AC15 passing signal when volume at zero (and a few other questions)

[shooter]

If you followed Sluckeys layout there are 2 1 ohm resistors from el84s cathode (pin 3)
to R60.
measure milliVOLTS across the 1 ohm R.  That ='s tube current.  post those values

[liddokun]

If you followed Sluckeys layout there are 2 1 ohm resistors from el84s cathode (pin 3)
to R60.
measure milliVOLTS across the 1 ohm R.  That ='s tube current.  post those values

I followed Sluckey's layout but I missed this part.  The 1 ohm resistors are in the schematic but do not show up in the layout.

I'll add these and get to measuring.

[liddokun]

So the cathode current is 43mA

The hum is very very quiet now.  But there is still a "pop" as either of the volume controls or top cut is turned up.  The pop occurs about 30 degrees of rotation for the pot.

[shooter]

a "pop"

indicates a mechanical "switch", so something is going "open"/"Closed" in the signal path.  should be able to "see" a flat spot in a pot, by just dialing real slow watching the ohm's

[liddokun]

a "pop"

indicates a mechanical "switch", so something is going "open"/"Closed" in the signal path.  should be able to "see" a flat spot in a pot, by just dialing real slow watching the ohm's

I noticed that moving certain wires around made the pop more or less quiet.  Attaching the aligator clip to the turrets made the pop go away completely.

Gave the "twisted wire around the lead" suggested by Franco a few posts back.  It seems that did the trick in eking out the last of the pop. 

Super satisfied I've finally been able to sort this out, this amp's been through several rebuilds and debuggings.

I have attached a photo of it in the head cabinet I had made for it. Thanks all for the patience with me and the help. 

[PRR]

The "pop" is a stage(s) going into supersonic oscillation. A voltmeter on cathodes may show a sharp change at the same time, perhaps from normal 1.5V to a starved 0.3V. OR poking a voltmeter in there may spoil the oscillation.

Another tip is to tease it to the "pop" and then use a lead pencil to move wires around. The osillation is usually sneakage from one wire to another. Just like a mike on a PA system, moving things changes the howl. Usually for worse, it may take a while to make it better, and in all control settings.

[liddokun]

The "pop" is a stage(s) going into supersonic oscillation. A voltmeter on cathodes may show a sharp change at the same time, perhaps from normal 1.5V to a starved 0.3V. OR poking a voltmeter in there may spoil the oscillation.

Another tip is to tease it to the "pop" and then use a lead pencil to move wires around. The osillation is usually sneakage from one wire to another. Just like a mike on a PA system, moving things changes the howl. Usually for worse, it may take a while to make it better, and in all control settings.

Hi,

I was able to solve this by poking around with a chopstick and moving wires around.  It took a lot of prodding but somehow I figured it out.

[liddokun]

So I've returned to this thread because I don't want to start a new one just for the same amp.

Don't typically get the chance to crank my amps because I don't want to bother my family, but for a bit the entire family left the house to pick up some food so I got a chance to crank the volume.

There is a 60hz hum is not really audible at bedroom levels but gets pretty audible as the volume is turned up.  I hadn't noticed this until I had the volume wide open.  I'm trying to narrow the source of the hum down.  It's only present on the the EF86 channel, the 12ax7 channel has no hum with the volume wide open.  Hum is present as well when there is no input.

I'm *maybe* thinking it's the EF86, but I pulled the tube, and the noise is still present, albeit at a lower volume.  I'm thinking the hum is occuring before the preamp tube, and it's getting amplified once it goes through preamp.  Could it be a grouding issue?  Any suggestions?

[shooter]

60hz hum

If it's 60hz, it's from the filaments (tubes, or wires and the way they run)
120hz is a different thing with different "fixes"

[liddokun]

60hz hum

If it's 60hz, it's from the filaments (tubes, or wires and the way they run)
120hz is a different thing with different "fixes"

I just might be looking at 120hz afterall, I recorded the noise and put it through a spectrum analyzer, looks like the loudest frequencies present in the hum are around 120hz.  What kind of fixes should I be looking at? 

[Williamblake]

Maybe you can reduce hum by paralleling a filter capacitor to existing filter capacitors.