Fender Twin 135 Watt with on/off master volume switc (6L6X4)

[bsco]

Good day to everybody...I just received this amp for repair...It is a very old amp from the 70's...should be a very enjoyable experience..The first thing I checked on was to see if the fuse was wrapped up in tin foil...hahahhaaa..it's not...it has the proper fuse. I gave this amp a good visual...The output tubes are very loose in the sockets...so much so that they could probably work themselves out of the sockets...The original plate load resistors are still there. The original electrolytic caps are still there....including cathode bypass caps....I could not find any scratchy controls...the rca connectors on the tremolo are badly corroded...there are a couple of pre-amp tubes that are noisy when you tap them.....the sockets don't look too bad but they might need replacement after so many years...also noticed that the ground connections soldered to the chassis look like they have come corrosion around them....will have to check that out as well....I did notice one thing so far.....with all the controls turned down, when you advance the reverb control there is a setting that produces a high pitched squeal...(around the 7 or 8 position).....that is barely audiable until you turn up the master volume control...then it cuts the head off you...it does this with the tank connected and disconnected...the driver tube is a 12AT7 and the recovery tube is a 12AX7A...I swapped these out with two more but same thing...Could it be possible for this to be caused by the age of the filter caps??? I am just trying to complie a list of things that this amp needs in order to get it working again...I have not connected a guitar to it yet but I will do that today.....this amp was repaired once before but it was a long time ago....one screen resistor was replaced.....I can't really see anything else.....even the transformers look original....and speaking of filter caps...the owner had asked me what brand of caps I would be using...I guess he doesn't want any of the cheap Chinese ones that are flooding the market...Any suggestions on the brand of caps I should use here??? I was thinking Panasonic........
Cheers,
Bernie

[52 Bill]

Try shorting the reverb return jack to ground. Does the squeal stop?

The power tube sockets on these amps sometimes seem to be loose, but often the pins are tight in the connectors and the connector are loose in the shell. This makes the tubes seem to be loose, but the contacts are good and tight. Make sure that the tube retainer clips are tight and are gripping the tube bases.

I haven't looked for them recently, but I haven't seen Panasonic caps in the correct ratings for these amps.

[bsco]

I'll check the retainers again but I found them to be tight...grounding the reverb return line is something I did not think off...Would it be better to do this through say a 100 ohm or 47 ohm resistor instead of a direct short?? Just curious...If the problem is indeed tied to the pins in the sockets themselves, I think I will try and find 4 sockets which will be tight when the tubes are inserted......but I know what you are saying as I have noticed that with new sockets before.........I find that some people will blame something loose like that for their amp problems...especially if they get it back and something else happens even if it had no bearing on the socket issue...the fact that they appear to be loose could cause a customer to get his shorts in a knot....if you know what I mean...Thanks very much for the reply...It is much appreciated.....what brand(s) of capacitors would you recommend.....
Cheers,
Bernie

[52 Bill]

I don't think that a loose socket would cause your squeal. I see that happen when the reverb tank wires get loose and no longer have good ground connections. That's why I suggested grounding the return jack. I just touch a screwdriver tip across the inside contacts of the RCA jack.

I use all different brands of filter caps, Sprague, F&T, Illinois, etc. There are good points and bad points to all of the different brands out there right now. I've had good and bad examples from all of these manufacturers. I'm not certain that there are any caps that are not made in China anymore.

[Tom Phillips]

...If the problem is indeed tied to the pins in the sockets themselves, I think I will try and find 4 sockets which will be tight when the tubes are inserted...

Common practice is to re-tension the individual socket inserts using a small tool point pushed between the socket hole wall and the floating female sleeve. It is rarely necessary to replace those sockets because of loose pins.

[Enzo]

And don't confuse the pins with the tube overall. Many sockets allow the tube to move some, you can wiggle the tube. The tube may seem "loose," but the socket PINS are gripping the tube pins quite well. it doesn;t matter if the tube can wiggle as long as the contacts the pins make are solid.

[bsco]

Thank you both Tom and Enzo....I'll check that out and if they don't need to be replaced I will leave them...Too bad I can't find a very small round stiff brush that you could insert into the pins of tube sockets to give them a really good cleaning...almost something like you would use to clean your battery posts in your vehicle....only these would slide down into the pins of the sockets and with some contact cleaner give them a good scrubbing...
Cheers,
Bernie

[Enzo]

Shoving a tube in and out of the socket a couple times is usually all the scrubbing it needs. That won;t tighten it, of course, but usually cleans the contact surface.

[bsco]

OK Thanks....That is what I have been doing....just didn't know if there was some sort of cleaning stick manufactured for such a task...
Cheers,
Bernie

[Resonator Guy]

These micro brushes from Lee Valley will work on some sockets. Microbrush® Applicators - Lee Valley Tools

[Enzo]

Also:

Cleaning Brush, #B-SS116

Pointer Swabs, #SWPP-25


And I use these mainly on XLR connectors:

Connector Cleaning Brush, #AB-25

[52 Bill]

And my dentist is always pushing those tiny little brushes for in-between your teeth. Proxibrush or something like that. Those will fit into octal sockets.

[bsco]

OK 52Bill. I actually have a couple of those here....Enzo sent me a link for a cleaning brush with metal bristles...if I am not mistaken these are the brushes which are used to clean some of the Pace rework Stations...it certainly looks like them....and I checked out the link from Resonator Guy..All very good I must say...I have some of those proxi-brushes so I will give these a try first......
Cheers,
Bernie

[Tom Phillips]

I recommend against using metal brushes because the contacts are usually plated and the metal brushes "could" damage the plating. You don't want to start removing the plating layer just the dirt & corrosion. I use fiber brushes and Deoxit. Also good for the center contacts of RCA Phono sockets as used for foot switches and reverb pan connections.

[bsco]

Thanks Tom...I won't be using metal ones....
Cheers,
Bernie