Hell Everyone,
I'm near finished with a project building a Matchless 15W Lightning clone and am having some issues in regards to volume and gain. I previously built a matchless 15W Spitfire clone and it worked tremendously. The tone was great and volume this thing could get too was well lets just say too loud for indoors. Sourcing the same parts for a Matchless Lightning (since the circuit design is very similar with only adding an extra 12AX7 for cathode follower) I expected to see similar results. However the output stage doesn't seem to be amplifying correctly. In the very least I expected the volume to be similar to the spitfire in that it would be difficult to turn the volume up all the way without killing my ears but alas this is not the case. Having the master volume turned all the way up yields some gain but not what I would expect. The amp doesn't get much louder than a practice amp. Any advice on what may be causing this would be much appreciated. I have listed all relevant information(that I'm sure of) below.
PT : 275-0-275 173mA Hammond 270FX 5V-3A 6v-5A
OT: Hammond 125E Set to 4k Primary
Rectifier Tube: JJ 5AR4
Choke: 158M Hammond
Output Speakers: 2x10 35W Jensen Mod-10 each 8 ohm(wired in parallel for 4 ohm impedance)
Preamp Tubes: Tung-Sol 12AX7
Power Tubes: JJ EL-84
The Filter Caps in the layout from left to right are C1-C6. Voltages: C1=359
C2=326 C3=261 C4=356 C5=335 C6=267
C3 and C6 see the biggest drop in voltage. The power tubes are C3 and the 2nd stage cathode-follower is C6. I think this is where the problem lies. That the power tubes are not receiving a high enough voltage. The B+ is on C1.
The whole design is based off the old lightning schematic provided.
One other thing of note is decided to change the biasing resistor on the power tubes from 120 ohm to 215. The tubes were being pushed a little too hot at least in my eyes and maybe I should have left that alone and they should be biased hot. All the wiring for the whole circuit has been checked and there seems to be no issues with cold connections, grounding...etc.
I'm near finished with a project building a Matchless 15W Lightning clone and am having some issues in regards to volume and gain. I previously built a matchless 15W Spitfire clone and it worked tremendously. The tone was great and volume this thing could get too was well lets just say too loud for indoors. Sourcing the same parts for a Matchless Lightning (since the circuit design is very similar with only adding an extra 12AX7 for cathode follower) I expected to see similar results. However the output stage doesn't seem to be amplifying correctly. In the very least I expected the volume to be similar to the spitfire in that it would be difficult to turn the volume up all the way without killing my ears but alas this is not the case. Having the master volume turned all the way up yields some gain but not what I would expect. The amp doesn't get much louder than a practice amp. Any advice on what may be causing this would be much appreciated. I have listed all relevant information(that I'm sure of) below.
PT : 275-0-275 173mA Hammond 270FX 5V-3A 6v-5A
OT: Hammond 125E Set to 4k Primary
Rectifier Tube: JJ 5AR4
Choke: 158M Hammond
Output Speakers: 2x10 35W Jensen Mod-10 each 8 ohm(wired in parallel for 4 ohm impedance)
Preamp Tubes: Tung-Sol 12AX7
Power Tubes: JJ EL-84
The Filter Caps in the layout from left to right are C1-C6. Voltages: C1=359
C2=326 C3=261 C4=356 C5=335 C6=267
C3 and C6 see the biggest drop in voltage. The power tubes are C3 and the 2nd stage cathode-follower is C6. I think this is where the problem lies. That the power tubes are not receiving a high enough voltage. The B+ is on C1.
The whole design is based off the old lightning schematic provided.
One other thing of note is decided to change the biasing resistor on the power tubes from 120 ohm to 215. The tubes were being pushed a little too hot at least in my eyes and maybe I should have left that alone and they should be biased hot. All the wiring for the whole circuit has been checked and there seems to be no issues with cold connections, grounding...etc.
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> wiring for the whole circuit has been checked
Nevertheless, check it again and again, then with fresh eyes. It worked for Matchless. The most common reason a new build dont work right is a wiring error.
Then get P G K voltages on each stage. Although not noted on that plan, tubes is tubes. A B+ runs near 300V, plates tend to be 150-200V (the CF is different), most grids at zero +/-0.2V, and cathodes tend to be 1V-2V. Anything way off needs investigation.
Nevertheless, check it again and again, then with fresh eyes. It worked for Matchless. The most common reason a new build dont work right is a wiring error.
Then get P G K voltages on each stage. Although not noted on that plan, tubes is tubes. A B+ runs near 300V, plates tend to be 150-200V (the CF is different), most grids at zero +/-0.2V, and cathodes tend to be 1V-2V. Anything way off needs investigation.
Figured it out this morning. It was missing the connection point between the 220k on the Treble pot, the 100k and the 0.01 uf capacitor. The sound is much better now. Now I have to work out the oscillation that's occurring at high volume.
Thank you for the help. I checked over the layout like 10 times before this and of course the 11th time is the time I find out what I did wrong. Fresh eyes = best eyes.
Thank you for the help. I checked over the layout like 10 times before this and of course the 11th time is the time I find out what I did wrong. Fresh eyes = best eyes.
You have found it, so good, but for future thought, once I have stared at something long enough, it all just looks familiar and it is tough to spot mistakes. I find that if I turn the thing 180 degrees - work from the back instead of the front for example - it becomes a new perspective.
As to your parasitics, I'd wager on lead dress being involved. Set it up so it oscillates, then push grid wires around with a chopstick to see if wire position affects the noise.
As to your parasitics, I'd wager on lead dress being involved. Set it up so it oscillates, then push grid wires around with a chopstick to see if wire position affects the noise.
+1 on the chopstick. There's quite a lot of gain that amp and lead dress is critical. Any long signal leads may need to be shielded wire.
Sent from my phone. Please excuse any typpos.
Sent from my phone. Please excuse any typpos.
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