Calling all Valve Jr Modders.. help!

[Leonidas]

Hey guys, I finally got around to picking up a valve Junior. Been wanting to get one of these for a long while! I ended up buying it on eBay, and it has several mods already done to it. Sounds pretty darn good, but haven't had enough time to mess with it (holy crap is it loud!).

Anyway, here's my question for all you modders out there. I asked the guy I bought it from exactly what mods were done, and he laid them out for me, but I have no idea how they translate into change in tone! Anyone who wants to tell me what these mods did.. I'm really interested!

Mods are:
1) R1 was removed so more input signal would hit V1.
2) A 1meg resistor was added in front of R2 to ground to raise the input impedance. Better tone (IMHO)
3) Both preamp cathode resistors and caps were changed to 1500 ohm and 3.3uF, respectively. Less mush, better clarity and tone. (IMHO)
4) R6 changed to 100k ohm and R7 changed to 50k. Better chime and tone. (IMHO)
5) C1 and C2 replaced with better sounding caps (IMHO)
6) Toggle switch was added so you can select between 4 ohm or 8 ohm output at the speaker jack.
7) Output jack was replaced with higher quality piece.

I understand 6 and 7, obviously. But how exactly does 1-5 affect the final tone??

Thanks guys!

 

[Big K]

Sounds like a job for the one the only DVM....

 

[duhvoodooman]

Looks like the previous owner did some very nicely thought out & beneficial mods. First of all, it looks pretty evident that this must be a "version 2" VJr, because he doesn't mention a thing about fixing hum, which is pretty much the first thing everybody went after on the original version of the VJr. The redesign (all VJr's made from Jan. '06 on) addressed this issue, using the design improvements that had already been incorporated into the head version that came out in late 2005.

The 1-5 mods are to increase the overall amp gain (#1) and to "lift" the tone to give more/better sounding top end (#2-5). Other than the original hum problems, the main criticism of the VJr is that its tone is overly dark and a bit muddy in the bass, and lacking brightness and the liveliness that a good top end gives to the sound. This is what the comments like "less mush, better clarity" and "better chime" are referring to. The various resistor and capacitor changes (those R's and C's) are aimed at giving the amp a better overall tonal balance and lessening the design's intrinsically dark sound. #5 is one that's debatable as to its real benefit ("better" capacitors often times have no discernible effect on tone, according to several sources I've read; depends on where they are in the signal chain), but it certainly can't hurt.

 

[Leonidas]

Thanks, DVM! Your assumption is correct that this is a version 2 VJr (no hum, stripes at top), should have mentioned that..

Did some research, and I ended up tearing this little guy apart and looking at the circuit board, which allowed me to see exactly what was being referred to as R1, R2, etc. Very simple doings in there. Cool!

mod 1 - so this simply allows more signal to hit the first tube, since less is being bled to ground and mod 2, 3, 4 - improved brightness

I've been playing around with it a bit. Man is this amp loud. haha had no idea it would be quite this loud being rated at only 5 watts. So far I've only played it with my agile LP clone. I especially like it at the lower volumes (just before breakup). Nice warm tube tone. And it's REALLY dynamic to your picking attack, which is awesome.

The only thing i'm not so sure about yet, is when i start cranking the volume up, it seems like it gets kinda harsh, in that the highs really start to scream. Makes me wonder about them "top end" mods. But I'm also not used to playing that loud in my bedroom haha.. so its hard to tell if its just the volume or if its actually the tone being too bright.

 

[duhvoodooman]

Yeah, I agree--the VJr is impressively loud, given its size and 5W rating, but I guess it just goes to show once again that tube amp wattage ratings can be very deceiving. Plus, of course, wattage and volume are not linearly related. To double the volume of a 5W amp (other things being equal) will take 30 - 50W of power! So I guess it's not surprising that a 5 watter can shake the walls in a bedroom!