70s Twin Reverb - Unusual noise

[falconer333]

Hi all,
I've just joined as I have too many amps and most they have some form of issue! My current disappointment is a 70s Twin reverb that I had professionally serviced and fully re-tubed a little over a year ago. It's been kept in the same place since I got it back, played a handful of times and over-wise flight cased. Turning it on today, (for the first time today in around 6 months), it is suddenly producing this strange continuous noise a couple seconds after flicking the standby switch. (See video clip below)

https://www.youtube.com/watch?v=L9Pec-O-9J4

Any opinions on what could be causing this would be greatly appreciated.
Thanks,
Jonathan

[Chuck H]

Chances are good it's a bad ground contact, cold solder joint and/or bad filter caps. When amps sit, unused, oxides tend to stack up on bad contacts and cold solder joints and old filter caps can fail. If a "re cap" wasn't done when the amp was serviced I would definitely suspect caps. Start by cleaning tube pin and plug contacts. If the noise persists you'll need to open it up. Do you have any electronics experience?

[falconer333]

Thanks for the quick reply Chuck!
I believe a full re-cap was performed, however, at the least the worn out caps were replaced during the service.

Unfortunately, I have almost zero electronics experience (some very basic soldering!)
How quickly do cold solder joint typically take to appear?
With regards to cleaning the tube pins and plug contacts, would that be using an electrical contact cleaner spray or a soft metal brush?

I spent a lot on the previous service hoping this would have it good to go for at least a few years so would really like to try to figure out any simple fixable issues myself before giving up!

[stokes]

I'm with Chuck on this.Does the volume control, or any of the controls have any effect of the noise?
"I believe a full re-cap was performed, however, at the least the worn out caps were replaced during the service." Not a good idea to just replace the worn out caps.Caps deteriorate mainly from time.If cap A and cap B are the same age and cap A is faulty, you can be sure cap B isnt far behind.

[hasserl]

60 hz, could be failed filter cap. Even if all were replaced that doesn't mean one of them hasn't experienced a premature failure. A scope on the B+ would show a sawtooth pattern; if no scope checking for AC voltage riding on the filtered B+ could indicate a filter cap failure. Or, could be a disconnected ground, as the other guys said.

[falconer333]

Thanks guys, really appreciate your knowledge!

I've just switched it on again today to check if this issue was effected by the volume and the original noise has now disappeared!

However, it's been replaced with new noises that got increasingly worse up to around 5 minutes of having the amp on. I also noticed that both volumes are very scratchy and not responding accurately or producing the output they should be. On top of this, the tremolo is again producing a very loud ticking (an issue I had asked to be fixed during the previous service), and seems to have now stopped working all together. Short video clip to demonstrate noises: https://youtu.be/CvCD6fQzW2g

Also, here are a couple of pictures of all the parts that were replaced during the last service: https://imgur.com/a/cIUPEBs

It's become apparent that I won't stand a chance of repairing this myself now, so my question is really whether or not it's normal to expect all of these issues to have occurred within 18 months, (and a handful of plays at home), since the previous service, or if it was most likely a poor job? I've already spent a few hundred on this previous 'repair' so pretty disappointed to feel like I'm back at square one!

[g1]

Simple cleaning of the tube sockets and controls may be all it needs.

[The Dude]

That's a good place to start. Clean pots and sockets, as g1 said. Also retention octal socket pins.

[falconer333]

Thanks guys, are there any sites/videos you might recommend for me to learn how to do the suggested cleaning?

[The Dude]

Here's a sight detailing retensioning.

http://www.swartamps.com/tech/socket_retention/

Cleaning is just a matter of spraying a contact cleaner into the socket pins. If they are really bad, you may need a small brush, but usually a quick spray does the job. Deoxit or similar is preffered. Remember, a little bit goes a long way. Also check tube pins. I've seen lots of corroded pins on older tubes.

[g1]

As for quick fixes, or just for test purposes, sometimes just removing the tube from it's socket and re-inserting it will clean up the contacts. Even wiggling them around without removing them can help.

[stokes]

For cleaning octal sockets I use a pipe cleaner with some deoxit or such on one end and then use the dry end after the wet end.For 9 pin preamp sockets I wet the pins of the tube and insert and remove the tube a couple times.Looking at the caps he took out, I'd want to have a look at what he left in there.Why did he change all the pots? I hate to say it, but I think you got more than dirty tube sockets here.

[The Dude]

I agree about the pots. I rarely have to change those. Usually a cleaning does the job.