amp problems, sorta off topic, sorry im at my wits end

[freak scene]

so i have a garnet pro L190B with reverb.  this amp sounds awesome when it works but has been a thorn in my side since i bought it.  first the output transformer was dead, then i found out the amp was wired for 6l6's.  then it starts popping fuses, so i open it up and with a little help from some people on HCFX, deduce that the bias capacitor is probably bad, so i replace it with a bit beefier value with the intention of eventually installing a bias pot.  then i notice one of the power resistors is black and has burnt a wire resting on it, i replace both and a couple more power resistors just to be safe.  now i have a really bizarre problem. 

when i turn the amp on but leave it in standby one tube is getting about 31 milliamps and the other nothing.  they are both getting about 560 volts.  when i turn the amp off standby the tube that is getting 31 milliamps immediately turns red and my bias rite goes past the 100 milliamp mark.  at which point i panic and turn the amp off, and then curse and flip the amp over and try to figure out whats going on.

i am planning on replacing the filter caps (all cans) which is looking to be a bit pricey.  what are the pros/cons of using cans over just using regular electrolytics?  i need an odd value (2x20uf+2x40uf) which i have found but its 30.56 from tubes and more.com.  i also need 4 1x80uf cans which havent proven easy to find either.  i found some 80uf electrolytics on mouser but didnt know if that would serve my purpose.

i have a schematic for a pro without reverb, and this amp looks to have been mucked around with a bit.  though im not too familiar with the guts of other garnets. 

[The Tone God]

Check your bias supply further. It sounds like one of the tubes is not getting bias so back trace from the grid of the bad tube till you find the problem spot. I believe you can do this with the tubes pulled and the amp in standby for safety.

Andrew

[Mark Hammer]

With Gar Gillies now gone, our go-to guy for Garnet amps here will be J.C.Maillet.  Go to his Viva Analog site and you'll find some Garnet and contact info.  http://www.lynx.bc.ca/~jc/

[chillhuman]

so i have a garnet pro L190B with reverb.  this amp sounds awesome when it works but has been a thorn in my side since i bought it.  first the output transformer was dead, then i found out the amp was wired for 6l6's.  then it starts popping fuses, so i open it up and with a little help from some people on HCFX, deduce that the bias capacitor is probably bad, so i replace it with a bit beefier value with the intention of eventually installing a bias pot.  then i notice one of the power resistors is black and has burnt a wire resting on it, i replace both and a couple more power resistors just to be safe.  now i have a really bizarre problem. 

when i turn the amp on but leave it in standby one tube is getting about 31 milliamps and the other nothing.  they are both getting about 560 volts.  when i turn the amp off standby the tube that is getting 31 milliamps immediately turns red and my bias rite goes past the 100 milliamp mark.  at which point i panic and turn the amp off, and then curse and flip the amp over and try to figure out whats going on.

i am planning on replacing the filter caps (all cans) which is looking to be a bit pricey.  what are the pros/cons of using cans over just using regular electrolytics?  i need an odd value (2x20uf+2x40uf) which i have found but its 30.56 from tubes and more.com.  i also need 4 1x80uf cans which havent proven easy to find either.  i found some 80uf electrolytics on mouser but didnt know if that would serve my purpose.

i have a schematic for a pro without reverb, and this amp looks to have been mucked around with a bit.  though im not too familiar with the guts of other garnets. 

First, discharge your filter caps. Assume that tube amp voltage WILL kill you if you make connection from high voltage secondary into one hand, across your heart, and out of your other hand to ground. What I do is make sure I always have jeans on when I work so I can keep my free hand in my back pocket.

My suggestion is to find a schematic for the amp, check *all* components which you can, replace anything that looks bad, and squeeze all the filter caps. Any filter caps which crackle or don't feel right for any reason, replace them. Replacing the filter caps as a matter of course is a good idea anyway. Then desolder your transformer mains, and follow the steps here

http://www.paulrubyamps.com/info.html#FirstPowerUp

I am willing to bet that you will see your problem when you get to the "pull the preamp and power tubes section and check the voltages" section.

