Ticking tremolo

[catstrat]

This is where I turn when I needhelp. I have a 1974 fender twin reverb that has a clicking tremolo. I've done everything I know to do and it just flat will not shut up. I've done the cap mod and nothing. I've re flowed solder joints, cleaned and tightens grounds. Cleaned tube sockets and checked tension. What else can I do? Another problem with v 4 pin 6 , with tube removed I get close to 300 volts, install tube and pin 6 voltage drops to 78 volts. I've tried several different tubes and still the same. Help.

[Tom Phillips]

Work on the wiring dress between the parts board and the tremolo tube. Both the relationship between those wires as a group and other nearby wires and the relationship between individual wires within that group can make a significant difference.

[stokes]

Maybe a bad "roach",the optocoupler.

[Leo_Gnardo]

You can fiddle faddle with wire dress and bypass caps until the cows come home OR read this, grab a LED & have it done quick & cheap then all you got to worry about is deer ticks. The question does come up every couple months.

http://music-electronics-forum.com/t38440/

[g1]

As far as V4, what kind of cathode voltage does it have? Does it's plate resistor check out ok resistance wise? Assuming that you have tried swapping in a different tube.

[Raybob]

If by 'cap mod', you mean .01uF cap from ground to bug connection at 10M resistor, and it still ticks, then replace the wire from V5-Pin 2 to the capacitor with shielded wire grounded one end only at tube socket bolt. That should stop it. All my new builds with that bug get shielded wire to V5/pin 2.

[trobbins]

The high neon dV/dt can capacitively couple to the LDR and cause clicking. In that situation, increasing the separation can be your friend, as can a grounded metal mesh placed between.

Some aluminium foil, or silver paint around the rear of the neon can increase the amount of light towards the LDR.

[Chuck H]

I wouldn't fuss about the trem anymore before fixing the bigger issue of extremely low plate voltage at V4 pin 6. Some anomaly about that problem could actually be causing the trem to tick.

Since V4 has a shared cathode circuit on both triodes I might expect some problems visible on the other V4 triode as well. I assume you checked that since you wouldn't know about pin 6 being low if you weren't poking around. Pin 1 on that tube may also be out of spec but didn't send up any flags so I don't suspect the cathode circuit. The very first thing to try is a known good tube in that position. If you've tried that I might suspect a leaking coupling cap feeding pin 7 of that tube. Not the 10pf cap across the resistor but the .02uf before that in the circuit.

[catstrat]

ticking tremolo

Thanks everyone. We have plenty of solutions here. I installed a new LDR. The trem wasn't even working when it got here. I've fiddled with the wire dress but honestly, i didn't know which wires to spend time on until now.
As far as the low voltage issue, the cathode voltage on v4 pin 8 is about 2 volts which i believe is within in specs according to the schematic. But i'll verify that. It looks like to me, if it was a leaking coupling cap wouldn't the voltage be low with the tube removed also? I've tried a new tube also with no change. I tested the original tube and it test good. The reverb doesn't work either. I replaced the reverb driver tranny so now i'm sending signal to the tank but getting very little out of it. The owner replaced the original tank with a Belton and i'm beginning to think this may be a defective tank even though the P/N says this tank should work. The tanks transducers read .261 ohms and 1.3 ohms, assuming my meter is halfway accurate. Those readings don't make sense to me. I think we're supposed to have 2,250 ohms on one and 8 ohms on the other transducer. The other question i have, are all reverb drivers interchangeable on Fender amps? I think they are.
The amp works fine except for the listed problems. Thanks again for the suggestions.

[52 Bill]

The tanks transducers read .261 ohms and 1.3 ohms, assuming my meter is halfway accurate. Those readings don't make sense to me. I think we're supposed to have 2,250 ohms on one and 8 ohms on the other transducer.

You are confusing dc resistance with the transducer impedance. The resistance readings that you have are correct, with the 200 ohms as the output and the 1.3 ohms as the input.

That is 261 and not 0.261, correct?

[catstrat]

Thanks Bill for the reminder on impedence,i just forgot about it. I was going by the specs given by Antique electronics supply catalogue on the tank.. My meter shows .261.

[g1]

My meter shows .261.

On 1K range?

[catstrat]

ticking tremolo

That reading was on the 200 ohm scale. On the 2 k scale it measured nothing.My meter is not a Fluke, it's a budget meter from Harbor Freight but it's always measured resistances pretty accurate. As a matter of fact i measured a 1.5 K resistor on the bench and it was pretty close to the declared value considering tolerances. Un fortunately i have no test tank. I guess i'll order one to have around the shop.
What does V4 tube do anyway. It's the reverb receive tube but what does the other half of it do? It's just a gain stage isn't it?
Back to the ticking tremolo. I've messed with the wire dress, i installed a piece of shielded wire from V5 pin 2 to cap on board, grounded the shield to chassis and so far it's still ticking. I'll fool with the wiring some more. Thanks everyone.

[Chuck H]

if it was a leaking coupling cap wouldn't the voltage be low with the tube removed also?

No. The voltage would still be high with no tube in the socket. A leaky cap causes a failed bias condition for that tube so it draws excessive current which drags the voltage down. No tube, no current.

I've tried a new tube also with no change. I tested the original tube and it test good. The reverb doesn't work either.

It's probably not a coincidence that the reverb recovery triode is the other half of V4. This makes me think about the cathode again, though you say you're reading 2V at that cathode. I think that would actually be a little high. What could be happening is the other V4 triode drawing too much current is elevating the shared cathode voltage and the reverb recovery triode is now biased cold. Possibly even in permanent cutoff.

I installed a new LDR... I replaced the reverb driver tranny...

I really think you need to fix the basic amp first before any more work on peripheral circuits. Buying an LDR and a reverb transformer without verifying them as the fault and before fixing the actual amp is only asking for more trouble because:

Sometimes even new parts are bad and you might replace a working part with a broken one.
The possibility of a miswire due to an unnecessary operation exist.
Possible to cause a cold solder joint that wasn't there before.
Repeated heating of old CC resistors tends to drift them.
etc. etc. etc.

One or more of these things can greatly confuse things and compound troubleshooting any repairs. Not to mention that just throwing parts at a broken amp and hoping is just bad form. Not to mention that with the LDR and the reverb tranny you're trying to fix what might be symptoms instead of the real problem.

The amp works fine except for the listed problems.

With 78V on the plate of the mixer triode the amp is not working fine. Both channels pass through that triode. The reverb doesn't work and the trem is buggy. So what's fine?

I'll repeat, I really think you should fix the basic amp first, as in the instrument signal chain, before any more work on the trem or reverb. And I think you may have a leaky .02 coupling cap on the V4 pin 7 circuit.

[catstrat]

ticking tremolo.

Thanks Chuck H. I took my heat gun and re melted the wax on the parts board and low and behold the voltage at V4 pin 6 jumped up to 135 volts.I think that is still a little low but i'll check the schematic. Out of desperation i replaced the 100 K resistor on the LDR with a 180 K. The ticking problem is a lot better. I wound up using a 220 K and the tick is almost gone. It's my understanding the 100K resistor is a current limiter so i tried the higher resistances for grins. I read the ticking is caused by the neon bulb drawing a lot of amps, if i remember right. But, i don't know what it will destroy, if anything. I'll leave it for tomorrow and i'll check the reverb circuit and see if it works. I'll let you know then.