A little background history. When I got it, it had no tubes. The wires going to the speaker and the tabs they go to had detached from the speaker. The speaker still works and I reattached the tabs. There is some oxidation on the face place and paint is worn off where the knobs are and are unreadable. All other tubes light up, some appear brighter than others. I have not pulled the chassis out of the box. It has a padded reverb box and wires were in tact. That's all I know. I have never seen it produce sound.
As stated in the initial thread, a power tube (EL84), the last one in the chain before the 12AX7's, left to right. But if signal flows through the 12AX7's first, then it would be the 1st tube in the power section.. Or you could just call it the 4th EL84 from the left to right. Anyway, at this point I'm going to pull the amp apart and look for signs of damage and check the wiring on that socket and the ones it is attached to.
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Looking at the schematic, the heaters seem to be in series. Only situation where you could get your situation that comes to mind is a short in parallel to pins 4&5 of the tube not lighting up.
You should be able test this hypothesis by turning the amp of, drain the capacitors, remove the power tubes and measure the resistance between the socket's pin 4&5.
You should be able test this hypothesis by turning the amp of, drain the capacitors, remove the power tubes and measure the resistance between the socket's pin 4&5.
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> 1 does not light up, a power tube, .... Does this mean I have a bad socket?
That is the most likely situation. Especially as you have tried moving tubes around. No, it is not essential to have "matched" tubes, certainly for troubleshooting.
For lurkers: The Classic 30 is an odd duck. There is a 25VAC winding powering four 6.3V power tubes (EL84). This is also rectified and filtered to 36VDC to feed three 12.6V preamp tubes (12AX7). Yes, it has a mains transformer; this is not a 5-toobe AC/DC table radio but a professional grade stage amplifier.
The schematic is a little hard to follow because heater connections are hinted, not drawn out.
https://el34world.com/charts/Schematics/files/Peavey/C30_schem.gif
That is the most likely situation. Especially as you have tried moving tubes around. No, it is not essential to have "matched" tubes, certainly for troubleshooting.
For lurkers: The Classic 30 is an odd duck. There is a 25VAC winding powering four 6.3V power tubes (EL84). This is also rectified and filtered to 36VDC to feed three 12.6V preamp tubes (12AX7). Yes, it has a mains transformer; this is not a 5-toobe AC/DC table radio but a professional grade stage amplifier.
The schematic is a little hard to follow because heater connections are hinted, not drawn out.
https://el34world.com/charts/Schematics/files/Peavey/C30_schem.gif
The heater connections are there, they are just not drawn as in a common amp. It takes some bouncing around the drawing.
If you had three of four power tubes working, the amp would still make sound.
As others have said, this amp runs those four tube heaters in series, so if any one of them goes out, ALL FOUR go out.
If you had three of four power tubes working, the amp would still make sound.
As others have said, this amp runs those four tube heaters in series, so if any one of them goes out, ALL FOUR go out.
It is also possible one EL84 or its socket is shorted across the heater. In fact it can't work if one EL84 heater is dead-open, because all the EL84 heaters would be cold.
With one shorted heater the 6V EL84s will be eating 8 volts, will be a bit brighter than normal, and heater life may fall to days instead of decades.
With one shorted heater the 6V EL84s will be eating 8 volts, will be a bit brighter than normal, and heater life may fall to days instead of decades.
I assume this is different from measuring plate voltage which is the only thing I could find on measuring tube voltage (440 volts). what pins will tell me if it is the 6.3 that each tube is supposed to be?
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Your tube heaters are wired i series anyway. There is little you can do if one tube has a "wrong" voltage across it. If all the tube heaters are lit, and the amp makes sound, then your heater string is working, and I would move on to the next issue. Even if heater voltages were off 20% r something, the amp would still make sound.
Pull the B+ fuse and measure it with an ohm meter. Look for missing B+, make sure the output transformer is plugged onto the right pegs.
Pull the B+ fuse and measure it with an ohm meter. Look for missing B+, make sure the output transformer is plugged onto the right pegs.
So what if they are wired in series --notice I said across EACH tube , series doesn't mean tubes designed to run at the same heater voltage can be wildly different that only applies if each tube is designed for series working and has different heater voltages that ADD up to the total voltage applied .
