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Old 12th September 2005, 01:06 PM   #1
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Exclamation Valves glow fierce

When I turn on my little valve amp, a couple of the valves instantly light up fiercesomly bright, then dim down to normal, and the amp works as it should.

can any one give any advice as to what to do to stop this?

it started when I moved the volume pot.

the amp is (I think) a New Zealand made Fountain brand (from a radio gram maybe, its just a chassis, with a front pannel)

10watt per channel push pull running EL 86's



looks the same circuit as my old Fountain Gemsonic 10-10 (if anyone is familiar to that circuit)



Thanks alot,



Matt
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Old 12th September 2005, 01:24 PM   #2
anatech is offline anatech  Canada
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Hi Slinkylink,
Can you show us a picture? I should be an easy circuit to trace the schematic. I don't even know what all the tubes are , so it's hard to give you a hand.

-Chris
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Old 12th September 2005, 01:55 PM   #3
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That is normal behaviour for certain tubes. My d3a's light up like a chrismas tree and then fade to normal.

I think a dc supply with a current source would stop that. But there is no need to in the case of say the d3a's.
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Old 12th September 2005, 06:44 PM   #4
SHiFTY is offline SHiFTY  New Zealand
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I have one of them kicking around somewhere. PP ECL86 with 2x EF86s IIRC.

If its a white flash at the base of the valve, and its a mullard one, then nothing to worry about. Happens with a lot of 9-pin valves.

Main problem with my fountain amp was the anode (big grey metal bit) of the valves started glowing a dull red after about 30 seconds. Sounded pretty good up till then

I thought it might be leaky caps so I changed every single cap in the damn thing, and lots of resistors. However it was some kind of oscillation I think.

Its in the pile somewhere...
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Old 12th September 2005, 07:10 PM   #5
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Moved the volume pot in which way?

Otherwise, as others said, it is normal. However, if you have never seen it before the volume pot move...

Let us know how you moved it. What do you mean by this?

Gabe
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Old 13th September 2005, 06:31 AM   #6
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It's got a real higgledy-piggledy lot of valves in it, there are a number of mullards (an ECC83, 2x EF86 and two of the output valves (ECL86))

but the other two ECL86's are TESA and Telefunken (I think, most of the silk screening has come off the tubes. But the types are printed on the chassis of the amp.


the other thing I'd been told, is that its bad to run a tube amp with no load on it? I was just wondering weather it is alright to run it with a 10:1 voltage divider so I can use it as a pre-amp? or if I can just tap straight on the output from the preamp valves without running a load on the output stage?




it use to be a tuner amp, but I removed all the tuner components, and moved the volume control from next to the tuning dial, to the center of the chassis (it was the stereo/mono switch, now hardwired on stereo), and I've just rememberd that I'd also replaced the two rectifier diodes (the old ones burnt out) but I'm sure it worked fine when I'd done that for a while.


CHeers
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Old 13th September 2005, 06:31 AM   #7
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Default Photo

this is what its like now.


the volume is in the middle.
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File Type: jpg fountain valve (1).jpg (75.1 KB, 427 views)
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Old 13th September 2005, 06:31 AM   #8
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this is what it was like, the volume control is the one on the top right.

so a relitivly simple thing to have changed, I thought?
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File Type: jpg fountain stereophonic.jpg (23.6 KB, 409 views)
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Old 13th September 2005, 08:14 PM   #9
SHiFTY is offline SHiFTY  New Zealand
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DON'T run it without a load on the output transformers, you may get a lightshow that destryos tubes and OPTs.

If you want a preamp, buy a 1960s table radio or reel-to-reel recorder, grab the power transformer. Use a metal box from jaycar and build one, using ECC88 or 6SN7. If I wasnt in th UK I could send you some stuff

If you want a power amp, rebuild what you have. Those fountains do actually sound quite good.

I seriously doubt you would have damaged the thing by changing the volume control. As posted already, a bright flash at turn on isn't too big a deal...

Buy a new set of ECL86s, change any out of spec components, and use the thing every day.
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Old 13th September 2005, 08:31 PM   #10
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Ahhhh. Love the sound of rusty iron! Just kidding!

Well, the only thing I can think of is that since you've removed much of the original circuitry (more than just the volume control has moved, I see), the 6 volt tap is now providing much more current to cold heaters. The initial resistance, if memory serves, of cold heaters is very low. So maximum current is drawn/supplied. That is why the flash. But again, not a real problem.

As for running the amp without a load, better to just remove the output transformers and tubes. Or really just the output tubes.

Gabe
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