I just finished building the S-5 Electronics K-16LS tube amp kit. It is in an aluminum chassis with Edcor CXPP30 output transformers. The problem is that as soon as the tubes warm up a high pitched squealing sound starts. This happens at every volume level, including zero volume. I have isolated the squealing to the preamp stage, since pulling the preamp tubes causes the squeal to stop. I have heard that this could be microphonics, but it seems strange that the preamp tubes for both channels would have this problem at the same time. I have tried tapping the preamp tubes, but this doesn't seem to change the sound, so I am not sure if microphonics is the problem. If anybody has any idea what might be wrong, I would be grateful for the help. Thanks.
Check your Output Transformer wiring to see if you have taken " positive " feedback off the OT secondarys instead of " negative " feedback.
Brgds Bill
ps, here is a link to ( I hope ) your amp schematic
http://www.diyaudio.com/forums/tubes-valves/186993-using-seperate-preamp-drive-s-5-electronics-k-16ls-integrated-amp.html
Other thoughts,
1) According to the above schematic the negative feedback needs to be taken from the 4 ohm tap
2) Looks like the output transformer frame needs to be grounded
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Hello Jsine,
It could well be due to the amplifier's feedback being positive and not negative. To test for this try disconnecting the feeback loop and see if the problem goes away. If the amplifier has global feedback from the output transformer to the input stage and the squeel goes away when the feedback is disconnected. The problem was due to positive feedback and can be fixed one way or the other based upon the amplifier's design. Mickeystan
PS. Same perspective as Soonorlater posted. We must have been typing at the same time.
It could well be due to the amplifier's feedback being positive and not negative. To test for this try disconnecting the feeback loop and see if the problem goes away. If the amplifier has global feedback from the output transformer to the input stage and the squeel goes away when the feedback is disconnected. The problem was due to positive feedback and can be fixed one way or the other based upon the amplifier's design. Mickeystan
PS. Same perspective as Soonorlater posted. We must have been typing at the same time.
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