V4 Red Plating while playing

[redlir]

Sounds good.

Just to clarify a couple things.
Most electronic buffs are anal about terminology and to use the accepted terms makes sure everybody can understand each other when talking about an amp.

I know you meant power tubes but generally the abbreviation PT, means power transformer.

Also the board in the amp is the circuit board or preamp board.

A bread board is a device that you prototype a circuit on temporarily to work the bugs out.

I know it seems trivial and perhaps it is but it just helps everybody when we all use the accepted terms in electronics.
Sure there are some slang terms thrown around like swamper resistors and grid stoppers, etc.
But most know those terms so it isn't unusual to use those.

Just a FYI type thing.

Ah yes I should watch that. The last thing I want to do is confuse people lol.

Cheers

[redlir]

Ok, finished most of the rewiring and I setup the different lugs and connections for the "Larry" grounding scheme.

I double checked all the component values on the board, and I can't see any error in placement. If anyone wants to double check my work, it would be appreciated! There are resistors missing where the LAR/MAR kit will go in ( swamp, 220K's), and the input resistors have been moved to the jacks and there is shielded cable to V1.

If you ignore the wires that will be attached to the board, I think I did a good job on keeping the other wires twisted and tight with clean lines.
This one is a thumbnail, click for a high res image

[jonamojo]

I think your supposed to solder the 68k input resistors to pins 2 and 7 then connect your shielded wire to the input jacks where you will also ground the braid, having your input resistors on the jacks defeats the purpose I believe, otherwise looks good but how are you going to connect those wires are you going to drill holes in the board so they will slip threw?

[redlir]

I think your supposed to solder the 68k input resistors to pins 2 and 7 then connect your shielded wire to the input jacks where you will also ground the braid, having your input resistors on the jacks defeats the purpose I believe, otherwise looks good but how are you going to connect those wires are you going to drill holes in the board so they will slip threw?

I'm trying to think if it matters. The red and black wire are just soldered together because it's a 2 conductor cable. So for each input the red and black are soldered to the socket, pin 2 in one case. Then that is shielded all the way up to the input jacks where the shield goes to ground on the input, and the red and black connect to both resistors on that channel. All I really did was replace the green wires on the layout with shielded versions. I'm not sure it matters which side of the resistors the shield is on, I 'think' the idea is just to shield the run of cable from the input to the tube so anthing that could hit the signal wires to cause noise on that lenght is absorbed by the shield and sent to ground.... I could be wrong

As for the wires, some of the critical ones like the Presence, PI to the filter cap etc are still under the board, but all the other ones I was just going to go straight to the posts on top with a full wrap around them and solder them in place.

[Structo]

Many feel for best results and lowest noise, the 68K grid resistors should be soldered to pins 2 & 7.
But the way you have yours will probably work ok.
If you start picking up radio stations or other EMI noise then that will likely be the cause.

If you don't hear anything there, then don't worry about it.

I typically mount the screen resistors so they are straight up over the power tube sockets.
They disappate the heat better that way and are out of the way for the grid resistors that go on pins 5 of each socket.

You should have 5K6 resistors on pin 5 of each power tube, then the green and orange wires from the board to those resistors.

[redlir]

Many feel for best results and lowest noise, the 68K grid resistors should be soldered to pins 2 & 7.
But the way you have yours will probably work ok.
If you start picking up radio stations or other EMI noise then that will likely be the cause.

If you don't hear anything there, then don't worry about it.

I typically mount the screen resistors so they are straight up over the power tube sockets.
They disappate the heat better that way and are out of the way for the grid resistors that go on pins 5 of each socket.

You should have 5K6 resistors on pin 5 of each power tube, then the green and orange wires from the board to those resistors.

Thanks Structo. I may have read a previous post incorrectly then. I can certainly move the grid resistors to the pins and run the shields to the input. My goal is to reduce as much noise as possible so I should probably do it this way if that's what's recommneded.

The screen resistors are just that way for the 'shot' so you could see the tube connections well. I will put them up vertically when I'm done. The 5.6k's will be coming off the LAR/MAR master volume that I"m putting back in since it was clearly not hte source of the red plating, and I could use the volume reduction functionality again!

[Structo]

But even with the Lar/Mar MV the 5K6 resistors still go on pins 5, right?

Remind me again what circuit this is.

2204? Or 1987?

[redlir]

But even with the Lar/Mar MV the 5K6 resistors still go on pins 5, right?

Remind me again what circuit this is.

2204? Or 1987?

Yes absolutely the 5k6 resistors go to Pins 5 with the lar mar. This is a 1987 circuit. The only resistors that get removed with the Lar/Mar are the 220K's

http://metroamp.com/wiki/index.php/Lar/Mar_PPI-MV" onclick="window.open(this.href);return false;

I'm wondering if I should use a higher value resistor if it still is an issue after I'm done?

[redlir]

Voltages look good. About to fire her up, cross your fingers!!

[redlir]

Ok so here's what I ended up with after ripping her apart and rewiring. It's definitely cleaner than it was before ( the wiring). I made sure the presence wires came nowhere near anything else. Also just a note that it only 'looks' like the brown OT wire is soldered to the corner, but I have shrink tubed it under the board with the choke wire and extended it with another brown wire.

