CHAMP ELECTRONICS -' THE VALVE AMPHOSPITAL'
Valves for Laney VC30 amplifier. The Laney VC30 amplifier uses 3 x ECC83 (also called 12AX7) preamp valves and 4 x EL84 matched power valves/power tubes. We always recommend JJ valves for the Laney VC30 amplifier. This is because they guarantee awesome tone at a very competitive price. Remember, JJ - ampvalves.co.uk. The range of VC30 combos offer classic British class A tone in a variety of speaker options. The VC30 features a single channel with footswitchable gain, with its own level control, three band EQ.
NOTTINGHAM, ENGLAND
Belonging to agentleman named Andy who lives quite close, this Laney VC30came in with the reasonably simple fault of randomly blowing the HTfuse;apparently when it was being driven hard.Iactually didn't think there would be muchto do in sorting out this problem, but as I went further into it thingsbecamemore complicated.
On poweringthe amp up it actually came on OK though it was only doingabout 21 watts. A little short of the claimed 30 watts! Afterremoval from the case and back onto test it was veryobvious that theset of Sovtek EL84's were well down and under-par. I stuck inmy faithful'test-set' quad set of used-but-good Mullard EL84's to seewhat sortof a difference that would make, but to my surprise there was noimprovement andall of a sudden one of my good ‘ole faithful Mullards gave mea fireworkdisplay! Obviously the power was removed immediately, followed by a bitof'head scratching', and wondering what the hell was going off.
On closescrutiny, I realised what had happened. Someone had changed the fourscreen grid resistors at some point in time. Normally 100 ohms, thesehad beenreplaced with 82 ohm, 2 watt wire-wound. No problem or big deal, but aspin No.9is the actual screen grid pin and pin No.1 on data sheets is 'IC'(internal connection), these 82 ohm screen grid resistors wereconnected betweenpins No.1 and No.9. This means that pin No.1 was being used as an'anchorage point'. Fine, but the problem with old Mullards and otherold brands is that as pin No.1 is this internal connection and inrealityconnected to pin No.2, being the control grid. So, more than350 volts wasnow being placed onto grid one, hence causing the firework display!
Most (but notall) brands of EL84's nowadays do not class this pin No.1 asan 'internal connection' anymore, but simply do not use the pin at allfor any kind of connection. So, with most new branded tubes thisproblem wouldn'texist. However it still would on some brands and most certainly on NOSMullards!! Myadvise would be that if you have one of the LaneyVC30's, don't put Mullards into it until you havehad your amp checked outto see if the pin No.1's have been used as an anchorage point for thescreengrid resistors!?
Laney Vc30 112 Manual Diagram
Moving on, Isimply ripped out the pin No.1 connections and mounted all thescreen (grid 2) resistors up in the air and rewired accordingly. (Thiscan beseen in the photos.) This amp had seen other tech guys before andsomeone hadfitted separate bias resistors and caps to the four EL84 output tubes!I haveseen this a few times and often wondered why. This does not changeanything and(or) improve performance in anyway. I therefore ripped this mod out andput allback to original as can also be seen in the photos. Personally, I thinkthispointless mod is simply a money spinning 'OK, I've done thisforyou' yarn!!
Having done theabove fore-mentioned changes I now fitted a complete new,matched set of JJ EL84's. These are far better than theRussian crap,'well-down', Sovtek junk that were in it. (Only my opinion ofcourse!).
After sorting aproblem with the low-gain input jack socket, everything wasnow all complete. It was looking great on the test gear and was readyto putback into the case. By the way, she was doing a good 32 watts plus nowat thisstage.
After fittingthe amp back into the case and one final test/check-up, I wassurprised to see that the power had dropped significantly to about 24watts, andthe picture on the scope was looking rather strange to say the least.Wonderingwhat was happening, I turned out all the lights to check inside thevalves(tubes), and I could see that the EL84 second from the right (lookingfrom theback) had it's screen grid glowing very badly on full drive.Swapping two ofthe tubes around didn't change things; the tube in this samesocket was stilldoing the same thing. So.........out came thechassis again to see what the hell was going on, but back on the bencheverything looked fine again!Afterputting the chassis back in the case for a second time, only todiscover that this strange fault was back again, I suddenly realisedwhat the problem was.
The four EL84output tubes are mounted hideously close to the internalspeaker's magnet on this model. The EL84 second from theright is the closest one to the magnetic field from the internalspeaker, and this was causing the drive to be crippled on one half,hence drastically changing the sound and performance of the amp. Inaddition, this particular EL84 had its grid two glowing so badly onfull drive because of the situation that it is likely to be unreliableand fail prematurely because of this.
I am not evensure if Laney (BLT Industries LTD) are actually aware of this problem.Theonly one thing that anybody can do to rectifythis problem is to install a shield between the output tubes andspeaker magnet,using a special metal called 'mu-metal'.Thistype of metal shields 'magneticfields' and is the only answer to this stupid, hideous design problem!
Thanks forlooking, John.
Somebodyhad modified the amp un-necessarilyby fitting separate bias resistors and caps to the four EL84output tubes.
Thingsrestored back to normal!
Laney Lc30 112 Manual
Thosetubes are too close to that magnet!!!
