My new amp build - not singing the blues!?

[matt h]

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[funkgang49]

Ok, to see if your squeal goes away, disconnect the negative feedback loop.

I removed 100K NFB resistor - squeal gone!

I'm guessing you copied the NFB circuit from the 5e5a schematic--thing is, that's not LTPI friendly. Look at a 5f6a for implementation with the LTPI. First disconnect the NFB entirely and see if your squeal problem stops before changing any values.

Nope. I took it directly from Aiken Amplifications website http://www.aikenamps.com/index.php/the-long-tail-pair

The bias resistor works in much the same way that it does for any triode in a normal preamp. The lower the value, the hotter the bias, the more current the tube pulls.

Isn't that true for the cathode resistor on the power tube as well? Higher value resistor sets the bias colder, lower value sets it hotter?

[matt h]

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[armillary]

Hurray!

[funkgang49]

But you'll notice that the aiken schematic doesn't have the the 100k feeding the top of the 10k tail, it has it feeding the bottom.

Matt, what you call the bottom of the tail resitor I was calling the top. I did have the 100K feedback resistor coming off of the junction of the bottom of the 10K tail resistor and the C2 (Aiken LTPPI diagram) .1uf cap then connecting to the tip of the main speaker out jack.

With NFB resistor in place there is alot of hiss. The hiss increases considerably when the Treble control is turned all the up. When MV is turned up all the way hiss increases similarly but even more pronounced and becomes a squeal as MV is fully clockwise, effectively out of the circuit (full 250K to ground).
With NFB out of circuit hiss is the same but much less pronounced. MV turned fully clockwise there is no squeal but there is alot of hiss.

[matt h]

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