Fender Tremolo tick - UK Vintage Radio Repair and Restoration Discussion Forum

ITAM805 · 25th Sep 2018, 1:50 pm

Hi folks

This early 70's Fender Dual Showman has a rhythmic tick when the tremolo in engaged. This is a fairly common problem on certain Fender amps and there are several suggested 'fixes' but so far none have worked on this amp except for adding a 22nF across the neon flasher which has reduced it but not stopped it.

Initially the trem didn't work at all but was ticking away. I replaced the bypass cap on the r/h triode and the trem started working but the tick persisted. So I then replaced the 'roach' (the neon/LDR device) but no change?

The r/h cathode voltage was 12V not the stated 21V in the diagram, this rose to 16V when I replace the bypass cap with a 47uF

Attached are pics of the signal at anode of V2 and the spike on the top of the LDR

Lucien Nunes · 25th Sep 2018, 2:20 pm

AFAIK it's caused by the ignition transient of the neon coupling into the audio circuit. Officially, according to Fender, lacing the reverb control wiring away from the audio, and/or adding the capacitor, should fix it. In the distant past, I think I did successfully tame one with something a bit more elaborate than one capacitor, although I can't recall what.

But I wonder whether it is still coupled electrostatically across the light gate? If that is the case, could a screening mesh be added between LDR and neon and the gate sealed up again with adhesive heatshrink?

Nuvistor · 25th Sep 2018, 2:20 pm

Have you checked what appears to be a 10MΩ resistor in the R/h anode triode load? You probably have but worth mentioning.

fetteler · 25th Sep 2018, 2:29 pm

I did a lot of work on my own Dual Showman about 10 years ago and read all the same stuff that you must have just read about the tick and how to cure it. Like you I tried 'em all and (though some of it sounded quite plausible) none of the cures actually worked. If it wasn't for the fact that I remembered a time when the amp didn't tick at all I would have given up... However, I found the cause on my own Showman to be that the funny impregnated cardboard stuff that Fender use for the circuit board goes a bit leaky and conductive with age, especially if it had been a little damp which, in the UK (compared to California!) isn't that unusual

. Once I rebuilt the entire thing on a tufol board copied from the original all was good and has remained so to this day. No extra caps,just the circuit as designed. I believe that these days replacement boards are available from folk on the internet for not much money.

Of course the problem is not just common to Dual Showmans, they all (Fender amps of a certain vintage that is) do it to some extent after a while.

All the best,
Steve.

ITAM805 · 25th Sep 2018, 3:17 pm

Thanks for the replies chaps

Lucien, yes I gathered it was a HV spike getting in the audio. I did try a cap from V2 anode to ground that didn't seem to help, but I shall try it again with some pF's rather than nF's

Frank, the 10M resistor measures 12M, but I didn't think in this case the drift would make much difference, could it?

Steve, that's interesting that you had to go to such lengths to cure the noise, but you have given me food for thought as the amp has been stored in a dingy attic for years I'm told? I dont know if I'd fancy replacing the board though and besides I dont think the owner would be happy with the bill

Nuvistor · 25th Sep 2018, 3:33 pm

I think you are right about the resistor.
Replacing the board may well be a step too far for the customer but Luciens idea of routing the cables sounds feasible and little cost, if it works good, if not you will have not lost too much.

ITAM805 · 25th Sep 2018, 4:40 pm

Ok Frank.

I tried in vain adding caps here and there but no change. I even disconnected the lead that runs from the LDR to where it joins the phase spitter, at both ends, but the bl00dy thing still ticks? A real puzzle, how is the spike getting there?

Andrew2 · 25th Sep 2018, 4:53 pm

If you could identify the part of the board that is causing the trouble (or most of it), could you drill/file away a slot to isolate it? We often did this with TV PCB's that had a habit of going conductive around HV points.

