To put a fine point on Wayne's comments, remove the output tubes, switch on and (following ALL safety precautions), make sure you have proper B+ going to the output tubes and that the grid bias voltage varies when you twiddle the bias adjust. If you've got those two things right, the rest of the troubleshooting is more likely to be smoke-free.
Yes, I already checked the voltages (446V, 336V, 244V if I remember correctly) before plugging in the tubes and bias adjust is working too. I read the security thread and was a little frightened
, as first rule I make sure to be extremely conscious and slow down when taking measurements, but also not losing confidence... it's a little double-sided.
regards
theduke
, as first rule I make sure to be extremely conscious and slow down when taking measurements, but also not losing confidence... it's a little double-sided.regards
theduke
amp's ready
@cogsncogs
Yes, the OPT primaries needed changing. That did the trick. My amp is working now 
first word on sound: very, very promising.
Somehow, I made another stupid mistake.. I left the right output open when adjusting the bias for these two tubes. This channel then sounded bad, but after a few "restarts" everything is fine again
!
One tube in the right channel needs -40V for 350mA cathode current, the other three -34V.
cogsncogs, thank you for your great help! Right now I am listening to a piece from Johannes Ockeghem (15th cen.), and it sounds quite beautiful.
I'll sure be back for more
theduke
@cogsncogs
Yes, the OPT primaries needed changing. That did the trick. My amp is working now
first word on sound: very, very promising.Somehow, I made another stupid mistake.. I left the right output open when adjusting the bias for these two tubes. This channel then sounded bad, but after a few "restarts" everything is fine again
!One tube in the right channel needs -40V for 350mA cathode current, the other three -34V.
cogsncogs, thank you for your great help! Right now I am listening to a piece from Johannes Ockeghem (15th cen.), and it sounds quite beautiful.
I'll sure be back for more
theduke
@ SY
I've been wundering why,
www.diyaudio.com/forums/showthread.php?s=&threadid=30172
wasn't made sticky in our beloved tube forum, which is were most toob noobs and not so toob noobs directly go to read or post posts about tube equipment and projects, where I think it would do the most good since it's dealing mostly with the high voltages found in tube circuits? Why not have it sticky in both places? Tube circuits (as you already know) are inherently more dangerous because of the high voltages involved.
Yes, I assumed since he seemed to know these things already, I didn't post about the precautions to take. Wrong on my part. I think I should have posted about the safety issues involved anyway in case there was a noob reading the post and was having a similar problem. So I'm going to change my posting behaviour and also in the interim I'm placing the link in my signature. We want every-one who visits here to be safe and be around to enjoy their own DIY work. 
Cheers
Wayne
I've been wundering why,
www.diyaudio.com/forums/showthread.php?s=&threadid=30172
wasn't made sticky in our beloved tube forum, which is were most toob noobs and not so toob noobs directly go to read or post posts about tube equipment and projects, where I think it would do the most good since it's dealing mostly with the high voltages found in tube circuits?
Why not have it sticky in both places? Tube circuits (as you already know) are inherently more dangerous because of the high voltages involved.Yes, I assumed since he seemed to know these things already, I didn't post about the precautions to take. Wrong on my part. I think I should have posted about the safety issues involved anyway in case there was a noob reading the post and was having a similar problem. So I'm going to change my posting behaviour and also in the interim I'm placing the link in my signature. We want every-one who visits here to be safe and be around to enjoy their own DIY work.
Cheers
Wayne
I would consider the voltage needed to drive a video tube CRT, well the anode voltage needed to clear the tube of an electron clould, would be considered ultra high voltage. Otherwise, wouldn't the 60,000 - 80,000 volts for a high resolution computer monitor tube would be considered, I suppose, Super High Voltage?
Might not have much current, but I bet it will still light up your eyeballs. 
Might not have much current, but I bet it will still light up your eyeballs.
@ theduke
Good to hear you've found the problem!
350mA!!!
