Crate Palomino V8

[Structo]

I've got this little Palomino V8 amp, Class A single 12ax7 and EL84 that I dug out of the pile and was playing with it today.
It has a gain control, tone and volume.

This amp is the same as a Crate V5 amp.

It has sat about a year.

I couldn't believe how scratchy the pots got in that time.

Anyway I fire it up and when I turn the gain up past half way it starts squealing like a stuck pig.

I think, ok, just needs a new tube.

So I swap in a new JJ ECC83 and a new JJ EL84.

Same story.

I don't ever remember this amp doing this when I bought it.

What I find is that when I have the gain down and it's not squealing, if I move my hand near the EL 84 I can make it squeal by my hands proximity.
Like a capacitance effect or something.

This thing is like brand new, just been sitting.

It didn't matter on which tubes I put in either, I even tried a lower gain preamp tube, didn't change anything.

I've Googled the problem but the only thing people talk about is changing the tubes.

The new tubes are not microphonic.

Anybody got a guess why it would oscillate?

I attached a schematic. It's the only one I was able to find and it has some mods on it but I haven't touched the circuit.

[Cygnus X1]

Bad input cable?

[Structo]

Nope, tried several and three different guitars.

[1966Riff]

Sorry for the joke, but...... maybe the name "Palomino"

http://buscon.rae.es/draeI/SrvltGUIBusU ... A=palomino


1. m. Chicken pigeon "brava".

2. m. colloquial. Stain of feces in the underwear.

[Structo]

Funny.

It is a piece of shit right now.

Anybody have a guess why the thing would squeal with a very high pitch when the gain is turned up?

The thing about the power tube and moving my hand close to it is weird.

On a whim, I reversed the OT primary wires, got the howl that is normal for them when they are backwards plus the squeal.

Again, this amp did not do this when I bought it. It sat for about a year without use.

Bad cap?

[Voodoo_Man]

Funny.

Again, this amp did not do this when I bought it. It sat for about a year without use.

Bad cap?

I pulled the one I have out tonite and no sccratchy pots or piggy noieses at any gain/MV/ tone settings. I was able to squeeze some bell tones on the edge of ringing with a LP and loud settings. Mine has sat at least a year in the shipping bag indoors. If it has been stored in less than ideal conditions, I'd be looking at the solder joints.

God Bless,
John

[jaysg]

cold solder joint...

[Structo]

Yeah, I even pulled the pcb out and looked it over.

Nothing glaring.

Those tubes sockets sure are POS.
Do those even solder to the pads or are they just held on with the twist of that tab?

I wonder if the power tube socket has a problem.

Like I said, it worked fine last time I used it.

I'll have to pull it out again and measure some voltages. ( which I should have done when it was out the first time......)

I was really amazed that you have to pull the chassis to replace the tubes on this thing!

[Voodoo_Man]

I haven't had the chassis out. For that matter, it has only been turned on twice. Still has the Cellestion tag hanging off one of the knobs. I wonder if the input could be jumpered around the opamp. What exactly does that thing bring to the table anyway?

God Bless,
John


P.S............I'm sure there's solder on them sockets somewhere. At least I hope there is!

[Voodoo_Man]

Nevermind the opamp. DOH!(Brain fade) I see they're using it for the gain. A built in tube screamer I guess.

God Bless,
John

[LeeMo]

Do those even solder to the pads or are they just held on with the twist of that tab?

My guess is bad QC on the assembly line. I'd touch them up with a bit of molten metal.

LeeMo

[Structo]

cold solder joint...

Well after thinking about it and your comment I pulled the pcb back out and looked it over carefully.

There was one resistor near the input that didn't have much solder, basically it had the lead through the hole and bent over.

So I hit that and all the tube socket pins again with solder.

This must be a ROHS soldered board because when I went to solder the joints or just reflow them the solder on the board turned all dull and crystally.

I can't recall ever soldering a ROHS piece of equipment.
I think I have some lead free solder somewhere but I didn't use it.

I also did the tone control mod that joins to the wiper to the CC lug so it operates more like a regular tone control.

I fired it up and no squeal. It had been squealing even when there was no guitar cord plugged in.
So I plug in a guitar and it much better.
On a strat it really didn't squeal unless I had everything dimed and that was probably some kind of feedback squeal.

On a cheap humbucker guitar, it did the same thing as before so maybe the problem is in that guitar or it's impedance doesn't match something.

So in the end it is 90% fixed.