Oh yeah i had to remove the board to replace Q7. I did check for broken traces and the like. But i did find a bad mica cap on that little terminal board that has the thermister on it. Im going to replace that monday.But being an amp tech , i still have lots of other amps that are problem children. So ive ordered a bunch of parts. From Digikey . Hopefully they will fix all these amps problems. Digikey was not familure with those orange drop mica caps. At least i had those in stock.
in checking for broken traces or bad solders did you by chance use a magnifying glass?
i myself have often dismissed things on casual inspection only to have fooled myself, subsequent re-examination under magnification revealed things that i had dismissed with the naked eye.
i now take the time to go over things very carefully in a visual inspection and am still amazed by what it reveals.
as a long time service tech myself i try to remind myself that thinking "i know better" can lead me to false conclusions and take me down the rabbit hole of "it can't be that simple" and waste lots of time "looking for a more complex problem" that is not there.
what testing confirmed the mica cap was bad? (please don't think i'm questioning your abilities here i've seen other techs as well as myself make mistakes in diagnosing things)
if the signal is not making it past the first stage you need to take the time to verify things there before moving on.
in the immortal words of Jack Darr "no matter how confounding, complex and frustrating a service problem appears to be only diligence and perseverance and proper methodology will help you find it!"
i myself have often dismissed things on casual inspection only to have fooled myself, subsequent re-examination under magnification revealed things that i had dismissed with the naked eye.
i now take the time to go over things very carefully in a visual inspection and am still amazed by what it reveals.
as a long time service tech myself i try to remind myself that thinking "i know better" can lead me to false conclusions and take me down the rabbit hole of "it can't be that simple" and waste lots of time "looking for a more complex problem" that is not there.
what testing confirmed the mica cap was bad? (please don't think i'm questioning your abilities here i've seen other techs as well as myself make mistakes in diagnosing things)
if the signal is not making it past the first stage you need to take the time to verify things there before moving on.
in the immortal words of Jack Darr "no matter how confounding, complex and frustrating a service problem appears to be only diligence and perseverance and proper methodology will help you find it!"
Turk 182 , thank you so much sir for the pics and all of the great info. The mica orange cap i was talking about , one of leads of the cap came out of the cap on my inspection of it , which leads me to believe that wasnt making a good connection. This may be the cause of my humming problem. It sounds like 60 hz hum noise coming from the driver. Hopefully when i replace it , it will solve both problems , both the hum and the fact it wont pass a 440 hz signal or any signal unless i turn up thr attuation on my freq oss full blast. Thanks so much for your help . i will keep you posted on my progress.
there's a few versions designated 5150 exactly which model do you have, the EVH, the mark II ?
and just what is the board designation for the cap in question ? ( would be C followed by a number) it would help knowing just where it's used in the circuit.
are you up on the use of "dim bulb testers" for amplifier servicing?
bizzare hums can have components "eating" consequences!
and just what is the board designation for the cap in question ? ( would be C followed by a number) it would help knowing just where it's used in the circuit.
are you up on the use of "dim bulb testers" for amplifier servicing?
bizzare hums can have components "eating" consequences!
I have not worked on this amp in while as I had other amp repairs i had to do . but i finaly got back on the 5150, i have no signal on the plates of V4 .pins 1 and 6. But i do have signal up to V3 on pins 1 & 6. I will check for bad solder pads in that area. There is only a few caps and resistors in that circuit. I have not had a chance to study the schematic as i had to leave from work unexpectedly. If anyone has any ideas , please let me know. Thanks.
I also replaced the broken orange drops which were marked .01 so i ordered some .01 from Digi Key. The mica caps they sent were marked 103 which is a .01 cap. I installed those caps and hum is still there . i will check around V3 where i have no signal this coming Monday
I finally got back on the 5150 .The signal ends at pin 1 on pre amp tube V3 but signal wont get past that point , small distorted signsl on V4 pins one and six. Shows on schematic that signal goes to some caps .0047 and a .047 also a .022 cap as well. I will keep you posted . if anyone has any ideas please let me know.
