hans-jörg on Wed Feb 01, 2012 11:50 am, edited 2 times in total.
So i have a question about the 4-4-0. I've always thought that the big honking resistor between the B+ and screen supply had a lot to do with the compression characteristics of the Wreck. This is obviously missing on the 4-4-0. I've also always found the bass response on low wattage amps to be lacking.
For someone who has built both, can you describe the differences?
LeftyStrat wrote:So i have a question about the 4-4-0. I've always thought that the big honking resistor between the B+ and screen supply had a lot to do with the compression characteristics of the Wreck. This is obviously missing on the 4-4-0. I've also always found the bass response on low wattage amps to be lacking.
For someone who has built both, can you describe the differences?
The amp has very similar sounds to the express. I took the 1k choke resistor out and put a choke in instead. There is a ton of gain on tap, the volume control is more of a 'gain' control. There isn't a clean bone in its body.
I actually hear fuller frequencies with the 440 although the bass is a little flubby, the Express was much tighter and brighter, and in your face!! The 440 is cool but it just can't push the air a bigger amp can. I built it to jam at home and its great for that. My Express was just blowing the doors off the house. The harmonics aren't as good as the Express either, but it gets in the tone zone.
Great amp though, this is the second one I built. I changed the power section a bit from the schematic and really improved the tone from the first build. I also think adding paralleled triodes in the power section really beefed up the tone.
I almost have the matching 1x12 built...this thing is cool. That is "hammered red" tolex with inlay beading and the 1x12 has a recessed 4x12 side handle in the top of it. Selloutrr faceplate (the coolest!) I'm trying to figure out the best port size for the back panel.
amplifiednation wrote:
... I actually hear fuller frequencies with the 440 although the bass is a little flubby...
As I mentioned above, try reducing the combined value of C14 a & b (the coupling cap between the 2nd and 3rd stages).
'Stock' Express has 2n0 here, the 4-4-0 has a combination of 2 caps making up 3n2. Taking this cap down to 2n2 total clears up the flubb without losing the fullness - I think it could go even lower.
I agree with the lack of clean, which is why I ended up going my own way with a split load PI
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