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PROBLEMS! Repacing EL34 valves (Marshall TSL122)

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PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby _ Six _ » Wed Jan 17, 2007 1:21 am

I have just tried to replace my valves with a new set however i noticed that two of the Marshall EL34s had a blue sticker and two had a yellow sticker on them. I replaced the old ones in my amp and when i switched it on i got a loud hum and one of the tubes glowed up really bright like a light bulb! I knew something wasn't right so I removed and refitted the valves making sure that the numbers on the pins corresponded with the holes in the amp... same thing happened!

I've managed to fit the two yellow stickered ones with two old ones but it will not have the blue ones. They keep glowing hotter like they are about to blow.

On Marshalls website it says that the valves should be all of the same make... which they are.... and that the amp needs to be biased.??????

What is biased... Why does Marshall only have engineers in Milton Keynes????

Any ideas what is going wrong here?
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby Wonks » Wed Jan 17, 2007 8:24 am

Unless you have a low power valve amp with an 'open ended' design using a single valve, then valves in the power amp section work together in pairs, (thats why you get 2,4,6 or 8 etc. power valves in amps - never 3, 5 or 7) and each pair needs to be 'matched'.

Not all valves are the same - if they were, the cheapest Chinese ones would sound just the same as vintage Mullards or GECs and they are built to work around a general specification. Because they operate in slightly different ways it's important that a) 'matched' pairs are used (you buy them this way from the shop) and b) the bias voltage is adjusted for that type of valve. Once the bias voltage is set up is shouldn't need adjusting unless the replacement set of valves has a very different characteristic to the previous set.

This is probably why you have two valves with one colour sticker on and one with another - these indicate the matched pairs. So these pairs need to be loaded in the correct place within the amp so that they work together. It may be that you've done this, it may be that you had a 'yellow' working with a 'blue'. Unfortunately the Marshall website or TSL manual doesn't give any info on valve replacement on these amps. However the valves are normally arranged in a line and typically the first two and last two valves in the line are the pairs.

Marshall service is always reported as being excellent, so give them a ring and they will probably be able to assist you. Otherwise any decent amplifier technician should be able to set up the amp for you - it's not rocket science.
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby Andy5 » Wed Jan 17, 2007 1:34 pm

This is very weird. Firstly, what gives a valve that warm glow is the 'heater', this is a filament just like a lightbulb - but it shouldn't light up like one! This leads me to believe that there is either a fault with the valve (or it's even the wrong type) or there's a problem with the heater voltage (it should be 6.3v AC, in this case) but, according to the schematic, each heater is fuse protected.

Now this is where it gets a little scary; the TSL122 schematic does indeed specify EL34's, however, it also shows the heater across pins 2&6 whereas every EL34 data sheet known to man will tell you that it's across pins 2&7. I can't really work this out other than it being a genuine mistake or even a tripwire for those copying the design. The whole thing is obfuscated by the fact that the AC heater voltage gets rectified after the power valve heaters, what I'm saying is there maybe something wrong with the amp other than the EL34's.

Athough biasing it vitally important, incorrect bias will not cause the valve to light up. Also, using a matched pair will not necessarily ensure that the biasing will be correct. The colour coding on the valves will mean that Marshall have grouped them according to their electrical characteristics and that these characteristics will operate with the preset bias of the amp. If you didn't buy your valves from Marshall then it's a knocking bet that they will have characteristics outside specification, matched or not.

Whatever the case, it's going to be a good idea, as Simon suggests, to have either Marshall or an amp repair guy take a look at it. My overriding feeling is that you have a dodgy valve - if there was a problem with the heater supply then one would imagine that all four EL34's would light up.

Can you tell us why you wanted to change the valves in the first place and secondly, are the heater fuses ok (fuses 1-4)?

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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby Spiked Lunch » Wed Jan 17, 2007 2:38 pm

Does this happen when the amp is on standby/warm up or only when switched fully on?

I’ve had failing valves to glow very brightly like a bulb.
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby IvanSC » Wed Jan 17, 2007 11:05 pm

If it was all of them I would suspect the caps in the power supply, but it does sound like you might have aq dodgy valve - either way it is beyonmd your scope to repair it atr home and beyond our scope to diagnose by web on here (!)
Get thee to an amp chappie!
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby Andy5 » Thu Jan 18, 2007 2:44 pm

Just as an addendum, I asked you to check the heater fuses - DON'T! Looking at the schematic, it would appear that these are on the main power amp board and I don't want you getting in there and electrocuting yourself - there's a lot of scarey voltage in there even with the amp switched off.

Take care,

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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby IvanSC » Thu Jan 18, 2007 7:50 pm

Andy wrote:Just as an addendum, I asked you to check the heater fuses - DON'T! Looking at the schematic, it would appear that these are on the main power amp board and I don't want you getting in there and electrocuting yourself - there's a lot of scarey voltage in there even with the amp switched off.

Take care,

A.

Years ago I accidentally leant on the hot bits of a couple of psu caps in a big valve amp whilst cleaning my solder sucker.
The resultant shock caused my arm muscles to spasm and ram the central rod of the sucker right through the top of my other thumb!
And the amp had been switched off for ages - I just forgot to short the psu caps!!

so B careful!
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby Wonks » Thu Jan 18, 2007 8:18 pm

Ivan, is there any disaster that hasn't befallen you? :headbang:
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby _ Six _ » Fri Jan 19, 2007 8:06 am

Thanks for all your help guys.

