Amp/tech experts, reverb question.

[strtdv]

The reverb on my amp has got very quiet. It's an accutronics Type 9 spring reverb tank, solid state driven.

 

You can still hear the reverb, but it's very quiet compared to the dry signal it's mixed with.

 

I took the tank out, and the input resistance is only ~1 Ohm (DC resistance). It's meant to be 10 Ohms Impedance.

 

To me it sounds like there's a short in the input coil on the reverb tank. would this account for the symptoms? And would a new reverb tank solve the problem?

 

Thanks

[knucklefux]

tank would be my first guess based on what you describe...

[strtdv]

Thanks.

 

I had an idea it might be that, but wanted someone who was more knowledgeable (rather than just a DIY hack like me) to give me their opinion first.

[knucklefux]

if something's supposed to measure 10 ohms and it only measures 1, there's a problem with that something

[FXR]

Measuring impedance with an ohm meter does not work.

 

You need to know the DC resistance for such a test.

 

http://www.teamrocs.com/technical/pages/resistance_impedance.htm

[strtdv]

Measuring impedance with an ohm meter does not work. You need to know the DC resistance for such a test. http://www.teamrocs.com/technical/pages/resistance_impedance.htm

 

 

I realise that, obviously field effect and such like will alter the result, but I figure it's quite unlikely that something with a 10 Ohm impedance could give a 1 Ohm DC resistance.

 

A 16 Ohm speaker for instance has a DC resistance of 12-14 Ohms rather than say 2 Ohms.

[FXR]

I realise that, obviously field effect and such like will alter the result, but I figure it's quite unlikely that something with a 10 Ohm impedance could give a 1 Ohm DC resistance. A 16 Ohm speaker for instance has a DC resistance of 12-14 Ohms rather than say 2 Ohms.

 

 

I'm not going to try and change your mind. Carry on. You might get lucky part swapping.

 

Good luck.

[tommythelurker]

I realise that, obviously field effect and such like will alter the result, but I figure it's quite unlikely that something with a 10 Ohm impedance could give a 1 Ohm DC resistance. A 16 Ohm speaker for instance has a DC resistance of 12-14 Ohms rather than say 2 Ohms.

Since FXR gave up I'll take a stab.

A reverb transducer is not a speaker. According to this website the DC resistance for a type 9 is in fact 1 ohm:
http://www.tubesandmore.com/scripts/foxweb.dll/extpage@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?page=TECH_REVERB

[knucklefux]

i know about the impedance/resistance thing. i figured strtdv used the terms interchangeably.

 

so, i went out and measured a known good reverb tank. it was 1.5 ohms on the input side and 212 on the output.

[strtdv]

Ok, so the reverb tank might not be the culprit..

 

I wonder what else would explain the symptoms I'm getting.

 

Unfortunately I think it's an opamp setup which would make changing bits much more fiddly, and there doesn't seem to be a reasonable amp tech in Northern Ireland.

[strtdv]

Problem solved.

 

One of the RCA jacks wasn't making a good connection. Some contact cleaner and a bit of fiddling around to get a good connection and it all works perfectly again.

 

 

I found a cool site for troubleshooting reverb problems HERE. It's designed for tube driven reverb on Fender amps, but the methods all work for any reverb.

 

Basically the problem can be in one of 3 areas: the reverb pan, the reverb driver, and the reverb recovery.

 

To check the reverb driver:

Unplug the RCA lead going to the reverb pan and plug it (via an RCA to 1/4" jack adapter) into the input of a cheap amp. Turn the master volume right down on the amp you are testing and turn the reverb on. If your guitar sound comes out of the cheap amp, then the reverb driver works.

 

To check the reverb recovery:

Turn on the reverb, have the master volume fairly quiet, and give the reverb tank a sharp tap/thump in order to make the springs hit the walls of the tank.

If you hear a loud "clang" as you do this, then the reverb recovery stage works.

 

If after both these steps you still have no reverb, the last thing is the tank itself and the connectors.

Swap out the RCA leads for a spare set, and ensure good contact with the tank input/output. If this doesn't work then the problem is probably with the tank itself and you should change the tank.