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Old 15th October 2012, 01:12 PM   #11
Simon B is offline Simon B  United Kingdom
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The OP's problem is feedback, and this looks like a clue to why it's happening:

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Originally Posted by ArcticBreaze View Post
..
With the first triode turned turned way down about 2,3 and the second all the way up I can stand right in front of the amp putin out about 35 watts and no feed back..

But turn the primary Chanel up and the second down feedback city.

This is why i think an effects loop may help. get the pedals after the primary triode.
So maybe the first triode, or possibly the circuit immediately around it has a problem?

Have you tried swapping another valve into that position ArcticBreaze? I think that would worth trying. Certainly try tapping it gently with a rubber ended pencil to test for microphonics. If you get a note sounding like your feedback that would be a strong indicator to try some replacements, with whatever ECC802, ECC82, 12AU7 you can lay hands on.
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Old 15th October 2012, 11:58 PM   #12
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Quote:
Originally Posted by Simon B View Post
The OP's problem is feedback, and this looks like a clue to why it's happening:

So maybe the first triode, or possibly the circuit immediately around it has a problem?
No just using a modified guitar amp for harmonica.Its been the harp players curse For decades, put a mic into a guitar amp it sounds great till the guitarist drowns you out so ya turn it up a bit an it howls at you. (we don't do quiet lol)

After 2 years of tweaking, moding and annoying you good folks at DIY I can now turn up loud enough to be herd.

but there are limits, the more I raise the input gain the more sensitive the mic gets, by taking in a real low lvl signal and then boosting hell out of itI can get the sound lvl i want with out feedback (I don't know exactly why this works it was derived from sugestions in earlier thread here on diy and it worked) pedals tend to lift the gain going to the preamp or mayby stomp box's just dont like mic's and I cant afford a kendrik harp amp so moding my own (and learning a whole dmn lot in the process.) I've just about gone as far as i can with this amp it doesn't really fit in its case any more (new out put trany hits the speaker) so I'm going to build a whole new amp with plenty of room for a reverb tank, using the old amp as a prototype, its getten pretty messy in the with all the moding i,ve done (don't know why it doesn't hum).

But now I'm just waffling, thanks guys for all the help and suggestions past and future.
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Old 16th October 2012, 12:58 AM   #13
Simon B is offline Simon B  United Kingdom
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Glad to hear that feedback is not a problem for you, just an opportunity to put in an effects loop.............
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Originally Posted by ArcticBreaze View Post
I want to put in an effects loop for foot pedals etc. but they cant go before the first stage of the preamp as this causes feed back on the mic.
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