keithpgdrb
Super Member
bump because I'd like to do some of this today. Power tubes out, what about the rest for the slow bring up?
Fisher 500c
- Thread starter keithpgdrb
- Start date
Threads are all merged! It may make for some interesting reading as we bounce from topic to topic, but it's all here.
If the item being tested has a rectifier tube, you can follow the linked directions and start with just that tube in. Obviously, that doesn't apply to a 500-C. I am not a fan of leaving out the power tubes. That will affect the balance of the voltages to some degree, and thus carries some risk. Some folks like to leave them out, I prefer to have all of the tubes present and accounted for when you start to ramp up the voltage. It's personal preference, pretty much. Starting with anything in the 40-60 watt range should be fine.
If the item being tested has a rectifier tube, you can follow the linked directions and start with just that tube in. Obviously, that doesn't apply to a 500-C. I am not a fan of leaving out the power tubes. That will affect the balance of the voltages to some degree, and thus carries some risk. Some folks like to leave them out, I prefer to have all of the tubes present and accounted for when you start to ramp up the voltage. It's personal preference, pretty much. Starting with anything in the 40-60 watt range should be fine.
keithpgdrb
Super Member
I get that. At this point I'm just trying to figure out if I'm to take out all the tubes or not. In the tube care guide, he makes it sound like you bring up the unit with no tubes at all, then do it again with only the power tubes. Or maybe he means that if you take out the power tubes, no power reaches the other tubes, so you can leave them In.
It's a great post, but it's a little unclear in places. I wish they wouldn't have closed it.
So, I'm going to wing a process here. My plan is to bring the unit up with NO tubes, then bring it up again with all tubes in place, plus speakers. There are some expensive tubes in this thing, I really don't want to ruin any.
If the tubes all test fine, leave them in. With the FISHER, the increase in system voltage at any supply voltage with the tubes OUT can be enough to overload caps when you start getting up in DBT Wattage.
I always leave tubes in. That way I can check items while it's at a lower voltage and monitor changes as it comes up.
Another thing is time. You don't need 12-24 hours on each bulb. Usually 1/2-1 hour on 60, then 1/2 hour on 75, 100W ea., then straight to wall outlet. It doesn't take long to bring a cap back up.
Larry
I always leave tubes in. That way I can check items while it's at a lower voltage and monitor changes as it comes up.
Another thing is time. You don't need 12-24 hours on each bulb. Usually 1/2-1 hour on 60, then 1/2 hour on 75, 100W ea., then straight to wall outlet. It doesn't take long to bring a cap back up.
Larry
keithpgdrb
Super Member
Just a quick update.
-I ran the dim bulb test with NO tubes at all through the various bulbs. no shorts. Yay!
Then, I screwed up. Please let me know if I've killed the amp. I reinstalled all the tubes, hooked up my mp3 player to the aux, hooked up some speakers, and started back with the 60w bulb. I let it go for about an hour.
Heres the mistake. as I was walking back to check on everything, I glanced at the speaker connection on the back of the speakers, and one wire was disconnected. I had been running the amp with the 60w bulb with only one wire connected to the right speaker for almost an hour. As soon as I saw it, I shut the amp off and made sure all the connections were solid. everything looked ok, but what does that really mean. I said a little prayer, and moved on to the 75w bulb. I can see some glowing in all 4 power tubes.
so tell me, assuming it was good before I started, what damage might I have done by my mistake? I'm kicking myself here.
also, at what point should I hear music out of the speakers. I've heard nothing so far on the 60 or 75.
-I ran the dim bulb test with NO tubes at all through the various bulbs. no shorts. Yay!
Then, I screwed up. Please let me know if I've killed the amp. I reinstalled all the tubes, hooked up my mp3 player to the aux, hooked up some speakers, and started back with the 60w bulb. I let it go for about an hour.
