| Author | Message | ||
| Doug Hartford (wideglide85) Username: wideglide85 Registered: 01-2011 |
After my HD 130 head is on for a couple hours, it seems to lose the "fat" tone and sustain. It sounds perfect for most of a gig, but towards the end it sounds kind of lifeless. (The volume stays the same.) I put JJ EL34s in it a couple years ago when I first got it, and then had Mathis Amplification in Lincoln NE replace all of the capacitors and give it a thorough cleaning & tune-up. It had this same issue before I had it worked on, but much worse than it is now. I leave it on during our intermission breaks, but flip the standby switch off. I thought maybe a tube was going bad so I ordered a matched quad of EH 6CA7s and a new 12AX7 to try. They haven't arrived yet, so I thought I'd ask for ideas here while I'm waiting. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
That sounds like a cap letting down due to heat to me. You're going to have to either track in down with a signal after it fails or just replace every cap on the main board. It just sounds like heat failure to me. Also, check the resistors on the power tube sockets for cracks. Mike | ||
| Doug Hartford (wideglide85) Username: wideglide85 Registered: 01-2011 |
Thanks for the reply. I forgot to mention that I've also left it on for several hours at home without playing through it, and it still sounds fine. So apparently the problem is caused by working the output section. I'll also try running it on the 65w setting for the next gig and see if it makes a difference. Do you think installing a cooling fan might also help? | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Fans ALWAYS help but it won't cure the problem. It's aticking time bomb as to when it stop entirely. At least THEN, it will be easier to find! | ||
| Doug Hartford (wideglide85) Username: wideglide85 Registered: 01-2011 |
Thanks for the advice. I'll get it checked first chance I get, and mention what you said about heat failure. I have a Fender Blues Jr. also, but it's just not the same! | ||
| Doug Hartford (wideglide85) Username: wideglide85 Registered: 01-2011 |
My new output tubes haven't arrived yet, so I went ahead and put a new 12AX7 EH in the phase inverter (which made an immediate improvement in the sound) and played it on the low power setting. It seems to work just fine, no loss of tone at all for the entire gig. So whatever was causing the problem may still be there, it just doesn't show up under these conditions. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
I did fail to mention that the FIRST thing I would do is clean the sockets and retension them. More problems caused by dirt sockets than anything. Retension is IMPORTANT. Mike. | ||
| Doug Hartford (wideglide85) Username: wideglide85 Registered: 01-2011 |
My amp tech did that when he replaced the caps. I have a feeling it was the PI tube, but I'll check out the other things you mentioned if the problem continues. Thanks again! | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
The PI was a very weak spot in the early MM's. that was the reason that they went to the SS driver circuit and changed them to a cathode driven amp. A good quality 12ax7 is a FIRST step in reliable use with a MM. That and good tubes. Mike. |
Tue, 03/25/2014 - 09:53
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