7591 is glowing RED

dognut · 28th February 2009, 10:31 PM

Hello to all.Getting ready to recap & freshin up my sansui 1000a tube reciever.It works ok. However after 5 or 6 minutes one of the 7591s start to glow red. #A tube. (the vertical plate inside the tube). I did some voltage measurments when I first turned it on.Tube A cap +230v/-20 trim pot -18/-27/-23. Tube B cap +34v/-22 trim pot -17/-27/-22. Tube C cap +223v/-17 trim pot -18/-26/-22. Tube D cap +33/-21 trim pot -18/-27/-22. The last # on the trim pot looked like the wiper lead. Just for the heck of it I swaped the #6AN8 tubes There next in the circut line up & after 5 or 6 minutes # C tube started to glow red. Can I assume that I have a weak #6an8 tube???? By the way the next tube set in the circut lineup would be #12AX7s. Thanks in advance, tom

Eli Duttman · 1st March 2009, 01:26 AM

Replace all 4 coupling caps. between the phase splitters and the O/P tubes. Leaky caps. put a positive potential on the 7591 control grids, which leads to red plates.

danFrank · 1st March 2009, 06:16 PM

WOW, deja vu!

I stated the following when you asked a couple of weeks ago:

"Hi, Definately replace the 4 caps that go to the control grids of the 7591 output tubes. These are almost always bad, so to change them is a must. The other caps in the unit will also be leaky but those are the main 4 that need to be replaced."

Now you probably have a 7591 that is no longer good. Why did you evn bother asking in the first place if you were just going to plug it in and see what happens? Maybe you have money to burn?

There are a lot of smart people on here that offer good advice from their own experience... you should take it, it's free.
Daniel

1st March 2009, 01:26 AM	#2
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Replace all 4 coupling caps. between the phase splitters and the O/P tubes. Leaky caps. put a positive potential on the 7591 control grids, which leads to red plates. __________________ Eli D.

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28th February 2009, 10:31 PM	#1
dognut diyAudio Member Join Date: Oct 2007	7591 is glowing RED Hello to all.Getting ready to recap & freshin up my sansui 1000a tube reciever.It works ok. However after 5 or 6 minutes one of the 7591s start to glow red. #A tube. (the vertical plate inside the tube). I did some voltage measurments when I first turned it on.Tube A cap +230v/-20 trim pot -18/-27/-23. Tube B cap +34v/-22 trim pot -17/-27/-22. Tube C cap +223v/-17 trim pot -18/-26/-22. Tube D cap +33/-21 trim pot -18/-27/-22. The last # on the trim pot looked like the wiper lead. Just for the heck of it I swaped the #6AN8 tubes There next in the circut line up & after 5 or 6 minutes # C tube started to glow red. Can I assume that I have a weak #6an8 tube???? By the way the next tube set in the circut lineup would be #12AX7s. Thanks in advance, tom

1st March 2009, 06:16 PM	#3
danFrank diyAudio Member Join Date: May 2005 Location: California	WOW, deja vu! I stated the following when you asked a couple of weeks ago: "Hi, Definately replace the 4 caps that go to the control grids of the 7591 output tubes. These are almost always bad, so to change them is a must. The other caps in the unit will also be leaky but those are the main 4 that need to be replaced." Now you probably have a 7591 that is no longer good. Why did you evn bother asking in the first place if you were just going to plug it in and see what happens? Maybe you have money to burn? There are a lot of smart people on here that offer good advice from their own experience... you should take it, it's free. Daniel

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