ECC83 Valve Replacement

[Dave]

Hi everyone. I started a thread almost a year ago after purchasing a Marshall JCM800 Super Bass head at [url="http://basschat.co.uk/index.php?showtopic=6872&hl=valves"]http://basschat.co.uk/index.php?showtopic=6872&hl=valves[/url] as I was looking for a particular sound and believed this was the amp I needed to reproduce it (as another bass player I'd heard was using this amp and it seemed to have the sound I have always been looking for). Unfortunately I was unable to get the distorted tone I was after at that time, and a number of basschatters provided some excellent suggestions as to what I might try in order to obtain it.

Not so funnily enough I've only just got around to actually thinking about replacing the preamp valves, and so I've recently acquired a couple of Mullards on fleabay. What I'd like to know is if there are any precautions I need to take when swapping out the valves. I've read I should avoid contact with my skin in order to prevent oil deposits which can create weakspots on the valves, so that's not a problem, but then I guess I can't be sure the seller hasn't handled them with similar care. Is there any way I could/should clean the valves before inserting them? Also because I've never done this before, do I assume correctly that I simply need to pull the old ones out and insert the new ones by pushing them into the slots? The Mullards weren't cheap, so obviously I don't want to damage them when trying to insert them. Not sure how much resistance I'm going to encounter when I attempt to do the swap, so thought I should ask someone more "in the know" for any pointers. I assume using even pressure with a vertical pulling (removal) and pushing (insertion) motion should do the trick? I've done a thorough search on this site, but didn't come across any technical info with regards the procedure itself. I've also heard you need to be careful about getting shocked from the voltages stored in the capacitors, but not sure if this applies when swapping out preamp valves or not. Any help/advice/suggestions you can give me would (as ever) be greatly appreciated!

Cheers in advance!

Edited October 8, 2008 by Dave

[obbm]

There's a lot of nonsense talked about valves. It's very straightforward, simple and as easy as changing a fuse. It's not a black-art. Just use your common sense.

Switch off the HT and the main On/Off. Let the valves cool down a bit and then pull the one you want to change straight out. Line up the pins on the replacement and slot it in. Switch the main On/Off back on and allow the valves to warm up, then put the HT back on. Job done.

From memory there are no high voltage connections on top of the chassis. They are all underneath. You should be able to do the change easily without removing the chassis from the case. If you do have to remove it for whatever reason and have had it powered or plugged into the mains then do not pick up the chassis by hooking your fingers underneath. Pick it up by the transformers.

For what it's worth I've never cleaned a valve because it might take off the manufacturer's labelling and you might end up with an expensive no-name ECC83. If the pins are bent the straighten them carefully with pair of long-nosed pliers.

[Dave]

[quote name='obbm' post='302015' date='Oct 8 2008, 11:24 AM']There's a lot of nonsense talked about valves. It's very straightforward, simple and as easy as changing a fuse. It's not a black-art. Just use your common sense.

Switch off the HT and the main On/Off. Let the valves cool down a bit and then pull the one you want to change straight out. Line up the pins on the replacement and slot it in. Switch the main On/Off back on and allow the valves to warm up, then put the HT back on. Job done.

From memory there are no high voltage connections on top of the chassis. They are all underneath. You should be able to do the change easily without removing the chassis from the case. If you do have to remove it for whatever reason and have had it powered or plugged into the mains then do not pick up the chassis by hooking your fingers underneath. Pick it up by the transformers.

For what it's worth I've never cleaned a valve because it might take off the manufacturer's labelling and you might end up with an expensive no-name ECC83. If the pins are bent the straighten them carefully with pair of long-nosed pliers.[/quote]

Cheers for that OBBM, great advice. Valve "black-arts"... I like it! If only I knew what the HT was, I'd be sure to switch it off. I assume it's the "stand-by" switch?

[obbm]

[quote name='Dave' post='302031' date='Oct 8 2008, 11:38 AM']Cheers for that OBBM, great advice. Valve "black-arts"... I like it! If only I knew what the HT was, I'd be sure to switch it off. I assume it's the "stand-by" switch?[/quote]

Sorry. Tech talk. HT is the High Tension supply to the valves. This can vary from 350-volts DC up to 700-volts. This is the lethal voltage that is talked about and is controlled by the Standby switch. However when you switch it off the voltage takes quite a long time to decay so that is why you have to be extra careful. Just switching off does not mean that it is safe to have a poke under the chassis.

[Waldo]

Changing valves is like changing lightbulbs

Oil on your skin can make weakspots on the valves? Is there anyone who seriously beleives that?

[Hamster]

Where do you live? - sticking it in your profile is a good idea

If you are very very lucky you'll be living near Steve - [url="http://www.stevesamps.co.uk/"]http://www.stevesamps.co.uk/[/url]

He will make your amp sing / cry / weep / scream / disembowel etc

[Bassmec]

[quote name='Waldo' post='303314' date='Oct 9 2008, 08:40 PM']Changing valves is like changing lightbulbs

Oil on your skin can make weakspots on the valves? Is there anyone who seriously beleives that?[/quote]
Not oil for tubes but even that is true of some hallogen bulbs. I have seen a hot fender bass man 100 picked up by a sweaty roadie go plink when a drip of his sweat dropped onto one of the hot output 6l6 tubes cracking it and turning it a milky color we just wiped it out and its corresponding pair in the push pull arrangement and he then had the equivalent of a fender bassman 50 for a couple of dates on the tour, as he was a guitard he was as usual normally too loud in the stage mix so we put off getting him a new tube for as long as possible. we gave in in the end but after that he kind of turned down a bit having enjoyed his limited power more than he cared to admit.
Output tubes in most amps need to be in matched sets unless there are bias controls for each tube and correct biasing is essential for all output stages. Pre amp tubes are not a problem to just swap without doing anything else and If you are lucky
you can get some real great tone from all the usual old suspects like Mullard, Rca, Ge, Brimar, one of my favorite 12 AX7
or ECC83 tubes is the Mullard CV4004 mil spec tube they are hard to find but well worth it.
I have an original set of 1970 GEC KT88's that have been in an amp in a busy studio and tested just like new when we recapped it recently, the oldest set of tubes I use every day are a set of rca JAN 1620 valves dated 1938 they are still fine.
Those old tubes where made like jewelry, quality is not getting better in new tubes at all.

[Dave]

[quote name='Hamster' post='303385' date='Oct 9 2008, 10:35 PM']Where do you live? - sticking it in your profile is a good idea

If you are very very lucky you'll be living near Steve - [url="http://www.stevesamps.co.uk/"]http://www.stevesamps.co.uk/[/url]

He will make your amp sing / cry / weep / scream / disembowel etc[/quote]

Cheers for the recommendation, but I'm just south of Birmingham, so not really local for me. Plan to swap out the "no-name" preamp tubes for the Mullards sometime this weekend, so if it still doesn't sound right, I guess I'll just have to keep looking/try something else. Thanks for all the helpful responses. Always appreciated.