WT400 does some nasty while warming up, then is fine.

[Michael7S]

My '93 Eden WT400 (factory upgraded in 2001 from WT300) has started to do something awful while warming up.

The sound output cuts out for a second or two with a pop and I noticed the EQ clip light comes on during that time. This happens to signal from the preamp as well as the sound from the auxiliary inputs. Two to three of those cut/pops in the first five to seven minutes and then all is well. For fun, I replaced the Ruby tube with an EH 12AX7 and thought I was good the first few uses. But then the same problem started a few warmups later.

I've been using this amp since I bought it new in 1993 and would love to repair it or send it to someone reputable for repair. I can read a schematic, desolder and resolder components and do basic voltmeter measurements of components. Scopes and hz and tube bias and I'm lost. But I have no idea where to start and again, happy to pay someone else.

I noticed @AudioTaper did some great mods (thank you for sharing those here). So it seems there are known issues and established fixes.

Any advice on a repair path? Thanks!

 

[agedhorse]

Find yourself a QUALIFIED and EXPERIENCED service tech, they will be able to sort it out.

 

[12bass]

Sounds like the classic Eden zener regulated supply resistor solder joint failure. There are some large power resistors on the preamp PCB that get hot and the joints underneath go bad from thermal stress over time. Had the same symptoms and repair on my WT-500. Fresh solder will probably fix it in the short term, but the fundamental issue will remain, which is why some have adopted more robust solutions. Additionally, the amp is somewhat risky to use in its current state, as it may pop and cut out under use.

www.talkbass.com/threads/eden-wt400-repair-mod.1489568

 

[Michael7S]

Find yourself a QUALIFIED and EXPERIENCED service tech, they will be able to sort it out.

A great idea. I've been trying for a year and found many old places that worked on Edens closed, or the new kids have never worked on an Eden amp. Several here in California said they'd look into Eden repair feasibility, get back to me... and then silence. Happy to ship to a qualified and experienced service tech and very open to introductions to one who knows what an Eden amp is.

 

[Michael7S]

Sounds like the classic Eden zener regulated supply resistor solder joint failure. There are some large power resistors on the preamp PCB that get hot and the joints underneath go bad from thermal stress over time. Had the same symptoms and repair on my WT-500. Fresh solder will probably fix it in the short term, but the fundamental issue will remain, which is why some have adopted more robust solutions. Additionally, the amp is somewhat risky to use in its current state, as it may pop and cut out under use.

www.talkbass.com/threads/eden-wt400-repair-mod.1489568

Thank you! Any answer that contains "Sounds like the classic..." is what I was looking for. I'll pop it open and have a look. Thanks again.

 

[Michael7S]

Sounds like the classic Eden zener regulated supply resistor solder joint failure. There are some large power resistors on the preamp PCB that get hot and the joints underneath go bad from thermal stress over time. Had the same symptoms and repair on my WT-500. Fresh solder will probably fix it in the short term, but the fundamental issue will remain, which is why some have adopted more robust solutions. Additionally, the amp is somewhat risky to use in its current state, as it may pop and cut out under use.

www.talkbass.com/threads/eden-wt400-repair-mod.1489568

Spot on. This "before". I resoldered and will order parts to do a more permanent repair.

the input and headphone jack plastic disintegrated, but are still usable. Will hunt for replacement jacks.

First test after resolder sounded great

Thank you.

 

[12bass]

Spot on. This "before". I resoldered and will order parts to do a more permanent repair.

Yikes! Those solder joints are nasty. This problem seems to commonly occur with early Eden WT amps, before they updated the preamp design to use proper regulators instead of zener diodes and resistors. Glad you got it working and have a more permanent solution in the works. Suggest being careful with those boards and wires so as not to cause future reliability issues and double or triple-check your work.

 

[Michael7S]

OK I moved the resistors away from the board. Was only able to do a quiet test (kids just tucked in). I decided to wire from under the board and this worked well. One thing I missed was clearance for the fan. So after the photo below, I moved one of the resistors further to the left.

 

[agedhorse]

Use both mounting screws or it will loosen up on you and twist, possible causing bigger problems.

 

[Michael7S]

Use both mounting screws or it will loosen up on you and twist, possible causing bigger problems.

Insightful. Thank you. It seems to have some issues with the preamp so I'll go back in and re do.

 

[12bass]

Those 25W resistors should permanently solve the problem. Other than that, there aren't many common issues. Dirty contacts in the effects return sometimes cause the signal to cut out; a tiny amount of DeoxIT worked in-and-out will usually fix that. Another quick tip is to rotate the transformer if you're hearing hum at the output; no hum... no worries. But if there's a bit of hum, just loosen the fastener, rotate slightly in both directions until the hum is minimized, then snug it down. The relative position of the internal cabling can also add hum, so I moved those around a bit in my WT-500. The early WT amps had issues with idle hiss and noise, which was improved in later revisions, something I addressed with a few modifications.