5150 gurus...I need help please

[glpg80]

Did you try different power tubes?
Jerry

I only tried the =C='s that were in the 6505 that sounded awesome in that amp...and still do.

As soon as kick it off standby they started red plating so I would turned it off before it would damage the tubes. Put the tubes back in the 6505 and it roars and sounds great. I dont have any other 6L6's laying around

you know i just thought of something, a common problem on 5150s

have you checked to see if the socket pins are visually stretched to the point of not making contact? specifically pin 8 on each socket? if the previous owner(s) wiggled the tubes out and did not pull them straight out - it is possible pin 8 on those sockets are not making contact with the tube floating the tubes to 500VDC causing them to redplate. minus checking the bias circuit first, i would almost bet the ribbon cables check out fine but i bet you those socket pins are stretched the reason i say this is because i repaired a similar problem on a block letter original 1992.

also you cannot go by the glow of a preamp tube. peavey does not connect every envelop to a heater element. how many are connected will dictate the visual brightness of the tungsten elements you are seeing visually glow due to pulled vacuum.

 

[Lord Toneking]

Did you try different power tubes?
Jerry

I only tried the =C='s that were in the 6505 that sounded awesome in that amp...and still do.

As soon as kick it off standby they started red plating so I would turned it off before it would damage the tubes. Put the tubes back in the 6505 and it roars and sounds great. I dont have any other 6L6's laying around

you know i just thought of something, a common problem on 5150s

have you checked to see if the socket pins are visually stretched to the point of not making contact? specifically pin 8 on each socket? if the previous owner(s) wiggled the tubes out and did not pull them straight out - it is possible pin 8 on those sockets are not making contact with the tube floating the tubes to 500VDC causing them to redplate. minus checking the bias circuit first, i would almost bet the ribbon cables check out fine but i bet you those socket pins are stretched the reason i say this is because i repaired a similar problem on a block letter original 1992.

also you cannot go by the glow of a preamp tube. peavey does not connect every envelop to a heater element. how many are connected will dictate the visual brightness of the tungsten elements you are seeing visually glow due to pulled vacuum.

I cleaned all the tube sockets when I had the board out and though I guess it's possible it sure seemed like the tubes were seating in nice and tight

 

[glpg80]

without it on a bench there are too many other variables going on to say for sure - but it is worth mentioning to the tech to check, i did repair a similar problem.

food for thought. pass it on

 

[JerryP]

Did you try different power tubes?
Jerry

I only tried the =C='s that were in the 6505 that sounded awesome in that amp...and still do.

As soon as kick it off standby they started red plating so I would turned it off before it would damage the tubes. Put the tubes back in the 6505 and it roars and sounds great. I dont have any other 6L6's laying around

you know i just thought of something, a common problem on 5150s

have you checked to see if the socket pins are visually stretched to the point of not making contact? specifically pin 8 on each socket? if the previous owner(s) wiggled the tubes out and did not pull them straight out - it is possible pin 8 on those sockets are not making contact with the tube floating the tubes to 500VDC causing them to redplate. minus checking the bias circuit first, i would almost bet the ribbon cables check out fine but i bet you those socket pins are stretched the reason i say this is because i repaired a similar problem on a block letter original 1992.

also you cannot go by the glow of a preamp tube. peavey does not connect every envelop to a heater element. how many are connected will dictate the visual brightness of the tungsten elements you are seeing visually glow due to pulled vacuum.

Pin 8 losing it's connection can't cause the tube to red plate, it will turn the tube off. That's all many half power switches do is lift the ground at pin 8.
Jerry

 

[JerryP]

The only way you'll get red plating is the tubes are bad or you have no bias voltage.

Measure the voltage on both sides of resistors R55 & R54 on the main circuit board near the bias circuit and the ribbon cable to the power tube board. Since two tubes are red plating I'm guessing one of those resistors is open. The should each read about the same.
Jerry

 

[glpg80]

Pin 8 losing it's connection can't cause the tube to red plate, it will turn the tube off. That's all many half power switches do is lift the ground at pin 8.
Jerry

I do not have a schematic nearby - i was thinking pin 8 was part of the bias reference for some reason - i knew about lifting ground but could not remember if it was 7 or 8

 

[Lord Toneking]

The only way you'll get red plating is the tubes are bad or you have no bias voltage.

Measure the voltage on both sides of resistors R55 & R54 on the main circuit board near the bias circuit and the ribbon cable to the power tube board. Since two tubes are red plating I'm guessing one of those resistors is open. The should each read about the same.
Jerry

I will do that, thanks! Took it to a tech but they were closed when I got there. Hopefully this is the culprit!

thanks again!

 

[Lord Toneking]

The only way you'll get red plating is the tubes are bad or you have no bias voltage.

Measure the voltage on both sides of resistors R55 & R54 on the main circuit board near the bias circuit and the ribbon cable to the power tube board. Since two tubes are red plating I'm guessing one of those resistors is open. The should each read about the same.
Jerry

Didnt have a chance to do that this weekend but am doing it when I get home from work.

Question...What if those read ok? then what do I look for next? If I remember correctly I believe they are the two yellow ones

Thanks

 

[O'Rourke]

They're 220k so should be striped red/red/yellow then the tolerance band, check those first.

 

[JerryP]

The only way you'll get red plating is the tubes are bad or you have no bias voltage.

Measure the voltage on both sides of resistors R55 & R54 on the main circuit board near the bias circuit and the ribbon cable to the power tube board. Since two tubes are red plating I'm guessing one of those resistors is open. The should each read about the same.
Jerry

Didnt have a chance to do that this weekend but am doing it when I get home from work.

Question...What if those read ok? then what do I look for next? If I remember correctly I believe they are the two yellow ones

Thanks

The yellow things are caps. The resistors are near some caps. Tell me what voltage readings you get and we'll go from there. Measure them with the amp on and on standby.
Jerry

 

[bionicmark]

The only way you'll get red plating is the tubes are bad or you have no bias voltage.

Measure the voltage on both sides of resistors R55 & R54 on the main circuit board near the bias circuit and the ribbon cable to the power tube board. Since two tubes are red plating I'm guessing one of those resistors is open. The should each read about the same.
Jerry

Didnt have a chance to do that this weekend but am doing it when I get home from work.

Question...What if those read ok? then what do I look for next? If I remember correctly I believe they are the two yellow ones

Thanks

send the amp to jerry and have him go through the whole amp so you're up and running w/ zero issues...while it's there , have him do his metal mod and be the coolest guy w/ the best sounding 5150 on your street!

 

[rottingcorpse]

send the amp to jerry and have him go through the whole amp so you're up and running w/ zero issues...while it's there , have him do his metal mod and be the coolest guy w/ the best sounding 5150 on your street!

i also recommend this. by far the best sounding 6505 in all of dallas/ft.worth is sitting in my amp room, thanks to mailman and jerry at fja. worth the extra bucks, and the horrible glares the old lady gives you across the dinner table.