Tick..... Tick..... Tick..... 1972 Fender Bassman

[garytoosweet]

Hello all,

I have a '72 Silverface Bassman on the bench. It had been heavily modified and owner wanted it returned to stock so I ripped most things out and it is now AB165 up until the phase inverter, and AA864 phase inverter/output section. I believe this is a fairly common configuration with these amps. I've attached a schematic of both. The only change is a 1.5k NFB resistor instead of stock.

The amp is working and sounds good but I am left with a faint ticking. I've attached a soundclip recorded right next to the speaker. In person it is very faint, but just loud enough to be heard and annoying.

It is not controlled by the volume and not effected by audio signal/playing guitar.

It disappears when V2 is pulled but not V1 or V3.

If I AC ground the grid or plate of V3, I get a loud buzz as if I was shorting a guitar cable tip to sleeve with my finger. The tick goes away and just buzz is heard.

If I AC ground the grid of the phase inverter the amp is silent.

Almost every resistor in this thing is new. All electrolytic capacitors have been changed.

Things I've done/tried:
- Adjust lead dress, all usual under board connections have been made above board with shielded wire. (drastic cut down on running water noise)
- Tried paralleling a new electrolytic capacitor across each of the two 22uf that feeds the preamp section (no change)
- Tried turning off all lights to see if any arcing was apparent (in standby switch or lamp or something) - nothing
- Power tubes are brand new set of JJ's, I tried swapping in a new set (also JJ), no change
- Tried rolling many preamp tubes (no change)
- All ground have been checked - especially doghouse and brass plate - rotated lock washers on pots and together to ensure good connection etc.
- Turned off all other equipment in the shop and put cell phone in other room (everything off except amp - no change)
- Extensive chopsticking/prodding everything including caps in the doghouse - nothing

What am I missing? What else can I check?

Thanks in advance!

[Pedro Vecino]

I cannot hear the audio file. What happens if you disconnect the feedback? I remember seeing in some conversion (I don't remember if they were exactly those two models) a problem with the phase in the primary of the output transformer.

[g1]

I cannot hear the audio file.

I had to turn all volumes up full and use headphones. It sounds like a metronome.

gary have you tried it in any other locations, or scoped your AC line at the wall? I used to get a similar click I could hear on our phone line, caused by our electric fence charger.

[garytoosweet]

Here is an upload of the audio file incase the forum attachment ins't working: https://vocaroo.com/1kis3dPsS8ub

I will try the amp in another location, and scope the AC line.

Also should mention, the ticking was accompanied by intermittent sizzling. It would happen like a rush of sizzling/crackle for a second or so. I think I may have solved that with shielded cable and switching 2 (new) carbon comps out to carbon film's as it hasn't happened in awhile, unsure if related.

[The Dude]

That sounds like something arcing to me. You said you tried paralleling caps to the PS node caps, but if a cap is arcing you'd probably still hear it even with a parallel cap. You may need to actually substitute a cap instead of just paralleling. If you have a scope, first scope each node and see if you see anything.

[garytoosweet]

I went back to give it one more go before calling it a night. Fired it up and... no ticks, no noise. Played it for about 30min and it was all good. Very quiet amp due to me chasing down everything today.

I will give it another go in the morning and maybe bring it somewhere else to play for a bit to see if I can replicate the problem.

Possibly some sort of electrical interference? Or I have an intermittent issue with the amp.

[Mick Bailey]

I spent a lot of time trying to track down a similar ticking. It turned out to be my (then) new electric fence energizer.

[Leo_Gnardo]

What am I missing? What else can I check?

All good work and good suggestions too.

Let's not leave out the infamous black circuit board material Fender used. They tend to start conducting, mostly between high voltage nodes and sensitive audio circuit points, causing all sorts of unpredictable noises. Sometimes they mimic bad tube noises - hiss, scratching, pops & ticks, squeeks & squeals. Even in an amp that usually behaves, sometimes a spell of damp weather can bring on the racket-making demons. Enzo has suggested using a hair dryer or heat gun and simply warm up the board a while, to evaporate water that may have been absorbed and is making the conductivity worse. Easy enough to do, it's worth a try.

And then, there's always cell phones & smartypants phones, they broadcast noises. Ticks & clicks, blips & bleeps. All the more easily heard if the phone is near the amp.

[garytoosweet]

All good work and good suggestions too.

Let's not leave out the infamous black circuit board material Fender used. They tend to start conducting, mostly between high voltage nodes and sensitive audio circuit points, causing all sorts of unpredictable noises. Sometimes they mimic bad tube noises - hiss, scratching, pops & ticks, squeeks & squeals. Even in an amp that usually behaves, sometimes a spell of damp weather can bring on the racket-making demons. Enzo has suggested using a hair dryer or heat gun and simply warm up the board a while, to evaporate water that may have been absorbed and is making the conductivity worse. Easy enough to do, it's worth a try.

And then, there's always cell phones & smartypants phones, they broadcast noises. Ticks & clicks, blips & bleeps. All the more easily heard if the phone is near the amp.

I forgot to mention, I did suspect a conductive board at one point, and completely isolated the part of the circuit before the PI from the board, lifting all connections and temporarily tacking together, no change.

But it's solved....

It was a cheap USB wifi adapter. It's plugged into the computer that was reasonably close to the amp. It's been there for 3-4 months and never had an issue with any other amps. When I spent the majority of the day tracking the tick yesterday, the computer was on. When I went back in the shop around 10pm or so to give it one last try, the computer had put itself to sleep, thus there was no ticking. I'm happy I was able to repeat the issue and I know it's not some weird intermittent fault in the amp. Can't believe I let that thing eat up most of my day. When I turned off all electronics in the shop I forgot about the computer. I've had similar ticking (also in a Fender Bassman) from my soldering iron in the past.

Thanks for all the suggestions and help

[Jazz P Bass]

Resistive heaters turning on & off will play heck with you too.

[Leo_Gnardo]

Can't believe I let that thing eat up most of my day.

I can, it's happened to me & probably lots of others here. Chasing tiny problems that would upset almost nobody is how I fail to earn a decent living... Glad to see you got it sorted.

1985 I was working on a project at a new studio in Ft. Lauderdale. Every now and then a tick noise would come up from the EMT plate reverb, of course with lots of reverb on it. One of the observant studio engineers noticed it only happened while one of those big radar jets (E-3 or similar) was in sight, flying along the coast line. One of the hazards of modern life I s'pose.

[Enzo]

Cell phones will do it, especially if you set the phone on top of the amp.