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felipemuniz 8th April 2012 06:16 PM

Damaged tube? EL84
 
1 Attachment(s)
I turned on my amp this morning and noticed right away many blue sparks inside on one of the valves (EL84) ... Immediately I pulled the plug. The attached video can explain better than me.

note: I made this amp 4 months ago, the schematic is from Orange Tiny Terror..

indianajo 8th April 2012 06:29 PM

What is your plate voltage? Maximum is 300. This is pretty low. If you have a problem, you can put a 47 ohm 3 w resistor between the transformer and the rectifier tube cathodes. Use a terminal strip like those from TRW Cinch, or a turret board designed for tube voltages. (guitar amp shop accessory)
If you are using a solid state rectifier, try a 6x4 tube instead or put in a B+ voltage delay circuit.
Some people buy 7189's (?) instead of 6BQ5's for higher voltage rating. Check the datasheet, I'm going on memory here.
Read tube voltage safety rules in the sticky threads above before you measure or change anything under the deck.

felipemuniz 8th April 2012 08:09 PM

3 Attachment(s)
Quote:

Originally Posted by indianajo (Post 2977656)
What is your plate voltage? Maximum is 300. This is pretty low. If you have a problem, you can put a 47 ohm 3 w resistor between the transformer and the rectifier tube cathodes. Use a terminal strip like those from TRW Cinch, or a turret board designed for tube voltages. (guitar amp shop accessory)
If you are using a solid state rectifier, try a 6x4 tube instead or put in a B+ voltage delay circuit.
Some people buy 7189's (?) instead of 6BQ5's for higher voltage rating. Check the datasheet, I'm going on memory here.
Read tube voltage safety rules in the sticky threads above before you measure or change anything under the deck.

Thank you.
I removed the tube, then I measured the pin 9, and 7, around 280V~... The amp works without this tube, but I think is with half from total power output, right? On attachment there is some pictures, you can see the power supply, the rectifier tube is a 5Y3-GT..

indianajo 8th April 2012 08:26 PM

5Y3 should delay warm up fine. I would try to buy a EL84/5BQ5 made in Russia or Slovakia. Tubes sold in matched pairs have been through more warm up hours than singles. Note sales names reflecting former Soviet origin are not country of origin. In the US, all the old trade names were owned by the distributor instead of the Russian manufacturer, so the distributor has the option of sourcing from another factory. I've recently bought JJ 6CA7 (Slovakia) and Sovtek 6BQ5 (2008 production) and been pleased. I believe I've read the Petersburg, RU factory now owns the Mullard and Tungsol names, formerly UK and US origin.
What was the country of origin of your defective tube?

felipemuniz 8th April 2012 08:50 PM

Is from here, Brazil, produced by Miniwatt, but this pair was build in 1968, I bought on box, from a friend at about 6 months ago.. He told-me that were kept in a box from an old radio (TELEFUNKEN) along with the manual from this radio... They never used this tubes, until I buy.

EDIT: To import products from other countries, by law, I can only import a maximum of 50USD, including shipping I think. Otherwise, If i buy more than this, I'll have to pay taxes, which are VERY expensive (60% from price I think)

indianajo 8th April 2012 09:30 PM

I imagine a guitar amp shop or organ supplier will have 6BQ5/EL84 in Brazil.
I bought the 6BQ5 pair of Sovtek's from tonewheel-general.com in 2011 in Kansas City, USA, for $28 the pair. I would look around in Brazil first, though.


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