Here is to reviving an old Thread..... :-\

I finally got my grubby mits on the VC-30 to see what I can do. First off, here are a few things I noticed when I stripped the chassis out of the Cabinet.
1. No Choke and SS rectification.
2. V1a has a 47uF (C50) Cathode bypass capacitor across a 1k5 Resistor - V1A has a fair bit of gain.... :-\ :-\
3. V1b has a 330K resistor in series with a 220K on the output of V1b as a potential divider. There is a 100p Cap (C41) in Parallel with the 330k - Fixed Top Boost cct on the Clean Channel

So I did the following Mods:
1. Dropped the 47Uf Cathode Bypass down to 1Uf to dial out some of the gain in V1a.
2. Removed the 100pf Top-Boost Cap at the output of V1b

BTW.....working with double sided PC boards in a Tube amp really sux......total pain to change or remove components... > >...Snot Fun at All.... > >

Powered up for a test.......Clean Channel lots more manageable in terms of Gain.....Amp only starts to break up at 8-9 out of 10.......nice control now instead of breakup at 4.....
Amp still has lots of highs but some of the glassiness has now gone. Bass control has lots more tonal range than before....Good so far......

SNAG......!!!!
Switched to the OD channel and all went papper than soggy toilet paper......all the overdrive was virtually gone.....the amp obviously required the gain of V1a to drive the OD channel properly......Hmmmmm....back to the schematic........
Further inspection revealed that:
1. The cathode bypass cap in V2a and V2b is only 1uF each (C3 & C5)....not much real gain there.....
2. Voltage divider between V2a and V2b....2 x 470K resistors......Level suck there....Although probably only about 3dB
3. No Grid Stopper Resistors on the grids of V2a or V2b

So...What I did was......
1. Replaced V2a Cathode bypass with a 10uF Cap to up the gain
2. Dropped the first 470K resistor to 10K to increase the signal voltage to V2b.

Put it all back together to find the amp go into oscillation when the drive was turned up......Forgot to put in Grid Stoppers......Take the amp apart again..... >
Fitted Grid Stoppers (10K...probably a bit low in value but was all I had) to both V2a and V2b....Reassembled amp and tested.......Still oscillation...... ? ......
After some head scratching.......wait, maybe that voltage divider between V2a and V2b is there for a reason...... :-\ :-\.....Reverted back to the 470k Resistor again......reassemble.....Test...oscillation gone and much better OD.....can push the drive to 10 without any instability.....Lot more and bigger distortion than before the mods.....

In Summary

Clean Channel is much more usable....Fuller cleans with less glassiness to the tone.....Tonetsack seems to be generally more responsive......
OD channel has more gain than before with V2a driving much harder and breaking up nicely......


Cost....Parts no more than a couple of rand......Experience Gained....priceless......


BTW...all the pre and power tubes are Sovtek...Looking at chucking a couple of JJ's to hopefully warm things up a little more......

Oh how I love these threads.... I feel like going into complete nerdynessness

Cool thread and great info. almost makes me wish i hadn't sold my VC100 ?

Styles wrote: Cool thread and great info. almost makes me wish i hadn't sold my VC100 ?

? Thanks Styles. Cool thread Tom - lots learned.

We're going to use the amp at band practice tonight to see how the changes worked out.....

I'll post and update to let you all know how it went....

TomCat wrote: We're going to use the amp at band practice tonight to see how the changes worked out.....

I'll post and update to let you all know how it went....

Update....

Ran the VC-30 on stage tonight and definitely a difference in tone......Glassiness is almot gone with the cleans almost Fender like now..... 8) 8)

The amp just sounded Bigger without it getting too loud.....Also picking dynamics seems to come through a lot more......

The general feeling was that the amp was a lot more playable and sounded better.......so I'm chuffed......

OD channel was also nice and grainy....although not as sweet at the Twin Tube Classic hooked onto the amp...That just sounded unbelievable..... :dance: :dance:


Mission accomplished....... 8) 8)

Hey Tom, quite interested to know why you didn't touch your tonestack

Nicholas L wrote: Hey Tom, quite interested to know why you didn't touch your tonestack

That was to have been my next port of call but we felt that the work done had done enough to improve the amp's tone and working with a double sided board is a pain in the proverbial whatsit.... >.... so I felt enough is enough....... ? ?

However....who is to say I might not revisit sometime in the near future...... :-\ :-\

PCBs are more trouble modding than P2P / turret boards. I can only imagine what it is like modding double sided boards, eish.

Hey Tomcat,

I just made the same mod as you did and guess what? What you have mod was simple turning off the bright switch (which the amp already has). Removing the cap C7 (you said C41) but it is C7 does not affect the tone controls and its range at all, mantains exactly the same.

The most interesting change that you might make in amp is simple put a EQ pedal in front of this amp and take out some of the high freq or simple boost the lows.

it works like a charm.

And of course, changing the speaker it might help also in having a little bit more accurate sound.

Cheers,
Marco

I recently bought a Laney CUB10 off this forum. The archives say dull and dead, my ears say bright and glassy and thin. Even with humbuckers. The first step will be the speaker (many choices), and then a peep at the bias. This will all go in a new thread (do not hold your breath) but I agree - speaker swop does make the difference. "Easy", if not cheap. I can vouch for the 12 inch A-Type.