I'm thinking more rodded with the Sylvania's though like well into SLO like...you know them really Drunk rodded Bar Riffs/sounds etc xD,
them short bottles sound a lot more like that, the tall bottle's are more balanced/laid back. Both are unbelievably detailed, I still keep going back to,wanting to use them.
them short bottles sound a lot more like that, the tall bottle's are more balanced/laid back. Both are unbelievably detailed, I still keep going back to,wanting to use them.
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Anyone know how the old GE 5-star 6L6GCs do in this amp, same thing do they tolerate the voltage well and sound decent?
Just noticed here that the plate rating is 500V and 450V for the screen, I didn't remember the GC being that high, should be fine:
http://www.radiostation.ru/tubes/6L6GC-GE.pdf
Just noticed here that the plate rating is 500V and 450V for the screen, I didn't remember the GC being that high, should be fine:
http://www.radiostation.ru/tubes/6L6GC-GE.pdf
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Any 6L6GC will be OK in this circuit, it is older versions of the tube with lower specs, and even then, most of those will be happy too. it isn't the voltage that kills these tubes, it is the parts dissipating. Your plates should not be redplating, and you don't want to melt the screens. 500v isn't the issue, too much current is.
All 6L6s will still sound like the amp, any differences will be nuances of tone, and will not always turn up at high levels. SOme only reveal their character when cranked for example. Such differences will be a matter of taste.
All 6L6s will still sound like the amp, any differences will be nuances of tone, and will not always turn up at high levels. SOme only reveal their character when cranked for example. Such differences will be a matter of taste.
After doing some research, as of 2001, the US had not banned lead based solder. I also discovered that lead free solder is pretty much worthless unless you have a much hotter soldering iron. I would use the standard 60/40 or if you want lower melt temps, 63/37.
There is a history of these jacks being cheap and since they are PCB mounted, adds to the poor quality. And as I recall in an earlier post, you are missing the locknut on the outside of the jack. Sounds like a recipe for failure no matter what solder was used.
I'm also wondering since you have the correct schematic in hand, have you done those voltage measurements? You still need to determine what caused the redplating and the low 25mA bias. A complete assessment of B+ supply should be done both at the B+ rail and at the tube sockets to find posible bad resistors or solder joints.
There is a history of these jacks being cheap and since they are PCB mounted, adds to the poor quality. And as I recall in an earlier post, you are missing the locknut on the outside of the jack. Sounds like a recipe for failure no matter what solder was used.
I'm also wondering since you have the correct schematic in hand, have you done those voltage measurements? You still need to determine what caused the redplating and the low 25mA bias. A complete assessment of B+ supply should be done both at the B+ rail and at the tube sockets to find posible bad resistors or solder joints.
The US still has not banned lead solder, but US manufacturers usually use lead free solder because they are not going to make separate circuit boards for the US and Euro markets. I don't think Fender was using lead free that far back.
You are in the US, and you may feel free to use leaded solder.
In any case, cracked solder under the input jacks is almost always due to the jack moving and flexing. A stripped or missing nut on the jack bushing is a primary cause of that.
You are in the US, and you may feel free to use leaded solder.
In any case, cracked solder under the input jacks is almost always due to the jack moving and flexing. A stripped or missing nut on the jack bushing is a primary cause of that.
We heard a high pitched squeal when it red plated and I'm thinking that perhaps the ground being open at the jack might have let RF in, that somehow beat down into the audio range - but really who knows. We plugged into the #2 jack after the red plate and it never happened again.
My son noticed that it was only one tube, and sure enough the paint is only browned out on one tube.
I want to get all the solder connections fixed first, then we will go on to debugging the rest. The low bias was due to it being set low, we were able to get it back in range.
I notice that the output tube coupling caps are quite small, are these prone to failure? I'm tempted to just put in some Sprague orange drop or whatever is considered best.
I'm going to use my usual Kester 60/40 or whatever lead solder that I have on hand.
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The adjustment range for these Hot Rod amps won't allow you to get down to 25mA for two tubes unless somebody modded the bias network or there was a huge change in design between 1996 and 2001, but you seem very knowledgeable and will find something. Depending on what tubes I have in, I can only adjust between about 50 to 70mA. Or maybe it was associated with the redplate incident and won't surface again. It also could be due to a bad tube; again maybe the redplating caused the tube to go bad.I still would be on the lookout for an intermittent problem such as a lose solder joint or resistor problem that changes as the amp heats up. This is the problem I found and fixed in mine. R58 only failed when the amp changed due to heating/cooling
Do you mean the coupling caps are physically small or the uF rating is small? I know some mods call subbing in Orange Drops but I don't think you want to too much larger uF rating wise, you could run into a possible blocking distortion problem.
Do you mean the coupling caps are physically small or the uF rating is small? I know some mods call subbing in Orange Drops but I don't think you want to too much larger uF rating wise, you could run into a possible blocking distortion problem.
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Well, 50ma at the test point is 25ma per tube.
There are a bazillion Hot Rod series amps out there, and they are not known for eating coupling caps. I highly recommend leaving them alone unless they are misbehaving.
Just a thought, if the input jack grounds were passing some sort of RF through the amp, it ought to affect all the power tubes, not just one.
I hate when someone expects "common issues" to be present in their amp, but as a Fender service shop, if I had to list things that happen to the Hot Rod series more than it should, I can think of maybe three.
First, every time I open one of these up, the first thing I do is inspect the solder on the 6L6 socket pins, they tend to crack. I usually just resolder them regardless, and move on. That could even be involved in occasional red plating.
Next, not really common, but be on the lookout for open plate resistors in the phase inverter, particularly the 82k one.
And lastly, there are two five watt power resistors near the bottom edge of the main board. They are dropping resistors for the zener diodes in the 15v supplies. 470 ohm. They get very hot, and can unsolder themselves. By mounting new ones up off the board on their leads, you give them better air space, and the lead length acts as a bit of heat sink. Also, by baring the traces underneath and laying the remaining lead length down along the trace and soldering all along, it also acts as a heat sink. Of course we could go all anal about it and mount some larger resistors, like the aluminum Dale type, on the chassis and run four wires to the board. Also, some amps have 330 ohm there. Those will run even hotter and should be changed back to 470 ohm.
There are a bazillion Hot Rod series amps out there, and they are not known for eating coupling caps. I highly recommend leaving them alone unless they are misbehaving.
Just a thought, if the input jack grounds were passing some sort of RF through the amp, it ought to affect all the power tubes, not just one.
I hate when someone expects "common issues" to be present in their amp, but as a Fender service shop, if I had to list things that happen to the Hot Rod series more than it should, I can think of maybe three.
First, every time I open one of these up, the first thing I do is inspect the solder on the 6L6 socket pins, they tend to crack. I usually just resolder them regardless, and move on. That could even be involved in occasional red plating.
Next, not really common, but be on the lookout for open plate resistors in the phase inverter, particularly the 82k one.
And lastly, there are two five watt power resistors near the bottom edge of the main board. They are dropping resistors for the zener diodes in the 15v supplies. 470 ohm. They get very hot, and can unsolder themselves. By mounting new ones up off the board on their leads, you give them better air space, and the lead length acts as a bit of heat sink. Also, by baring the traces underneath and laying the remaining lead length down along the trace and soldering all along, it also acts as a heat sink. Of course we could go all anal about it and mount some larger resistors, like the aluminum Dale type, on the chassis and run four wires to the board. Also, some amps have 330 ohm there. Those will run even hotter and should be changed back to 470 ohm.
Especially 6l6s I think they need really cooking to sound their best..EL34s to me can loaf around a bit lower bias still sound pretty good...but I think 6l6s sound uglier trying to run them on the cold side...
/6l6s has always been more go to for me though, because of being a lot more laid back/just coming off as more balanced imo.
/6l6s has always been more go to for me though, because of being a lot more laid back/just coming off as more balanced imo.
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I have been thinking that both should red plate at the same time, so I swapped them and we'll see the outcome.
I have re-flowed all the tube connections and anything else that looks like it might need it.
I have already raised the 5W resistors but they are the 330 ohm value, odd that nothing looks hot around them. I've read that they involve the foot-switch which probably has never been used with this unit. Edit: just looked at the schematics and this is a myth. The resistors are in the zener regulator and it makes no sense that this unit shows no sign of heating.
I will check the plate resistors, and voltages once everything else is ready to go.
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No, the resistors don't involve the footswitch, the footswitch involves the resistors, if you get me. The resistors are simply the source of current for the +/-15v supplies. Those supplies are for the op amps which the footswitch circuit uses, but they are also used for other things in the amp, so using the footswitch or not has no impact on them.
It really sounds to me like you have a situation where, for whatever reason, only one of the output tubes is actually pulling current and producing sound. This is in line with all the symptoms you are describing: bad sound, random oscillation, only one tube redplating, 25mA (about half the expected) even though bias voltage at the grids is correct at -50V. I once had an amp in for repair that showed exactly these problems, and it turned out that one side of the primary winding of the OPT was burned open, so plate voltage only came to one of the output tubes, effectively running the OPT single ended...
