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FDP Forum / Amp Mods, Repairs, and Projects / Help me diagnose this Blues Jr issue

Contributing Member

Washington DC

Jun 28th, 2017 08:07 AM   Edit   Profile  

I'm getting bad tone and crackling on my 10-year-old Blues Junior, (second, cream-board edition) and I suspect that the issue is broken solder joints for the power tubes. What do you think?

I've bought a complete new set of tubes and the problem remains. Whenever I replace or push in the power tubes, seating them firmly in the sockets, the tone is great. The crackling and bad tone appear after I've played a while, especially if I turn up the volume and drive it (causing more vibration that aggravates the connection?).

Also, when once I took out the original power tubes because of the bad tone, only one of them was hot. The other tube, at the end of the line of tubes (V5 position), was just slightly warm. Should I start looking at solder joints between V4 and V5?

In sum, are solder joints the most likely culprit or could there be other components failing?

Is this a reasonable DIY fix for a newbie at tube amp repair? I've soldered lots of guitar electronics. I have never figured out how to discharge the capacitors of an amp but would do so before venturing further.

Thank you very much!

Contributing Member

So. Cal. USA

Jun 28th, 2017 09:38 AM   Edit   Profile  

Sounds very possible. Those joints tend to fail on the Fender HotRod series amps. If you have the soldering skills why not give it a try?

Do a web search on discharging caps.. Basically you are going to be connecting the positive side of the filters, the large grey caps on the board to chassis ground with an insulated jumper to discharge. Many put a 100K ohm resistor in series with the jumper to prevent sparks however that is not absolutely needed. Confirm discharge with a volt meter (DC volts).

Use a 30-40 watt soldering iron not a gun and be careful not to over heat the solder joint. Too much heat and you will lift the foil pad(s) off of the board. Add some new rosin core solder to the joint and get it to flow nicely across the foil pad and pin. Do all the pins on all the sockets.

Contributing Member

Washington DC

Jun 28th, 2017 11:07 AM   Edit   Profile  

Thank you, Hammond. I'm heading out of town for the 4th but will try to fix this next week. Excited...

Contributing Member

Memphis, TN

Jun 28th, 2017 12:28 PM   Edit   Profile  

Re-flow ALL the solder joints on all the tubes sockets, paying careful attention to the power tubes.

The EL84's run awfully hot and the heating / cooling cycles stress the dickens out of the solder joints on these areas.

I've run into this many times with the BJ's.

Contributing Member

So. Cal. USA

Jun 28th, 2017 02:21 PM   Edit   Profile  

Where the real issues are IMO is when Fender does not get the socket fully inserted into the board. the pins have a shoulder that should be contacting the board on the tube/socket side of the board. When that space between the shoulder and the board is there, the tube retaining springs and vibration of the amp in use break the solder joints.

Many times I desolder the socket, insert it fully into the board then re-flow everything.

The amps are also made with lead free solder now so the solder is much more brittle. This and the heat cycles you mention make the problem worse for sure.

All amps regardless of manufacture that have board mounted tube sockets seem to suffer from this.

Contributing Member

Washington DC

Jun 28th, 2017 03:43 PM   Edit   Profile  

Thanks, Stratm

Hammond, would a Fender amp manufactured in 2008 (possibly a year earlier) use lead-free solder? Do I need a different kind of flux for that? (I know this site has a FAQ on lead-free....)


Contributing Member

I walk

between the raindrops
Jun 28th, 2017 06:10 PM   Edit   Profile  

Howdy Tiller2

Use leaded solder and it will be compatible.

If you don't want to tackle this, you can drop it off and I'll get it going for you.

Cheers brother!

Contributing Member


Jun 28th, 2017 06:18 PM   Edit   Profile  

I've used leaded solder with RoHS gear with no downside. I just get a good flow of all the solder - the existing and the leaded stuff - and it's fine. For my own gear, of course.



Are there power outlets in Heaven?
Jul 6th, 2017 10:57 AM   Edit   Profile  

I had this exact problem with my 2003 green board BJ. I bought new sockets thinking the pins were corroded and worn. Reflowed all of the solder joints on the power tube sockets and badda bing, badda boom. No need to replace sockets. Works perfect now.

FDP Forum / Amp Mods, Repairs, and Projects / Help me diagnose this Blues Jr issue

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