Need help tracking down problem with original Foreplay

[danforthf]

I've got a stock Bottlehead Foreplay, ASL Wave-8s, and some speakers of my own design that recently came out of more than 2 years of storage.

After set up I discovered some problem with the system. There was no audible signal unless the volume was turned up to max. At max the sound was muted(obviously) and crackily. I isolated the amps and discovered that they are are working just fine so the problem is with the Foreplay.

The tubes were replaced just months before being put into storage so that wasn't the problem. After pulling out the amp and checking for bad joints and loose wires, I reconnected and everything worked beautifully, for a little while. After a few days of listening and enjoyment I changed an interconnect and the jostling of that action reverted the preamp to its previous state of disappointment and near silence.

My first instinct is still that it's a bad joint somewhere. There are a few connections that have a tarnished, dull, and sloppy look to them but even measuring resistance across them they seem to be OK. At one phase of my testing a little tap on the side of the enclosure caused a spike in the gain of the preamp which then slowly faded back to almost nothing.

I'm comfortable with the use of a multimeter, I'm not just not sure where to start looking short of following the instructions step by step. Does this sound like a bad capacitor or transformer? How does one discover if that is the case?

Where should I start and what am I looking for?

Thanks in advance.

[Grainger49]

Which Foreplay do you have, FP 1, FP 2 or FP III?  That makes a difference in the circuit.

Just a SWAG, it sounds like the signal is not getting through the selector switch to the volume pots.  You can set your meter on ohms and trace the input through the selector switch to the output of the pots.  Just keep one meter lead on the input "hot" and go till you get to the output of the volume controls.

Your troubleshooting, tapping on the side, would indicate a bad solder joint but the meter will let you know which one you need to rewet.

[Paul Joppa]

It does sound like there is an intermittent contact somewhere.Two years in storage is a good chance for some trace corrosion to happen. The non-soldered contacts are an easy place to start.

Of course the resistance and voltage checks in the manual will lead you to many possible problems. If all those pass muster, then you can start looking for other problems.

Sometimes just removing and re-installing the tubes will clean their pins enough (otherwise there are plenty of cleaning methods in the archives and on the web). Same for the selector switch and Whispers if you have them - cycle the rotary switches and/or potentiometers a few times, or get some contact cleaner and give 'em a shot.

Next step would be to look for bad solder connections. If your preamp has any of the old super-good magnet wire with the incredibly tough varnish that was used for ground buss wiring at one time, that's a likely place to look.

[danforthf]

After finding the old manual and going through the resistance checklist, found a couple of bad joints in the power supply circuit. Reheated, cleaned up a little bit of sloppy work, and I'm back up and running.

Now if only I would stain/finish the box...