[freak scene]

With Gar Gillies now gone, our go-to guy for Garnet amps here will be J.C.Maillet.  Go to his Viva Analog site and you'll find some Garnet and contact info.  http://www.lynx.bc.ca/~jc/

damn, when did gar pass?  i didnt hear about this.  sad news.

ill check the site thanks!

[freak scene]

so i have a garnet pro L190B with reverb.  this amp sounds awesome when it works but has been a thorn in my side since i bought it.  first the output transformer was dead, then i found out the amp was wired for 6l6's.  then it starts popping fuses, so i open it up and with a little help from some people on HCFX, deduce that the bias capacitor is probably bad, so i replace it with a bit beefier value with the intention of eventually installing a bias pot.  then i notice one of the power resistors is black and has burnt a wire resting on it, i replace both and a couple more power resistors just to be safe.  now i have a really bizarre problem. 

when i turn the amp on but leave it in standby one tube is getting about 31 milliamps and the other nothing.  they are both getting about 560 volts.  when i turn the amp off standby the tube that is getting 31 milliamps immediately turns red and my bias rite goes past the 100 milliamp mark.  at which point i panic and turn the amp off, and then curse and flip the amp over and try to figure out whats going on.

i am planning on replacing the filter caps (all cans) which is looking to be a bit pricey.  what are the pros/cons of using cans over just using regular electrolytics?  i need an odd value (2x20uf+2x40uf) which i have found but its 30.56 from tubes and more.com.  i also need 4 1x80uf cans which havent proven easy to find either.  i found some 80uf electrolytics on mouser but didnt know if that would serve my purpose.

i have a schematic for a pro without reverb, and this amp looks to have been mucked around with a bit.  though im not too familiar with the guts of other garnets. 

First, discharge your filter caps. Assume that tube amp voltage WILL kill you if you make connection from high voltage secondary into one hand, across your heart, and out of your other hand to ground. What I do is make sure I always have jeans on when I work so I can keep my free hand in my back pocket.

My suggestion is to find a schematic for the amp, check *all* components which you can, replace anything that looks bad, and squeeze all the filter caps. Any filter caps which crackle or don't feel right for any reason, replace them. Replacing the filter caps as a matter of course is a good idea anyway. Then desolder your transformer mains, and follow the steps here

http://www.paulrubyamps.com/info.html#FirstPowerUp

I am willing to bet that you will see your problem when you get to the "pull the preamp and power tubes section and check the voltages" section.

thanks a ton, im bookmarking these sites. 

the filter caps are cans so i cant really squeeze them.  i have ordered replacements for the ceramic disk caps, and plan on replacing the electrolytes soon.  just trying to find the right values.

[jrc4558]

Could you possibly post pictures? It will be easier to diagnose. Also, if you are in Toornto by any chance - let me know, I could help you.
Take your power tubes out of the amp and check that the bias voltage is equal on both tubes. Check the polarity of the caps in the bias netwirk. Check your tubes as well!

[freak scene]

Could you possibly post pictures? It will be easier to diagnose. Also, if you are in Toornto by any chance - let me know, I could help you.
Take your power tubes out of the amp and check that the bias voltage is equal on both tubes. Check the polarity of the caps in the bias netwirk. Check your tubes as well!

tested tubes, ei 6ca7's on my heathkit tc-2 they were good but not great. 

i was poking around tonight and i could not get any measurements on any of the resistors in the power amp circuit.  i tried de soldering one and when i grabbed it with my needle nose's the middle came out leaving the two ends attached.  so i wrote down all the values of all the resistors, ceramic caps, and electrolytic caps in the amp to A: compare to schematic i have and B: price how much it would be to replace them all.  i suspect a lot has been done to this amp (and not in a good way) since half of the resistors are carbon film and half are carbon comp.  the caps are even more mixed, some blocks, some mustard plugs, some orange drops, some ceramic, some tantalum's.

thats about the time i turned the lights over the bench off and got on here.