I hope that's a typo! 350mV is what you would measure across the 10R cathode resistor.
On a tube amp that uses NFB esp, leaving an output unloaded with a signal applied can damage the opt and the associated tubes (OVERLOAD!). It can also cause to go into oscillation and you wouldn't even know it! Maybe a squeal coming from the opt or red plates. With no signal it shouldn't cause any significant harm, though it may and can happen! So always have a LOAD on a tube amp.
The channel that sounded bad, is that one with the poorly matched pair (-34V & -40V) and is that the one you left unloaded? Regardless I would replace that pair. I had the same problem. Look closely at the one tube that requires -40V bias for 35mA of current. Is there a significant portion of the filament hanging out of the bottom (or top, maybe) of the cathode sleeve? I would bet on money on it! I actually replaced them all with a matched quad, and kept the old ones for an emergency back-up. And yes having no tube amp IMO is an EMERGENCY! 
Shucks
Wayne
Good to hear you've found the problem!
Somehow, I made another stupid mistake.. I left the right output open when adjusting the bias for these two tubes. This channel then sounded bad, but after a few "restarts" everything is fine again
One tube in the right channel needs -40V for 350mA cathode current, the other three -34V.
350mA!!!
I hope that's a typo! 350mV is what you would measure across the 10R cathode resistor. On a tube amp that uses NFB esp, leaving an output unloaded with a signal applied can damage the opt and the associated tubes (OVERLOAD!). It can also cause to go into oscillation and you wouldn't even know it! Maybe a squeal coming from the opt or red plates. With no signal it shouldn't cause any significant harm, though it may and can happen! So always have a LOAD on a tube amp.
The channel that sounded bad, is that one with the poorly matched pair (-34V & -40V) and is that the one you left unloaded? Regardless I would replace that pair. I had the same problem. Look closely at the one tube that requires -40V bias for 35mA of current. Is there a significant portion of the filament hanging out of the bottom (or top, maybe) of the cathode sleeve? I would bet on money on it! I actually replaced them all with a matched quad, and kept the old ones for an emergency back-up. And yes having no tube amp IMO is an EMERGENCY!
cogsncogs, thank you for your great help! Right now I am listening to a piece from Johannes Ockeghem (15th cen.), and it sounds quite beautiful. I'll sure be back for more
Shucks
Wayne
@cogsncogs
Very good idea with that sticky thread though.
theduke
Typo. 350mV...
Lucky me, there was no signal applied. The last thing I would have is a broken OPT... But now it's GOOD. Maybe I put a few hundred reminder notes in my room or something...
Yes, all the same channel. Now there is a _very_ little bit of hum in that channel, barely noticable. In the other channel even less hum. No noise in that amp, as far as my ears can tell. But you can hear the power transformer hum if it's lying on a wooden ground (amp head over).
Very good idea with that sticky thread though.
theduke
Yupp... there's no way you can pull 350mA through an EL34.
I have to get within a couple of feet (meter) to hear my pwr tranny in a quiet room to hear any buzz. Before I installed the 10nF 2kV caps across all the secondaries that are (SS-sand)rectumfried, I could hear it across the room and while music is playing. Of course I have good ears...
Wayne
I just had one of my JJ's go bad on me 2-nite after abouute 8 mos. I was hoping I had a bad socket. No such luck. Good thing I had a bakup JJ! Pretty much matched with the others, almost dead on; not even worth mentioning the diff. @theduke, if you decide to go with JJ E34L's be prepared to adjust your bias quite a bit. They take less bias voltage than an EL34. Higher gm. Also it's a good idea to re-bias your amp after a couple of weeks or so, tube break-in. Dang now a light bulb blew, jeez! Scary! I think I'd better get outta here before the CRT blows in my monitor! 
What is it with me and vaccum tubes/bulbs/valves tonight?
Wayne
Scary! I think I'd better get outta here before the CRT blows in my monitor! What is it with me and vaccum tubes/bulbs/valves tonight?Wayne
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