Matchless Lightning inspired build

Status
Not open for further replies.
Jump to Latest
#63
Bad news I'm afraid: I swapped out the resistors for brand new ones... no change in the voltages :-(

I was certain that was the issue. I'm pouring over the wiring again but not seeing any issues.

Any other possibilities? Bad caps??
 
#66
lightreel said:
I was certain that was the issue. I'm poring over the wiring again but not seeing any issues.

Any other possibilities? Bad caps??
Click to expand...

Sometimes re-drawing the schematic from your built circuit will turn up something - I've had luck with that..... a.k.a. thinking with a pencil.

The way the Matchless PS wiring 'splits' into separate legs is a bit more complex than the 'linear' style, so more chances for a wiring problem.

If the caps are new, from a reputable supplier, I doubt that they are at fault.

Can you post pics with labels of the section of the turret board with those PS components?
 
#68
lightreel said:
Is there any possibility everything is correct and these voltages are right??

I just found another schematic/layout by Steve Luckey:
http://home.comcast.net/~seluckey/amps/lightning/matchless_lightning.pdf

Voltages are nearly identical to mine!
Click to expand...

Well, if different currents are flowing in those loops from the power supply, (because the total resistances are different) we shouldn't expect the same voltage drop across each 22k resistor.
It's too bad the original schematic, or a schematic with values from an actual Lightning, can't be found.
The screen voltage seems low - perhaps that's part of the 'magic' ??
 
#69
Now I don't know what to think! It is rather uncommon for the plate and screen voltages to be so far apart, although there is nothing wrong with that. It just means that your power tubes will be well below the 16-18 watts that is so common for a pair of EL84s. I fail to see how the same schematic can have 217v and the other (Trinity) has 329v for the screens. I'll have to look more closely but they appear to be the same schematic. They both have four points where 22K resistors connect to the output of the choke. Steve's choke output is 335v and the Trinity is 349v, hardly enough to make so much difference in the screen. Both have screen resistors at 100 ohms. You can run your amp like this but you will be sacrificing power tube grind because of the low screen voltage. I have a Hammond 18watt chassis I use to build amps with and those EL84s really break up nicely to give some great power amp distortion. Obviously all the points taken off the 22k resistors will be different because of different current through them but the glaring difference is the screen voltage.
 
Last edited:
#72
I've decided just to drive on. I'm virtually certain I've done nothing else wrong on this build and I have no other symptoms of failing or or out of spec components. There is literally no hum or buzz worth mentioning, there's a *tiny* bit of hiss (I might try sort this out, but it's actually quite pleasant) and there's only a tiny bit of RF when the master and volume are pinned and it's upside-down and open on the bench.

It sounds like all the positive superlatives I can think of and my only complaint is that it's possibly too clean. But a clean "pedals" amp was one of my goals! So it's nitpicking.

It's my belief that what happened here is someone measured the voltages on a build that didn't have the 22k screen resistor (or had a 4.7k, or fed the screens directly off the B+), and transferred them to a schematic that included the 22k. I *think* I can extrapolate that a 4.7k would drop about 17.5 volts for the same current on my amp (vs the 82V I'm seeing with a 22k).

Fundamentally I don't think I'm killing it and it sounds flipping brilliant. So unless someone feels very strongly otherwise I'll get cracking on with a cabinet!
 
#73
Another option would be to reduce the dropping resistor by paralleling other values with your 22k and this will raise the screen to drive those EL84s a little harder or to hook the screen up to the output of the choke. It is perfectly fine to have the screen 2-5 volts lower than the plate. Maybe a good idea would be to monitor all voltages to see where the amp settles in at. These can change over time as the amp breaks in, although shouldn't change too drastically. Obviously, if you like the sound, do nothing. 🙂
 
#74
I had another thought on driving the EL84s harder. It doesn't necessarily translate to a ton more volume. When you drive them harder, they start to compress and distort and the result is power amp grind and not always just louder. As they distort, the peaks of the output wave are rounded and in extreme distortion, square-waved. This translates to more distortion and not necessarily a whole lot more volume. Sort of like your guitar vol. when you roll back on a distorted amp. The first thing is that the signal cleans up, then more vol. roll off leads to overall volume reduction of amp output. Driving them harder will get louder but maybe not as much as you think. If you don't like it, just change it back. Just presenting other options but if you like your clean amp, then you have a good base to apply your pedals to. One thing for sure is that having the screen lower, your power tubes should last longer because they are just cruising along at 11-12 watts. Great job on your first build!
 
