hellion102792 Posted October 4, 2012 Share Posted October 4, 2012 So I think it's time I change the tubes in the '67 Skylark. It's stocked with a 12AX7a pre, a 6BQ5A power and a 6X4 rectifier. As far as I know they are the originals and yesterday while jamming towards it started to sound really crappy after a couple hours. Very muddy, loss in volume, plenty of feedback, a ton of buzz, etc which leads me to believe the 12AX7A is going. I have a recording if anyone would like to judge it. Now the preamp tube and the 6X4 are relatively easy to find, but I haven't had much luck with the power tube. I've read on Google that a 6BQ5 can be replaced with an EL84, but can they replace a 6BQ5a? I really don't know much about tubes and don't want to harm the amp now that I just got it working again, hopefully someone more knowledgeable about this stuff can help out. If it can take an EL84 does anyone have any good recommendations that sound nice in a 5w amp? I'd like to eventually get a new 10" speaker too if anyone has any decent suggestions, the paper feels so dried out and brittle on the stock one. Thanks! Link to comment Share on other sites More sharing options...
jdgm Posted October 4, 2012 Share Posted October 4, 2012 Looked this up in 'The Tube Amp Book' and you should be fine with an EL84....the book was written by the founder of Groove Tubes and you can't go wrong with a GT EL84 although I bet they're expensive now. Their website is- www.groovetubes.com - but I got stuck on the cookies which are just ridiculous. As far as the speaker goes...here - http://www.tedweber.com/ Link to comment Share on other sites More sharing options...
RaysEpiphone Posted October 4, 2012 Share Posted October 4, 2012 Heres some info that may help http://www.youtube.com/watch?v=ZvW3D3XoHWY&feature=related Link to comment Share on other sites More sharing options...
hellion102792 Posted October 4, 2012 Author Share Posted October 4, 2012 Think I'll go for the EL84 in that case, thanks guys! I'm looking into those Weber speakers, just gotta find out what Ohm rating the Gibson Ultrasonic has (it's a 10" by the way, not an 8"). Took out the tubes a minute ago and noticed that all of the pins on the 12AX7a appear to be burnt and blackened near the end that goes into the glass...the tubes do still function but is this normal for old used tubes? The past 2 times I've brought it to jam it's been pushed to around 10 for upwards of 2 or 3 hours, often with my Digitech RP-1 cranked into it. These are probably the first few times in at least 20 years that it's been cranked and left on for this long. When practicing in my apartment I sometimes use a tube mic-pre effectively as an overdrive pedal. I crank it to distortion while keeping the amps volume around 1-2. Is there a chance I'm frying the living s**t out of the amp's preamp tube by doing this? I figure it's wearing on the tube by sending it that much signal, but could it cause it to heat to the point where the socket could burn or something? Also noticed a "smoked component" kind of smell when I opened up the back, though it's hard to distinguish from the amp's dusty basement smell. I'm just wondering for future reference, after replacing them I'd like to make them last and hopefully stop any damage I could potentially be causing. Link to comment Share on other sites More sharing options...
badbluesplayer Posted October 4, 2012 Share Posted October 4, 2012 You might as well replace the 12ax7 and the EL84 with something new and then you'll be set for awhile. Both the 12ax7's and the EL84's tend to wear out after awhile. They can wear out after six months, or maybe every couple of years, depending on how much you play the thing. Cranking it will wear out tubes faster but it won't wreck anything. Rectifier tubes tend to last a long time. Weber makes some good speakers. I have an 8" Weber in my Silverface Champ and it's very nice. Link to comment Share on other sites More sharing options...
jdgm Posted October 4, 2012 Share Posted October 4, 2012 No, the tube pins should not be blackened and burnt!! Oh my! Using a tube mic pre-amp should NOT damage the amps pre-amp tube as the amps vol pot controls the gain. But from your description it has got literally baking hot...I hate to think what the tube sockets look like, and it may be that other components will fail - in fact I'm surprised it hasn't died after that, what a good amp! So you must replace the tubes and the fuse (get a couple spare fuses too)- don't be surprised if afterwards something else goes because the new tubes are acting much more efficiently versus the other components. I would imagine you might have to source a few parts or find a good amp repairman if that happens. New caps (capacitors) would also make a big difference but you must get replacements as near as possible to the original spec and appearance. I got a Weber 8" some years ago to replace the stock speaker in my Vibrochamp. It was well worth it and even though I'm in U.K., it was more suitable and cheaper than many British speakers. It is far better than the original speaker (which I've kept) and I do small duo gigs with the amp now! I can't imagine any 8" speaker sounding much better! Regards! Link to comment Share on other sites More sharing options...
hellion102792 Posted October 4, 2012 Author Share Posted October 4, 2012 Damn! Okay well I just checked all of the sockets in and out with a flashlight, no sign of any melting or scorching on those. The only thing I see is some of the resin from the solder joints attached to the socket has browned some, similar to the way solder resin will turn brown if you leave an iron on it too long. It's on all 3 sockets though and the pre tube is the only one with the blackened pins. I should've clarified that they're only black from the point they exit the glass to about a few millimeters up. Still I'm going to replace that fuse and the 2 tubes then, better safe than fried. When I got the amp the big old paper multicap was close to failure so I didn't use it. I replaced the filter caps this summer, added a 3-prong cord and cleaned dust off of all the components in the chassis so I'm getting familiar with working inside it, if it comes to it hopefully I'll be able to find all the right components. I got it after years of being used as a stand/decoration and put probably less than 10 hours of use on it, so if it is literally baking the sockets maybe I've caught it early enough where I can take your advice and prevent total failure. Thanks for that, the last thing I want is for this thing to burst into flames Link to comment Share on other sites More sharing options...
jdgm Posted October 4, 2012 Share Posted October 4, 2012 Ah then it sounds like you're ok - not quite as bad as I imagined!! The brown solder joints -'if it ain't broke, don't fix it'...but you obviously know what you're doing! Sure, it should get hot on a long session but I'd burn those new tubes in carefully ...I often think amps are like car engines, they get used to being operated in a particular envelope according to the driver. Uh...that's another thread! Link to comment Share on other sites More sharing options...
Riffster Posted October 4, 2012 Share Posted October 4, 2012 I say change the tubes and then go from there to see if there are any other problems. I am about to put in a new preamp tube in my Vox Student and I am curious to see what difference it will make if any. If you get a Weber Speaker make sure you get the right one for the amp, call them up and ask for suggestions, I have a 12" Weber Blue Dog rated at 15 watts and it is great with low wattage amps because the speaker gets driven but does not get to the point of distortion. This speaker does not have doping around the cone either, that makes it sound even better. Link to comment Share on other sites More sharing options...
Riffster Posted October 4, 2012 Share Posted October 4, 2012 ...I often think amps are like car engines, they get used to being operated in a particular envelope according to the driver. Uh...that's another thread! This is very true, the little Vox amp I have used to get played dimed all the time and under that setting it produces almost no hum. At lower settings it hums. Link to comment Share on other sites More sharing options...
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