Volume drop on dual gpultec

snipsnip

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Jun 17, 2009
Messages
520
Location
Brighton - UK
Hi Guys,

My dual gpultec functions fine when first turned on, and both tubes glow fine. After a short while the volume on 1 channel drops, and you can see the tube is burning less bright on that channel.

I lent my meter and scope to a friend so cant take any measurements until I get it back.

Does anyone have any ideas about what might cause this?

I have seen a few pultec questions asked recently. Should we start an offical help thread?

Thanks a lot
Jake
 

snipsnip

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Joined
Jun 17, 2009
Messages
520
Location
Brighton - UK
I hadnt as this is my first time with tubes and wasnt sure if they held any charge.... if I had my meter I could measure but didnt want to stick my hand in without knowing.

Is it same to touch them?

Thanks!
Jake
 

syn

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Oct 10, 2005
Messages
623
Check for the heat before touching the glass part of the tube. Be careful, as those 220uF caps will hold the charge even after the unit is being powered down for quiet some time, you might receive severe electrical shock from those. Glass part of the tube is safe to touch at any time, as far as I know, mind the heat tho.
Switch off, wait for the tube to cool down for a couple of minutes,  then you can change them. Don't thouch
any metal exposed parts on resistors caps or PCB tracks, if you are not sure what they are for as you might recevie electrical shock.
 

snipsnip

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Joined
Jun 17, 2009
Messages
520
Location
Brighton - UK
Thanks Syn,

I'll swap them round this evening and then hopefully I can see if its the tube thats failing of if there is some other failure in the circuit.

Thanks again
Jake
 

gyraf

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Aarhus, Denmark
.. for an error like this, make sure that the heater regulator(s) is properly heatsink'ed and does not get too hot and turn off..

Jakob E.
 

snipsnip

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Joined
Jun 17, 2009
Messages
520
Location
Brighton - UK
Thanks Jakob

I swapped the tubes, and randomly the issue disappeared. If it resurfaces I'll check the heatsinks and ensure the regilator is working. Its only got a fairly small sink on at the moment.

Anway, all is now working great except I have a lot of power hum in the audio. will play around with a few grounding schemes to see if I can get rid of it. Other than that, this unit sounds great!

thanks
jake
 

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