[freak scene]

oh, also i will try to post pictures tomorrow night as well.

[R.G.]

You could read "The Tube Amp Debugging Page" at GEO - http://www.geofex.com

It would put you through some already covered ground, but it is a good read for getting into the proper mind set.

1. Whenever someone says " (anything here...) and it pops it fuse(s)." my first thought is "make yourself a light bulb limiter so you can find out what's happening without spending twenty five cents a pop trying to find out what's wrong.
2. You at least have it narrowed down to the output stage. Pull all the rest of the tubes out. No sense abusing them too.
3. The amp has been modified. Put it back to stock before you go any further. At least then you'll know that the circuit is one that could possibly have worked at one time.
4. The amp has been modified, perhaps by a Harmony Central beginner with BUMS (Blind Urge to Modify Syndrome" and so you can't rely on ANY solder joint in the amp being in good condition. Having the center of a resistor come away all by itself is a good indicator that you maybe can't trust any component inside the amp . This amp is not a case of "fix the single problem and it'll work great". It's an example of "fix it until it has been PROVEN to work." If you fix a couple of things and go off thinking you're done, you'll have a dead amp in a little bit.

I have no doubt you're at your wit's end - you're faced with a half-modified amp of dubious reliability and possibly many faults. That's hard to work with unless you get into the mental attitude that you're going to fix it patiently until it sits up and eats out of your hand, metaphorically.

[johngreene]

You could read "The Tube Amp Debugging Page" at GEO - http://www.geofex.com

It would put you through some already covered ground, but it is a good read for getting into the proper mind set.

1. Whenever someone says " (anything here...) and it pops it fuse(s)." my first thought is "make yourself a light bulb limiter so you can find out what's happening without spending twenty five cents a pop trying to find out what's wrong.
2. You at least have it narrowed down to the output stage. Pull all the rest of the tubes out. No sense abusing them too.
3. The amp has been modified. Put it back to stock before you go any further. At least then you'll know that the circuit is one that could possibly have worked at one time.
4. The amp has been modified, perhaps by a Harmony Central beginner with BUMS (Blind Urge to Modify Syndrome" and so you can't rely on ANY solder joint in the amp being in good condition. Having the center of a resistor come away all by itself is a good indicator that you maybe can't trust any component inside the amp . This amp is not a case of "fix the single problem and it'll work great". It's an example of "fix it until it has been PROVEN to work." If you fix a couple of things and go off thinking you're done, you'll have a dead amp in a little bit.

I have no doubt you're at your wit's end - you're faced with a half-modified amp of dubious reliability and possibly many faults. That's hard to work with unless you get into the mental attitude that you're going to fix it patiently until it sits up and eats out of your hand, metaphorically.

+1

Just wanted to say, 'nicely done'. I really like the BUMS acronym. Hopefully you are not planning on copywriting it because I am forseeing it's use increasing, by me if not anyone else .

--john

[freak scene]

You could read "The Tube Amp Debugging Page" at GEO - http://www.geofex.com

It would put you through some already covered ground, but it is a good read for getting into the proper mind set.

1. Whenever someone says " (anything here...) and it pops it fuse(s)." my first thought is "make yourself a light bulb limiter so you can find out what's happening without spending twenty five cents a pop trying to find out what's wrong.
2. You at least have it narrowed down to the output stage. Pull all the rest of the tubes out. No sense abusing them too.
3. The amp has been modified. Put it back to stock before you go any further. At least then you'll know that the circuit is one that could possibly have worked at one time.
4. The amp has been modified, perhaps by a Harmony Central beginner with BUMS (Blind Urge to Modify Syndrome" and so you can't rely on ANY solder joint in the amp being in good condition. Having the center of a resistor come away all by itself is a good indicator that you maybe can't trust any component inside the amp . This amp is not a case of "fix the single problem and it'll work great". It's an example of "fix it until it has been PROVEN to work." If you fix a couple of things and go off thinking you're done, you'll have a dead amp in a little bit.

