stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
The difference in basic coupling cap type is not part of the issue you are having, in fact going back to the better audio quality of the Tantalum's might make the hiss worse.
I just took a good listen to my k150 that uses the 5066 and 5067 board combo and my 5067 board has less hiss then my 5066 board.
When playing both Boards with the treble up full there is far more highs then anyone could ever need, especially if you have the brite switch on.
This brings up another question, your brite switch shorted and on all the, because that adds a lot more hiss?
On boards 5066 boards made after 11 of 1971, R29 was changed from 8200 to 4700 to add more gain to the 5067 board, so maybe try going back to 8200.
Just to confirm and go back to square one here, when you turn down the volume pot on that 5067 board all the added hiss goes away, right?
On the 5966 board do R6 and R16 both test within 10%?