Last edited:
#75
I wonder if the focus should be elsewhere: shouldn't you be getting a considerable amount of crunch from the preamp alone at a high gain setting? If not, what happens when you smash the input with a clean (no gain!) boost pedal?

A preamp which is passing a weak signal to the phase inverter and/or a PI which is passing a weak signal to the power tubes might be another thing to consider.
 
#76
I'm using an 12AY7 instead of the typical AX in V1. I just love how the AY's sound, but I have a few AX's I can try to see if I get more preamp distortion that way. I might also try paralleling in another 22k on the screen resistor to drop it to 11k and raise the el84 screens.
 
#77
mcgruff said:
I wonder if the focus should be elsewhere: shouldn't you be getting a considerable amount of crunch from the preamp alone at a high gain setting? If not, what happens when you smash the input with a clean (no gain!) boost pedal?

A preamp which is passing a weak signal to the phase inverter and/or a PI which is passing a weak signal to the power tubes might be another thing to consider.
Click to expand...

Good point,mcgruff. We had a post earlier that determined that he was around 60 volts low on the supply voltage to the gain make up stage for the preamp vol. which is direct coupled to the cathode follower that drives the tone stack. And his new readings I think he lost another 5v, so 65v low. This according to voltages on the the Trinity schematic. Steve Luckey's schematic says he is OK. Don't know what to think about this one, but it shouldn't cause problems. I agree, try a 12AX7 just to see what happens.
Lightreel, you do like the sound you are getting, so that is what counts. If you are getting your other sounds from a pedalboard, this amp will provide a great platform and you have a great clean tone as well.
That's the beauty of a tube amp, you can sub in tubes, different resistors,caps and unless you totally screw up, you can get many different sounds without generating large amounts of smoke! Remember to keep track of all other voltages as well when changing things around, especially bias voltage on your EL84s.
 
Last edited:
#78
More test results:

fender 12ax7 in v1

b+ = 364
v0 = 361
v1 = 247
v2 = 329
v3 = 276
v4 = 339

r25 = 114
r26 = 31.5
r27 = 85
r28 = 21.5

cathode resistor = 9.15


fender 12ax7 in v1, 22k parrallel'd (11k screen)

b+ = 361
v0 = 360
v1 = 246
v2 = 328
v3 = 311
v4 = 338

r25 = 113.5
r26 = 31
r27 = 48.5
r28 = 21

cathode resistor = 9.04


ehx 12ay7 in v1, 22k parrallel'd (11k screen)

b+ = 360
v0 = 358
v1 = 245
v2 = 327
v3 = 310
v4 = 330

r25 = 113
r26 = 31
r27 = 48
r28 = 28

cathode resistor = 9.07

My thoughts:
There's definitely a bit more preamp gain and distortion with the 12ax7 (same dial positions, it makes up nearly 3dB according to my sound level meter). But I don't like the distortion, it's too nasal.

The difference with the 11k screen resistor is way more subtle and very hard to pin down - perhaps with a better speaker it might be more noticeable. I'll try again when I have my greenback.

I'm going to leave it as-is for the moment: 22k screen, 12ay7.
 
#79
I have to admit, I was surprised at the lack of increased voltage on the screen with a lower 11K resistance. That voltage really didn't move. That's why there wasn't much, if any,difference in the tone. The only way to get the power amp grind going is to hook the screens directly to the output of the choke. This is the "traditional" place to do it. But if you like the amp the way it is, that's what is important. You have a beautiful clean tone!! And you(we) got a chance to learn something.
 
Last edited:
#80
I'm an idiot, I just realised I paralleled r27 not r25 ... trying again now!

Ok, sorry, blood:coffee ratio was off earlier... here are the correct results:

ehx 12ay7 in v1, 22k parrallel'd (11k screen)

b+ = 357
v0 = 356
v1 = 286
v2 = 325
v3 = 273
v4 = 328

r25 = 70
r26 = 30.5
r27 = 83.5
r28 = 28

cathode resistor = 10.6
 
Last edited:
Status
Not open for further replies.
Top Bottom