Princeton Reverb II
Basic Troubleshooting
created Sep 2014
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email me... stratopastor (at) hotmail (dot) com

BEFORE YOU DO ANYTHING

Please be sure you've got a working guitar, with its own volume turned up,
a good guitar cable/cord/lead, and no effects units in between.

d'oh.

Thank you.

Safety / Damage Disclaimer
This page is a list of things you can check without going inside the amp. However, if you do go in... valve (tube) amps develop LETHAL VOLTAGES while running, and store them in charged components EVEN WHILE SWITCHED OFF AND DISCONNECTED FROM THE OUTLET / MAINS SUPPLY. These voltages are MUCH HIGHER than the outlet voltage, and higher than anything you'll find inside a non-tube amp. If this scares you, good. Inside a chassis, don't use your fingers to touch anything which isn't insulated or earthed (grounded). Don't stick more than one hand in at a time, and keep the other hand well away.  Use insulated fine-nose pliers to manipulate components. NEVER, ever, work inside a live amp while holding a connected guitar.If you're not sure what you're doing, get local help. I take no responsibility for damage, injury, death, loss of gig, etc etc. Have a nice day.

If you MUST go inside the amp,
       dismantling instructions are here and I have drawn the signal path onto the wiring diagram here. However...

I'm not trying to do techs out of a job
This page is written to eliminate some of the simple things that might be fixed without opening up the amp. Do not hesitate to take the amp to a trusted tech if these checks don't get the amp working and you're not experienced with high-voltage electronics. This page only gives advice about things you can diagnose or fix without opening up the amp.

What's the logic here?
For each section below the steps might not come in logical order if you follow the electronics, but I tried to put the easy, obvious things near the start. If any step fixes your problem, stop there. 

valves labelled
Princeton Reverb II Tube/Valve Set
If all you came here for was to find this out... the normal set is;
12AX7 = ECC83 = 7025 etc.... 3 tubes, v1,v3,v4
12AT7 = ECC81.... 1 tube, v2
6V6GTA.... 2 tubes, v5 and v6
there is no rectifier tube - this amp has a solid-state rectifier


Useful info for troubleshootingelementary

Amp is quiet / has lost volume
 1 - check speaker connections are clean
2 - pull out each tube (valve) and push back in again 2 or 3 times. This is to move dirt from the pins (there might be 30 years of dirt and oxidation in there).
3 - try a spare known-good 12AX7 (ECC83) in v1, then v3, then v4
4 - try a pair of known-good 6V6GTAs in v5 and v6. If you keep the new ones in position, you're best to check the bias (see at least step 11 here)
5 - try the amp with a different speaker (spare one in a different cab, 8 ohm PA speaker, speaker in another guitar amp (disconnect the other amp, only use the speaker))


Plenty of volume, but can't get a clean sound
1 - do 2,3,4,5 in the section above.
2 - check the speaker by driving it with something else and/or by gently pushing the cone in and out. There should be no 'feel' or sound of anything scraping.
If the power valves/tubes are biased way too 'cold', they will introduce distortion which won't go away with any knob setting.


 Amp is dead - no red light, no sound
 1 - check the outlet is good - try something else plugged in
2-  check the plug fuse if fitted (as in UK-style plug)
3 - check supply fuse on rear panel - 2A (110v), 1a (220v)


Amp is dead - red light but no sound unless you've got a different colour lamp jewel, hi there Larry
 1 - check volume, treble, mid, bass and master knobs are all non-zero
2 - do all the valves / tubes glow? v2 is only concerned with the reverb; all the others need to be lit up for the main amp to work.
3 - check the speaker connection is good
4 - If v1,3 or 4 is dead the amp will kind-of work if you take the tube from the v2 position and use it as v1,3, or 4
5 - check the speaker fuse on the rear panel, left of the speaker jack - 315mA
6 - try driving the speaker with some other amp, hifi, whatever


No Reverb
0 -  check the 'lead' sound works. If 'yes', check 1,2,3,6,7,8 below. If 'no', check 4,5,9.
 1-  check reverb knob is turned up
2 - if you're using a footswitch, check you're using it correctly
3 - pull, push and twist all four connections on the reverb cable (2 at each end) - my amp needs this from time to time.
4 - pull and push v2 in and out of its socket a few times.
5 - check v2 glows when the amp is on
6 - check the cables aren't crossed over. If the reverb tank is in the base of the cab where it belongs, and the connectors are pointing toward the front of the amp; then the tank connection nearest the serial-number end of the amp should go to 'reverb output' RCA socket on the amp rear panel, and the tank connector at the mains-cable end of the amp  should go to 'reverb input'. 
7 - check the cables' continuity is good. No multimeter? see if they work as hifi cables, like connecting a CD player to a stereo hifi amp.
for the next steps, disconnect the footswitch;
8 - turn up the master volume and the reverb, both to '10'. Shake the amp. You should hear the reverb spring sound, loud, from the speaker. If yes, try step 9. If not, something is wrong with the tank or the circuitry which recovers the reverb signal and feeds it back into the main signal path. That would include v3,the reverb knob, and the tank itself.
9 - Turn up the input volume to 10 and the master volume to zero. Connect a speaker to the 'reverb input' RCA socket on the back panel and play the guitar. If the reverb driver circuits are working, this should sound like a tinny transistor radio. If not...the driver circuit includes v2, the reverb transformer (though I've never heard of a reverb transformer dying), and the tank itself.
10 - The reverb tank should read 8 or 9 ohms in the input side and about 200 ohms on the output. Easiest way to check is measuring across pin and ground at the 'amp' end of the RCA reverb cables. The Accutronics part number is 8AB3C1B. Other manufacturers offer an equivalent.


No 'lead' sound
1 - check volume, lead level and master are all set to something other than zero and the volume knob is pulled out
2 - if you're using a footswitch, check you're using it correctly
3 - check the reverb works. If 'yes', you've probably got a problem with the internal switching action.
    - if 'no, then you've got to get the driver section of the reverb circuit working, so see 'no reverb' above and do steps 3,4,10.

Nasty hum or other Interference
1 - try moving the guitar away from the amp. Hum induced in the guitar pickup is a special problem for single-coil guitars.
2 - try a different guitar cable / cord
3 - switch off nearby machinery and/or fluorescent lighting
3 - find a way of checking the earth / ground on the power outlet
4 - for hum, adjust the 'hum balance' control on the rear panel. This is rarely the problem and is usually a once-in-a lifetime adjustment

Strange 'singing' tone with no guitar connected
This can be caused by a buildup of dirt making an unwanted connection between the pins of a valve/tube. Remove all valves. Use alcohol and a small brush to clean the valve sockets, specifically the circular area which is the home for the eight pin-sockets. 
 

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