I also put the 6 pt grounding system in which really seems to have helped with noise. I can pretty much get right on top of the amp before I hear any noise or squelching sounds. I also moved the grid resistors to V1 and used shieldied cable to the input jacks.

Ok so.... red plating... I've done some initial testing and I don't 'think' I can produce it. *knock on wood*. I'm also wondering if I didn't fix the original problem some time ago and then spook myself into thinking there was red plating. I notice if I look at the tubed head on, I see what looks to be red on the plates, but if I shift my view more looking down at the tubes it's not there. As far as I can tell it's a reflection off the glass.

I played both channels full on into the weber mass.... I'm going to do another test when it's really dark to make sure... I don't want to declare victory just yet...

[redlir]

So in the dark with everything on '10', it does still red plate a little. It used to be a lot worse so I'm thinking it may just be in conjunction with the weber mass dimed to bedroom attenuation. I'm also able to get rid of the red plating if I dial back the master volume to 8 or 9, so I think I'll live with it for now. If I ever get a chance to put her wide open directly into a 4x12 we'll see if it does it sans weber mass.

[Structo]

I'm wondering if you are confusing normal filament glow with redplating?

The big structure visible inside the tube is the plate.
When a tube is red plating this plate structure will glow cherry red.
When I say this I mean the whole plate will glow cherry red.

It's common in some power tubes for the filament to glow pretty brightly and it may appear that more than that is glowing.

What do you have the tubes biased at.

If you have the bias current too high, it will redplate.

Remember when you adjust the bias, you are setting the idle current.
It will go from that point to much higher when you are actually playing through the amp.

Also remember when setting the bias that all volume controls should be set to zero and no guitar should be plugged in.

[redlir]

I'm wondering if you are confusing normal filament glow with redplating?

The big structure visible inside the tube is the plate.
When a tube is red plating this plate structure will glow cherry red.
When I say this I mean the whole plate will glow cherry red.

It's common in some power tubes for the filament to glow pretty brightly and it may appear that more than that is glowing.

What do you have the tubes biased at.

If you have the bias current too high, it will redplate.

Remember when you adjust the bias, you are setting the idle current.
It will go from that point to much higher when you are actually playing through the amp.

Also remember when setting the bias that all volume controls should be set to zero and no guitar should be plugged in.

Hi Structo,

It's the big grey plate in the tube. It's starts to glow in the center then expand outwards as I keep playing, but much less so than before. It doesn't ever get to be anywhere near the whole plate. As soon as I stop, it goes back to solid grey. This only seems to happen on V4 and only apparent in the very dark. These are the mesa tubes and they were biased at idle per the instructions you state. I kept them on the low side, they are at 31 and 25 I believe, so maybe the red plate would be worse if I brought them up a little more I don't know but they sound decent at this bias.

It does seem suspicious though that I can only get it to happen at full volume.. and of course I'm forced to use the weber mass, and that it goes away if I dial back the master volume a tad, so perhaps it is related to the load box. I had reproduced it some time back without the mass at full volume, but it doesn't seem to be as drastic now and I haven't had the opportunity to unleash the beast without the mass unfortunately. Having redone the whole amp and every solder point, I find it hard to believe that I've made a wiring error in the same place twice ( although it could happen). Unless there is some component attributing to it on the board who knows. But it's always that tube socket, and i"ve swapped out the .022 caps already. I'm also wondering if it's only on that tube because it gets hit harder than V5 ( per George).

Cheers

[Structo]

Looking at your picture it looks like you are grounding the 1 ohm resistors somewhere else than right at the tube.

I would run that resistor right to the ground lug on the tube socket bolt.

It doesn't need to go elsewhere.


Have you tried a different pair of EL34's?

I find it strange that you are still redplating.

A 5ma difference in bias is enough to cause me concern.
Is the tube that redplates the one with the higher bias current?

[redlir]

Looking at your picture it looks like you are grounding the 1 ohm resistors somewhere else than right at the tube.

I would run that resistor right to the ground lug on the tube socket bolt.

It doesn't need to go elsewhere.


Have you tried a different pair of EL34's?

I find it strange that you are still redplating.

A 5ma difference in bias is enough to cause me concern.
Is the tube that redplates the one with the higher bias current?

The 1 ohm resistors are grounded to point 5 of the 'Larry' Grounding scheme. Previously the were at the lug itself.
I was originally using Winged C's with a 3mV difference. I'm not impressed with the gap on the Mesa's I think they were actually a 6 mV difference so I'm going to ping their support for a replacement set if I can.. that's just too far out to call 'matched' I'd say.

The tube that red plates is always V4. With both sets, I had tried swapping the tubes to different sockets and it was still the case.

I find it strange too, but I had read other posts where guys would redplate a little when they strapped a hotplate to the system so it could be the case. Also, doing some reading on load boxes, I think mine might be inadequate for the task at hand. It is a weber 'mini' mass to be clear which is the 50 watt version... I'm pretty sure this amp can put out a lot more of that at full tilt ... I read correctly this amp is 50 watts of 'clean' power, so I may just be overwhelming the thing with the amp dimed.