Heres the mistake. as I was walking back to check on everything, I glanced at the speaker connection on the back of the speakers, and one wire was disconnected. I had been running the amp with the 60w bulb with only one wire connected to the right speaker for almost an hour. As soon as I saw it, I shut the amp off and made sure all the connections were solid. everything looked ok, but what does that really mean. I said a little prayer, and moved on to the 75w bulb. I can see some glowing in all 4 power tubes.
so tell me, assuming it was good before I started, what damage might I have done by my mistake? I'm kicking myself here.
also, at what point should I hear music out of the speakers. I've heard nothing so far on the 60 or 75.
audiodon
Addicted Member
You should be Ok. The voltage isn't that high. Tube gear likes a load at the speaker outputs, but if it's not there for a while, it won't break, especially at low voltage. One of the reasons there are so many people willing to take on working on tube gear is that the gear is very forgiving and typically only burns out one thing or sometimes nothing.
In some solid state circuits, if something goes, there are often cascading failures in the surrounding circuitry.
In some solid state circuits, if something goes, there are often cascading failures in the surrounding circuitry.
keithpgdrb
Super Member
Very good to hear. I'm heading downstairs to put in the 100w bulb right now. no smoking yet.
I'll agree that you should be fine.
At the reduced voltage I'm assuming the glowing he's seeing is filaments.
Jailtime
Standin' on a corner
:stupid: Yeah, I'm just being dumb right now. I 'spose those outputs won't be doing much red plating with the DBT.
I remember the filaments in my little EL84 Soundcraftsmen coming on around 70V on the variac.
keithpgdrb
Super Member
ok then, here is snafu #1
There are 4 small lights in the 500c. two on each side of the glass tuner plate, and two behind the plate on the actual chassis. throughout this process, the chassis bulb on the left (when facing the unit head on), has been consistently dimmer, and flickers now and then. If I rolled the tubes in the audio amp section, the light would get a little brighter, sometimes staying brighter, sometimes going back. I figured it might be a messed up bulb, but did not worry too much about it.
When I put in the 100w light bulb, the unit powered up like before, and after about 15-20 seconds, the bulbs on the left of the unit go out, as well as two of the power tubes in the back. this is accompanied by a relay click sound. I repeated the test a few times, and the little relay underneath does indeed switch off. what confuses me, is that the bulbs on the right stay on after the others go off.
I assume there is a bad part somewhere, but I would think that when the relay (protection circuit?) clicks, the whole unit would shut down. but it does not.
I replaced the 100w bulb with the 75 again, and everything stays on. I do not have any bulbs in between 75 and 100, so I cant test how far it can go.
at this point, I have put the 75w bulb back in, and continue to let it go. what should I do next? Or, it could be that I have done as much as I can, and I must wait for outside assistance.
There are 4 small lights in the 500c. two on each side of the glass tuner plate, and two behind the plate on the actual chassis. throughout this process, the chassis bulb on the left (when facing the unit head on), has been consistently dimmer, and flickers now and then. If I rolled the tubes in the audio amp section, the light would get a little brighter, sometimes staying brighter, sometimes going back. I figured it might be a messed up bulb, but did not worry too much about it.
When I put in the 100w light bulb, the unit powered up like before, and after about 15-20 seconds, the bulbs on the left of the unit go out, as well as two of the power tubes in the back. this is accompanied by a relay click sound. I repeated the test a few times, and the little relay underneath does indeed switch off. what confuses me, is that the bulbs on the right stay on after the others go off.
I assume there is a bad part somewhere, but I would think that when the relay (protection circuit?) clicks, the whole unit would shut down. but it does not.
I replaced the 100w bulb with the 75 again, and everything stays on. I do not have any bulbs in between 75 and 100, so I cant test how far it can go.
at this point, I have put the 75w bulb back in, and continue to let it go. what should I do next? Or, it could be that I have done as much as I can, and I must wait for outside assistance.
keithpgdrb
Super Member
Would this still be true if the selector switch is on aux? It shouldn't be dealing with the radio if it's on aux right? I'm a little less scared now.
