[Harp-L] 5F6-A circuit problem

["Steve Rowse" <steven@xxxxxxxxxxxxxxxxxxxxxx>]

- could be a bad tube socket or circuit board - can't think of anything 
else. The fact that the charge is on both sets of inputs makes me suspect 
the circuit board first and a socket second.

Are you confident opening the amp up? (beware residual voltage which can 
still kill you even if the amp is unplugged - the caps need discharging 
before you do anything. Take care.). If so, looking in from the tubes side 
of the box (controls away from you), have a look in at the circuit board. 
Look at the solder eyes that line the board, the ones on the edge facing 
you. Counting from right to left there should be an eye with two things 
attached, a hole with two wires coming through it, and another eye with two 
things attached. Look at those three points. The wires coming through the 
hole are the signal wires, the ones with the charge on them that's worrying 
you (rightly - don't use the amp till it's sorted). How's the insulation as 
they pass under/through the board? The eye to the left of the hole has 150v 
on it - could some of that be sneaking across the board somehow? Any sign of 
'tracking' (little wiggly line of black carbon)? How about the opposite side 
of the board, the side near the controls? Counting from the right edge 
again, the second and third eyes carry the signal wires, you can see they go 
to the input sockets. Any tracking lines going to those eyes, especially 
from the left? A good cleanup with pcb cleaner spray around that area might 
help.

Is it a 40-yr-old board? They do degrade and can start to conduct.

Now the tube socket - any tracking going to pins 2 and 7?

Clean up the board first, then replace the socket. If that doesn't work it's 
going to have to be a new board (unless it's something I haven't thought 
of). Big job but do-able.

Good luck. Don't try this if you're not sure of how to discharge caps!! 
Remember to unplug the frickin thing!! Don't die on me!!

Steve


----------Message: 19
  Date: Tue, 4 Oct 2005 17:18:10 EDT
  From: Grbullets2@xxxxxxx
Subject: [Harp-L] 5F6-A circuit problem

    I'm hoping one of you 5F6-A experts can help me find out how I'm 
getting
voltage on the input jack tip connection.It's causing a pop noise when the
tip breaks ground when you insert a jack.All 4 inputs are well grounded,all 
to
each other and then a wire directly to the chassis.There is 3.5 volts on the 
#1
bright and 1 volt on the #1 normal inputs,somewhat less on the #2 inputs.It
only shows on the meter when the ground from the tip shunt is opened.All 
wiring
is correct to the inputs,tubes and the pots.Could this possibly be a bad 
tube
socket?
      The voltage increases to about 7 volts with the V1 tube pulled.The 
amp
does work and sounds good but I know theres not supposed to be voltage on 
the
input jacks.The 68K resistors are all good.Anybody got any ideas where this
voltage could be coming from? Every obvious cause has been looked at many 
times
over.You can reply directly to me if you'd like.Many thanks...........Dave
grbullets2@xxxxxxx
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