Home » VintageKustom.com » Repairing Kustom Amps » Thermal Paste (Replace thermal paste of k200a-1)

Show: Today's Messages :: Show Polls :: Message Navigator

Thermal Paste [message #11930] Tue, 22 September 2009 12:28   LZBass Messages: 16 Registered: September 2009 Junior Member I'm in process of repairing my first K2001-A. Does it make sense to replace the thermal compound on the power transistors while I'm inside? The head was manufactured around 1968 and I'm sure nothing has been done to it since it left the factory. Thanks for the help! Report message to a moderator

Re: Thermal Paste [message #11931 is a reply to message #11930] Tue, 22 September 2009 12:53 chicagobill Messages: 2005 Registered: April 2003 Senior Member It certainly wouldn't hurt. Whenever I buy a Kustom amp, I will always go through it to see what has been done to it in the past. I also check for any loose parts, wires, etc. And in order to know that the transistors are mounted correctly, I will remove all the old grease and re-mount them. It only takes a half an hour or so, and then I know that they are ok. I'd suggest that you at least tighten up the mounting screws. Report message to a moderator

Re: Thermal Paste [message #11932 is a reply to message #11930] Tue, 22 September 2009 15:48   LZBass Messages: 16 Registered: September 2009 Junior Member Thanks for the advice. This is my first time attempting something like this. I've also heard it suggested that all of the solder joints be reflowed. I expect a few issues as the main power fuse is blown. The fuse the fuse that was installed did not fit the holder properly. Would you happen to know what is the proper sized fuse for this model? Thanks for the good advice! -- Phil -- Report message to a moderator

Re: Thermal Paste [message #11933 is a reply to message #11932] Tue, 22 September 2009 18:10 chicagobill Messages: 2005 Registered: April 2003 Senior Member The original fuse was probably soldered in, but I'd have to check my A series head to be sure. In any case the originals used 3AG sized fuses rated for 3 amps. If the fuse is blown, I'd check the output transistors and the bridge rectifier for shorts. Report message to a moderator

Re: Thermal Paste [message #11935 is a reply to message #11933] Tue, 22 September 2009 18:57   LZBass Messages: 16 Registered: September 2009 Junior Member Thanks. There are actually two fuses in the unit. The fuse I refered to is the one located in a fuse holder by the power lamp on the front chassis. The blown fuse was a Buss AGC 7 1/2A - 250V fast-blo. I'll get a few replacements as I think I'll need them troubleshooting the problem. Do you also recommend replacing the filter caps because of their age? They are currently Mallory 4500mfd @ 50vDC. Any other suggestions are GREATLY appreciated. Thanks for your help, -- Phil -- Report message to a moderator

Re: Thermal Paste [message #11938 is a reply to message #11930] Wed, 23 September 2009 05:59   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member A 7.5 amp fuse is a nightmare of a problem in that amp even if its in serise with the speaker output jack! The earlyer Frankenstein type heads used a 5 amp fuse to protect the amps output stage from a shorted speaker cord or a shorted speaker. A 5 amp fast blow fuse will hold for a 100 watt rms output, a 6.25 amp fuse will hold for 125 watt rms output. The most clean rms power I have ever seen even the latter k200b amps put out( bigger power transfomer amps) was 95 watts rms so unless you have a test rig and you want to check what the amp will do once you get it back up and running, or unless you will be blasting the amp when you play it, I would install a 5 amp fuse if it indeed turns out that the current fuse in wired for output stage protection. Report message to a moderator

Re: Thermal Paste [message #11941 is a reply to message #11935] Wed, 23 September 2009 07:05   pleat Messages: 1452 Registered: June 2004 Location: Belding, Mi Senior Member I've seen a lot of kustom amps with 2 fuses. The original soldered on the terminal strip and the second fuse was attached to the original blown fuse, with S shaped clips. The S clips saved the tech from trying to solder a fuse to the terminal block that didn't have leads on the new fuse. Is this what you are refering to? Since you mentioned the amp is a K200A, are there two white circuit breakers next to the power switch that may have be disconnected in favor of glass fuses? Don Report message to a moderator

Re: Thermal Paste [message #11942 is a reply to message #11941] Wed, 23 September 2009 09:48   LZBass Messages: 16 Registered: September 2009 Junior Member I've included a couple of pictures of the fuse I'm refering to. The first picture is of the fuse located on the front of the chassis. It appears to be the main power fuse. This is the fuse that was rated at 7 1/2a @ 250V. It was blown. To confirm, this fuse should be a 3AG 3A or 5A fuse... is that correct? The second photo is on the fuse that is soldered in to the output board. It appears fine. There are no additional fuses or circuit breakers located anywhere in the unit. The circuit cards in the unit are: Ross PC 102 Ross PC 502 Ross PC 702 http://s593.photobucket.com/albums/tt17/LZBass/ Thanks again for the help! Report message to a moderator

Re: Thermal Paste [message #11943 is a reply to message #11942] Wed, 23 September 2009 11:35 chicagobill Messages: 2005 Registered: April 2003 Senior Member 7 1/2 amp is way too high a value for that fuse. The fuse located on the front panel near the power switch is the main ac line fuse. The standard value is 3 amps. The original one was probably a soldered in pigtail fuse. The one on the power amp pc board is the speaker protection fuse. It is rated at 8 amps. Its real purpose is only to help prevent damage to the speakers in case an output transistor should short and place dc voltage across the speaker output. Normally if an output transistor shorts, the main fuse will blow long before the speaker protection fuse does. If the main fuse was replaced with one with too large a value, then the output fuse would still be there to help protect the speakers from damage. Because the Kustom ac line fuse was inside the chassis and was soldered in, it would take a lot of effort to try and bypass the main fuse. I've seen a lot of amps damaged by people that would use tin foil and gum wrappers to replace a blown fuse. On the later B-series heads the speaker fuse was removed from the design, as they weren't really needed. For my own Kustom amps, if I need to replace a power fuse, I remove the existing terminal block and replace it with a fuse holder that will accept standard size fuses. In your photos, there are two green wires added to the power switch. What are they there for? Report message to a moderator

Re: Thermal Paste [message #11960 is a reply to message #11943] Wed, 23 September 2009 21:51   LZBass Messages: 16 Registered: September 2009 Junior Member The installation of the fuse holder seems to have been done by a tech as they even installed an isulator to the front chassis between the chassis and the fuse holder. Looks like a clean install. I wonder what else was done... It appears that the original power ON lamp was replaced with a 110v AC lamp. That's where the two green wires are attached. Was the chassis used as a common ground? Doesn't seem like it from what I can tell. Thanks again for all your help. -- Phil -- Report message to a moderator

Previous Topic:	Kustom 150 Guitar Head
Next Topic:	K100C-8 Schematic Needed

Goto Forum:

- VintageKustom.com  Comment Board  Replacement Part Suggestions  Repairing Kustom Amps- Classified Ads  For Sale  Wanted- FUDforum Questions & Problems  Questions & Problems about FUDforum