Yet more reverb trouble

knuckleberryfinn

I just finished building a cross between a Princeton Reverb and a 5E3 Deluxe and can't get any reverb out of the new TAD tank I bought for it.  I've tried it with an old Hammond tank which has a nominal impedance mismatch with the fender reverb circuit, but this works okay (though there isn't the ludicrous Fender amount of reverb you'd expect).  I've knocked the TAD tank and it crashes fine, so it's definitely the input.  I'm getting a reading of 1.3ohms across the input coil (I'm getting 3.5ohms on the input of another 4AB3C1B tank I've got, whose output is broken).  

I've contacted TAD, who are adamant that there is nothing wrong with the tank.  Is it possible that the circuit is operating at the wrong impedance, and so kicking out more reverb with the Hammond tank?  But even if that were the case, wouldn't I get at least some reverb?  Can I test the tank's input without another reverbified amp (I don't have one)?

EDIT: I should make it clear that TAD haven't actually tested this tank, they've just told me that they've never had one DOA.

ICBM

If it works with a different tank and the coil meters ok, it has to be the jack on the tank.

How is the input grounded?

jpfamps

8 ohm tanks have DC resistance around 1-2 ohms, so it looks as though the tank is OK.

What is the Accutronics number of the tank?

knuckleberryfinn

ICBM said:

If it works with a different tank and the coil meters ok, it has to be the jack on the tank.

How is the input grounded?

The jack seems to be fine - I've just measured at the socket and at the other end of the lead tip to ground and it's measuring 4.1ohms (why does the resistance keep changing?!)

jpfamps said:

8 ohm tanks have DC resistance around 1-2 ohms, so it looks as though the tank is OK.

What is the Accutronics number of the tank?

The input isn't grounded because the tank is 4AB3C1B which, according to the coding, means the input is insulated and the output is grounded.  When I first tried the tank out I messed around with grounding the input and not grounding the output and nothing worked, so I don't think it's that either.  Could it be the connection between the coil and the springs?

ICBM

knuckleberryfinn said:

The jack seems to be fine - I've just measured at the socket and at the other end of the lead tip to ground and it's measuring 4.1ohms (why does the resistance keep changing?!)

Probably because there is a bad connection at the tank.

jpfamps

The resistance will also change if you vibrate the tank due to the back emf from the coils.

knuckleberryfinn

Well I've solved this issue and it's a bit confusing.  I borrowed my friend's Princeton Reverb to test the tank, and it worked.  So I took readings of the resistance to ground at the reverb input socket of his amp.  According to the Accutronics codes, the reverb input when using a 4AB3C1B tank should be insulated, but the Princeton Reverb was grounded.  All it took to get my build working was to ground the input - and that was that.  I don't understand why the guidance conflicts with reality.  What a ball ache.

ICBM

knuckleberryfinn

^ Ha!