212-HD 130 loud hum and 'redplating'.

Hello all and a happy new year...i'm a new boy from dublin,ireland and i have a problem with my 212 HD 130,it's the one with the 12ax7 phase inverter,serial number C003354..with the script logo/silver badge.. i've had this amp for nearly 20 years and never a major problem like this before, i recently had to replace the hi/off/lo switch when flipped to on it took the amp fuse and the whole venue we were playing in back to the breaker on the main board...!! shortly after replacing the switch with one of the same type the amp worked fine for a couple of months before starting with a crackling/popping sound when turned on,eventually it starting losing volume all together,cutting in and out. and lately it has stopped working altogether with a loud hum and the output valves redplating.... i tried changing the valves for for a set of jj's including the 12ax7 but it's still doing the same thing......any help with this would be very welcome as i love this amp.....thanks
Tony

Could be filter caps, I suggest you to take it to an amp technician...
take care

thanks for the reply... the problem is that there doesn't seem to be anyone around dublin anymore too well up on fixing amps like this,i'm not too well up on the more tech side of amps but i've picked up a few bits and pieces over the years..are they the big silver ones that look like batteries beside the transformer and output tubes.....???...thanks

That's them but there are also smaller ones on the main board AND the bias supply caps are over on the little board near the switch. THESE are very important, especilally since you say it's plating. MAKE SURE you orient the caps properly(+ and -) and the bias caps are backwards, in case you're paying atttention-(+ goes to ground). Then bias it a little on the cool side,around 23mA PER tube and you should be fine. Also, there are a couple on the driver board. MIke.

mike..thanks for the reply i have read a lot of the other threads and posts and this one your wrote to another forum member about changing filter caps i assume would apply to me as well in regard to draining the caps before attempting to change them...one of the guys in our band is a qualifed electrician with over 20 years experience and has helped me in the past so i was going to get him to give me a hand with this as i know from reading a lot of posts here thats there are some serious voltages floating around inside these bad boys, and would this apply to all the caps or only the big ones....??
thanks
tony
Posted on Saturday, September 15, 2007 - 01:48 pm:
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Make a 10k-1 watt resistor with two wires on the ends and a gator clip on each end. Clip the one end to the chassis and clip the other end to the "+" side of the filter cap. Wait 2 minutes and check with a voltmeter to make sure it's safe. Leave it hooked up while working on it as caps sometimes have a memory and kind of re-charge a little. Just remember to UN-hook it before you fire the mutha up. Mike.

The littler(?) ones hold voltage as well but they are usually lower and are in a resistive circuit(usually) that drains THEM. The filter caps are off of a transformer that is directly charged. HOWEVER, it's always a good idea to check the + side with a DMM or something before touching. Mike.

I did a recap Job on some MM. Just for a reference, I used 100uF 500V from JJ , 22uF 500V from Illinois Capacitors (instead of 20uF), and 220 uF 63V from F&T (in stead of 150uF). I choosed 500V caps instead 450V for safety.
It's hard to find axial caps, if you can't find them in Dublin, try to buy online, banzaieffects.com and tubetown.de are good stores.
Bye!

thanks guys for the replies...a friend just sent me a DVD on valve amp repair so i will study it and i'm gonna give this a go with a little help hopefully from my friend....giorgio thanks for the heads up on the online stores..we have a big electronic suppliers here called 'radionics' who usually stock most stuff i've ever needed...thanks again guys i'll report back how things pan out.....
tony

Hi all
sorry i haven't been back for a while,but i finally got around to ordering the parts a few weeks back and installing them..(changed the filter caps and the two on the bias supply board also found one of the orange wires to the bias supply board from the transformer had broken off ....i got the amp back up and running apart from one slight problem..there is still a very faint hum from the back of the amp and there is a blue glow in the valves when you flip it off standby,i don't think the blue glow is the gases people talk about,in looks like electricity to me but i'm no expert...!! otherwise the amp sounds fine but i don't leave it on for more than a minute of two just in case until i get to the bottom of this problem...when i had the amp out of the box and on the bench i didn't see this,it only seemed to start when the amp was back in the box with the valves pointing down as normal(i had it upside down cleaning the sockets and left it like that when plugging the guitar in for the first time)i cleaned the tube sockets with servsol circuit cleaner...do the sockets maybe need to be re-tensioned...???...another strange thing the reverb started working as well....!!...to hear the hum you really need to put your ear up to the back of the amp it's that faint but the blue glow in the centre of the tube worries me a bit....i got new tubes when i got the caps but would this be a symptom of a need of a re bias..i have a multimeter and from reading other posts pin 5 seem to be the one for reading the voltage where do you put the other probe...? is it the two blue dials on the main board for ajusting the bias or the single black one.?.also i didn't change the caps on the main board or the one the smaller board beside it yet..as i'm not quite sure what the smaller board does..and they are different to the blue mallory ones that i changed on the bias supply board.......i think i'm nearly there as the amp in all other respects sounds pretty sweet and seems to be pushing full volume....
thanks
Tony

Ok ...panic over.........just a bit paranoid about my first major amp repair.... took the back off my marshall superbass head to compare and it is the normal blue glow inside the plate body.....just for anyone wondering the reverb can is salavaged out of an old peavey solid state amp and seems to work fine,i'll probably stretch to the proper long tank one in the new year...the hum is very faint and could of even always beeen there..it's certainly a lot quieter than my little '62 selmer stadium for noise,the marshall also has a little hum when you listen hard enough..i don't use these amps at home,mostly in noisy pubs and clubs so i wouldn't usually notice....
a BIG thank you to Steve,Mike and Giorgio for their help and to all the other posters who come back with 'fixes'...trawling through them all has been very helpful......if i can help in any way but i'm not a expert like steve,mike,terry etc..... i know it can be a labour of love but i can't begin to tell you all how happy it makes me to have my 'old friend' back up and running...i've had her since i was 18 so 20 years and this is the first time she has really played up.....i think the old girl deserves a xmas present of a flight case.....!!!
thanks and a Happy Christmas and peaceful New Year to you all
Tony

A little hum is always present. I would like to say that unbalanced tubes can cause a hum too but if you are biasing with the 10 ohm resistor, it's hard to check balance. Good luck and merry CHRISTMAS(yes, we say that here!)