UPDATE:
Sincefirst doing this article I have done more of the VC30's and it lookslike BLT Industies have done something about this magnet/tubes distanceissue. It seems they are now fitting them with a 12' Celestion Model'Seventy 80'. This has now given about an extra half an inch clearencefrom the magnet and the problem doesn't exist with thisdriver.......only the ones fitted with the HH Invader driver are thetroublesome ones.FURTHER UPDATE - DECEMBER 2008:
On poweringthe amp up it actually came on OK though it was only doingabout 21 watts. A little short of the claimed 30 watts! Afterremoval from the case and back onto test it was veryobvious that theset of Sovtek EL84's were well down and under-par. I stuck inmy faithful'test-set' quad set of used-but-good Mullard EL84's to seewhat sortof a difference that would make, but to my surprise there was noimprovement andall of a sudden one of my good ‘ole faithful Mullards gave mea fireworkdisplay! Obviously the power was removed immediately, followed by a bitof'head scratching', and wondering what the hell was going off.
On closescrutiny, I realised what had happened. Someone had changed the fourscreen grid resistors at some point in time. Normally 100 ohms, thesehad beenreplaced with 82 ohm, 2 watt wire-wound. No problem or big deal, but aspin No.9is the actual screen grid pin and pin No.1 on data sheets is 'IC'(internal connection), these 82 ohm screen grid resistors wereconnected betweenpins No.1 and No.9. This means that pin No.1 was being used as an'anchorage point'. Fine, but the problem with old Mullards and otherold brands is that as pin No.1 is this internal connection and inrealityconnected to pin No.2, being the control grid. So, more than350 volts wasnow being placed onto grid one, hence causing the firework display!
Most (but notall) brands of EL84's nowadays do not class this pin No.1 asan 'internal connection' anymore, but simply do not use the pin at allfor any kind of connection. So, with most new branded tubes thisproblem wouldn'texist. However it still would on some brands and most certainly on NOSMullards!! Myadvise would be that if you have one of the LaneyVC30's, don't put Mullards into it until you havehad your amp checked outto see if the pin No.1's have been used as an anchorage point for thescreengrid resistors!?
Laney Vc30 112 Manual Diagram
Moving on, Isimply ripped out the pin No.1 connections and mounted all thescreen (grid 2) resistors up in the air and rewired accordingly. (Thiscan beseen in the photos.) This amp had seen other tech guys before andsomeone hadfitted separate bias resistors and caps to the four EL84 output tubes!I haveseen this a few times and often wondered why. This does not changeanything and(or) improve performance in anyway. I therefore ripped this mod out andput allback to original as can also be seen in the photos. Personally, I thinkthispointless mod is simply a money spinning 'OK, I've done thisforyou' yarn!!
Having done theabove fore-mentioned changes I now fitted a complete new,matched set of JJ EL84's. These are far better than theRussian crap,'well-down', Sovtek junk that were in it. (Only my opinion ofcourse!).
After sorting aproblem with the low-gain input jack socket, everything wasnow all complete. It was looking great on the test gear and was readyto putback into the case. By the way, she was doing a good 32 watts plus nowat thisstage.
After fittingthe amp back into the case and one final test/check-up, I wassurprised to see that the power had dropped significantly to about 24watts, andthe picture on the scope was looking rather strange to say the least.Wonderingwhat was happening, I turned out all the lights to check inside thevalves(tubes), and I could see that the EL84 second from the right (lookingfrom theback) had it's screen grid glowing very badly on full drive.Swapping two ofthe tubes around didn't change things; the tube in this samesocket was stilldoing the same thing. So.........out came thechassis again to see what the hell was going on, but back on the bencheverything looked fine again!Afterputting the chassis back in the case for a second time, only todiscover that this strange fault was back again, I suddenly realisedwhat the problem was.
The four EL84output tubes are mounted hideously close to the internalspeaker's magnet on this model. The EL84 second from theright is the closest one to the magnetic field from the internalspeaker, and this was causing the drive to be crippled on one half,hence drastically changing the sound and performance of the amp. Inaddition, this particular EL84 had its grid two glowing so badly onfull drive because of the situation that it is likely to be unreliableand fail prematurely because of this.
I am not evensure if Laney (BLT Industries LTD) are actually aware of this problem.Theonly one thing that anybody can do to rectifythis problem is to install a shield between the output tubes andspeaker magnet,using a special metal called 'mu-metal'.Thistype of metal shields 'magneticfields' and is the only answer to this stupid, hideous design problem!
Thanks forlooking, John.
Somebodyhad modified the amp un-necessarilyby fitting separate bias resistors and caps to the four EL84output tubes.
Thingsrestored back to normal!
Laney Lc30 112 Manual
Thosetubes are too close to that magnet!!!
UPDATE:
Sincefirst doing this article I have done more of the VC30's and it lookslike BLT Industies have done something about this magnet/tubes distanceissue. It seems they are now fitting them with a 12' Celestion Model'Seventy 80'. This has now given about an extra half an inch clearencefrom the magnet and the problem doesn't exist with thisdriver.......only the ones fitted with the HH Invader driver are thetroublesome ones.FURTHER UPDATE - DECEMBER 2008:
The following two photos are ofan early Laney LC30 MkI. I believe this model preceded the VC30. (?) Ascan be seen, the front baffle is sloping, and although it still sportsthe HH Invader driver, because of the sloping front panel the drivermagnet is nowhere near the output tubes.....No problem with these!
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