The right side light stays on even if the selector switch is set to Aux. Not sure about the two power tubes going off, though. At this point, since you've gone up to a 100 watt bulb and there's no sign of anything smoking, I'd hook up a cd player and some speakers and let's see what we've got.
keithpgdrb
Super Member
I changed the selector switch to "FM Stereo" instead of AUX, and now all the lights stay on. when I look back, I must have been wrong about the power tubes going off, because now everything is on. I'm going to let this sit for an hour or so, then plug it into the wall and see what happens. One think I can tell for sure is I need to deoxit everything again. I heard some radio static, but also lots of crackling as I played with the volume. plus, I only got sound out of one speaker. I've had this happen before with dirty switches. I'm hoping that is the case.
So, official Snafu #2. the light on the front right of unit (looks like a fuse) came apart when I was trying to turn it a little. the bottom metal cap came right off. is there a way to fix it? I put it back together and stuck it in, and its working, but its still just a band aid fix.
So, official Snafu #2. the light on the front right of unit (looks like a fuse) came apart when I was trying to turn it a little. the bottom metal cap came right off. is there a way to fix it? I put it back together and stuck it in, and its working, but its still just a band aid fix.
Yup, one of the most common causes of one channel out is dirty switches. If the one fuse lamp is still working, super glue works just fine to hold on the loose end.
keithpgdrb
Super Member
friends, it looks like we have a working amp. The left channel was working fine when I got her up to wall voltage. I've checked all the inputs, and they seem fine. I have static on all the radio channels, but that is because I am in the basement with no antenna. But, there is sound.
There is just a little bit of crackling and static sometimes, but I'm going to clean the pots and switches again to see what that does. The power tubes also run pretty darn hot, but I've read that is what they do. The output transformers do not get hot, so that should be a good thing. one concern, is that it really seems that V10 and V11 (back left power tubes) burn a bit brighter then the others.
So, now that I see the unit is functioning, I should probably take some measurements with my multimeter to check out general health. I do know there are key parts that need replacing (selenium rec.) because of the many threads on it. What do you all suggest as the next step? Should I order up the metalbone kit right away? or should I do some checking first? (by the way, I dont know where to take measurements.)
One thing I will say, is that having your tubes checked takes a huge worry off of your mind.
thank you all so far. we're moving along here. and I'm excited.
There is just a little bit of crackling and static sometimes, but I'm going to clean the pots and switches again to see what that does. The power tubes also run pretty darn hot, but I've read that is what they do. The output transformers do not get hot, so that should be a good thing. one concern, is that it really seems that V10 and V11 (back left power tubes) burn a bit brighter then the others.
So, now that I see the unit is functioning, I should probably take some measurements with my multimeter to check out general health. I do know there are key parts that need replacing (selenium rec.) because of the many threads on it. What do you all suggest as the next step? Should I order up the metalbone kit right away? or should I do some checking first? (by the way, I dont know where to take measurements.)
One thing I will say, is that having your tubes checked takes a huge worry off of your mind.
thank you all so far. we're moving along here. and I'm excited.
Congratulations, Keith!
You've been quite cautious all the way, and it has paid off. At this point, you know two very important things, first, everything works, and, second, you need to do the basic restoration before you play it because of the output tubes being noticeably red.
So, yup, I'd go ahead and order the metalbone kit and get started! Replace the rectifier, bias supply rebuild, diodes, coupling caps, and a few resistors. You'll be a professional before you're done!:thmbsp:
You've been quite cautious all the way, and it has paid off. At this point, you know two very important things, first, everything works, and, second, you need to do the basic restoration before you play it because of the output tubes being noticeably red.
So, yup, I'd go ahead and order the metalbone kit and get started! Replace the rectifier, bias supply rebuild, diodes, coupling caps, and a few resistors. You'll be a professional before you're done!:thmbsp:
