Crate VC5310 power tube failure ,and fuse blown.

[gtrplayr1976]

It's correct. But you have to know that in such meters (only on current range) there is quite often a fuse and sometimes the fuse fails. In this case you can still measure voltages but you cannot measure any current. Please check that you can measure curent; connect the meter to a 9V battery with 1k resistor in series. If in this case you also get 0 mA, then you need to fix the meter (the fuse inside) first.

Mark

Ok Mark. I'll check that out. I know it has worked in the past, but it could have blown somewhere along the line. Thanks

[gtrplayr1976]

It's correct. But you have to know that in such meters (only on current range) there is quite often a fuse and sometimes the fuse fails. In this case you can still measure voltages but you cannot measure any current. Please check that you can measure curent; connect the meter to a 9V battery with 1k resistor in series. If in this case you also get 0 mA, then you need to fix the meter (the fuse inside) first.

Mark

it was the fuse indeed. i`ll have to find some. Don`t know why I didn`t think of that. I`ve seen it happen before at work. Getting old sucks

[gtrplayr1976]

If the current is correct, this will be a waste of time. But if it is not correct, you could save some money (needed for new tubes). That's why I would do it. And it will help you to be on the safe side (I mean having the knowledge what is the current).
Can you also make a photo of the cap in the middle (from a different angle)? It looks a little bit suspicious.

Mark

I fixed the meter good enough to get a reading , and I`m seeing 76.3 ma. I have also noticed the standby switch doesnt go out immediately. It fades out..

[g1]

76.3mA for how many power tubes? Divide that number by however many power tubes to know the current per tube. Then multiply by the plate voltage to find your idle dissipation in watts.

[gtrplayr1976]

76.3mA for how many power tubes? Divide that number by however many power tubes to know the current per tube. Then multiply by the plate voltage to find your idle dissipation in watts.

Thanks g-one. That was with two tubes. Plate voltage is around 370 I think. I will have to check that again.

[MarkusBass]

So you have (76.3mA /2) *370 = 14W. This is a little bit too much. It should be 12W. I don't see a possibility to adjust the bias voltage in this amp. Maybe you should repeat the measurement with 4 tubes. It is possible that the plate voltage will be slightly lower in this case and the resulting power dissipation will decrease.

Mark

[gtrplayr1976]

So you have (76.3mA /2) *370 = 14W. This is a little bit too much. It should be 12W. I don't see a possibility to adjust the bias voltage in this amp. Maybe you should repeat the measurement with 4 tubes. It is possible that the plate voltage will be slightly lower in this case and the resulting power dissipation will decrease.

Mark

Hey Mark. I may be giving you the wrong voltage. I`ll get readings with the new tubes ,and make sure I get a voltage reading at the right point. Checked again and voltage is 407 with two tubes. I`ll check with four to see if theres a difference. I know my other two el84 amps run high too.

[MarkusBass]

Hey Mark. I may be giving you the wrong voltage. I`ll get readings with the new tubes ,and make sure I get a voltage reading at the right point. Checked again and voltage is 407 with two tubes. I`ll check with four to see if theres a difference. I know my other two el84 amps run high too.

No problem. You know now how to measure the current and how to calculate the power dissipation of a valve. I would keep it rather closer to 12W than 15W.

Mark

[gtrplayr1976]

No problem. You know now how to measure the current and how to calculate the power dissipation of a valve. I would keep it rather closer to 12W than 15W.

Mark

Thanks Mark. With four tubes in voltage at pin 7 of power tubes 395 ,current is 134ma. so its down around 13.2 now.

[MarkusBass]

This is a little bit hot but I would leave it as it is (guitar amps have to be hot). I assume the amp is OK now, right? Have you tried playing it?

[g1]

You can try the power tubes one at a time like that (idle only, no signal) to see if they are somewhat matched, or maybe there is one drawing way more idle current than the others.
Not sure if these are the tubes you will be using or if you are still going to replace with new ones?
If you want to change the bias level (once you have the tubes you will use), you can adjust the value of R78 in the bias circuit. Raising the value will cool down the idle current. Alternatively you could add a bias adjust pot in series with R78 (10K or so).
If you don't want to play with the bias, some tube sellers will let you specify what you want if you are buying matched power tubes. If you told them you wanted something that runs cooler, they would send you something appropriate.

[gtrplayr1976]

This is a little bit hot but I would leave it as it is (guitar amps have to be hot). I assume the amp is OK now, right? Have you tried playing it?

I havent played it yet. I was going over all the solder joints. The original issue was one channel
bleeding into the other. Im also getting some hum with no input and controls at 0. It may partly be my house because it gets a lot worse when I turn on the ceiling light ,but the light isnt florescent.

[gtrplayr1976]

You can try the power tubes one at a time like that (idle only, no signal) to see if they are somewhat matched, or maybe there is one drawing way more idle current than the others.
Not sure if these are the tubes you will be using or if you are still going to replace with new ones?
If you want to change the bias level (once you have the tubes you will use), you can adjust the value of R78 in the bias circuit. Raising the value will cool down the idle current. Alternatively you could add a bias adjust pot in series with R78 (10K or so).
If you don't want to play with the bias, some tube sellers will let you specify what you want if you are buying matched power tubes. If you told them you wanted something that runs cooler, they would send you something appropriate.

Thannks g-one. This is a new matched quad. I may try replacing the resistor or adding a pot.

[gtrplayr1976]

You can try the power tubes one at a time like that (idle only, no signal) to see if they are somewhat matched, or maybe there is one drawing way more idle current than the others.
Not sure if these are the tubes you will be using or if you are still going to replace with new ones?
If you want to change the bias level (once you have the tubes you will use), you can adjust the value of R78 in the bias circuit. Raising the value will cool down the idle current. Alternatively you could add a bias adjust pot in series with R78 (10K or so).
If you don't want to play with the bias, some tube sellers will let you specify what you want if you are buying matched power tubes. If you told them you wanted something that runs cooler, they would send you something appropriate.

Hey g-one. I am putting a bias pot in. Do I need to put the wiper ,and outside pins at a particular place ,or just lift one end of the resistor attach a leg ,and attach the wiper where the other end of the resistor was ?

Thanks !

[g1]

just lift one end of the resistor attach a leg ,and attach the wiper where the other end of the resistor was ?

Yes. Then check so full counter-clockwise gives max resistance of the pot. That way turning clockwise will make tubes run hotter.