Are all 4 power amp tubes supposed to glow when turned on? I noticed 3 of the 4 were glowing, but the 2nd from the right (input jack side, looking from the back) is not glowing. Amp seems to sound fine, and switching tubes around yielded the same result. Do i have a problem that i should get inspected? or is this normal?
5150: one of my power amp tubes not glowing
- Thread starter pariah223
- Start date
Vinny
Member
Ok so, it turned out to not be a specific socket, i moved some tubes around again, and the same tube doesnt glow no matter where i put it, i just got this matched set from dougstubes, i guess its safe to assume i got a bum tube? or are all 4 not supposed to be lit?
All tubes should glow. The glow is the heater element heating up the cathode. Without the cathode hot, the tube is doing absolutely nothing. Time to replace it.
Thats what i was afraid of.. why would the amp sound fine though if 1 power tube was not working? thats the part thats throwing me off the most..
::XeS::
Member
Some people choose to run their 100/120 Watt heads with only ONE set of output tubes to effectively halve the output power.
This also halves the output impedance. So if you were running your 100W head @ 16 ohms, taking one set of the power tubes out would mean you're running 50W @ 8 ohms. Be sure to change your impedance selection accordingly.
To the OP, the reason your amp is still working is that only one tube has failed. You have two pairs of output tubes; each pair does one-half of the signal (one does the positive half, one does the negative half).
Since you've only lost one tube, there's still another tube working on whatever side (positive or negative) the failed tube is on. However, that means that one-half of your output signal (either the positive or negative half) is going to be 50% of the amplitude of the unaffected side. I can't imagine that would sound normal.
Also your output impedance will have changed. I can't imagine any situation where you'd want to continue running on only 3 power tubes. Either replace the bad one or run on only ONE set (either the outer or inner pair) and change your impedance selection.
This also halves the output impedance. So if you were running your 100W head @ 16 ohms, taking one set of the power tubes out would mean you're running 50W @ 8 ohms. Be sure to change your impedance selection accordingly.
To the OP, the reason your amp is still working is that only one tube has failed. You have two pairs of output tubes; each pair does one-half of the signal (one does the positive half, one does the negative half).
Since you've only lost one tube, there's still another tube working on whatever side (positive or negative) the failed tube is on. However, that means that one-half of your output signal (either the positive or negative half) is going to be 50% of the amplitude of the unaffected side. I can't imagine that would sound normal.
Also your output impedance will have changed. I can't imagine any situation where you'd want to continue running on only 3 power tubes. Either replace the bad one or run on only ONE set (either the outer or inner pair) and change your impedance selection.
crillemannen
Member
Not to highjack the thread but...
What about the preamp-tubes? I got some problem with my 5150. Checked the preamp tubes and only 2/4 are glowing. Shouldn't all tubes glow?
What about the preamp-tubes? I got some problem with my 5150. Checked the preamp tubes and only 2/4 are glowing. Shouldn't all tubes glow?
JakeAC5253
Frozen Sun Audio
- Nov 19, 2010
- 936
- 1
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Tubes glow when there is presence of gases in the glass which failed to be evacuated during the vacuum process. Tubes don't need to glow in order to function correctly, you only have a real problem if it doesn't sound right. I've found that power tubes typically glow more reliably than preamp tubes do. Lots of fully functioning 12ax7 preamp tubes will either glow very dull or not at all, and still function as they should.
Contact Doug and see what he has to say. Maybe it wasn't glowing there either, but still biased and metered in the right spot.
Contact Doug and see what he has to say. Maybe it wasn't glowing there either, but still biased and metered in the right spot.
so the tube is definatly at fault, i talked to doug and he already has a replacement in the mail, and im sending this bogus one back to him. I asked him if it would hurt the amp to use it with 2 of the new tubes, and 2 of the old tubes in pairs and he said it should be fine. So i put two of each in... and my GOD, i can not beleive how different my amp sounds than it used to. Not sure if its the new preamp tubes, or the 2 new power tubes (i think i was only running off of 2 tubes before i ordered new ones, because 2 of my old tubes do not glow, just never noticed because i never looked) Im sure you guys dont need to be told that new tubes are amazing, but ive had the same tubes in this amp since i bought it (10 years ago) and the guy i bought it from had it for 5 years without changing tubes. Amazing the amp still managed to sound decent, but NOTHING like this.
quick question im having trouble finding the answer to.. do the pairs go 2 outer, and 2 inner, or is it 2 left and 2 right? if you know what i mean. . ill draw a little picture in case i confused anyone:
1=new tubes, 2 = old tubes
1221 or 1122 ?
quick question im having trouble finding the answer to.. do the pairs go 2 outer, and 2 inner, or is it 2 left and 2 right? if you know what i mean. . ill draw a little picture in case i confused anyone:
1=new tubes, 2 = old tubes
1221 or 1122 ?
::XeS::
Member
Preamp tubes are different. For example Sovtek lps doesn't glow at all, other tubes glows..it depends also by the construction.
Power tubes always glow
