Studio Lead Questions

[Chris Fiore]

I just got my hands on a Sunn Studio Lead (50 watt solid state combo twin) and I have a few questions.
1. The serial number of the amp is 025150. Does anyone have a way to date the amp based on this? Someone told me he thought it was late sixties early seventies sometime.
2. Are speakers wired serial or parallel?
3. What is the impedance of the speaker out  jack? I would like to try hooking up to a 2x12 cab I have and do not want to damge anything.
4. Until the amp warms up (about 10-15 mins) the amp produces a loud poping or cracking sound if I play any notes on the low E string of my guitar. Is this the norm for an amp this old or is this the sign of something wrong. The amp sounds great after it warms up. Someone told me you had to wait for the capacitors to charge up, is this right or was he talking out his butt?

Thanks for any help!

[Joe]

On #4... your amp has what's called a "thermal intermittent".  In your case, the connection becomes better with heat.  Heat expands parts and makes the connection tighter.  It can also work in reverse....  where the expansion of heat pulls a connection apart.

Unfortunately, I don't know too much about this particular amp to help you out with real specifics.  

The first place I would look... would be the Power Amp... in particular, the output power transistors.  If there is a socket connection... check it, clean it... make sure the connection with the transistor pins are solid.

The second place... would be any connection with a power supply electrolytic.  Then I would move on to any printed circuit board trace and soldered connection.  It could be nothing more than a cold solder joint.

I have also seen them happen "inside" a power transistor.

But definitely, caps don't normally need any specific charge or warmup time.