The layout of the preamp tubes really confused me all this time i thought the tubes were in sequential order but there not . The pre amp tubes go as in order V1 V2 V5 V3 & V4 . this was confusing so now the story is : i dont have any signal at all to V4 preamp tube. There is signal on V5 the phase inverter which is in the center. But nothing on V4 or V5. If anyone has any ideas please let me know . I also have the right schematic now thinks to the folks at Peavey.
The Peavey EVH 5150 preamp tube layout has con -fused me . On the chassis they are layed out as follows : V1 V2 V5 V3 & V4. So now i dont have any signal on V3 or V4. On the schematic there isnt much in between V2 and V3 as it looks like on the schematic that V2 feeds V3 which feeds V4 which inturn that signal goes directly to the output tubes. If any one has any ideas please let me know. Thanks.
I also replaced the broken orange drops which were marked .01 so i ordered some .01 from Digi Key. The mica caps they sent were marked 103 which is a .01 cap. I installed those caps and hum is still there . i will check around V3 where i have no signal this coming Monday
I finally got back on the 5150 .The signal ends at pin 1 on pre amp tube V3 but signal wont get past that point , small distorted signsl on V4 pins one and six. Shows on schematic that signal goes to some caps .0047 and a .047 also a .022 cap as well. I will keep you posted . if anyone has any ideas please let me know.
The layout of the preamp tubes really confused me all this time i thought the tubes were in sequential order but there not . The pre amp tubes go as in order V1 V2 V5 V3 & V4 . this was confusing so now the story is : i dont have any signal at all to V4 preamp tube. There is signal on V5 the phase inverter which is in the center. But nothing on V4 or V5. If anyone has any ideas please let me know . I also have the right schematic now thinks to the folks at Peavey.
The Peavey EVH 5150 preamp tube layout has con -fused me . On the chassis they are layed out as follows : V1 V2 V5 V3 & V4. So now i dont have any signal on V3 or V4. On the schematic there isnt much in between V2 and V3 as it looks like on the schematic that V2 feeds V3 which feeds V4 which inturn that signal goes directly to the output tubes. If any one has any ideas please let me know. Thanks.
Peavey EVH 5150 .
I havent checked the bias voltage , but the weird thing is, someone did a mod on this amp , they put a pot in there , i guess to try and set the bias via a pot. But i dont think this amp is cathode biased , i believe it is grid biased. So the mod kind of throws me. As i dont know how they installed it. Sorry im not at the shop right now, so i dont know the values of the resisters they put in there in conjunction with the pot .However i will be there tomorrow and just see what there value is. Thanks Turk
I havent checked the bias voltage , but the weird thing is, someone did a mod on this amp , they put a pot in there , i guess to try and set the bias via a pot. But i dont think this amp is cathode biased , i believe it is grid biased. So the mod kind of throws me. As i dont know how they installed it. Sorry im not at the shop right now, so i dont know the values of the resisters they put in there in conjunction with the pot .However i will be there tomorrow and just see what there value is. Thanks Turk
Peavey EVH 5150 .
And since the owner installed a bias pot i wonder if the owner tried to do a mod on this amp to where it can use EL34s... If theyve done that ...it would explain why the amp isnt working . i mean it uses 6L6s , but there is a mod to configure this amp to use EL34s. Apparently the pot that was installed to set the bias has to use a 15 ohm resister along with a 5 ohm resister all connected to the pot . But for EL34s the screen resisters needed to be changed to 1k and pin one on the EL34 tubes needs to be grounded to pin 8 or to ground. I will check all of this tomorrow and call the customer on the mod. Because no wonder the amp wouldnt work if is in fact been modded to except EL34S.
And since the owner installed a bias pot i wonder if the owner tried to do a mod on this amp to where it can use EL34s... If theyve done that ...it would explain why the amp isnt working . i mean it uses 6L6s , but there is a mod to configure this amp to use EL34s. Apparently the pot that was installed to set the bias has to use a 15 ohm resister along with a 5 ohm resister all connected to the pot . But for EL34s the screen resisters needed to be changed to 1k and pin one on the EL34 tubes needs to be grounded to pin 8 or to ground. I will check all of this tomorrow and call the customer on the mod. Because no wonder the amp wouldnt work if is in fact been modded to except EL34S.
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