Express Startup Issues
Moderators: pompeiisneaks, Colossal
Express Startup Issues
Hello and thanks for all the great info on this board! Recently joined when I decided I needed to build an express - first post...
Just completed a build - parts from RJ, excellent quality and service!!
I've got a pronounced 60 cycle hum (pretty sure - deep, not raspy) that is not effected by the volume knob and very low output with some unexpected voltages at V1a. Pulled the phase inverter and hum disappears. Swapped preamp tubes on the off chance of a bad tube with no changes. All of the tone controls and bright switch seem to function - just bedroom level output at best. I'm attaching my voltages and some pics if anything looks obvious - Been though all of the connections over and over. I'm sure it will be something stupid that I've simply overlooked... thanks for your patience!
Just completed a build - parts from RJ, excellent quality and service!!
I've got a pronounced 60 cycle hum (pretty sure - deep, not raspy) that is not effected by the volume knob and very low output with some unexpected voltages at V1a. Pulled the phase inverter and hum disappears. Swapped preamp tubes on the off chance of a bad tube with no changes. All of the tone controls and bright switch seem to function - just bedroom level output at best. I'm attaching my voltages and some pics if anything looks obvious - Been though all of the connections over and over. I'm sure it will be something stupid that I've simply overlooked... thanks for your patience!
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Re: Express Startup Issues
RJ provided that build guide with voltage chart? Nice touch! Your voltages are good.
Very nice work, very clean. Is V1, pin 6 soldered?
Very nice work, very clean. Is V1, pin 6 soldered?
I build and repair tube amps. http://amps.monkeymatic.com
Re: Express Startup Issues
Yes, pin 6 is soldered. The chart came from the Express Build Guide 2.0 on this site. I was a little surprised at the high voltage at pin 1 and wondered between that and the higher cathode voltage at pin 3 if there was any correlation to the low output (and hum).
Re: Express Startup Issues
Hi Tueller, nice Build.
Maybe run a temp wire or alligator clip from the input jacks ground tab to ground, maybe the connection doesn't have a good ground?
does the 1 meg resistor have a jumper from sleeve to ground? something like this? sorry my snipping isn't very good, I have a ground tail hanging there
oh also I cant tell from the picture, are the first 2 47uf's connected together? (as they should be)
anyways good luck
Maybe run a temp wire or alligator clip from the input jacks ground tab to ground, maybe the connection doesn't have a good ground?
does the 1 meg resistor have a jumper from sleeve to ground? something like this? sorry my snipping isn't very good, I have a ground tail hanging there
oh also I cant tell from the picture, are the first 2 47uf's connected together? (as they should be)
anyways good luck
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Re: Express Startup Issues
Maybe you made the connection below board, but I am not seeing the usual connection between this plate load and the adjacent 0.1uF cap for the third stage. The dashed line is where there should be a hard connection.
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Re: Express Startup Issues
awesome catch, Dave. I was staring at that too but it didn't come to me.
Re: Express Startup Issues
Thanks!! I completely missed that. When I get home tonight I'll add that connection and see if that does the trick.
Re: Express Startup Issues
OK, so the missing connection was it. Tons of gain and hum is completely gone. Just some expected hiss when the volume is way up, but not too bad. My V1a plate voltage still seems high: 261 vs an expected 210, but if nobody thinks that is out of line, I'll just try to relax...
Thanks for the help, now the fun begins!!
Thanks for the help, now the fun begins!!
Re: Express Startup Issues
Oh, and thanks for the complements on the build - as I mentioned at first, I've had plenty of great inspiration from this site!
Re: Express Startup Issues
Good on you, congrats.
Yeah these guys here are the best
Yeah these guys here are the best
Re: Express Startup Issues
Double check the measured value of the cathode resistor on v1a. If it is high those voltages would move in that direction.
If it says "Vintage" on it, -it isn't.
Re: Express Startup Issues
Hey !
Nice Clen built !
What is your BIAS setting ?
Witch 12AX7 tube you use in V1, V2, V3 ?
Nice Clen built !
What is your BIAS setting ?
Witch 12AX7 tube you use in V1, V2, V3 ?
Re: Express Startup Issues
Thanks jjman, will do
Re: Express Startup Issues
Have Tunsol preamp and jj power just for start up. Looking forward to swapping/tuning. Even so, the sound isn't too bad and the amp is stable at full volume with the cover off - no grid stoppers yet...