Just for the record the valves are all EL34s supplied by Marshall themselves.

When looking at the amp from the rear it is the left most valve that is causing the problem regardless of what order I place the valves in so I am assuming it myst be a hardware fault. I am a little annoyed with my supplier for giving me incorrect advice but i suppose whatever a sales assistant tells you should be taken with a pinch of salt!

Looks like i'll be sending it to Milton Keynes for a service.

Silly how Marshall don't have certified tech's around the country?

Thanks again.

Scott
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby IvanSC » Fri Jan 19, 2007 8:31 am

Wonkey Wabbit wrote:Ivan, is there any disaster that hasn't befallen you? :headbang:

I work on the theory that if some idiot fresh out of school can learn to do something in six months or two years or whatever, I, with my Brain the Size of a Planet, should be able to master it in minutes.
Sometimes this doesn`t work out.

It all started in primary school when I leant on a school bench too hard and split my knee open. 6 stitches.
Then I fell off my bike a week later and split the other side of the same knee.
Wonder what would have happened if the two splits (separated by about 1/2 an inch) had joined up?
I was very tempted to wobble my kneecap about and see if it actually came out at the time....

Been the same for the rest of my life.
Accident prone, I guess.
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby green strat man » Fri Jan 19, 2007 7:05 pm

Ivan, is there any disaster that hasn't befallen you?


you calling ivan a bullshitter, wonk? :D
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby Wonks » Fri Jan 19, 2007 7:12 pm

green strat man wrote:
Ivan, is there any disaster that hasn't befallen you?


you calling ivan a bullshitter, wonk? :D
No, not at all. Just that every month or so some major disaster or accident seems to occur to him. If it can be broken, stretched, burnt, snapped, strained or crashed then it's happened to him or his chattels. He is a walking C&W song of around approximately 300 heartbreaking verses.
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby zenguitar » Sat Jan 20, 2007 2:03 am

green strat man wrote:
Ivan, is there any disaster that hasn't befallen you?


you calling ivan a bullshitter, wonk? :D

Nah, the Wabbit is fishing for even more Ivan anecdotes. If anecdotes were poker cards, I've been dealt a few good hands over the years. But head to head with Ivan... well, I'd soon be out of the game. Listen and learn guys 8-)

Andy :beamup:
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby Andy5 » Sat Jan 20, 2007 2:11 am

We were evicted from our 'ole in't ground...

:roll:

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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby IvanSC » Sat Jan 20, 2007 9:33 am

zenguitar wrote:
green strat man wrote:
Ivan, is there any disaster that hasn't befallen you?


you calling ivan a bullshitter, wonk? :D

Nah, the Wabbit is fishing for even more Ivan anecdotes. If anecdotes were poker cards, I've been dealt a few good hands over the years. But head to head with Ivan... well, I'd soon be out of the game. Listen and learn guys 8-)Andy :beamup:


Actually it is really down to living a really full, interesting life - the more you do that is good, the greater likelihood that something wierd will also happen - simple percentages.
I guess what I am saying is you guys don`t get out enough!

Surely there must be someone else on this forum who has lived a lot of different places and done a lot of different things over the years?

Oddly enough, I had never lived a healthy lifestyle until I hit around 40 and decided to slow down and fly right a bit & that is when most of my non-accident related health stuff started up.

Who was it said live fast die young and leave a pretty corpse?
I forgot to die young, is all.
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby green strat man » Sat Jan 20, 2007 2:06 pm

Nah, the Wabbit is fishing for even more Ivan anecdotes. If anecdotes were poker cards, I've been dealt a few good hands over the years. But head to head with Ivan... well, I'd soon be out of the game. Listen and learn guys


are you saying we should start stealing ivans anecdotes now andy??

:bouncy:

seriously, i was just laughing at simon and the way he put his observation.

good on yer ivan, you only get one life............
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby IvanSC » Sat Jan 20, 2007 4:58 pm

You guys should meet my mate Bob Schwartz.
Now he really IS accident prone!
Makes me cringe if he even looks at any of my gear....
Maybe I should start a BOb disaster thread.

I`ll give you one random quote taken from an idle conversation between four of us on the way to a gig.
"Y`know how sometimes you [ ****** ] your pants and it`s so runny it goes halfway up your back?"

Stunned silence from the Rest of Us.
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby green strat man » Sat Jan 20, 2007 7:05 pm

"Y`know how sometimes you [ ****** ] your pants and it`s so runny it goes halfway up your back?"

Stunned silence from the Rest of Us.


mmmm yeah know what you mean.....................................................


i hate it when that happens. you have to change your trousers and your shirt. :headbang: :D :headbang: :D
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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby peterhusband » Sat Jan 20, 2007 11:26 pm

You could try asking around your local amp techs to see if anyone has a valve tester. You could also have the matching checked.

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Re: PROBLEMS! Repacing EL34 valves (Marshall TSL122)

Postby zenguitar » Sun Jan 21, 2007 1:51 am

green strat man wrote: are you saying we should start stealing ivans anecdotes now andy??

That's exactly what I'm saying, I've already made a good start :angel:

Andy :beamup:
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