This website has plenty of odd heater voltage working tube circuits its the very reason radio tubes in mains derived voltage without a mains transformer serried up each tube to total the input voltage usually via a big ceramic drop-down resistor . as long as the current to each is similar then it works .
It is important to check across each tube for the correctly designed voltage--under voltage drops emission , I agree with JM Fahey once the OP has verified that everything is okay then get onto the next step.
This website has plenty of odd heater voltage working tube circuits its the very reason radio tubes in mains derived voltage without a mains transformer serried up each tube to total the input voltage usually via a big ceramic drop-down resistor . as long as the current to each is similar then it works .
It is important to check across each tube for the correctly designed voltage--under voltage drops emission , I agree with JM Fahey once the OP has verified that everything is okay then get onto the next step.
The Classic 30 has been around for decades. It uses three 12AX7s wires in series, and four EL84 wired in series. WHile it is possible we get an odd tube (of the types in this amp) that has a different voltage drop, I have yet to encounter it. Other than replace the tube, what would be the counter-measure? The same 150ma lights all three small tubes. And unless a 12AX7 is whacky, that will drop the expected 12.6vDC or close enough.
There were plenty of tubes with odd heater voltages, TV sets used to be full of them, and "All American Five" table radios. But the tubes in this amp are 12AX7 and EL84, about as common as tubes come these days. ANy they use standard 12.6v and 6.3v heaters.
Now one piece of advice I give my students is: never think up reasons not to check something. SO I have nothing against verifying he has 12vDC or so across each 12AX7 heater, and about 6vAC across each EL84 heater. But if you have never worked on a Classic 30, they are exceedingly difficult to get to with probes.
His problem is that he gets NO SOUND from the amp. If the heater voltages are skewed a little bit, it might sound funny, but it will sound. And if one is open, then the string goes dark.
There were plenty of tubes with odd heater voltages, TV sets used to be full of them, and "All American Five" table radios. But the tubes in this amp are 12AX7 and EL84, about as common as tubes come these days. ANy they use standard 12.6v and 6.3v heaters.
Now one piece of advice I give my students is: never think up reasons not to check something. SO I have nothing against verifying he has 12vDC or so across each 12AX7 heater, and about 6vAC across each EL84 heater. But if you have never worked on a Classic 30, they are exceedingly difficult to get to with probes.
His problem is that he gets NO SOUND from the amp. If the heater voltages are skewed a little bit, it might sound funny, but it will sound. And if one is open, then the string goes dark.
The signal path is like an obstacle course of switches /contacts etc and even the output goes through connectors , there are many places this could go wrong including broken jacks , without a good set of test equipment and a hope that the OP has the technical ability to trace this out .
For you and me its no big deal but I presume you have all the test equipment needed like myself , the problem is how long will it take without say an oscilloscope -a quality audio generator etc , we could be on this for a while as virtual instructions aren't the same as having on a bench with an illuminated magnifier , it would just be luck if he found the fault quickly.
If the plate voltages are okay -the heater voltages are okay then its a step at a time and -IMO the schematic could have been made a lot easier for those not good at reading schematics .
For you and me its no big deal but I presume you have all the test equipment needed like myself , the problem is how long will it take without say an oscilloscope -a quality audio generator etc , we could be on this for a while as virtual instructions aren't the same as having on a bench with an illuminated magnifier , it would just be luck if he found the fault quickly.
If the plate voltages are okay -the heater voltages are okay then its a step at a time and -IMO the schematic could have been made a lot easier for those not good at reading schematics .
This seems more productive than the phantom heater.
Is it "no sound" or "NO! sound"? With head on grill, any hiss or hum? Even fairly sick guitar amps make a little hiss or hum. When it is NO sound it would pay to look at speaker wiring all the way along Duncan's chain of weak links.
Right now he has a go/no-go situation. No sound. At this point any signal will do. Just a guitar cord and touch the tip with your finger to make hum. That is sufficient to tell if the amp is passing signal. I had a complete pro shop, but really most times I just lugged in a line from my bench stereo for a signal. I can look for distortion later. Right now he just needs the amp to make noise in the speaker.
One thing about the C30 not in most amps is the row of bare wire jumpers between boards. Power off, get under each little wire and GENTLY tug up on iy to see if it has broken free.
One thing about the C30 not in most amps is the row of bare wire jumpers between boards. Power off, get under each little wire and GENTLY tug up on iy to see if it has broken free.