This Saturday I started the upgrade by building the function generator kit shown in the picture here. It was very straight forward to assemble and only took around an hour, the kit doesn’t come with instructions as such so you’ll need a basic understanding of electronics or an understanding of what each component is and know how polarity works. Once constructed, a quick test then I moved on to the amp itself… You can grab this DIY kit from Maplin here…
I’m afraid this post isn’t going to be a blow by blow account of how to disassemble your amp, if you’re not sure how to do this then ask yourself whether you should really be diving in? So, I popped the back off and dropped the amp tray out. Click images to enlarge…
I removed the old TAD EL34’s and replaced them with a matched pair of Svetlana EL34’s I’ve had laying around for ages, I’m sure I bought these in 1998 for a Marshall TSL I had at the time as a backup in case I had a valve blow on me at a gig. After a good deal of research on the net, general consensus is that Svetlana Winged ‘C’ valves are among the best if not ‘the’ best and are closest to the original Mullard EL34’s. I’ve purposely chosen these for their sound – warm, deep bass, rich mids and well rounded treble and are typically ‘British’ voiced and used in just about every Marshall amp built. And here they are:
I chose JJ-Tesla ECC83’s after reading around on the Blackstar official forums, most of the users there recommend them for their warm sound and solid construction. After fitting all four valves I connected the still benched amp to the speaker or ‘load’ with an extra long cable – you must never power on a valve amplifier without it being connected to a load!! (Speaker). Next I connected the mains and turned the amp on but not the standby… Yet. I let the amp warm up for a good ten minutes before turning on the standby switch.
I’ve read some stories of wild swings in voltage when changing valves in a Blackstar, so here’s a tip: have the probes of your multi-meter on the test points ready when you switch on the standby – just in case! If you have a swing in voltage that goes high or ‘hot’ then you can at least tweak the pot down quickly so there’s no damage caused to the new valves. Here’s how it’s done:
In the middle of the main PCB you’ll find two white pots and two test points labeled TP1 & TP7:
The correct bias voltage is also displayed as 50mV. The red probe of the multi-meter needs to be on TP7 and the black on TP1, when I switched the standby to on the voltage was quite low at around 35mV. Turning the pot labelled BIAS ADJ clockwise slowly, I eventually settled on a voltage of 51.5mV, slightly hot. I noticed that even a slight adjustment made the voltage swing a great deal, so gentle accurate adjustments need to be made here! Setting slightly hot certainly makes a difference in tone which I found out later when testing the amp. I recommend experimenting with this setting but be careful you can shorten the life of the valve running them hot.
I left the amp on for around an hour and returned every 15 minutes or so to test the bias, it fluctuated around 50.5mV to 52mV but never higher than this.
This is where the function generator comes in. I placed the new Celestion Vintage 30 in it’s box into a crate then packed it with cushions to try and keep the noise levels down. I put the whole lot in the garage which is at the end of the garden. I set the function generator to a 50Hz sine wave, set the amp on the clean channel and run the master volume at just past a quarter, same with the volume on the clean channel .
At these settings there was plenty of cone movement, holding my hand over the cone it felt like a fan was blowing air! I left the rig running for a good 8 hours before switching off and fitting the V30 into the amp cab. Even after only 8 hours the cone felt a little less stiff than it was before, you can test this by gently pushing the cone down with your fingers to test the resistance in movement.
I took the amp to practice this Wednesday to give it a good run at volume. INSTANTLY different sound! First thing I noticed was how much louder it was, I didn’t need the volume up nearly as much as I did before. On the clean channel I found it to be warmer sounding as I expected it would, the high’s didn’t take my head off or puncture anyone’s ear drums! Using my PRS Studio I found the sound didn’t break up or start to distort, playing full chords hard, the amp still kept a nice rounded clean tone.
Moving on to the overdrive channel, I needed to tweak the EQ as the new components have made quite a difference. Firstly, to me there seems to be buckets of drive available, I certainly didn’t need the gain up so high as before – how good is that!!! What I did find surprising was that I still needed to keep the treble control down low to smooth off the highs. I’m putting this down to the fact the new V30 probably still needs more ‘break-in’ to loosen things further still. However the treble is not harsh like before, it’s far more rounded and not in ya face, probably due to the characteristics of the new valves. If you remember I chose this combination purposely to warm the overall tone of the amp. It seems to have worked well, the EL34’s are performing as ‘advertised’ bringing the sought after deep, rich classic sound. The amp is ‘dripping’ in tone, it’s like you can almost take a bite out of it, especially on the clean channel which I’m well in to using and experimenting with at the moment!
Lastly and this is where I can hear the biggest improvement is on the boost channel. With the middle boost switch activated I can get an amazing singing lead which cuts right through, no messing! It’s incredible to hear, holding a sustaining note with vibrato the channel will go forever. Stand closer to the amp and it will feedback with an element of control and little amount of effort.
Is the upgrade worth it? Yes, it is. If you own a Blackstar go out and do it or have a pro do it for you. The sound will change for the better and with decent components added you can look forward to a more reliable piece of equipment, they say you pay for what you get and it’s certainly true.
Go treat your Blackstar…
I also have a rare Marshall 30th Anniversay 100W head, after this experiment with different valves I’ve decided to replace the current Sovtek’s with Svetlana’s. The 30th Anniversary uses 6L6’s or 5881’s however a review carried out by Watford Valve say the same can be achieved as with the EL34’s, the Marshall is well overdue a valve change so I think it’s time to upgrade too.