Tweet
OK i checked the heaters and they were V1-2.62 V2-2.632 V3-2.620 V4-2.2 V5-2.2VDC i also checked C49+ and it was 2.642VDC
-
Last edited by bfglp; 06-03-2010, 12:42 AM. -
V4 and V4 use AC, so set your meter on AC for those two.
If you have good AC there, the problem is in the rectification that produces DC, the diodes are bad or have a bad solder joint.
If you don't have good AC at V4 or V5, the problem lies upstream. Check the schematic and measure the AC coming out of the power transformer for the heaters, I don't have my schematic handy. If that's good, then there's likely a poor connection on the wiring--those Molex connectors are terrible.Comment
-
-
OK, there's likely a bad connection somewhere. I don't have the layouts handy, so going from memory, I think the AC heater voltage went from the PT through Fuse 1. I think this is also on both legs of the hum cancel pot. Check there, following the schematic. The heater supply then goes through the top power board, then down to the power amp board, then back up to the preamp board. (again, going from memory)
I'm suspecting a bad connection on the ribbon cables between the poweramp board and the preamp board, but first you've got to make sure everything's OK on the power supply board.Comment
-
3VAC to ground? Measure AC volts between pins 4/5 and pin 9. I bet you find 6v.Education is what you're left with after you have forgotten what you have learned.Comment
-
i checked the connections across the ribbon and had the same voltage.
yes Enzo it was to ground.
thanks for the help, i have to hit the road for a couple weeks. so i'll have to bench this project till i get back.Comment
-
-
sounds fine, you have swaped out the tubes right, and replaced ALL the fuses? IME thats where 90% of the PV problems are unless a component is visably burnedComment
-
yep, amp works fine on clean channel but not on crunch or ultraOriginally posted by tedmich View PostComment
-
When you say it doesn't work on Crunch or Ultra: are you getting any sound at all through, or are you getting sound but no gain?Originally posted by bfglp View PostComment
-
yes just fired it up and was able to get crunch and ultra. now if i play at bedroom levels on crunch it will get crackely and the volume will slowly fade and if i switch to ultra with the gain cranked i can get the volume back up.Comment
-
Could be any of several things...1) Have you tried Deoxit on the volume controlpots? Might have dirty pots. 2) Might have bad solder joint 3) Might have a relay that's going south 5) Maybe a tube socket needs retensioning, might be losing V2 6) Bad tube...Comment
-
pots are clean, i went over the solder joints with my iron. found that V4 had been changed, tightened the sockets, im playin with the tubes now and the amp is still acting up. i need to get new preamp tubes i may just be swaping bad tube for better tube.
if i keep pushing the amp it will get some funny harmonics then it goes into all out feedback in all channels. the V5 tube an ecc81 made by tesla gets super hot. i put in a new electro-harmonix ecc81 and it was screaming feedback when i turned off the standby so i took it out and replaced it with another harmonix ecc81 from a different store and got the same result.Comment
-
V5 calls for a 12AX7. This is the PI, I've tried a 5751 in there (which is almost your ecc81) without those types of feedback problems (but the gain was too low).
I would check the NFB coming from the speaker jack. Find the white wire going to the speaker jacks. It should be joined with a yellow wire that goes back to the preamp board on a 3 conductor Molex plug, kinda in the center of the preamp tube board. Make sure this is connected good and that the wire is actually making contact, not broken where it pushes into the Molex plug
Check all the voltages around V5, see if they match the schematic.Comment
-
oops i had it backwards, its V4 that has the ecc81 and V5 socket was replaced some time ago.Comment
Comment