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Post by Peegoo 🏁 on Mar 23, 2023 9:59:07 GMT -5
^^^Make look like Sovya Choonyun submarine!
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Post by Pinetree on Mar 23, 2023 11:26:45 GMT -5
I dig how V4 and 5 are angled.
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Post by Peegoo 🏁 on Mar 23, 2023 12:49:36 GMT -5
If they stood straight up the case would need to be taller. I like how this cabinet is constructed; it's extremely heavy duty. The perforated steel top slides out the back after removing two little screws.  |
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Post by Pinetree on Mar 23, 2023 14:10:31 GMT -5
Cool.
Looking forward to the video of the smoke being released.
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Post by Peegoo 🏁 on Mar 23, 2023 14:44:21 GMT -5
The dim bulb stayed dim and no fuses popped. No jellybeans let out any smoke and all heaters are working...but I'm getting some crazy voltages, and V5 redplated about three minutes following power-up with the tubes in.
Further Study Is Needed!
This is the fun part.
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Post by Peegoo 🏁 on Mar 24, 2023 19:02:10 GMT -5
Oh, this is kicking my butt. Both tubes share a bias resistor and only one is red-plating? Weird. I have something goofed up. Not asking for any help YET because I want this to be a learning experience. I'll poke at it some more for a few days.
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Post by Pinetree on Mar 24, 2023 19:08:56 GMT -5
Have you tried swapping the tubes?
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Mar 25, 2023 3:40:06 GMT -5
Common causes of redplating in new builds include
- the control grid not having a DC path to its cathode.
- with shared cathode bias if one valve isn’t conducting (perhaps due to it having no voltage on its screen grid) the resulting bias voltage will be insufficient and so will allow excessive anode current.
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Post by Peegoo 🏁 on Mar 25, 2023 6:54:58 GMT -5
Thanks gentlemen!
Yes, I have swapped tubes in the sockets...the problem stays with the socket. They were the original tubes that were in the amp (Hammond, marked Made in Holland...Phillips made?). I swapped in a new set of JJs and same issue persists. I haven't posted a voltage chart because I do have one glaring discrepancy between the power tubes and I'm keen to find the cause myself...it's probably something so obvious a third grader can see it. I think it's one of those cases where I've looked at this thing a hundred times and I simply cannot see it.
I am getting a very low hum from the speaker but it's not affected by rotating any of the controls. I'm close, but not quite there yet.
I'm taking a break for a day or two and hit it with a fresh set of eyeballs.
Cheers!
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Post by Leftee on Mar 25, 2023 8:12:29 GMT -5
That, “take a break for a day or two” is an important part of the process for me. That includes woodworking, finishing and electronics.
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Post by Peegoo 🏁 on Mar 25, 2023 14:24:40 GMT -5
Well I cannot leave well enough alone and stay away. Voltages coming off the power supply should be in the range of 350 vDC, and right now it's about 100v too high. The voltages in red on the schematic below are measured across the power supply and ground. I also think there's something goofy going on with the master volume, which I wired per the Matchless Lightning schematic. With no tubes in and power off, resistance across tube pins 2 & 3 are as follows: V4 .2 M Ohms V5 130 K Ohms...and fast rising, with the master vol at 0. With the master vol at 10, it reads 190 K and slowly rising. With no tubes in and the amp powered up, I'm getting the following: V4 pin 2 to ground = 0 v V5 pin 2 to ground = 279 v with the master vol at 0 V5 pin 2 to ground = 78 v with the master vol at 10 I've quadruple checked the wiring and components and all is good. But I've probably missed something so basic it's gonna be a yuk-fest. Here's the schematic as I built it. I did not include the bleed resistor R2 and the line out.  |
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Mar 25, 2023 15:09:38 GMT -5
Has terminal #1 of the output valve sockets been used for anything?
Some valves brands have an undocumented internal link between 1&2.
Are those terminal #2 voltages affected if the valve in V3 is removed?
