Loud Hum on Fender Twin Reverb 65 reissue when standby swith is off (play mode)

[jalexquijano]

I have a Fender Twin Reverb reissue with series number AC064286 which produces a horrible hum when its cold and you switch it to play mode. After a couple of minutes the hum dissapears. Is this normal? I have never recapped this amp as i bought it used in 2010. Based on the above facts, i would like to know the following:

1. What year is this amp from

2. Should i consider changing all electrolytic caps? Which ones should i start with? Will this get rid of the hum when cold?

[J M Fahey]

I have a Fender Twin Reverb reissue with series number AC064286 which produces a horrible hum when its cold and you switch it to play mode. After a couple of minutes the hum dissapears. Is this normal? I have never recapped this amp as i bought it used in 2010. Based on the above facts, i would like to know the following:

1. What year is this amp from

2. Should i consider changing all electrolytic caps? Which ones should i start with? Will this get rid of the hum when cold?

Is this a joke?
You have started 21 (twenty-one) different threads asking about various very minor and normal "problems" regarding your Twins, both this very same one and the 1990 red knob one.
Including this very same question about "hum after flipping Standby switch on, which disappears on its own after a few seconds"
http://music-electronics-forum.com/t45283/

plus:

http://music-electronics-forum.com/t45448/

http://music-electronics-forum.com/t45362/

***http://music-electronics-forum.com/t44973/***

By the way, you have NOT answered your latest thread , where you were suggested some practical solutions to try: http://music-electronics-forum.com/t45487/

Are you pulling our collective legs?

[Jazz P Bass]

"What year is this amp from?"

The first letters of the serial number (AC064286) indicate that the amplifier was manufactured in 1990 in the month of March.

[jalexquijano]

Thank you very much for your replies. I will buy some good quality electrolytic caps and recap this amp.

[DrGonz78]

Thank you very much for your replies. I will buy some good quality electrolytic caps and recap this amp.

I would be curious as to what is causing the noise in such short duration at start up. Can you monitor AC voltage on the DC power supply while starting up the amp? At least by doing that test you will may see what you think is actually there.

[nevetslab]

Before you go out and replace all of the power supply caps, I'd suggest you first open up the lower power supply compartment, lift the board off (removed the 5 screws holding it in place) and look very close at the solder joints of the caps. I'd go as far as suggesting de-soldering and then re-soldering them. If the exposed plating is way smaller than the copper pattern, I'd recommend scraping away the rest of the green solder mask and tin that newly exposed copper, then clear the lead holes and re-insert the supply cap leads and fold them back over how they were before, THEN re-solder them. I'd also do the same on the main PCB. That takes a lot more effort, though, as all the AC Mains primary and secondary wiring is plugged in. Those will have to be disconnected (label each connector), and unplug the front panel PCB, so you can lift up the main PCB, folding it up, hinging on the socket wiring, and look closely at all the power supply caps soldering there as well. Look closely at the swagged male fast-on terminals that pick up all the grounds and cap connections from below, as well as from the P/T secondary wires.

Your amp is old enough to have suffered one or several solder fractures, that can lead to the hum behavior you describe. If after repairing all of the soldering, yu still have the issues, AND after measuring the AC ripple on the power supply taps as DrGonz78 suggests, then I'd go for replacing the supply caps, if it's warranted.

[jalexquijano]

The rear of the Fender twin reverb reissue says 4A SLO BLO 125VAC. How come i cant use a 7A SLO BLO 125V Fuse? Just blew the fuse while testing some power tubes i had lying around.

[Enzo]

Because it offers no protection to the thing.

[Jazz P Bass]

Besides which, at idle (if that is where the fuse blew) the amp pulls less than an amp.

[pdf64]

It would be very beneficial to build and use a light bulb limiter when doing this kind of thing.

[jalexquijano]

Before you go out and replace all of the power supply caps, I'd suggest you first open up the lower power supply compartment, lift the board off (removed the 5 screws holding it in place) and look very close at the solder joints of the caps. I'd go as far as suggesting de-soldering and then re-soldering them. If the exposed plating is way smaller than the copper pattern, I'd recommend scraping away the rest of the green solder mask and tin that newly exposed copper, then clear the lead holes and re-insert the supply cap leads and fold them back over how they were before, THEN re-solder them. I'd also do the same on the main PCB. That takes a lot more effort, though, as all the AC Mains primary and secondary wiring is plugged in. Those will have to be disconnected (label each connector), and unplug the front panel PCB, so you can lift up the main PCB, folding it up, hinging on the socket wiring, and look closely at all the power supply caps soldering there as well. Look closely at the swagged male fast-on terminals that pick up all the grounds and cap connections from below, as well as from the P/T secondary wires.

Your amp is old enough to have suffered one or several solder fractures, that can lead to the hum behavior you describe. If after repairing all of the soldering, yu still have the issues, AND after measuring the AC ripple on the power supply taps as DrGonz78 suggests, then I'd go for replacing the supply caps, if it's warranted.

I would need at least 3 22uf 500v and 2 220uf 300 V axial electrolytic capacitors for this amp. Which Brand would you recommend? F & T or Illinois?

[J M Fahey]

If after repairing all of the soldering,

which you didnīt

you still have the issues, AND after measuring the AC ripple on the power supply taps as DrGonz78 suggests,

which you didnīt

then I'd go for replacing the supply caps, if it's warranted.

which so far isnīt because you refuse to test and post results.
All you want is "a Brand".

[jalexquijano]

which you didnīt
which you didnīt

which so far isnīt because you refuse to test and post results.
All you want is "a Brand".

I checked the PCB and those Illlinois Caps are the stock ones. They were never changed. THey are not that much expensive so why not try it?

[The Dude]

Because it's easier and cheaper to simply check for ripple and see if they actually need replacing.

[nevetslab]

.....and, stating again, just replacing power supply buss caps, there's no guarantee that will solve your problem. Those of us who are trying to help you find the problem do this sort of thing for a living and have been at it for years. I cure Fender amps of this sort of problem on gear that makes it's living going out on tour in road cases, and they often come back in behaving like the amp you're trying to cure. It takes some effort to open it up and look. I cure fractured solder joints constantly, and it's probably what you're facing. it takes bright light, magnification during inspection and patience. If it's on the main PCB in the chassis, yes, there is some effort involved to get that board lifted up to look, and care is required so as NOT to break wire leads off in the process. Loads of quick-disconnects need to be removed, so you use a black sharpie to label the female push-on terminals so you can return them to their proper places when re-assemblying, after you've found all the solder fractures. If nothing else, it's a good exercise in maintenance work.

That head light and loupes on my avatar (to the left of this text) is my surgical eyewear that I use in this process. It reveals all the bad solder joints clearly.