I have no doubt you're at your wit's end - you're faced with a half-modified amp of dubious reliability and possibly many faults. That's hard to work with unless you get into the mental attitude that you're going to fix it patiently until it sits up and eats out of your hand, metaphorically.

+1

Just wanted to say, 'nicely done'. I really like the BUMS acronym. Hopefully you are not planning on copywriting it because I am forseeing it's use increasing, by me if not anyone else .

--john

yeah i need to throw together a light bulb limiter.  i have read the tube amp debugging page, its been a while though. 

i just had to take a day off of wrestling with it. 

the problem with returning it to original specs is that there doesnt seem to be a schematic for a pro with reverb.  there were some made but its not even in the garnet book.

[freak scene]

some pictures.

[aron]

My guess is that Andrew is correct and for starters it's a bias circuit problem. Assuming the tubes are ok. GEO's amp debugging page is great - check it out - also the Tube Amp FAQ.

You should be able to measure the bias voltage and verify that it's correct for each tube.

[The Tone God]

In this picture the resistor from pin 5 to 6 needs to be replaced. It should be a 1.5K IIRC. This would explain the lack of bias and response of the power tube.

Andrew

[johngreene]

My guess is that Andrew is correct and for starters it's a bias circuit problem. Assuming the tubes are ok. GEO's amp debugging page is great - check it out - also the Tube Amp FAQ.

You should be able to measure the bias voltage and verify that it's correct for each tube.

It looks to me that the standby switch on this amp is somehow switching the bias to the output tubes only. I can see where the power transformer goes directly to the recitifier diode board and then directly to the output transformer. I assume that the switch that is the farthest 'left' is the standby swtich (with the "SA" on it). Is the pot next to it the bias pot? The 1.5K that you accidentally 'removed the middle' from is the grid resistor for that power tube so it will not be getting any bias voltage now, and if that resistor was broke before, would explain why it wasn't biasing.

It's really difficult to follow things in the pictures but I would assume the two 51k resistors connected to the phase splitter tube would be the plate resistors and the two yellow 'brick' capacitors connected to them the coupling caps to the output tubes. The bottom one looks like it could be connected to the 100K to ground and 1.5k grid resistor of the output tube but the top one looks like it is connected to ground.... Seems like that cap should be connected to the lug below the one it is connected to. Dunno, hard to tell.

--john

[Paul Marossy]

1. Whenever someone says " (anything here...) and it pops it fuse(s)." my first thought is "make yourself a light bulb limiter so you can find out what's happening without spending twenty five cents a pop trying to find out what's wrong.

That works great! I made one to safely power it up and check everything out after my Marshall literally blew up a filter cap. It was a great tool to have available. I've still got it in case I ever need it again. 

[freak scene]

My guess is that Andrew is correct and for starters it's a bias circuit problem. Assuming the tubes are ok. GEO's amp debugging page is great - check it out - also the Tube Amp FAQ.

You should be able to measure the bias voltage and verify that it's correct for each tube.

It looks to me that the standby switch on this amp is somehow switching the bias to the output tubes only. I can see where the power transformer goes directly to the recitifier diode board and then directly to the output transformer. I assume that the switch that is the farthest 'left' is the standby swtich (with the "SA" on it). Is the pot next to it the bias pot? The 1.5K that you accidentally 'removed the middle' from is the grid resistor for that power tube so it will not be getting any bias voltage now, and if that resistor was broke before, would explain why it wasn't biasing.