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Post by Peegoo 🏁 on Mar 25, 2023 15:16:22 GMT -5
Has terminal #1 of the output valve sockets been used for anything? Some valves brands have an undocumented internal link between 1&2. Are those terminal #2 voltages affected if the valve in V3 is removed? "Has terminal #1 of the output valve sockets been used for anything? Some valves brands have an undocumented internal link between 1&2." I read up on that a few weeks back, and since I'm using modern tubes and the schematic from the Matchless I figured that cannot be the issue here. The weirdness is the voltage difference between V4 Pin 2 and V5 pin 2. The V4/V5 pin 2 voltages don't change with V3 installed or removed. |
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Mar 25, 2023 19:51:11 GMT -5
It seems most likely that C16 is leaking DC.
I suggest to lift the C16 leg at the R31&32 node, leave it in free air.
Power up and check for V DC on it.
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Post by Peegoo 🏁 on Mar 25, 2023 22:04:14 GMT -5
I suggest to lift the C16 leg at the R31&32 node, leave it in free air. Power up and check for V DC on it. Okay...I went into the cave. Across the free end of the cap and ground and powered up, no DC or AC voltage. Across the free end of the cap and the DC side of the rectifier, 0.2 V AC and 0.0 V DC. Across the free end of the cap and the AC side of the rectifier, 327 V AC per leg and 1.5 mV DC per leg. Is this the V DC you're suspecting? Or did I measure this wrongly? Thank you sensei. 'Tis good to have a Yoda when The Forces of Evil abound  |
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Mar 26, 2023 5:45:31 GMT -5
I suggest to lift the C16 leg at the R31&32 node, leave it in free air. Power up and check for V DC on it. Okay...I went into the cave. Across the free end of the cap and ground and powered up, no DC or AC voltage… Hmm, this is getting strange! With the C16 leg still disconnected, and the amp powered up with the EL84 removed, is the V DC on the V5 socket control grid pin 2 (previously 78-279V) still present? Could you recheck the V DC (with respect to chassis common) at V4 socket pin 2? And at the C15 R27 28 29 node? |
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Post by Peegoo 🏁 on Mar 26, 2023 9:19:47 GMT -5
This is why I am so darn befuddled.
C16 leg disconnected/amp powered up/EL84s removed, V5 pin 2 voltages:
Master vol on 0, 279 V DC
Master vol on 10, 78 V DC
Across chassis common and V4 socket pin 2:
0.0 V DC; none of the controls have any effect on this.
Across the C15 R27 28 29 node and ground:
Master vol on 0, 277 V DC
Master vol on 10, 77.3 V DC
I cannot figure why there's voltage on V5 pin 2 and none on V4 pin 2. I'm going to pop the phase inverter into the V3 socket and recheck...
Okay, that made no difference having V3 installed.
So I wondered if perhaps the issue is the master volume pot. I bypassed it by clipping a jumper across terminals 1 and 2 of the pot and got 198.8 V DC on V4 pin 2 and 198 V DC on V5 pin 2. Could that be the reason for V5 red plating?
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Post by Peegoo 🏁 on Mar 26, 2023 9:30:53 GMT -5
For reference, here is the schematic for the Eico amp. I used this power transformer in this build. I tested both sides of the transformer and it's in spec. Same for the output transformer. With the exception of the tube rectifier, wafer switches, tone control placement and no master volume, it's pretty close to this build. I've compared both schematics several times and I see no errors. Whatever it is...I'm missing it.  |
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Post by Peegoo 🏁 on Mar 26, 2023 11:01:23 GMT -5
Here's another interpretation of the Matchless Lightning, by Steve Luckey.  |
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Post by Peegoo 🏁 on Mar 26, 2023 11:21:57 GMT -5
One thing my circuit does not have is an artificial center tap on the heaters' AC supply...but I cannot understand that as being the cause for the weirdness at the power tubes' control grids.
The humdinger should be serving this purpose though. I'm going to test that pot (R1) and make sure it's conducting.
EDITED: Yep, R1 is fine end to end (107 Ohms) and smooth through the sweep to both stops.
I need to take a break or I will achieve the 'singularity' Ray Kurzweil enjoys talking about.