ITAM805 · 25th Sep 2018, 5:08 pm

Hi Andy, I suppose the board could have become conductive as with Steve's experience, but that said the phase splitter component are some 60mm away from the roach? I suppose though there are a myriad leads that might be picking up?

25th Sep 2018, 2:20 pm	#2
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Fender Tremolo tick AFAIK it's caused by the ignition transient of the neon coupling into the audio circuit. Officially, according to Fender, lacing the reverb control wiring away from the audio, and/or adding the capacitor, should fix it. In the distant past, I think I did successfully tame one with something a bit more elaborate than one capacitor, although I can't recall what. But I wonder whether it is still coupled electrostatically across the light gate? If that is the case, could a screening mesh be added between LDR and neon and the gate sealed up again with adhesive heatshrink?

25th Sep 2018, 2:20 pm	#3
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Fender Tremolo tick Have you checked what appears to be a 10MΩ resistor in the R/h anode triode load? You probably have but worth mentioning. __________________ Frank

25th Sep 2018, 2:29 pm	#4
fetteler Octode Join Date: Jul 2011 Location: Staffordshire Moorlands, UK. Posts: 1,479	Re: Fender Tremolo tick I did a lot of work on my own Dual Showman about 10 years ago and read all the same stuff that you must have just read about the tick and how to cure it. Like you I tried 'em all and (though some of it sounded quite plausible) none of the cures actually worked. If it wasn't for the fact that I remembered a time when the amp didn't tick at all I would have given up... However, I found the cause on my own Showman to be that the funny impregnated cardboard stuff that Fender use for the circuit board goes a bit leaky and conductive with age, especially if it had been a little damp which, in the UK (compared to California!) isn't that unusual. Once I rebuilt the entire thing on a tufol board copied from the original all was good and has remained so to this day. No extra caps,just the circuit as designed. I believe that these days replacement boards are available from folk on the internet for not much money. Of course the problem is not just common to Dual Showmans, they all (Fender amps of a certain vintage that is) do it to some extent after a while. All the best, Steve. __________________ Those who lack imagination cannot imagine what is lacking...

25th Sep 2018, 3:17 pm	#5
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Fender Tremolo tick Thanks for the replies chaps Lucien, yes I gathered it was a HV spike getting in the audio. I did try a cap from V2 anode to ground that didn't seem to help, but I shall try it again with some pF's rather than nF's Frank, the 10M resistor measures 12M, but I didn't think in this case the drift would make much difference, could it? Steve, that's interesting that you had to go to such lengths to cure the noise, but you have given me food for thought as the amp has been stored in a dingy attic for years I'm told? I dont know if I'd fancy replacing the board though and besides I dont think the owner would be happy with the bill

25th Sep 2018, 3:33 pm	#6
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Fender Tremolo tick I think you are right about the resistor. Replacing the board may well be a step too far for the customer but Luciens idea of routing the cables sounds feasible and little cost, if it works good, if not you will have not lost too much. __________________ Frank

25th Sep 2018, 4:40 pm	#7
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Fender Tremolo tick Ok Frank. I tried in vain adding caps here and there but no change. I even disconnected the lead that runs from the LDR to where it joins the phase spitter, at both ends, but the bl00dy thing still ticks? A real puzzle, how is the spike getting there?

25th Sep 2018, 4:53 pm	#8
Andrew2 Nonode Join Date: Mar 2010 Location: Dukinfield, Cheshire, UK. Posts: 2,038	Re: Fender Tremolo tick If you could identify the part of the board that is causing the trouble (or most of it), could you drill/file away a slot to isolate it? We often did this with TV PCB's that had a habit of going conductive around HV points. __________________ Andy G1HBE.

25th Sep 2018, 5:08 pm	#9
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Fender Tremolo tick Hi Andy, I suppose the board could have become conductive as with Steve's experience, but that said the phase splitter component are some 60mm away from the roach? I suppose though there are a myriad leads that might be picking up?