newbie questions on Bogen M330A repair

GregC81 · 22nd November 2007, 12:51 PM

Hi!
I recently purchased a Bogen M330A tube amp which I've been using with a record player. Having no prior tube amp knowledge except having a new tube guitar amp. I thought I'll see what this one will do. Its worked excellent for about a month. Now my sound quality is getting flat. Especially when it heats up. The one 7868 tube in the rear glows bright orange and gets very hot after 10-15 mins of use. The transformers and power cord do not appear to be overheating. Being mechanically inclined I pulled the bottom cover off to discover that the capacitors are leaking oil. Thats not good I assume, so could anyone direct me to some good inexpensive replacements? What type of capacitor would be best? I see there are many different kinds. And I don't know what the original ones are. It looks like this amp is untouched has all original Bogen tubes etc. Any chance my tubes could be fried too? How would I know? Replace the caps first then tubes or do them all at the same time? I apologize for all the simple questions lol. I feel I can tackle this but just need to know where to start.

fauxpas · 22nd November 2007, 01:54 PM

Being a tube and electronic nube, I'd be wanting to know how to safely discharge the capacitors, then I'd remove and take to my closest reputable electronic store (or online if marked well enough), and install new ones...

Tom Bavis · 22nd November 2007, 03:53 PM

If the tubes have warmed up, they'll usually discharge the capacitors at shutdown. Check with a voltmeter to be sure!

Leaky coupling caps are the likely cause (electrical leakage - not physical, but leaking oil is reason enough to change them...). The glowing tube COULD be bad (grid leakage), swap the pair and see if the problem stays with the tube or the socket.

The M330 is in Sams Photofact folder 497-4, but 330A isn't covered. I have the folder for the L330, which uses 6AV5 output tubes - don't think it's very close, but email if you'd like a scan - tbavis(at)rochester(dot)rr(dot)com.

GregC81 · 23rd November 2007, 07:50 AM

Thanks for the input! Yes I've been reading everything I can to learn how to do the job safely. I'm confident in my soldering skills too so shouldnt be a problem there. Just need to know as much as I can about troubleshooting the amp. Hopefully can start moving forward soon as I know what capacitors to get. Hope to get it back up and running soon!!

22nd November 2007, 12:51 PM	#1
GregC81 diyAudio Member Join Date: Nov 2007	newbie questions on Bogen M330A repair Hi! I recently purchased a Bogen M330A tube amp which I've been using with a record player. Having no prior tube amp knowledge except having a new tube guitar amp. I thought I'll see what this one will do. Its worked excellent for about a month. Now my sound quality is getting flat. Especially when it heats up. The one 7868 tube in the rear glows bright orange and gets very hot after 10-15 mins of use. The transformers and power cord do not appear to be overheating. Being mechanically inclined I pulled the bottom cover off to discover that the capacitors are leaking oil. Thats not good I assume, so could anyone direct me to some good inexpensive replacements? What type of capacitor would be best? I see there are many different kinds. And I don't know what the original ones are. It looks like this amp is untouched has all original Bogen tubes etc. Any chance my tubes could be fried too? How would I know? Replace the caps first then tubes or do them all at the same time? I apologize for all the simple questions lol. I feel I can tackle this but just need to know where to start.

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22nd November 2007, 01:54 PM	#2
fauxpas diyAudio Member Join Date: Nov 2007	Being a tube and electronic nube, I'd be wanting to know how to safely discharge the capacitors, then I'd remove and take to my closest reputable electronic store (or online if marked well enough), and install new ones...

22nd November 2007, 03:53 PM	#3
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	If the tubes have warmed up, they'll usually discharge the capacitors at shutdown. Check with a voltmeter to be sure! Leaky coupling caps are the likely cause (electrical leakage - not physical, but leaking oil is reason enough to change them...). The glowing tube COULD be bad (grid leakage), swap the pair and see if the problem stays with the tube or the socket. The M330 is in Sams Photofact folder 497-4, but 330A isn't covered. I have the folder for the L330, which uses 6AV5 output tubes - don't think it's very close, but email if you'd like a scan - tbavis(at)rochester(dot)rr(dot)com.

23rd November 2007, 07:50 AM	#4
GregC81 diyAudio Member Join Date: Nov 2007	Thanks for the input! Yes I've been reading everything I can to learn how to do the job safely. I'm confident in my soldering skills too so shouldnt be a problem there. Just need to know as much as I can about troubleshooting the amp. Hopefully can start moving forward soon as I know what capacitors to get. Hope to get it back up and running soon!!

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