Foreplay 3 amp no output (Paramount)

[Rob C]

Barely Touched (A) side 2n2907a transistor collector w meter probe, amp turned off.  Meters other probe was not connected to anything so it could have been a bic pen, anything metallic.
 Therefore since the 2n2907a transistors Collector goes to the MJE5731A transistor's emitter, that is also sensitive.
 When the amp cut out I touched the metal probe to 16  Randomly and it came back on. A wooden stick does not do anything.  has to be metallic touching it. Tapped 5731a emitter, amp cut out, Touched 5731 base, came on. Those points seem to be the only point that makes a slight tick in speaker. The 2 transistors on A side. Also the center most csd01060 rectifier will Emmitt ticking thru speaker when metallic probe touches. It will also bring amp back on. Touching the mje350 w probe also cut off amp. Probing 907a base will turn it on.

[Rob C]

The 12at7 wouldn't have anything to do with this issue would it? because half of it operates as an actively loaded hybrid shunt regulator. I dont know, just asking.

[Paul Birkeland]

You have two amps and each has a 12AT7, so you can simply swap the tubes between amps to check for that.

[Rob C]

Doing that now. Just thought I'd ask to see if that's absolutely out of the question. Also the power choke tabs are sensitive too.

[Rob C]

Not the tube. 20 mins on, turned off, used ballpoint pen poked section A and came on. I have no clue. Sad.

[Paul Birkeland]

Part of the problem with what I'm seeing here is that when you poke at some connections with a meter and you get a noise, that may not mean anything is actually wrong with the amp.  If you poke at one of the high voltage rectifier diode tabs with a meter probe and get noise out of the amp, that's not abnormal.  The same goes for the choke connections. 

We used to sell the soft-start retrofit for the Paramount that would provide a fresh set of parts and the updated driver board, but that has been discontinued. 

One thing you could do is to switch the C4S boards between amps to see if the problem follows a board or sticks around in one amp chassis despite swapping C4S boards.

[Rob C]

Swapped the c4s. Issue followed.

[Rob C]

Is there any type of replacement?

[Paul Birkeland]

Two of these would give you the boards and a bunch of the parts you'd need:
https://bottlehead.com/product/stereomour-ii-shunt-regulator-upgrade-kit/

If the bosses give the OK, we can send you the soft-start manual so you can source the rest of the bits.

[Rob C]

Hi, ok I've replaced both 2n2907a and 2 LEDs on B side. Playing strong fingers crossed.  New leds are like twice as bright. A more pro solder station, magnify light, and 63/37 solder definitely improved my work.

[Paul Birkeland]

The B side LEDs should be a bit brighter since they have a bit more current going through them.

[Rob C]

Cool to know. Thanks. I would love to understand more about this circuit. Seems interesting.