BC30 no sound on CH1

[chosenfool]

... but channel 2 is fine. everything else works fine.

 

Hello, all! Happy new year to all fellow BC30 enthusiasts, i hope youre all enjoying the amp. i purchased mine on new years day, been playing it about an hour or so everyday since. LOVING IT!

 

just tonight channel 1 stopped working. not sure whats going on, unless its the channel switch itself thats busted. everything else works. ch2 controls (drive/mid/level), tone controls (treble/mid/bass), reverb, the pentode/triode switch, the EQ switch.

 

heres what i did after i got it, and before ch1 went:

1) changed the stock preamp tubes to good old stock tubes (2 telefunkens, 1 RCA, 2 mullards. all pulls from my other amps)

2) changed the stock power tubes to good old stock 6L6G's (the coke bottle kind).

 

thats it. i kept the stock rectifier tube. waiting on a NOS for that.

the 6L6G's were probably getting pushed too hard, but it sounded great.

no cap cuts, no circuit bending done. not yet anyway.

 

In thinking that maybe one of the preamp tubes may be causing the issue, i moved the preamp tubes around. still works on ch 2, still no ch1. now that i think about it, its really a pointless move, since if one or more of the preamp tubes are dead, there may just be no sound at all on ANY channel (please correct me if im wrong). but it wont hurt to try.

 

i also pulled the 2 coke-bottle 6L6G's, and put in old stock sylvania and raytheon 6L6GC's. I also took out the stock tube rectifier, and put in an old stock tung-sol 5U4GB.

 

****now this is just an experiment on my part. I was curious, since old stock 5AR4's are too expensive, and it seems like a hit and miss on new production tubes. I researched online for about 3 days, and found conflicting information. some say its ok to swap a 5U4 for a 5AR4, some say dont, some say it depends (if its a low powered amp like a champ, its fine, on bigger wattage amps, its a no-no). Doing it on the BC30 is still unknown up to this point.

 

So i went ahead and stuck a 5U4 in it anyway. Fired it up, using the standby button this time (from what i read 5U4's have faster startup than 5AR4's, and needs to use the standby button). Again, everything works except channel 1. Dimed the knobs, and pushed hard for a good half hour, no red-plating or blown fuses. the 5U4 worked!

 

****i digress for a moment here to say that the tone of channel 2 has greatly improved! sweet soulful distortion and sustain. NO PEDALS! maybe its the 6L6GC's, or the tung-sol rectifier, or both. I noticed the tone to be tighter, more responsive when overdriven (as what is expected of a change from 5ar4 to 5u4, per what i read). The distortion is more focused, the sound more solid and articulate. At least thats how it sounds to me now...

 

right now i got the chassis pulled out, i smell no silicon burns, no black charred spots, no bulging caps, no abnormally hot components. im thinking its just the channel select switch thats busted. im going to lift the PCB off the chassis and tinker around there tomorrow.

 

just wanna spitball it with you guys, if you got any educated guesses yourselves as to why ch1 doesnt work, but everything else does. Maybe clue me in to what to look for before i dive in and whip out the old DMM. Thanks!

 

- Marc

[twanger]

Welcome Marc!

 

Sounds like you're on the right track with the channel switch. Do be sure to check out the footswitch jack too. If these function as advertised I would check out the solder joints on the V1 socket.

 

Silly question - I didn't buy mine brand new (Hurrah! for CraigsList!) so I don't know for sure but is yours under warranty? If so I'd take it back before monkeying with anything on the PCB board.

[chosenfool]

thank you!

i got it from musician's friend, condition 3 - blemished, works, no warranty. i can send it back within 45days, but i can only get a refund. they wont replace it, unless theres another condition 3 unit (theyre obviously not gonna want to lose out). i wish they did though! :)

 

i like the BC30 so much, and i got for so cheap (almost half off), im choosing to keep it. even if it was most likely a returned item in the first place. im finding out that MF doesnt really fully test their returns (i got a condition 4 nonworking solidstate combo supercheap that i was gonna use the cab for a project, turns out it was just a loose speaker wire- now fully works! brand new too. im not big on solidstate amps, so its off to ebay or CL)

 

so with that in mind im prepared to break the clear hotglue seal on the PCB screws :). feels odd working with PCB's, ive tinkered more with PTP wiring on older amps...

 

i forgot about the footswitch jack!

i got the footswitch for it the day before, though CH1 had already started getting intermittent sound before that. Im thinking the footswitch may have excacerbated the intermittent issue more. CH1 stopped while i was jamming, with the footswitch plugged in. switching to CH2 and turning the reverb on and off still works though...

 

Another thing i remember: right before CH1 went out, for about 15 mins or so CH1 was overdriving and sounding like CH2 when the level was just turned past 10oclock (in both 30W and 15W modes). it used to just stay loud and clean right up to diming it. Any idea as to why that overdriving/distorting happened on CH1? The tip on checking V1 may reveal the answer also...

 

Ill start those troubleshooting when i get home later. any other advice is always welcome! thanks again!

 

- Marc

[chosenfool]

SOLVED!

turns out its a bad solder connection with the CH1 volume pot lugs.

 

took out the chassis, and propped it up so i can turn it on with the tubes in, while the PCB is exposed. i took off the chickenhead knob, removed the nut and washer, and suddenly (with the guitar plugged in and CH1 selected) theres SOUND!

 

a little tiny wiggle of the volume pot would cause intermittent sound. i guess the louder it gets and vibrates the whole amp, it moves the pot enough to lose connection.

 

i just got done spot-soldering the issue points. now back to the fun!

 

- Marc

[twanger]

Very cool! I love finding items that need just a simple repair.

 

When I got my BC30 it was purchased very inexpensively because:

1) it had been dropped by the UPS driver and,

2) it was being used for "research" (known as circuit copying)

 

The amp functioned and the chassis was in excellent cosmetic condition but the case was in bad shape and all of the tubes and a few other components needed to be straightened out. The force of the fall broke the cabinet, bent all the transformer brackets, bent all of the tube pins. Fortunately, Epiphone used a decent grade of plywood to build the cab but when the plywood broke (split the ply lamination) it ripped the tolex and the guy I got it from did a halfarse job of stapling it down. despite all the problems I could just tell that it had "good bones" so putting it back in order shouldn't be too difficult.

 

The new cab is all piney wood. I used a 1x12 I had in the shop so it's a little deeper than the original cab and used box (finger) joint construction. I used a better handle, feet and corners. I also changed the speaker mounting screws and t-nuts to stainless 10-32 threads. I used some red oak I had laying around for all the blocking for the baffle and back. I used the Gibson style black tolex which is a pretty good match for the original covering (mine had a blue-ish tint and was a bit more shiny. The material was thinner than real tolex too). Looks just like a BC30 you'd pick up in a store and sounds much better now due to the mods I learned about here and new tubes. The BC30 may just be one of those great "sleeper" deals that so many miss out on over the years.