18Watt.com

Some of you may recall I built the head kit I bought from Graydon last summer with an EF86 normal channel and the early AC15 power supply/phase inverter values (called Jason's PI mods around here).

Just today I made the wiring changes that have been recently suggested to match the actual 18 watt amp that surfaced, mostly involved swapping sides on the phase inverter and rewiring the volume and tremolo depth pots, and changing the phase inverter tail resistor from 56K to 47K (I had already done that for the AC15 values).

Everything works fine now (with one exception), if there are sonic changes they're subtle.

Graydon's head kits come with a tremolo jack which is wired to a DPDT switch which allows the tremolo to be switched on and off manually when the footswitch isn't plugged in, by grounding and ungrounding the lead that goes over to V3, pin 2 (under the new wiring scheme). When the switch is in the manual position, an LED lights up. When the switch is in the footswitch position, the LED doesn't light up.

My exception to the "works fine" is the manual switch to allow use of the tremolo on the tremolo channel without the footswitch plugged in. (Remember the sides of V3 were swapped, now the footswitch jack is attached to pin 2 instead of pin 7 of V3). With the footswitch plugged in, the tremolo works fine. With the footswitch not plugged in and the switch in the footswitch position, it correctly doesn't have tremolo. However, with the footswitch not plugged in and the switch in the manual position, the LED lights up, but I get a very fast and loud paced ticking noise instead of the tremolo. I swapped in a different DPDT switch, and double checked all the wiring and the footswitch jack, and all that seems to be correct. The multimeter shows me that the switch is grounding and ungrounding pin 2 of V3 as it should. I checked the value of the resistor that reduces the voltage to the right level for the LED, it's about right. If I plug the footswitch in, the loud ticking stops, regardless of the position of the switch.

Does any of this sound familiar? I'm sure it's something very simple but I can't figure out what it is.

Amps are mysterious things.

Sounds very familiar! I get that fast paced ticking (under the new wiring scheme, never tried the old one), no matter what JJ ECC83S tube I use. I've tried several.

When I switched to a Fender branded tube I had laying around, the problem was completely fixed - it's probably a Sovtek 12AX7WA. Same with a Marshall branded tube.

Could it be something related to the new layout mixed with the gain or construction of JJ ECC83S tubes?

Give it a try.

Alex

p.s. Graydon, this also implies that all the tubes you sent me were fine!

I replied tp Wayne privately, but I'll recap briefly for everyone's benefit.

I had a similar problem on an amp that someone else built that came into my shop for repairs. I ended up replacing the entire switch and jack assembly. It read OK on the meter but whenever I moved the wire or touched it, the ticking would stop. I wasn't abotu to accompany the amp everywhere it went, so I had to do something. I don't know if it was a microscopic short in the soldering or the switch, but after I rebuilt it and rerouted the wire, the ticking stopped.

I know that the wire is very susceptible to outside electromagnetic interference so I would suggest trying a shielded wire there. I haven't tried it as I succeeded in exorcising that noise without going to those extremes. However, it might be worth a try.

HTH

That is FUNNY!!!


This is the very thing I am battling with right now!
The only exception is that I have also some noticeable (not loud...) buzz when I switch the tremollo off... check here:

http://www.mamaliga.com/gallery/view_al ... -Watt-Head

I even unsoldered the wire that comes from pin2 and touched it on and off to the chassis directly to see if there is any difference. Same story...

However. I might endup re-wiring the whole footswitch input/switch all over again as Graydon did...

gabi.

Gabi: many things can cause the problems..loose grounds,and lead dress..

As i said when we first did the changes that wired the amp like Ians amp.

The "real" 18s didn't have a trem jack,and switch.although it can work..
Cause i've used them on my amps without problems.

But the old layout had many problems too..and as i said,it still may be funky to get it right.
but the added extra wire for the footswitch jack..and switch could cause some problems if you don't get things just right.

Heres one of you pics,and a couple things to watch out for. From this pic

http://www.mamaliga.com/gallery/view_ph ... d=P9010054

See the extra length of wire to the FS jack..shorten this.. the plate wires are laying on the jack wire..I would try to keep the plate wires next to the chassis..pull the cathode and input wires up off the chassis..re-route those
plate wires going to V2.. Put them next to the chassis. Do this to the V2 And V3..

The little cap on the Vol Tone of the Trem channel.. try to mount the end of cap closer pot tab..and keep it pushed back, away from sticking out..
I know alot of this may sound weird, but all these can help.

Even the wires going to the speed and intensity pot..may have to move them apart some.. Shorten the ground for those pots..not a long run to a ground.

Richie

Well, I tried several of these suggestions today. Not one of them worked. Note that the tremolo works fine when I plug the jack in and use the footswitch, but when I try to use the manual grounding switch without the footswitch jack plugged in, I get the fast ticking instead of tremolo. When I moved/rerouted the wires from the board to pins 1 and 2 of the phase inverter, I got a louder or softer ticking, sometimes without the tremolo switched on, so I went back to the earlier routing. It made no difference connecting the tremolo jack wire from the board or pin 2 on the phase inverter, and using shielded wire, with the shield grounded at one end, for the tremolo jack connections made no difference either.

What would stop the ticking was (i) my holding the wires connecting pins 1 & 2 of the phase inverter between my fingers, but I can't do that all the time, or (ii) plugging in the tremolo footswitch plug into the tremolo footswitch jack, or (iii) putting my thumb across all six of the terminals on the dpdt switch that grounds the tremolo wire when the footswitch isn't plugged in.

I haven't yet tried different tubes; I've got an EI gold elite in the phase inverter and in V3; a Mullard EF86 in V1.

I just rerouted everything back to like it was before, so I can use the tremolo or not with the footswitch.

Anyway you could post a pic, it might help us see where it might be..
it still sounds like a lead dress problem.. What kind of jack are you useing for the trem? Use a short of a run of wire as possible.. maybe try a different jack. Sometimes the new jacks can be bad.
Richie

Richie, it's a plastic Cliff-type jack. I'll post pictures in awhile if I can't solve this. Interestingly, this did not happen until I swapped sides on the phase inverter with the newest more authentic version of the layout.

I had the same problem with this head version I finished...

I followed Richie's advice in making those leades as short as possible. Also I made that grounding lead that goes from the switch really short. In fact I turned it around the switch shaft, then tighten the switch nut.
It works perfectly fine now.

Here is a pic:

http://www.mamaliga.com/gallery/view_ph ... d=P9060087

g.