Laney LC15R - which ECC83 goes where ?

[chazpope]

Hi

Bought this UK made LC15R on ebay - and it arrived with the valves in a box.

The 2 Output valves and 1 ECC83 are made in Russia, the other 2 ECC83s made by Marshall - one has a yellow dot.

Now then - which of the 3 small valves goes where ? I plugged them randomly and the amp works ok, bit noisy perhaps.

There is another problem that the line out does not work at all - so I am about to open it and see why and I would like to put the valves back in the correct order..

Thanks

[g1]

All the preamp tubes are ECC83 (European for 12AX7), so there is no right or wrong as to which brand goes where. Which brand of ECC83 you put in which spot is a matter of personal preference. I shuffle the preamp tubes around to get the least noise, some people arrange them depending on slight tone or gain differences.

[Chuck H]

+1

And add... I think that amp has a Marshally type of circuit. That means there is a "cathode follower" in there. Some Russian preamp tubes don't hold up to the higher cathode voltage of this type of circuit. So, I'll guess that the "Marshall" tube with the yellow dot is marked for a reason. Try it in the first socket (the one furthest from the power tubes). Then use the other "Marshall" tube in the second socket. That'll be where the cathode follower is. Then put the Russian tube in the last socket nearest the power tubes. Now try swapping the two "Marshall" tubes and go with whatever arrangement performs best for gain, low noise and low microphonics.

[chazpope]

well Chuck - turns out I had done them your way - dot first, its mate next, russian last - seemed right at the time

I opened the chassis to fix the line out - what a weird design - valves and smds, smells of trouble I think. Found that one of the 2k2 smd resistors was not connecting to the pcb though it looked ok visually. resolder fixed that.

I then proceeded to resolder the pcb and struggled with some weird gooey sticky pads whose glue was stopping the flow of solder - crap - on top of that there was a dodgy tin-foil thing threatening to short the whole thing + caps stuck on the back of the board with glue. Put it back together and to my horror there was a lot of preamp noise and crackle - a sort of 'frying eggs' sound I used to hear on my grandad's radio in the 60ies. In desperation I scraped cleaned and resoldered the
gooey area of the pcb again and thank God it works now. Still these tiny smds within the valve's socket make me nervous...

[Chuck H]

Never seen inside one. Sounds like trouble. Make sure the socket contacts are clean and try not to plug in and out too much. Why anyone would make a product that needs to withstand road, musician and vibration abuse and includes expensive components like tubes, transformers, big cabinet and hardware would make the PCB SMD I can't imagine. Well, that's not true. I expect it's cheaper that way. Just treat it nice. Keep the contacts clean and deoxit'ed. Don't bump it around like you would any eyelet board amp. Don't even set the head directly on the speaker cab. It'll be fine

[chazpope]

well last night I took it to a pub gig and played it at close to full volume for 2.5h - didn't miss a beat ! However - it got really really hot - the chassis almost too hot to touch. I heard these have overheat problems but I wonder that this can't be good long term and one day it the heat will brake it. I am starting to think of solutions - drilling the chassis, putting a fan - someone must have done this before ?

[Chuck H]

Sure. Just put a fan in it. Here's some tips:

The fan should suck air through the chassis, not blow air into it.

Mount the fan on one end of the chassis and make a couple of filtered vents at the other. Just drill multiple small holes for the vent area and tie foam to with wire.

Listen to any fan you consider. Very quiet ones are available. A small fan should be plenty.

Your not trying to cool things off by blowing on them. You just need to replace the hot air in the spaces with cooler air so the heat can conduct out of the parts better.