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fire spark in 5AR4 rectifier tube for PrimaLuna Pr

All of a sudden, I see fire spark in one of the 5AR4 tube in my PrimaLuna Prologue 3 preamp so I turn it off immediately. I tried it again, and the same thing happen. What is going on?

Does it mean my tube is bad that I need to replace it? Or there is something wrong with my preamp? I did some research, it seems people said it may be the capacitance is too high, but I didn't change anything, could it be something goes wrong in the unit that results in capacitance being too high? Did I already damage my unit?

Thanks.
gte357s
rrog
1,958 posts
 
5AR4's are one of those tubes you should keep on hand. A weak one usually shows up during the turn on transient. Some are more rugged than others and the various brands can have an impact on the sound quality.
gte357s OP
281 posts
 
I tried switching the tubes, and the spark appears on one of the tube, so, it is in fact the tube has gone bad.

So, now, can I just replace one or do I need to replace both with a matching pair?
pehare's avatar
pehare
835 posts
 
just replace the bad one...they don't need to be a matched pair. Although I'd probably replace the pair w/a nice pair of matching NOS & then keep the good single for a backup. enjoy!
rodman99999
6,125 posts
 
Just a little FYI; The best sounding, most reliable and longest lasting rectifiers out there, are the Blackburn Plant, Mullard tubes(the earlier the production-the better). Unfortunately, do to all of the aforementioned facts; they are also the most expensive. ie:(http://www.ebay.com/itm/Mullard-Blackburn-Branded-Amperex-Bugle-Boy-GZ34-5AR4-Rectifier-Matched-Pair-/220910480753?pt=Vintage_Electronics_R2&hash=item336f4a6d71) (http://www.ebay.com/itm/vintage-Mullard-Blackburn-5AR4-GZ34-NOS-Hi-Performance-rectifier-tube-/200687014748?pt=Vintage_Electronics_R2&hash=item2eb9e0d35c) (http://www.ebay.com/itm/NOS-box-Mullard-GZ34-5AR4-double-halo-tested-1958-Blackburn-never-used-/120827434079?pt=Vintage_Electronics_R2&hash=item1c21e0545f) Personally(being your preamp is a dual-mono design), I'd replace both rectifiers, with a matched pair, to insure a balanced presentation from the two channels.
gte357s OP
281 posts
 
Yes, mullard blackburn tubes are too expensive. Any cheaper but good NOS alternatives? Also, if I don't want to spend too much, is it still worthwhile to get 1 Mullard Blackburn? Or better to get a match pair of new stock?
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