Power Tube Rattle

[tonecat]

Hello Everyone,
I have a '59 5F6-A Bassman clone that I built with 6L6GC's in it. Within a couple of hours of playing, this amp will make any set of power tubes rattle. It is definitely the tubes because the rattle stops when I grab the glass envelope of the tube with a glove. This happens with NOS as well as new production tubes. Do any of you have any advice on fixing this problem? I can't keep sending back every set of power tubes I buy a week later or my vendor is gonna kill me. Please let me know. I have tried the Duende Criatura tube rings Duende Criatura 32 - 36 mm without much luck. I have not tried the o-ring damper types as of yet. If anyone has any ideas that work for this type of problem, please let me know. These combo amps are torture chambers for tubes, but there has got to be a way to minimize this rattle to an acceptable level. Any help would be greatly appreciated!! Thanks to Everyone!!

Paul

[Diablo]

What chassis and tube sockets are you using? Perhaps it's the sockets moving? Also try tightening the chassis bolts that mount it to the cabinet.

[tonecat]

I am using a Weber 5F6-A chassis and Belton Micalex tube sockets. I have tightened and retightened everything imaginable on this amp. The rattle only happens on certain notes and when I grab the power tube with an Ove Glove, the rattle stops. I've swapped tubes and the rattle goes away for a few hours or sometimes days, and then its back. Some tubes are less prone to rattle than others. Its like the amp is shaking them loose on the inside. I push this amp pretty hard and I play heavy blues/rock with a lot of gain. If you touch the amp when I'm playing through it, it is really vibrating alot. I really am sure it is the tubes themselves and not some other mystery rattle. Thanks for the response though!!

[txstrat]

Because combo amps torture the tubes due to the vibrations of the speakers inside the cab I'd try to do everything to keep the vibrations off the tubes.
You could use rubber or plastic washers for the power tube sockets (you might have to use something from a plumber supply) and try to use some rubber in between the cab and the baffle board to keep vibrations to a minimum. Or some rubber between the baffle and the speakers might help.
Just my 2C

[Enzo]

6L6s are not prone to rattles like the very loose EL84s. I am very suspicious when ANY 6L6 tube new or old rattles in the amp. I can believe one pair of tubes being loose, but not 10 or 12 tubes.

Holding the tube may stop the rattle, but you are not only holding the tube. By extension the socket pins clamped around the tube pins are now also being held. I'd really have to vote for the problem being somewhere in the socket or under the chassis.

[Diablo]

Another data point. I've got a Weber 5F6A with the Weber tube sockets. I'm using NOS Phillips 6L6WGB, and I don't have any tube rattle. However, I don't play the amp super loud on a regular basis. I have cranked it up just to let the neighbors know there's a crazy guy living next door.

[melvin]

Perhaps something else is heating up and getting microphonic or causing circuit conditions that make the tubes microphonic. At this point I would check the bias current when they are noisy. Perhaps clean and retension the sockets and check the solder joints to the pins (especially #5).

[MWJB]

+1 on what Enzo says. 10 or 12 tubes rattling in the same amp? It's not the tube's fault.

You could try some spring retainers if you are sure that the rattle is mechanical. It's a band aid rather than a fix though.

Have you played the amp out of the cab, with a long speaker lead, to isolate the chassis fom any vibration from the cab? What kind of cab are you using (homemade/mojo/weber etc)? These amps are not typically prone to power tube rattling, make sure all panels fit flush before being screwed down, make sure the baffle is free to move unhindered at the sides, make sure the baffle is flush against the cab at top & bottom mountings.

If you have something rattling in the cab, this is making life worse for the tubes as regards noise.

What happens when you back off treble & presence controls? Many 5F6A inspired amps can have a metallic "tinkling" sound that is not a product of mechanical vibration, but poor layout.

Did you use 1500ohm grid stoppers at pin 5 of the 6L6s & 470ohm screen grid resistors at pin 4? Try some larger grid stoppers, see what that does?

How have you mounted the filter caps, are they secure? If you have used a filter cap doghouse on the back of the chassis, do you have adequate clearance between that and the speaker magnet?

[tonecat]

Thanks for all the responses everyone. After some more testing, it is definitely something vibrating in the chassis which in turn is causing the power tubes to rattle. I removed the chassis from the cabinet (which is a Mojotone 4 x 10 Bassman cab) played through it, and no rattles. After bolting the chassis back into the cab, I checked to make sure there was clearance between the top speakers and the filter cap doghouse and the power transformer and all was good. I checked all solder connections at the power tube sockets and re-tensioned them. Made sure all the mounting bolts were tight. I started playing through it again and the problem was back. Granted this vibration happens at loud volume levels and only on certain notes, I am almost deaf now from trying to figure out a cause. It seems that when I bolted the chassis back into the cab, something is out of whack with the cab causing the chassis to twist when I tighten it up. This seems to be making the turret board vibrate excessively which could be transferring the vibration to one of the coupling caps which then causes the vibration to be amplified making the power tubes rattle? This is extremely frustrating!!! I have the turret boards mounted on bolts with metal standoffs on them like early Marshall amp heads did. This may not be ideal for a combo amp. Short of pulling the whole amp apart and putting maybe some rubber standoffs to help deaden the vibrations of the turret boards, or somehow maybe trying to isolate the chassis from the cab, I am at a loss. None of this was a problem until I started recording the amp and could hear the vibrations on the recording. When I just play the amp along with the band, they are masked by all the other sounds. This is my first combo amp build and I can see why an amp head is the better way to go for high volume/gain applications.

There is not much room to put anything between the cab and the chassis to help isolate it because the power transformer is pretty close to the top speaker magnet. As far as other questions that were asked, I did use 1.5k grid stoppers, 1k screen grid resistors, tried messing with the treble and presence controls to no avail, and I also removed the tube clamps on the 3 octal sockets to no avail. I have include a couple pics of my build also. If anyone has any ideas, PLEASE HELP!!! My mind and ears can't take much more of this troubleshooting. Thank You ALL!!!

http://music-electronics-forum.com/u...4373-albums89/

[txstrat]

Since your amp is built like thousands of others I'd assume the vibrations are caused by the way you bolted everything together. The more the chassis can move due to the vibrations the more the tubes can rattle.
On your pics I can see only two bolts holding the chassis. Are there any others? I'm about to build a Super 5F4 and had no idea how the chassis was held. I opened this thread: Chassis mouting. On one of the pics you can see a third bolt holding the chassis (using an angle bracket).
Hope this helps

[tonecat]

Thanks txstrat,
I don't have the 3rd bracket installed. Good thread on chassis mounting!!! I may try out the bracket from Bruce at Mission Amps instead of taking the transformer apart to install the angle bracket. This along with some kind of insulating material between the cab and chassis may go along way to fix my problem. Tubeswell says he uses some type of rubber door weather seal stripping padding. I don't know exactly what product this is, can anyone help with this? Thanks again everyone!!

[txstrat]

I don't know exactly what product this is

They are different kinds of self adhesive foam or rubber strips (on a roll) to be stuck inside window (or door) frames to keep air drafts out.