night train mods...

[waznew]

hi guys..
so i've been asked to mod one of these vox night trains. the customer wants a bit more of a cleaner fenderish vibe.
i found a schematic..and figured out on paper quite a few changes to clean her up a bit. i'm also going to install a choke.. i've attached the schematic.. my question is.. on the output of the p/s there are two sets of 0.1 caps in series with a 470k to ground...could i just replace this with a single .047? my thinking is.. i'll be pulling back the gain in the preamp..so a stronger signal to the output grids might be better. and also it will help with actually physically fitting caps. the .1's in there are small.. way smaller than the size of say a .022 sozo.. so having one cap rather than 2 will help with fitting better grade components in the amp.
what do you think? am i missing the point of the existing arrangement.

Vox NT15.pdf

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[waznew]

well.. after the overwhelming response... .. i've decided to just do it and listen to the difference.
is anyone here interested in mods on these amps? if so i'll post my findings and possibly some sound clips.

[bluesbreaking]

I'd be interested in hearing your results.

[JimiJames]

This is a kool head for sure. A friend of mine installed a Metro-Zero-Loss FX Loop Kit
with good results. Like to do that for the one I have here. It definitely can use one.

(BTW-We also A/B'd speakers/cabs. A 4x12 Jimi bottom w/G12C's, 4x12 Marshall w/BB's, 2x12 Celestion Golds, Suhr 1x12 Gold. 1x12 Boogie w/Vintage 60, and a 2x12 Boogie w/75's which ended up being the best match sound wise.
Go figure... my least fav.) *scratches head*

[waznew]

i've already clipped the 47p bright cap on the bright channel... helped to take away that icepick top end.
i'll post some clips next week hopefully.. i'm going to do it in stages.. first with a choke, the output caps..then with sozo cap upgrade.
we use the head with a vox ac30h 2x12 cab with 2 blue bulldogs. sounds great. at home i plug into my old late sixties greenback quad. have you tried it with the matching vox cab...with the greenback... yuk! horrible sounding box.
will have to dig up a box with 75's and try it.
and the fx loop is a great idea. those metro zero loss loops are gold! i've used quite a few of them.. i don't think i'll ever build a tube loop again.

[waznew]

ok, i've done a little more work on the amp..
i've recorded some clips.. but ive got to edit them.. so they might be a while.
the stock recorded tone is quite good..pokes out nice in a mix..but theres no body to it. basically, i want to keep that mid poke..clean up the top end..make it not so fizzy.. and add more low end.
the mods i've done so far are..
1.. clip the 47p cap on the bright switch.. removed the icepick highs.
2. installed a choke. i had a 4h fender choke lying around so i installed that in place of R1. the choke made it feel a little nicer. the top end distorts better.. not so cheesy...
3. replaced the caps in my original post. i kinda knew that the .1-470k to ground-.1uf arrangement was attenuating a bit of top end.. i re-read George's rc calculating time constants topic..
well i put the .047's in there(removed the 4 .1ufs and the 2 470k's).. signal was better,and as expected there was a lot more top end. i decided to leave it as the top end sat with other changes in the preamp.
i later replaced the .047uf's with .1's. the night train cab is quite thin.. and the .1's fatten it up nicely.
4. replaced the .022's in the tonestack and the following .002 ceramic cap with regular .022uf sozo's. pretty standard stuff.. drive is much thicker.. its starting to sound a like a real amp now.
now i'm messin around with cathode caps in the preamp, mucking around with voicing the pre.

i've got another stock one here so i can compare.. i've left the stock sovteks in there..for comparison.. i'll be changing them next..there is a massive difference in the way the amp responds.. it sounds bigger, way more fun to play. these aren't my final mods.. still a work in progress.
i'll post clips when i get some time...

[robert]

Hi waznew,

this sounds very intersting to me!

Can You draw a schematic for the Metro- guys after You've finished Your work, please?

Thanks in advance.

Regards

Robert

[jjjimi84]

Any chance for a layout on some of these mods, im thinking about picking up one and have the effects loop kit lying around here. I've been going to guitar center weekly to play this thing so I think i am ready to take the plunge.

[Rs16iandy]

Hi really interested in the mods you have done. When you say clipped the cap do you mean removed it?
If you could let me know the bumpers of components changed that would be great.
There is a useful scematic on the mercury magnetics web site
cheers Andy

[Rs16iandy]

Hi really interested in the mods you have done. When you say clipped the cap do you mean removed it?
If you could let me know the bumpers of components changed that would be great.
There is a useful scematic on the mercury magnetics web site
cheers Andy

[Rs16iandy]

very intrested in your mods can I have some more info. When you say clipped the cap do you mean removed it ?
There's a good scematic on the mercury magnetics web site
Cheers andy

[waznew]

hey guys,
sorry i forgot about this post.
andy: yep, you cut it out. you can do this quite easily, without removing the board.
i'd suggest you just cut one leg.. leaving enough of the leg to solder back together, in case you prefer the sound of the cap in place.
c27 is a 47pf cap. it only effects the bright setting. that switch connects it across the gain pot.
i usually use these with celestion blue alnico's and greenbacks. i find the top end sounds fake with this cap in place.

change out the tubes too. i like the EH el84's and the JJ's. in mine ive got jj's at the moment. el84's are cheap..so you can experiment. i always keep a varied stock of tubes. see whats right for you and your amp... its cathode biased..so you can swap them with out setting bias.
also pre tubes...usually i go a NOS 12ax7 for 1st pre and a something like a mullard or tungsol RI for second. but play around and see what you like

these are the changes that i do to all night trains i see. All have been happy with those changes....

if you are a novice..id say stop right there. the board on these can be a pain in the ass to work on. especially if you are trying out different cap combinations. the stock caps are quite small and replacements like sozo's&OD's should be installed by someone who knows what they are doing.

if you do know what your doing, upgrade the signal caps and install a choke. one of those small fender replacements will do fine.
have fun..

[Rs16iandy]

Hi thanks with that I will give it a go. I have already replaced the el84s with jj's and the 12ax7s v3 with a Mullard at7 and v4 with a tung sol 12ax7 and made a good improvement. I have just ordered a pair of Mullard el84s and will ad a choke in the new year. I have changed caps 21 and 7 for 22 uf and sorted the low end out .
I have a pair of .022 od caps for the tone stack should help to thicken it up a little more.
What else would you recomend and what is involved in fitting a choke?
Cheers Andy

[Rs16iandy]

I ment to say I have an celestion blue and a gold which will be going in a 2x12 open back pine cab when I build it after Christmas. My main guitar is a strat and it sound far to bright with the nt.
Cheers Andy

[Rs16iandy]

These are the mods I'm considering

1. change R9, R11, R26, to 100K 0.5W carbon comp
2. change C22, C31, C32, to 0.022uF/630V Mallory
3. change C29 to 250pF/500V silver mica
4. change C10, C16, C26, to 0.1uF/630V Mallory
5. remove and link (jumper) C15, C30
6. change R4 to 130R 5W wirewound
7. change R7, R8, to 100R 3W metal oxide
8. change R2, R7, to 470R 3W metal oxide

Also, output transformer should be 8K plate to plate for max power output.