Express Startup Issues

Express, Liverpool, Rocket, Dirty Little Monster, etc.

Moderators: pompeiisneaks, Colossal

Tueller
Posts: 7
Joined: Fri Feb 17, 2017 5:07 pm

Express Startup Issues

Post by Tueller »

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!
You do not have the required permissions to view the files attached to this post.
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Express Startup Issues

Post by xtian »

RJ provided that build guide with voltage chart? Nice touch! Your voltages are good.

Very nice work, very clean. Is V1, pin 6 soldered?
I build and repair tube amps. http://amps.monkeymatic.com
Tueller
Posts: 7
Joined: Fri Feb 17, 2017 5:07 pm

Re: Express Startup Issues

Post by Tueller »

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).
joeboo88
Posts: 400
Joined: Thu Mar 28, 2013 8:51 pm
Location: Way up North

Re: Express Startup Issues

Post by joeboo88 »

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
You do not have the required permissions to view the files attached to this post.
User avatar
Colossal
Posts: 5038
Joined: Sat Oct 20, 2007 9:04 pm
Location: Moving through Kashmir

Re: Express Startup Issues

Post by Colossal »

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.
Express.jpg
You do not have the required permissions to view the files attached to this post.
joeboo88
Posts: 400
Joined: Thu Mar 28, 2013 8:51 pm
Location: Way up North

Re: Express Startup Issues

Post by joeboo88 »

awesome catch, Dave. I was staring at that too but it didn't come to me.
Tueller
Posts: 7
Joined: Fri Feb 17, 2017 5:07 pm

Re: Express Startup Issues

Post by Tueller »

Thanks!! I completely missed that. When I get home tonight I'll add that connection and see if that does the trick.
splgeo
Posts: 97
Joined: Fri May 23, 2014 1:44 am

Re: Express Startup Issues

Post by splgeo »

BEAUTIFUL WORK!!!
Tueller
Posts: 7
Joined: Fri Feb 17, 2017 5:07 pm

Re: Express Startup Issues

Post by Tueller »

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!!
Tueller
Posts: 7
Joined: Fri Feb 17, 2017 5:07 pm

Re: Express Startup Issues

Post by Tueller »

Oh, and thanks for the complements on the build - as I mentioned at first, I've had plenty of great inspiration from this site!
joeboo88
Posts: 400
Joined: Thu Mar 28, 2013 8:51 pm
Location: Way up North

Re: Express Startup Issues

Post by joeboo88 »

Good on you, congrats.
Yeah these guys here are the best
User avatar
jjman
Posts: 753
Joined: Sat Oct 06, 2007 2:33 pm
Location: Central NJ USA

Re: Express Startup Issues

Post by jjman »

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.
User avatar
DaveWell
Posts: 246
Joined: Wed Feb 25, 2009 9:59 pm

Re: Express Startup Issues

Post by DaveWell »

Hey !
Nice Clen built !
What is your BIAS setting ?
Witch 12AX7 tube you use in V1, V2, V3 ?
Tueller
Posts: 7
Joined: Fri Feb 17, 2017 5:07 pm

Re: Express Startup Issues

Post by Tueller »

Thanks jjman, will do
Tueller
Posts: 7
Joined: Fri Feb 17, 2017 5:07 pm

Re: Express Startup Issues

Post by Tueller »

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...
Post Reply