36 watter vs. Vox Night Train

[zaphod_phil]

Schematic: http://ampgarage.com/forum/viewtopic.php?t=9095

Yikes, what a mess. The preamp's not really all that close to the Trainwreck's either, apart from the general tone stack after the first stage, followed by two gain stages thing.

It's neat the way they do the PI with one triode stage, leaving three stages available for the preamp. I wonder how this might work for an 18 watt, and if we'd be getting too far away from the original's tone.

Yes you would be significantly changing the gain structure of the amp, since cathodyne PIs, unlike LTP PIs, don't provide any gain. So this would be more in PPwatt.com territory.

[conger]

Yes you would be significantly changing the gain structure of the amp, since cathodyne PIs, unlike LTP PIs, don't provide any gain. So this would be more in PPwatt.com territory.

Although as the PI is only one half of the 12AX7, usually the other half is used as a gain stage. I built an 18 Watt with 6V6's and changed the PI for a cathodyne PI and gain stage and it had more gain than the LTP PI.

However, that Night Train schematic is interesting and I wonder if there are any tricks in there that could be used in an 18 Watt?

E.g. Why is the master volume configured like that? The PI is essentially a Tweed Deluxe PI which was used in the Blues Express to dive EL84's.

Also why all the small caps on the main filter caps? Are these a PCB/production band aid or is something alse going on?

And is that a feedback network in the pre amp (R25, R28 & R38)?

[zaphod_phil]

However, that Night Train schematic is interesting and I wonder if there are any tricks in there that could be used in an 18 Watt?
E.g. Why is the master volume configured like that? Also why all the small caps on the main filter caps? Are these a PCB/production band aid or is something alse going on?

There appear to be some errors in that schematic. The MV is actually pretty normal post-PI MV, simply drawn wrong. The small caps on the filter caps is a hi-fi amp trick to help filter out high frequency noise, and in theory also help the amp respond better to high frequency transients. I'm not convinced they're all that useful in a guitar amp, but you could certainly try them in an 18W. There also seems to be some band-aid measures at the first 12AX7 grid to filter out high frequency interference.

Although as the PI is only one half of the 12AX7, usually the other half is used as a gain stage.

Yes, the gain is higher than with an LPT PI, if you use the other triode as a preamp stage before the PI, but the end result is the gain structure of a Tweed Deluxe rather than an 18W. So more of a PPwatt thing IMHO....

[conger]

So more of a PPwatt thing IMHO....

OK. I hear you. I'll spend 5 minutes on the naughty step and promise never to ask again.

[doctornorbert]

Just a thought, keeping in mind that this forum is for the Marshall 18 watt and its recognizably close relatives:

You can't really understand the human genome without comparing it to related, but sufficiently different, genomes such as chimp, macaque, and rat. In fact we understand ourselves (at the genomic level) even better when we see how different something like a yeast genome is, and yet how certain features are highly conserved. We see what some of our most important genes are in light of them being nearly identical to ones found in yeast! We also see that handful of genes that makes us unique, since they aren't found in any other organism.

So I argue that our understanding of the great 18 watt is most fully reached if we compare it to other amps, especially great PP amps such as Fenders and Voxes. And I believe that a comparative analysis of the Night Train, Tweed Deluxe, and the 18 watt (clearly in no danger of blowing up like the VJ thread) does nothing to water down our discussion of 18 watt amps - it in fact enhances it.

[zaphod_phil]

Sure, there's never been any argument when it comes to the matter of *comparing* relevant features of Marshall 18W type amps vs other ones within the context of an 18W discussion topic. However, doing detailed analyses of non Marshall-18W type amps, for their own sake, would be considered OT.

[BackwoodsJoe]

I was surprised to see that the NightTrain uses a cathodyne PI, I've heard it has a lot of headroom. I think one of the amp wiz's on this board should rebuild this amp and share the schematic with everyone (me). This is how it should be.
A genuine Marshall style 18 watt combo cabinet but 2 inches deeper
B. genuine Marshall 18 watt iron, PT & OT
C. genuine marshall style power supply (EZ81 Recto)
D. main schematic principles of the NightTrain
E. Throw in a VOX AC 15 style choke to smooth it out a little more

Please post ASAP!
THX Joe

[zaphod_phil]

I was surprised to see that the NightTrain uses a cathodyne PI, I've heard it has a lot of headroom. I think one of the amp wiz's on this board should rebuild this amp and share the schematic with everyone (me). This is how it should be.
A genuine Marshall style 18 watt combo cabinet but 2 inches deeper
B. genuine Marshall 18 watt iron, PT & OT
C. genuine marshall style power supply (EZ81 Recto)
D. main schematic principles of the NightTrain
E. Throw in a VOX AC 15 style choke to smooth it out a little more

Please post ASAP!
THX Joe

That kind of an amp would be kosher on PPwatt.com, not here. Even if built with 18W style transformers, since the Night Train has none of the Marshall 18W architecture. Now if you wanted to builk an 18W Trex, that would be a different matter, and IMO it would blow away any Night Train. Just check out the Trex sound clips http://www.18watt.com/modules.php?name= ... &p=RICHAMP

[doctornorbert]

Holy crap the guitar sounds doubled on some of those takes! Probably just a room thing, or some echo applied on the recording.

Richie is a sick (frighteningly good) guitar player. To me, this always has a big influence on how an amp sounds...

I think a 36W 'Wreck needs to be my next build...

BTW ampgarage is a good place to discuss Trainwreck-inspired amps, in terms of there actually being some discussion there, not just in terms of it not being 18watt.com. They also have a thread or two going on the Night Train.

[zaphod_phil]

IMO it's a real shame how they bastardized the TW preamp in the Night Train. So that's another reason I think I prefer Richie's Trex, apart from the fact it's still a genuine 18W, complete with 18W Normal channel.

BTW ampgarage is a good place to discuss Trainwreck-inspired amps....

Yes, because it is the main meeting point of many TW builders. So that makes a lot of sense. Same as 18watt.com is for Marshall 18W builders.

And yes, Richie is a awesome player!

[manic]

Found some internal pictures here


http://media.photobucket.com/image/vox+ ... x_nt_1.jpg

There is a lot of .1uF capacitors in the Night Train. Actually there are alot of capacitors full stop in that amp.

Actually they are .001's but whos counting.


I know its practiced in some circles to bypass PS with .1's, which is probably why You said .1? Its practiced in the Hi-fi world more than in guitar amps, as ZF stated.

That said why did they use .001's ?

respectfully C. Smith

[doctornorbert]

This actually is being discussed at ppwatt.com.

[doctornorbert]

BTW, I played a NT the other day, and it's a fun little amp, for sure, but an 18 watt whoops its ass.