old fender amp making weird noises

1bassleft · Posted: Tue Jun 27, 2006 1:53 am Post subject:

Welcome to the forum, Whizz, and thanks for your post. Riz, there are a number of points, and Whizz has mentioned one. I'll give you some of my ideas, but it's impossible to really solve a valve amp problem by email. A good tech is your best bet. Here are some points, though:

1. Replacing valves requires a re-bias. You can't just put another pair/quad in and expect them to work as the previous did.
2. Whizz is absolutely right. As valve bases get older, they can build up carbon gunk. This can then lead to "sparking" which is bad for your sound and the amp. They can be cleaned up or replaced with new, ceramic, bases as Whizz suggests.
3. The other thing that sounds like a problem is one or more of your filter capacitors (the "condensers" you mention). These big canisters smooth out the humps in a 50Hz or 60Hz alernating current from the mains. They were only expected to last about 15 years but many amps still have their originals after 40 years. The more an amp is used, the longer they will last, but they will fail eventually.

A good way of inspecting them is to have a look with the chassis out of the amp case. Take a good look at those cylindrical cans; top and bottom (ie, where the wiring leads in). If there is any sign of white, powdery substance around the capacitors - they must be replaced IMMEDIATELY. If not, they will explode, throwing nasty puff all over the insides of your amp. And they'll possibly bugger up several components down the line.

You really could do with a tech taking a look. At least, post some photos up here if you can.

1bassleft · Posted: Tue Jun 27, 2006 2:03 am Post subject:

Another (easier to fix) possibility occurs to me. Your V1 preamp valve may have gone microphonic. This is quite common, especially with the Russian and Chinese types on the market. It usually results in whistles, "whoop" and "boing" noises. Look for the ECC83 or 12AX7 furthest from the power valves and nearer to the inputs, This is V1. Replace it with a new preamp valve from a trusted source if your filter capacitors are not the problem. It may solve your noises. The sparking is definitely something else, though. Dirty valve bases being the most obvious.

riz · Posted: Tue Jun 27, 2006 11:59 am Post subject:

Hi bass! Thanks for the advice, I just bought a new preamp valve and will try that soon. I'm replacing the filter caps in these days too, so let's see.
About the crackling noises once the amp is warm...
Could it be one of the resistors connected to the valve base being broken and begin to crick-crack when hot?
In the meantime I bought new valve bases too, so, if the noises do not disappear, I'll try to put them on.
Thanks for yer help!

riz · Posted: Tue Jun 27, 2006 12:10 pm Post subject:

ok, I did not notice you posted twice, so I missed the first post.
Anyway, I'll try to put some photos here (is it possible to place a photo in the post, or how can I do that?). For now, I sprayed some good (they told me it was) contact cleaner/lubricant on the bases.
I just checked, and on the "+" end of one of the two 70uf capacitors there actually IS a tiny spot of white dust of some kind. I'm going to replace them anyway in these days.
When everything is done, I'll post back what happened. If I can I'll put post pictures too.
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1bassleft · Posted: Thu Jun 29, 2006 1:39 am Post subject:

Riz, on this forum, you will see that I have posted a "sticky" thread, "Posting pics on Guitarsite". I hope this will help you to put pictures up. Keep in touch or PM me if you have any problems posting pictures. Once you find the problem and solve it, your info would be very useful to other readers here. Good luck, and keep coming back here for opinions and advice Smile

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