Hi All,
First time post. I have a 212-65 that I have not used in about 5 years I am looking to bring it out and start playing more. I am running into the following issue any insight where to begin troubleshooting would help. I am a licensed electrician by trade with lots of experience in troubleshooting electronics in industrial applications and would like to try my hand at troubleshooting this amp before I give up and find an amp tech to send it to.
It is not as loud as I remember and has a bit of a dirty sound. The main issue is that after ringing for a second or two for higher notes (more or less anything on b/e) the output just cuts out sharply. I have had a look inside and I don't see anything out of that looks fried or any capacitor that has budged.
I experience the same issue no matter what channel I run through so I expect my issue is somewhere in the schematic after the master pot. It has the same symptom on both hi/lo and with any combination of deep/bright selectors.
Just thought it would be worth a flier if anyone has seen this before and has any idea what to look at before I start testing caps/resistors/gates/pots/transformers.
Edit* I have swapped out tubes and problem is still present.
Thanks
Which Model?
Which model or vintage do you have? Does it use the 12AX7 tube phase inverter? The problem does sound like something in the output stage. Did the hi voltage power supply caps under the doghouse look good? Again, just asking. -mgriffin
Vintage
It does have the 12AX7 tube and a pair of el34s. I’m not 100% on specific vintage does 2275-65 make sense?I can snap some photos tomorrow when I have a few minutes in the shop. For now all I have is this one of the little one rocking on. I know the original owner has modified it back before I bought it 15 years ago to a single speaker. He passed away and I bought it consignment, the book on him was that he certainly knew his stuff. It worked great for 10 years before I stored it in the basement for 5 years.
Edit: checked nameplate on way out the door this morning 2475-65.
Economy Tune Up
Sorry for late reply. I recently had cataract surgery and now can see much better. Since the amp was in storage for years, it would be good to give it a poor mans tune up before throwing money at it. Check the speaker to make sure the contacts are clean and the voice coil is good. Pull each IC, clean the sockets and pins and reinstall. Same for the tubes and all jacks including reverb tank and foot switch. If you see a contact, clean it. Use contact cleaner on all pots. Also inspect the high voltage caps under the doghouse and make sure they're not blistering. Next, check/adjust the bias on the tubes. The procedure is on the schematic. Be careful of 750VDC on the HV caps and tube plates. Good luck. -mgriffin