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PostPosted: Wed Feb 03, 2010 6:24 pm 
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Location: Calgary,Alberta,Canada
rookie in trouble,finally got back to my 18 watt plexi build(with pa+pi vvr as per congers s111 with vvr schematic)installed tubes check voltages all seem high including output of trinity power trans,
123vac at fuse
pins 1+7 of ez81=315vac
pin 3 ez81=365vdc(tried more than 1 ez81 with similar results)
vvr at max
A=357vdc to output trans supposed to be 347vdc
B=335vdc before 100ohmto pin 9 of el84s supposed to be 324vdc
C=295vdcbefore 100kohm to 1+6 of PI supposed to be 285vdc
D=247vdc to V1+V2 supposed to be 236vdc
similar just slightly higher than spec values with vvr at min.(voltages and mods to trinity layout as per congers s111 vvr schematic at 18watt.com/downloads/vvr)
TMB channel works,sounds good but very clean,also alot of humm,turn gain up much past 7 it just squeels
normal channel not working,no sound what so ever(i need to recheck my cascade sw.wiring and inputs,quite likely made mistake here)
are these voltages too high?is it because of the 315 vac at power trans

I may have a couple things to troubleshoot here but want to start with B+ voltages and go from there,any help would be great(


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PostPosted: Wed Feb 03, 2010 6:46 pm 
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Location: Vancouver B.C. Canada
These discrepancies are insignificant and will probably change with breakin anyway! How close are the filament voltages?
Check around here for info on troubleshooting hum and squeal. It's normal to have these issues initially!
Stew


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 Post subject: filament voltages
PostPosted: Wed Feb 03, 2010 7:06 pm 
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getting 6.75vac at heater of ez81,about 6.6vac at el84/ecc83 heaters,I was hoping that those voltages were close enough
question.when i get squeel at higher gain settings or lower gain,higher MV settings it is with the VVR at 50volt(have to be very,quiet here right now)
could it be beacause i am overloading the PI(warning i am very "green")this build is always getting full B+ to preamp tubes and I read somewhere may want to lower value of master(V7)to avoid overloading PI,I was concearned about this happening with pa+pi only VVR
before I start changing parts gonna try and troubleshoot normal channel/cascade wiring and humm,and doublecheck everything
I know I am quite possibly in way over my head here,should have built a nice simple champ for 1st build but I figure troubleshooting this will be very educational and give me a better understanding of how tube amps work(as long as I keep one hand in my pocket should be fine right?)


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PostPosted: Wed Feb 03, 2010 7:14 pm 
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just started troubleshooting thru resource section
I ran shielded wire from gain pot to pin 2 of v2 under board not overtop
oops.


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PostPosted: Wed Feb 03, 2010 11:16 pm 
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Your mains is about 3% high, so all the B+ are going to be 3% higher.

So, they dont look so out of line. For fun, try turning the VVR down until you get the correct B+ then remeasure.

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PostPosted: Wed Feb 03, 2010 11:43 pm 
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set vvr to achieve desired 347vdc to output transformer,B+ to PI+PA were bang spec on but my non regulated B+ to preamp tubes was obviously still high,251vdc instead of desired 236vdc not alot higher,if this is a problem could I increase the resistor value on this part of circuit to bring down the voltage,this amp is going to be used at very low volumes most of the time,
still have other issues shrill noise/hum on TMB channel when turn up gain or volume,also tone controls affect symptom,no change after moving shield wire from gain to V2 under board to above
and I screwed up on normal channel inputs,have to get more coax and fix(this chassis req.normal inputs to be reversed similar to what has to be done on trinity combo TMB inputs,oops


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