It's really difficult to follow things in the pictures but I would assume the two 51k resistors connected to the phase splitter tube would be the plate resistors and the two yellow 'brick' capacitors connected to them the coupling caps to the output tubes. The bottom one looks like it could be connected to the 100K to ground and 1.5k grid resistor of the output tube but the top one looks like it is connected to ground.... Seems like that cap should be connected to the lug below the one it is connected to. Dunno, hard to tell.

--john

yes the switch farthest to the left, the knob is the reverb knob (yes its on the back of the amp).  i got a new resistor today for the grid resistor, metal film if that matters at all.

the 100uf 100volt cap used to be a 64uf, but it was leaking a little and i replaced it with the 100uf one, should i go back to a 64 uf if i can find one?

also about the standby switch, i noticed that it doesnt seem to be making a 100% connection, i put the multimeter to it and no connection when its in the off position, but when its in the on position its got a pretty high resistance.

[johngreene]

yes the switch farthest to the left, the knob is the reverb knob (yes its on the back of the amp).  i got a new resistor today for the grid resistor, metal film if that matters at all.

the 100uf 100volt cap used to be a 64uf, but it was leaking a little and i replaced it with the 100uf one, should i go back to a 64 uf if i can find one?

also about the standby switch, i noticed that it doesnt seem to be making a 100% connection, i put the multimeter to it and no connection when its in the off position, but when its in the on position its got a pretty high resistance.

Guess that would explain the bias current in standby. You probably need to replace, or at least try to clean, that switch too if you want standby to work. It seems like the bias current is about right when the standby switch is in the 'high resistance' position. The switch must be intended to pull the bias voltage way negative to turn the tubes off. So it is probably shorting out (or is supposed to) one resistor of in a divider that sets the bias voltage.

The 100uF shouldn't make a difference.

Because of the bad standby switch, someone may have set up the bias network such that it is correct when the switch is in 'standby' and left it that way. Unfortunately this means that the bias current will increase when taken off standby to the point of cooking the tubes. Judging by the number of newer components in there, just about anything could be possible.

This looks to be pretty simular to yours, except it doesn't show a standby switch and uses EL34s:

http://www.lynx.bc.ca/~jc/SessionManPwr.gif

--john

[freak scene]

yes the switch farthest to the left, the knob is the reverb knob (yes its on the back of the amp).  i got a new resistor today for the grid resistor, metal film if that matters at all.

the 100uf 100volt cap used to be a 64uf, but it was leaking a little and i replaced it with the 100uf one, should i go back to a 64 uf if i can find one?

also about the standby switch, i noticed that it doesnt seem to be making a 100% connection, i put the multimeter to it and no connection when its in the off position, but when its in the on position its got a pretty high resistance.

Guess that would explain the bias current in standby. You probably need to replace, or at least try to clean, that switch too if you want standby to work. It seems like the bias current is about right when the standby switch is in the 'high resistance' position. The switch must be intended to pull the bias voltage way negative to turn the tubes off. So it is probably shorting out (or is supposed to) one resistor of in a divider that sets the bias voltage.

The 100uF shouldn't make a difference.

Because of the bad standby switch, someone may have set up the bias network such that it is correct when the switch is in 'standby' and left it that way. Unfortunately this means that the bias current will increase when taken off standby to the point of cooking the tubes. Judging by the number of newer components in there, just about anything could be possible.

This looks to be pretty simular to yours, except it doesn't show a standby switch and uses EL34s:

http://www.lynx.bc.ca/~jc/SessionManPwr.gif

--john

i re soldered the standby switch and i got a good continuity reading. 

then i replaced the broken resistor and turned the amp on took some measurements and everything was looking ok.  so i put the power tubes in through my bias rite and the same thing happened that what was happening, the tube nearest the back of the amp was getting about 30 milliamps while on standby, then when i took it off standby it went off the chart.  so i took the tubes out again flipped the amp on forgot to turn on the variac, so i flipped that on and the fuse blew.  i didnt think the variac being turned on afterwards would blow the fuse, correct me if im wrong.