Grateful Dead Music Forum

I just bought a '73 Twin reverb today. The price was good and the amp is in nice condition both sound-wise and visually. With one exception: I was cautioned by both the seller and my local tech that while it is a good amp, it has a bit of a hum (which they both suggested is not uncommon for an amp it's age). While I love the sound and I'm very excited about the amp, the hum is definitley annoying. It's not as noticable when playing, but it is definitley there and is frustrating. My tech mentioned that he had an idea of what might be causing it, but I forget offhand what he said. I will follow up with him. Anyone have any experience with hum-producing vintage twins??? Any known causes and remedies? Also after playing for a while it seemed like it was starting to make some static-like, crackly kind of sounds, but I had to go and didn't have the time to mess with it any further. Finally, it has unoriginal speakers - Pyle Drivers - any thoughts on these? The seller said he had them reconed about a year ago. Can anyone offer any thoughts or advice for diagnosing this hum problem and hopefully fixing it??

I'm not quite sure about the hum, but the crackly static sounds most likely indicate old filter caps needing replacement. I'm not an amp tech, but I did stay at a Holiday Inn Express...

For starters, you must replace the electrolytic filter cap's in that pan underneath. These filter the power supply and it's the first place you should go. It's deadly in there, so let an experienced tech handle it.

If that doesn't get it, then there are other places to look. But on a 36 year old amp, you should make sure those are fresh.

Brad

Yeah, don't mess with the caps, they can still hold a charge. As for the hum, does it have a 3 prong power cord grounded to the chassis?

Also,

does it hum with the reverb off?


Brad

Thanks for your time and help folks! Yes, it hums with reverb both on and off. It gets a bit louder as you increase master volume or when you pull it out (the master volume, that is). Yes, to three prong grounded cord question. My local tech surmised that it is the electrolytic caps as well. How big a job is this? What would be a fair price for it? Any thoughts on the Pyle Driver speakers in it? Many thanks again!

You're looking at about $40 in cap's, and maybe a 1/2 hour to 1 hour in labor.


Brad

Brad - Many, many thanks!!!
What does the number on the tube chart, that people often ask about, tell you? Mine is: 047944G.
Also, anyone familiar with these Pyle Driver speakers I have in it? Any thoughts on them??? Thanks!!!

When I have the electrolytic caps replaced will this change or improve the sound or tone of the amp - aside from hopefully correcting the hum?