camross Posted March 11, 2021 Share Posted March 11, 2021 One of my pre amp valves (5AR4) sparked on start up tonight this lasted about 5 seconds. I have never noticed this before and the amplifier is working with no notable affect. Is this normal? Link to comment Share on other sites More sharing options...
stereo coffee Posted March 11, 2021 Share Posted March 11, 2021 No not normal, with power off and AC cord disconnected, and allowing 8 hours for capacitors to discharge, I would carefully inspect the valve socket wiring for anomalies. The 5AR4 is a rectifier valve. Its information sheet is here: http://www.r-type.org/exhib/aaa0997.htm Link to comment Share on other sites More sharing options...
xlr8or Posted March 11, 2021 Share Posted March 11, 2021 (edited) 54 minutes ago, camross said: One of my pre amp valves (5AR4) sparked on start up tonight this lasted about 5 seconds. I have never noticed this before and the amplifier is working with no notable affect. Is this normal? No, this is not normal. What's the pre amp please? Edit: I'm asking the question above to try and establish if the filter input caps are too high in value for use with the 5AR4/GZ34 rectifier. Edited March 11, 2021 by xlr8or 1 Link to comment Share on other sites More sharing options...
Telecine Posted March 11, 2021 Share Posted March 11, 2021 8 hours ago, xlr8or said: No, this is not normal. What's the pre amp please? Edit: I'm asking the question above to try and establish if the filter input caps are too high in value for use with the 5AR4/GZ34 rectifier. From the OP's signature block: Prima Luna Prologue Pre Amp. Link to comment Share on other sites More sharing options...
camross Posted March 11, 2021 Author Share Posted March 11, 2021 1 hour ago, Telecine said: From the OP's signature block: Prima Luna Prologue Pre Amp. Correct Prima Luna Prologue Pre Amp. I tried to video the sparking but it burnt out before I manged to start the video. Is it a possible error in the Tube? Link to comment Share on other sites More sharing options...
camross Posted March 11, 2021 Author Share Posted March 11, 2021 The valves are around 6 months old and Prim Luna Link to comment Share on other sites More sharing options...
xlr8or Posted March 11, 2021 Share Posted March 11, 2021 (edited) Great - can now see that info in the block. 5AR4/GZ34 use in the prologue is recommended so there doesn’t seem to be wrong rectifier use in circuit. Is the rectifier a new production type? Your rectifier is arcing and needs to be changed ASAP as it is at high risk of taking out your power transformer. Edit: Yep, it’s a new production type. You need to change it. I would recommend switching to vintage UOS/NOS types. Try searching for a Mullard Blackburn UK late 1950’s f31 black micanol fat base 5AR4/GZ34. Edited March 11, 2021 by xlr8or 2 Link to comment Share on other sites More sharing options...
camross Posted March 11, 2021 Author Share Posted March 11, 2021 11 minutes ago, xlr8or said: Great - can now see that info in the block. 5AR4/GZ34 use in the prologue is recommended so there doesn’t seem to be wrong rectifier use in circuit. Is the rectifier a new production type? Your rectifier is arcing and needs to be changed ASAP as it is at high risk of taking out your power transformer. Edit: Yep, it’s a new production type. You need to change it. I would recommend switching to vintage UOS/NOS types. Try searching for a Mullard Blackburn UK late 1950’s f31 black micanol fat base 5AR4/GZ34. Thanks I will look around for new tubes. Just to make sure I should not use the amp until I have new valves? Link to comment Share on other sites More sharing options...
xlr8or Posted March 11, 2021 Share Posted March 11, 2021 (edited) 13 minutes ago, camross said: Thanks I will look around for new tubes. Just to make sure I should not use the amp until I have new valves? Yes - don't use it or switch on until you have replaced the rectifier. Edited March 11, 2021 by xlr8or 1 Link to comment Share on other sites More sharing options...
camross Posted March 11, 2021 Author Share Posted March 11, 2021 30 minutes ago, xlr8or said: Edit: Yep, it’s a new production type. You need to change it. I would recommend switching to vintage UOS/NOS types. Try searching for a Mullard Blackburn UK late 1950’s f31 black micanol fat base 5AR4/GZ34. Gee, looking for the above is a little like looking for needle in a haystack. Can anyone recommend a good local 5AR4 to get me back up and running? Whatever I get maybe in the system for some time so Ideally best available local. Link to comment Share on other sites More sharing options...
xlr8or Posted March 11, 2021 Share Posted March 11, 2021 Here are some local ones to consider. https://www.ebay.com.au/itm/One-1-x-Mullard-CV1377-GZ34-5AR4-Electron-Vacuum-Tube-Valve-/224379184750 https://www.ebay.com.au/itm/Tube-5AR4-GZ34-Miniwatt-Holland-twin-square-getters-Strong-Tube-/133517984808 Here is a fat base: https://www.ebay.com.au/itm/1-x-Mullard-GZ34-5AR4-Rectifier-Tube-FAT-BASE-Very-Strong-Balanced-2-Avail-/373484536461 Link to comment Share on other sites More sharing options...
camross Posted March 11, 2021 Author Share Posted March 11, 2021 8 minutes ago, xlr8or said: Here are some local ones to consider. https://www.ebay.com.au/itm/One-1-x-Mullard-CV1377-GZ34-5AR4-Electron-Vacuum-Tube-Valve-/224379184750 https://www.ebay.com.au/itm/Tube-5AR4-GZ34-Miniwatt-Holland-twin-square-getters-Strong-Tube-/133517984808 Here is a fat base: https://www.ebay.com.au/itm/1-x-Mullard-GZ34-5AR4-Rectifier-Tube-FAT-BASE-Very-Strong-Balanced-2-Avail-/373484536461 Thanks unfortunately these are all for one only, other than the Fat Base which does have two available price is slightly out of my range at the moment with a new Power amp on layby. I have just remembered I still have the old two valves that I replaced. They still seemed good just replaced them as I wasn't sure how long they had been used for prior to my purchase of the amplifier second hand. Link to comment Share on other sites More sharing options...
xlr8or Posted March 11, 2021 Share Posted March 11, 2021 (edited) 54 minutes ago, camross said: I have just remembered I still have the old two valves that I replaced. They still seemed good just replaced them as I wasn't sure how long they had been used for prior to my purchase of the amplifier second hand. Use those for the moment and I'll contact you offline with a recommendation on a suitable pair. Edited March 11, 2021 by xlr8or 1 Link to comment Share on other sites More sharing options...
Tony@melb Posted March 13, 2021 Share Posted March 13, 2021 I had a similar problem with a rectifier in my PL Prologue preamp once. I replaced both rectifiers. I first tried the PL rectifiers and then replaced them will new issue Mullard. I find the new issue Mullard better than the PL stocks. They are relatively inexpensive, about A$60 each. If you'd like to spend the $$$, then NOS Mullard is much better. See links below to get the cheap version and the good version: https://www.thevalvestore.com.au/32-rectifiers http://tubes.tw/shop/index.php?cPath=25&osCsid=0e5d92f6d13d177c121750bd8d6aaa25 Good luck. 1 Link to comment Share on other sites More sharing options...
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