I can't find a Lightning schematic with voltages but I do have a Spitfire which has almost the same topology. Your screen is definitely too low. The plate should be around 340-350 and screen about 2-5 volts less. I know they show the screen and plate at 348 but I feel there should be about 2-5 volts less for safety.I'm sure there are other opinions about this, but you will be giving up little power in the name of safer operation. Also, cathode voltage on the EL84s maybe a little low? For the screen voltage as is ,you might be OK but if you raise your screen to 344 or so then re-check your cathode. It might go up because you have biased your tubes hotter by raising the screen. Note the schemo says 11.2 and you have a 150 ohm, so yours should be a little more than that.
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That voltage is a function of the choke, so measure voltage on both sides of your screen grid resistor or right at the output of the choke and right at pin 9. Also, your bias voltage for the EL84s is a little low, but if you figure out the screen grid situation, the tube will conduct hotter and more cathode current will flow thus biasing hotter. The schemo says 11.2v. As I recall, you have a 150 ohm so it should be a little more for yours. You're correct, plate voltage is a little high. Make sure you check both tubes. Maybe keep a chart for all voltages. Are your preamp tubes OK?
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I listened to your clip. Wonderful clean tone. You say that it doesn't break up much? You'll need to fix the voltages on the power tubes first to see what happens. That probably has a lot to do with it, as the screen is so low, you can't get any power amp grind. Did you say you don't have a schematic with voltages? If not, we'll just have to go with the Spitfire and get close to those.
I just had a thought, is your screen for sure 246 and not 346 and just wrote down the wrong number?
I just had a thought, is your screen for sure 246 and not 346 and just wrote down the wrong number?
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Unfortunately yes: screens are 245 in relation to ground and 118 in relation to either wire on the choke.
I checked through everything gain: I measured every resistor, every wire is in the right place and all the caps are correct. Choke rated resistance is 150 and it's reading bang on that. There's some evidence that Matchless used a larger dc resistance choke, and possibly that they wired it in different than their published schema (this thread is not alone in taking about the subject: Untitled Document)
As in, it fed the screens directly - not through the 22k resistor.
Any thoughts to this effect?
I calculate each tube is currently dissipating about 11W, which is fine. But cathode current is about 30ma - which is quite high I suppose.
URGH.
I checked through everything gain: I measured every resistor, every wire is in the right place and all the caps are correct. Choke rated resistance is 150 and it's reading bang on that. There's some evidence that Matchless used a larger dc resistance choke, and possibly that they wired it in different than their published schema (this thread is not alone in taking about the subject: Untitled Document)
As in, it fed the screens directly - not through the 22k resistor.
Any thoughts to this effect?
I calculate each tube is currently dissipating about 11W, which is fine. But cathode current is about 30ma - which is quite high I suppose.
URGH.
Sorry, I should have had you also check the voltage on each side of the choke also. Not at my best today. I think it would be best if you posted a schematic as you have built yours, as there will be differences in yours and others. I was just using the Spitfire as a reference.
Is yours like this? I found one with voltages. 352 and 329. They are listed down by the power supply. Still not the difference you have.
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Yes, that appears to be nearly identical to the "Matchless" one: http://elektrotanya.com/PREVIEWS/63463243/23432455/egyeb/matchless_lightning.pdf_1.png
I found that one too but no voltage readings. The one I posted is Trinity's take on the Lightning. So if it is like yours, now you have something more realistic as to what voltages to expect. Check as many as you can and fill in that recommended chart. You need to get as many as you can to track down the problem. Although I don't see voltages directly at the pins of the tubes, but compare as many as are given .
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Is it possible either or both 22k resistors between V0 and V1/V3 are toast?
They read correct on the multimeter, but I know it can be a different story when there's current drawn across them.
They read correct on the multimeter, but I know it can be a different story when there's current drawn across them.
I was just about to say V0,2,and4 are good. Get voltage readings on both sides of R25 and 27 and also resistance readings, but you have the resistance readings, so get the voltage readings. Also, voltage on both sides of the choke. It almost seems it has to be those two resistors. The only other thing I can think of right now is if the filter caps associated with those two low readings are somehow affecting the voltages. Are all of the components new? Are those the two resistors that are at an angle? Those leads on the one end are pretty short. Maybe damage from heat during soldering? Actually all of the ends are pretty short. If it is those, you will have to re-do them and elevate them rather than squeezing them between the turrets.
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Yea all the components are new. I soldered pretty quickly and they were never too hot to touch, but it's possible they overheated alright. Where I could I clipped a flat alligator to any leads but obviously that wasn't possible on those crammed resistors.
Voltage across:
- R25: 108.5
- R26: 30
- R27: 82
- R28: 27
Voltage across:
- R25: 108.5
- R26: 30
- R27: 82
- R28: 27
According to the schematic each 22k should have 20v dropped across it, so I think you found the problem. R26 and 28 are fine but R25 and 27 are bad or the cap associated with those are somewhat leaky and losing some voltage to ground. I would obviously replace the resistors first. I'm not sure if it is happening but theoretically when current passes through a resistor, heating would take place and resistance could change. Your reading with the meter is such a different scenario, such low current. I wonder it you took a reading when they are warm if it would be different? Obviously, discharge all caps with the amp unplugged. Take a reading on all caps first to make sure all voltage is gone. Take a reading with warm resistors if indeed they are warm.
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No capacitance meter unfortunately :-(
I'll replace the resistors and see how things go. Hopefully I can get some tomorrow.
I'll replace the resistors and see how things go. Hopefully I can get some tomorrow.
No resistors available locally :-(
Ah well... I'm chuffed to get this far so quickly. It will be hard not to run the amp while I wait, but I guess I probably should be patient!
I can start designing the head and cab boxes. This is my inspiration:
http://www.rainbowguitars.com/imagesproduct/wf/wfcyclonegreenhd112-xl-01.jpg
Ah well... I'm chuffed to get this far so quickly. It will be hard not to run the amp while I wait, but I guess I probably should be patient!
I can start designing the head and cab boxes. This is my inspiration:
http://www.rainbowguitars.com/imagesproduct/wf/wfcyclonegreenhd112-xl-01.jpg
Thanks dude. I think it actually sounds like a boutique-ified version of my blues junior -which is a good thing - but admittedly is probably a lot to do with running them both through the same crappy 'fender' speaker. I did A/B them at similar volumes: BJ is noisy as hell (and I have a quiet one), is lovely for bluesy lead, but goes mushy on chords or complex finger picking with accented bass notes. The lightning has a *lot* nicer mids: more detailed, richer, with better string definition. Bass is tighter too, highs are less icey. Chords especially are much clearer overall. I'm certain that with the voltages sorted and running through the right speaker it will be just magic.
You should have a very different amp because you should get breakup and more output from your EL84s with your screen hotter and you are under-voltaging your gain make up stage after your pre volume and your cathode follower driving your tone controls.Usually in this stage, 20 volts or so won't matter much but the 60v that you are short will. You should still get good cleans but it should give you more grind. BTW, I like the choice of cab to emulate. Nice.
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