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Need help on the TRL DUDE

It appears that some of you are familiar with Paul's (has since sadly passed) Dude preamplifier from TRL.  I bought one from him about 6 years ago with the 12SN7's.  Later versions all had 6SN7's.  Fantastic sound even though this build is a bit sloppy.  The 2 - 12SN7 filaments don't light indicating the power transformer is open on the 12v ct secondary.  Also, didn't get a 12V reading on either side but I'll be checking again when my surgery allows as I'm having trouble bending to take any readings.  The transformer is labeled as such;  TC00273 and A05327233,  12v - 0 - 12v  6.3v - 0  260v - 0.  The bias is about 262V but I'm not that far into this as it just went out.  Where can I find another replacement  transformer?  It looks like this was manufactured to Paul's specs. with a 260V secondary.   Another option is to get a 12 - 0 -12 transformer and just replace the bad secondary.  However, higher quality transformers have better sound.  Also, if anyone can help me with a schematic of any DUDE so I don't have to draw one up.  My pics suck!!!  Thanks a bunch.  Missing my audio!!!!!!!  Eric
128x128eburg
eburg's avatar
eburg OP
1 posts
 
Rectified - so DC filament and that was my initial thought too.  Each side of the 12V supply is fully rectified which feeds the 12SN7's, I believe individually.  Both tubes are out so probably common cause.  Also, the 2 rectifier blocks look small but they should easily take an amp.  Don't know the mfg or PN as yet.

Thanks to teo_audio and atmasphere for the transformer advice as that is a relatively easy repair solution.  As you mention, they rarely go bad but I've seen it happen before.  It also appears that the power from each voltage winding is individually filtered and choked (12V, 6.3V, 260V) but I haven't looked at it that closely.  I get the rectifiers but really don't understand how the 0D3 is working in the system.  The same board has a 6AS7G and 6SN7 and I've seen where they can be used with a voltage regulator like an 0D3 for voltage regulation.  The 6.3V filament supply and HV 130V (260V total) are working fine.  I need to spend a bit more time to see how the Dude is put together (knowledge and curiosity) and functions but would just prefer to get it working quickly for now.  I know the choke supplier and the transformer looks like the product they produce.  
grannyring's avatar
grannyring
6,479 posts
 
Sent you a PM. I built a couple of these as Paul taught me a ton about them. Do mods/upgrades to them also. I don’t think it’s the tranny BTW.  

Take care,

Bill
atmasphere's avatar
atmasphere
11,803 posts
 
I agree with @grannyring .

@eburg
For the transformer winding to open up without provocation is an extremely rare event, but failure of other components in a DC power supply such that the DC supply isn't running is fairly common.

I'd also look at a failing filter capacitor at the input of the DC supply, right after the rectifiers. If this capacitor fails the DC output will be quite low, perhaps not enough to light up the filaments so that they can be seen in daylight. Check for AC at the input of the rectifier, this will tell you a lot.
The other tubes in the unit are all employed in the high voltage regulation.
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