That's exactly why I have been trying to have them get those B+ rail voltages taken and then the corresponding voltages at the tubes and other points on the board after they leave the power supply to determine if any resistors or solder joints are bad in between. This is what I was thinking when they had only 25mA at TP 30, maybe only one tube conducting or sending output to the OT. Or a bad resistor or solder joint between the B+ and plates of the 6L6s. Could be a bad screen voltage., who knows. Since the redplating has stopped, there should be no danger in doing this procedure. Fender is very generous with their info for test points.
It also makes sense to repair solder joints first, but I don't know how you find these since there are so many. The voltage test would go a long way to help determine this.
It also makes sense to repair solder joints first, but I don't know how you find these since there are so many. The voltage test would go a long way to help determine this.
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Makes a lot of sense thanks I'll check that.
We will begin debugging with voltages once all the obvious problems are fixed, of course we will check voltages and the resistors mentioned.
One output tube screen was at .5 V, tacked another resistor across it and now it is back to about 498V. Centered bias pot and am getting 76 mV before making the adjustment. This looks to be the main problem in the output stage but I will check the other resistors there also.
I'm curious to run the tubes at their rated 30W to be sure that they do not red plate and we get 112 mA total with the control all the way up, now. That works out to 27.5W per tube, plate voltage is 491, screen is 490 - no red plating.
Might leave the bias at about 40 mA per tube which works out to 20W per tube, well within the spec.
Driver tube has 306V on pin 1 and 296 on pin 6, I assume that means that the plate resistors are okay?
I'm curious to run the tubes at their rated 30W to be sure that they do not red plate and we get 112 mA total with the control all the way up, now. That works out to 27.5W per tube, plate voltage is 491, screen is 490 - no red plating.
Might leave the bias at about 40 mA per tube which works out to 20W per tube, well within the spec.
Driver tube has 306V on pin 1 and 296 on pin 6, I assume that means that the plate resistors are okay?
I'm seeing 36 V one one side, and 16V on the other of the 330 ohm resistors, that is a drop of 20 V so the power is:
P = 20^2/330 = 1.21 W on a 5W resistor
It makes no sense at all that the board would be scorched, unless there is no air flow and the temp inside the chassis gets very hot. I have already elevated them so we should be fine.
Ventilation should be added if it does get that hot. I'd guess that they don't want to have holes in the case since it might be a shock hazard if a paperclip or whatever were to fall inside but they should get some airflow through the case or put a heatsink on the chassis to get some heat flow out of the case. Just remembered that the small tubes vent inside the chassis so they will add quite a few watts to the power inside.
Here is the theory for heat rise for a sealed enclosure, it seems that the curve is backwards since I'd expect a case made from an insulating material to have a greater rise than a metallic case:
http://www.hoffmanonline.com/stream_document.aspx?rRID=233309&pRID=162533
P = 20^2/330 = 1.21 W on a 5W resistor
It makes no sense at all that the board would be scorched, unless there is no air flow and the temp inside the chassis gets very hot. I have already elevated them so we should be fine.
Ventilation should be added if it does get that hot. I'd guess that they don't want to have holes in the case since it might be a shock hazard if a paperclip or whatever were to fall inside but they should get some airflow through the case or put a heatsink on the chassis to get some heat flow out of the case. Just remembered that the small tubes vent inside the chassis so they will add quite a few watts to the power inside.
Here is the theory for heat rise for a sealed enclosure, it seems that the curve is backwards since I'd expect a case made from an insulating material to have a greater rise than a metallic case:
http://www.hoffmanonline.com/stream_document.aspx?rRID=233309&pRID=162533
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That the phase inverter has B+ voltage on its plates tells us the plate load resistors are not open. That 10v difference is negligible.
When those 330/470 ohm resistors burn, it isn't so much the temperature in the chassis. A 2w resistor or a 10 watt resistor both generate the same heat with 20v (or whatever) across them. But the 10w spreads it over a larger surface. 1.2 watts doesn't sound like a lot, but it is concentrated in a small area. That is what causes the issue. And that is why raising them helps, and the other ways to add metal mass to the part.
When those 330/470 ohm resistors burn, it isn't so much the temperature in the chassis. A 2w resistor or a 10 watt resistor both generate the same heat with 20v (or whatever) across them. But the 10w spreads it over a larger surface. 1.2 watts doesn't sound like a lot, but it is concentrated in a small area. That is what causes the issue. And that is why raising them helps, and the other ways to add metal mass to the part.