crate palomino v8

TragicTravisty · Post by **TragicTravisty** » 23 Nov 2008, 14:47

so, havent been here in a while, and still havent worked up the hair to pop open any of my amps, but my palomino is truly unuseable. Its schreechy, brittle, and oscillates w/changes in tone/volume on my guitar. and the tone control sucks. Note that ive loved the tone of every other palomino ive played.
http://www.guitarnuts.com/amps/vc508/index.php
theres an article ive read about modding the v5, the newer (MORE suckier) version of the palomino, but according to crate, it is electronically the same.
http://www.guitarnuts.com/amps/vc508/mo ... ematic.pdf
thats a schematic of the amp, with the mods in red. before i start pouring money into this amp, ill try the simpler mods to cut the treble, get red of c9 (treble boosting cap after first gain stage) and ground c11, making the tone control act as a low-pass filter. are these good ideas? anything else youd suggest?

JHS · Post by **JHS** » 23 Nov 2008, 16:23

Maybe a bad tube or IC. Before you start modding it, I would check this first.

The VC508 work quite well, soundwise you can't expect the tone of a bigger tubeamp. The mod should convert it in a usable practice amp.

JHS

John G · Post by **John G** » 23 Nov 2008, 20:37

HI,
If my menory serves me right I have had a couple of these amps (Palomino) suffering from HF oscillations.
It's been a while so the brain is a bit foggy, but I do remember having to move the multiway ribbon cable that connects the pre amp to the power amp to the left and reroute the o/p trans wires, also wrapping foil around the ribbon and earthing it.
You need a scope connected to the o/p to see what you are doing.
I also remember the rear panel pres ??? control having an effect on the point of oscillation.
John

John G · Post by **John G** » 23 Nov 2008, 20:39

Hi,
Correction, should be move cable to the right, away from o/p wiring.
Sorry.
John

TragicTravisty · Post by **TragicTravisty** » 24 Nov 2008, 13:59

ok. as for bad ic, how do i check this without replacing it? the amp sounds fine (not great) clean, how else do i check?

iwantmypie · Post by **iwantmypie** » 27 Nov 2008, 15:47

TragicTravisty wrote:ok. as for bad ic, how do i check this without replacing it? the amp sounds fine (not great) clean, how else do i check?

an easy one to do is just touch the IC while the amp is on and see if it gets pretty hot

TragicTravisty · Post by **TragicTravisty** » 08 Dec 2008, 20:56

if i got rid of the solid state preamp stages, making a few clippings + starting the circuit at r8, if i got rid of c9, and sent c11 to ground, id have something similar to a champ, right?

TragicTravisty · Post by **TragicTravisty** » 08 Dec 2008, 21:03

could i move the gain pot to in front of (or after) r14 to starve the amp a bit for more gain? or can the pot not handle that voltage?

cpnyc23 · Post by **cpnyc23** » 11 Dec 2008, 17:37

I'd love to hear what you end up doing to this amp. I own one and have a love/hate relationship with it.

Thanks
-chris

mojah63 · Post by **mojah63** » 11 Dec 2008, 19:52

TragicTravisty wrote:could i move the gain pot to in front of (or after) r14 to starve the amp a bit for more gain? or can the pot not handle that voltage?

I wouldn't put a pot there... You could raise r14 to 120k maybe 150k and get some more gain out of it. It will probably sound like crap... I've modded a few amps in my day, the more gain you try and squeeze out of a single triode section the more brittle it will sound. There is a reason why there are more than 1 or 2 gain stages in a modern tube amp. You will get more crunch moving the volume pot to where the mod schematic says to move it to. You pick up the second triode at full tilt. My JMP 50W has a ganged pot after the phase splitter to take advantage of overdriving that a little. Yeah you could cut out the opamp circuit and have a valve JR type of amp. I'm thinking along the lines of an earlier poster.... Change the 12ax7, you may just have a microphonic preamp tube. A 12ay7 is cool is Champ like circuits lower gain 12ax7's... Sometimes a lot of gain is not what you need.... Just what you think you need...

TragicTravisty · Post by **TragicTravisty** » 11 Dec 2008, 19:59

i'll pull a tube out of my bassman and see before i do anything

TragicTravisty · Post by **TragicTravisty** » 12 Dec 2008, 21:19

being unplugged for aweek should dissipate the caps, right?

Fuzzer · Post by **Fuzzer** » 13 Dec 2008, 02:19

Play safe and always discharge them with a resistor, and then measure the voltage on them.

TragicTravisty · Post by **TragicTravisty** » 13 Dec 2008, 06:27

dont have any multimeters or high wattage resistors (actually, i dont know what the wattages are....)

Fuzzer · Post by **Fuzzer** » 13 Dec 2008, 19:50

mmm, well, get a cheap multimeter. A common presentation for high wattage resistors is white chalk-like, its a ceramic embodiment. There are others, though, but the ones I mentioned are like the garden variety high wattage resistors.

I have used a 15k, 10 [W] resistor to discharge high voltage caps in amplifiers, but you need the multimeter to make sure the cap was discharged.

TragicTravisty · Post by **TragicTravisty** » 14 Dec 2008, 05:56

so unplugging it for a week is no good?

JiM · Post by **JiM** » 14 Dec 2008, 12:31

TragicTravisty wrote:so unplugging it for a week is no good?

I should be, but you never can be sure ... unless you measure the residual tension.

So go grab a multimeter, they're cheap and you'll need it all the time when diy-ing electronics, or even if you just play the guitar : checking cables, fuses, wall power at the gig, etc.
Even the cheapest ones are good enough : http://www.futurlec.com/Multimeters.shtml

About discharging the caps, you don't need high wattage resistor to do that, you just need a large enough value.
For example, a very small resistor (a wire) will discharge the caps quickly, but with a lot of sparks ...
A large-ish value will discharge them slowly, and you might still get shocked even after discharging for several seconds, if there remains enough energy in the caps.

I've taped a 470k 1/4W resistor on a wooden stick (from ice-cream), and apply it on each cap for at least 30 seconds. Then i measure the remaining tension and do it again if it's not zero.
On my Valve Jr. clone, a built-in 220k resistor discharges the caps in about 20 seconds, but i don't rely on it. Of course, the discharge time depends on the number of caps, their value(s), the voltage they were charged at, etc. There might also be several circuits to discharge (high-voltage supply, heater supply, sometimes a separate supply for preamp and poweramp ...)

Fuzzer · Post by **Fuzzer** » 15 Dec 2008, 03:29

Well, you could've gone the 'screwdriver way', but I wasn't going to suggest that; I feel safer with a big sturdy resistor.

And yes, the time of discharge depends on several factors, so you REALLY want to re-check afterwards.

JiM · Post by **JiM** » 15 Dec 2008, 20:30

Fuzzer wrote:Well, you could've gone the 'screwdriver way', but I wasn't going to suggest that;

I did that once with the cap from the flash of a disposable camera

the screwdriver was almost welded to the pins

I can't imagine doing that with bigger caps, it might burn the house

Fuzzer · Post by **Fuzzer** » 15 Dec 2008, 22:29

Once, a friend of mine was screwing around with his screwdriver changind an outlet; thing is, he forgot to turn the main power off, so in a moment he touched phase and ground and there was a big spark, It left the screwdriver Scarred, I'll try to post some pictures.