Amp Reverb not working- how to fault find

rsvmark

hi all
i have an old sessionette 75 combo which i am trying to bring back as my gigging spare. The amp works ok and I have just acquired a second hand (bright onion) foot switch. Channel switching works fine.

Without the footswitch there is no reverb. I had assumed that the previous footswitch had deactivated it. The new footswitch led activates on and off but no reverb is present even when the dial is on 10. 

i suspect the reverb tank is knackered. However I am well outside my area of expertise. I can just about wield a multi meter. Could anyone help me fault find on why I am getting no reverb? 

Many thanks

ICBM

It's most likely to be either a broken wire inside the tank, or a bad connection at the RCA jacks that connect the cables to it. These amps are old enough that it won't be the notorious broken-transducer problem with newer Accutronics tanks, so it's probably fixable without replacing the tank.

Take the back off the amp and wiggle the connectors - rotate them if you can, that usually cleans any corrosion off them. If that doesn't fix it, take the reverb tank out of the amp and have a look inside for any of the four thin wires from the jacks to the transducers being broken, usually at the jack end.

If there's nothing obvious you can test the send and return transducers using the amp itself, but you'll need to do it with the power on so I wouldn't do that until you've checked physically.

Almost forgot - the first thing to check when you look inside the tank is that there are actually springs in there! I recently repaired a Marshall Valvestate where they had all broken and fallen out. With a Sessionette it would be obvious since they will be in the bottom of the cabinet, so you'll spot that even before you take the tank off.

rsvmark

Thanks. That's tomorrow evenings job then!

rsvmark

Ok so this evenings results are:

I took out a reverb tank from another amp. Plugged into the session and buckets of reverb. Reverb from the session plugged into said functioning amp- no reverb. ergo fault with reverb tank.

visually inspecting the broken tank reveals no broken wires or springs. What can I do to test the dead reverb?

ICBM

Do the tank transducers have clear plastic jumper connectors on the ends, or just thin green and black wires which go directly into the coil?

If they have plastic jumpers (they shouldn't, given the age of the amp, but unless you've had the amp for more than about fifteen years it's possible the tank has already been replaced with the later type), pull them off and measure resistance between the two pins. It should be under 200 ohms at each end (well under at the input end). If not, you almost certainly need a new tank - it's occasionally possible to repair them but very difficult.

If they meter OK, cut off the plastic jumpers and solder the wires directly to the pins right against the red bobbins, then add a little hot-melt glue to reinforce them.

If the tank doesn't have the plastic jumpers or you've done the above and it still doesn't work, there's a good chance the green or black wires are broken inside their plastic insulation where they pass under the little metal strain relief clips. You can usually find which one by taking both out and flexing them there - a broken one will kink sharply. If so you need to cut it and solder the broken ends together, and heatshrink or tape the joint.

If all that fails or it just sounds like too much hassle - and it can be! - replace the tank with a TAD/Ruby equivalent… they're not too expensive. There is a list of equivalent Accutronics type numbers on the TAD website -

http://www.tubeampdoctor.com/en/shop_Reverb_Cans_Effects_TAD_Reverb_Cans/

Don't buy a new Accutronics, sadly they're junk.

rsvmark

Thanks dude. No plastic jumpers (what ever they are) because there are thin green and black wires. I shall take a look at them tomorrow and assess....

rsvmark

TAD reverb on order....