Ceriatone Forum

Hello to all, and thank you in advance for the help.

I just finished wiring my stock OTS 50 kit.  This is my third build.  The first was a Weber 40W Blackface kit and the second was the 'Two Stroke' amp from Gerald Weber's 'Hip Vintage Guitar Amps' (just so you can gauge my experience).  Both were successful from startup.

My OTS 50 passed the current limiter test, but the sound test @ full power exhibited some problems.  No sound from the FET input and a weak guitar signal from the NORMAL input with loud humming/buzzing.  The hum increased with turning the Volume and Master controls up.  All front panel controls appear to operate, but it is difficult to tell due to the weak signal.  The PAB / OD are difficult to discern as well.  The foot switch lights work, and it appears to have the same effect as the rear panel switches.

Please take a gander at the chassis pics and let me know what you think.  I will run any tests you guys suggest right away, I aim to have this done ASAP.

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Hey guys, this got me taking a second look and I realized that my inputs are NOT GROUNDED!!  :-[

Oops.

The FET input was grounded as per the layout, so this doesn't explain (to my understanding) why that input doesn't work.  Sound test #2 is about to happen with the NORMAL input grounded.

ok, that elimiated the buzz/hum.  Still no FET signal.  Also, Switching the OD off seems to kill the signal.  Basically, the amp always sounds as if it is in OD mode.  PAB is apparently working.  The output is very weak, not loud with Vol / Master on 10.  The 'Level' and 'Ratio' controls for the OD section don't seem to have an effect.

-Chase

Hey Chase,
I'm pretty much at the same level as you with a couple of other builds under my belt when I took on the OTS 50.  I had a similar problem where the overdrive was 'on' always until I finally figured out that i was missing a wire from one of the relay coils (the little black rectangular box) in the foot switch circuit to the voltage divider (the three prong tiny black part) in your picture ending in #190851.  Also, that voltage divider needs to be down flat (grounded by contact) to the chassis.
I'm not sure if this has anything to do with the FET problem, but it couldn't hurt to check these two things...
Anyway, good luck and it will be worth it when you get your bad boy straightened out.  Your pics look like you did a really nice job!
Cheers
Sam

Thanks for the reply I was wondering if anyone was still active on this forum.  I noticed the mounting of the voltage regulator that you mentioned but I think is is okay because the heatsink and the middle lead of the part are equivalent - only one has to be grounded - maybe I'm wrong, if you know for sure.  I'll doublecheck the relay board.

Here is where I'm at now:

I did some tests last night on the amp.  The power supply going to the relay boards reads 12V, which is what the power regulator is rated for so that is ok.  The voltage where the power filter connects to the turret board reads 330V to ground - not sure if that is normal but it didn't seem low.  I checked the voltages on the legs of the FET transistor and they were something like 7.5, 2.5 and 0.2 - I'll have to look up the pinout

The power filter daugherboard for the FET board didn't have the cap grounded, I fixed this before I checked the voltages on the FET transistor.

The FET input jack isn't working correctly, the 'ring' contact isn't switching off when the plug is in, causing the 'tip' of the NORMAL jack (also the return for the FET circuit) to remain grounded.  This explains why I'm not getting a signal through the FET input.

The amp is still anemic and only works in the OD mode - not sure if one of the relays is bad, wouldn't know how to test them.   If anyone could recommend any tests for me to run I'd appreciate it.

Thanks,
Chase

UPDATE - Got the amp working 100%.  Not sure if anyone is reading the thread.  In a nutshell, I didn't have the output tubes cathodes grounded and needed to adjust the trimpot on the FET daughter board to get it working.

-Chase