crate vintage club problem
Hello everyone, very nice community you have here. Before I get started I would like to say that I have read the toob/noob post, and there was a lot of good info there. I am still digesting it all. I especially love the rca manual, I got a kick out of how old the science was! I have also searched and can't come up with anything "on point" with my problem. Here goes.
I have had my first tube amplifier, a crate vintage club 50 (50 watt with the 3x10 speaker configuration) for about 7 months now. For a month now the amp has been making crackling noise after taking it off standby. I always let the amp warm up for 3-5 minutes or so before taking it off standby. The amp has four 12ax7s in the preamp stage and four el84s in the output stage. It was supposedly retubed recently before I purchased it, and it currently has all mesa boogie tubes in it (russian made I believe). I have been trying like heck to figure out what is wrong with it!
Yesterday when I took it off standby the amp crackled, I heard the guitar for a minute and then it went dead. The power switch no longer even lights up. I have tried it in other outlets. It was being run through a furman power conditioner. Before it had died, all four el84s appeared to be glowing and operating correctly. I could not observe the 12ax7s as they are shielded and out of view anyway.
I don't even know where to begin diagnosing the problem, any suggestions?
Also just checked the fuses and they're ok. I think it's a preamp tube. If one failed during operation, is it likely that it harmed other components? I know such is the case with output tubes.
I'd suggest you find a technician to service the unit, perhaps he would be willing to allow you to watch the diagnostic process, helping you to become familiar enough with technique to allow you to eventually do your own work.
A failed pre-amplifier tube is not going to cause the amplifier to not power up, (or blow the primary power fuse) however a blown fuse would, and in a properly designed amplifier fuse blowing is a symptom of some underlying fault. Are you sure the fuse is not blown?
How did you check the fuse - with an ohm meter? Visual inspection can be misleading.
How many fuses does this amplifier have, and does it have a detachable or fixed line cord?
Check continuity of the primary circuit, with the power switch in the on position you should see a dc resistance of something considerably less than 10 ohms from hot to neutral - if not you need to figure out what component has failed.
All sorts of minor things could be wrong to prevent the amplifier from powering up, from a defective power cord, blown fuse, bad switch, cold solder joint, broken faston connection, to worst case a fried power transformer. (Least likely IMO)
I checked it visually. My father is a retired electrician, so I'm going to be borrowing some of his tools for this. To be honest, I'd rather have an idea of what's wrong before I take it to a technician. This is partially because I feel like the guy could tell me that there's five things wrong with the amp and overcharge me to fix it, when in reality something small needs repair. I will end up taking it to somebody to do the repair though. I just want to know what is wrong. This thread probably belongs in one of music forums, so mod you can move it if it's necessary.
I'm going over there later this week to pick up a couple of meters and some tools. Maybe I can convince the old man to take a look at it as well. I will keep you guys updated! Thanks for the hints so far.
I know there are plenty of unethical people out there, but the guy who finds 5 things wrong might be giving it to you straight.
I would not give a piece of equipment to a fellow I didn't implicitly trust in the first place.
Get a couple of referrals from people you do trust.
I think it is not a bad idea to try and figure out what is wrong with the amp ahead of time, but lack of trust should not be your motivation, and unfortunately given your current lack of experience you are unlikely to identify anything beyond the most egregious of issues. If your dad is an electrician (not an electronic tech) it is highly unlikely that he has many of the right tools to do the diagnosis work, at best he would have a serviceable meter.
It's a tube guitar amplifier so you posted to one of several appropriate places here.. I don't think it needs to move.
1] check for fuse, if it need replacement then
2] buy a bunch of fuses and replace fuse
3] pull out all tubes
4] turn on amp, see if fuse blows, if not
5] turn amp off, put in 1 pair of EL84s, turn on check for crackle or fuse
6]turn amp off, put in 2nd pair of EL84s, turn on check for crackle or fuse
if all works fine
6]turn amp off, put in each 12ax7 at a time, turn on check for crackle or fuse
This should tell you where the problem is..
my guess is an output tube gone short.. that would both explain the cracking (loose grid 3?) and the fuse blowing (grid 3 shorting) ..
just my 2 cts,
My son has the 2x12 version VC5212 which had a volume drop problem and some noise issues. The tech spent weeks figuring it out. Replaced the channel switch, some swollen caps, power tubes ( http://store.tubedepot.com/jj-el84.html ) $16 per matched pair
and ultimately had to replace the effects jack to correct a contact problem. He was glad to see that amp go. It is worth the repair - great tone.http://store.tubedepot.com/jj-el84.html
I think (maybe WRONG) that the Vintage Club Series was the forerunner to the Palomino.
The Schematic for the Palomino can be down loaded from Schematic Heaven (See Post 70's Amps).
It will give you some guidance at least and the power amp section is likely to be the same (4 x EL84 Cathode Biased).
Sweet. Thank you all for your posts. I took the amp down to a tech in my area and he confirmed some of your suspicions. One of the fuses did go, and rightly so, as an output tube went south. He also fixed some other things caused by the tube failure. I thought the fuse was fine because it appeared to be intact visually. I had him put in new JJ el84s and an entire new set of groovetube 12ax7s.
This amp is one of the rare ones that you don't want to ever let go of. The 3x10 speaker configuration really is a rarity! While Crate has made some really bad products, this amp is deserving of its place in my makeshift studio.
I have thought about upgrading the speakers, but i'm on the fence about that. There aren't that many 10 in. options. Either way, this is neither the time nor the forum for that discussion!
Thanks for the help gents.
This amp GOT a problem!
I'm servicing one. The amp HAS A problem within the output stage. Low resistors, poor bias.
|All times are GMT. The time now is 09:31 AM.|
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright ©1999-2015 diyAudio