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Post by Peegoo 🏁 on Mar 26, 2023 14:29:04 GMT -5
Okay...we're getting somewhere.  Unfortunately I gotta go have dinner with my hunnie, so it will be a few hours before I move that cap and see if it makes a change in the right direction. That is the only goof I found on the schematic, and it is 100% my doing. What a goob! |
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Post by Peegoo 🏁 on Mar 26, 2023 15:07:16 GMT -5
Who am I kidding? I couldn't eat without knowing. THAT was the issue. That one teensy cap out of place. No more V5 red plating, and no more voltage on V4 and V5 pins 2 with the tubes out. I am now getting a hum through the speaker that changes appropriately with the vol, master, bass, and treble controls. I am not getting signal through the input jack, however. Also, the power tubes are running HOT, probably due to the excessive DC voltage levels. Now that I can do a voltage chart without burning up V5, I'll get on that. I'll also see what's up with the signal path from the input jack through V1 and V2. AFTER dinner. Today was a good day |
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Post by Pinetree on Mar 26, 2023 16:16:07 GMT -5
That's the spirit!
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Post by Peegoo 🏁 on Mar 27, 2023 14:27:37 GMT -5
Alllrightythen. Here's a tube voltage chart for this amp. I was unable to find a chart for the original Matchless Lightning, so I've included Steve Luckey's version for comparison; he used a 5AR4 rectifier in his design. Most voltages are in the ballpark; some are higher and some are lower. Glaring issues with this build are 1. V4 & V5 pins 2 - unequal 2. V4 & V5 pins 9 - voltage seems excessively high  For ref, here are the B+ voltages. They came down quite a bit once the tubes provided a load.  Another issue is the heater circuit; it's making 7.2 vAC, which will cook the filaments faster than I'd like. I figure a .33 Ohm 5w cement resistor in series with one leg should drop that by about one volt, correct? I think this is running hot because this PT originally supplied the rectifier filament as well, and now there's less voltage drop with the diode rectifier. |
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Mar 27, 2023 16:52:10 GMT -5
Who am I kidding? I couldn't eat without knowing. THAT was the issue. That one teensy cap out of place. … With new builds etc, it’s a good idea to check all anodes have a resistive path back to the rectifier, all grids and cathodes a path back to circuit common / ground. Then power up with no valves, and check all anodes are up at high voltage, all grids and cathodes are 0V (except for fixed bias grids, which will be at an appropriate negative voltage). |
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Post by Peegoo 🏁 on Mar 27, 2023 18:53:08 GMT -5
With new builds etc, it’s a good idea to check all anodes have a resistive path back to the rectifier, all grids and cathodes a path back to circuit common / ground. Then power up with no valves, and check all anodes are up at high voltage, all grids and cathodes are 0V (except for fixed bias grids, which will be at an appropriate negative voltage). This is so obvious but I need to learn it! Thanks Pete. |
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pdf64
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Posts: 557
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Post by pdf64 on Mar 28, 2023 16:24:50 GMT -5
It’s too easy to let yourself get swept along at the final stages of a build or major repair etc, and stick some valves in there and power up, rather than dropping anchor and double checking that everything is in order.
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Post by Peegoo 🏁 on Mar 28, 2023 18:50:10 GMT -5
I sussed out a few of the puzzling issues (all minor), checked the bias, did some math and figured this is dissipating about 12.5 watts
The heater voltage was too high so I paralleled a pair of opposing diodes on one leg of the heater circuit and got it down to 6.8 vAC. That's still a bit hot and will shorten the life of the tubes. I'm guessing I might stick the EZ81 rectifier in there...dunno yet; it's a work in progress.
No red plating on the EL84s, but they are running hot. I think this is probably normal for EL84s that are up at the top end of their power spec. The only other amp I've built with a pair of EL84s has them parallel class A for a total of seven watts, so they don't get that hot. That's what I'm comparing this amp to. But what do I know? I'm still learning this stuff.
The amp works great, nothing has cooked, there have been no sparks, and I'm still on the original two fuses. I'll call this a win based on those four data points alone.
I just spent the last two hours playing through it and learning how the controls interact. The volume works as a gain control and the master controls overall volume as it should. The bass and tone controls are quite interactive; the treble control does a great job of reining in the highs but it also can make the amp really jangly and glassy, so I'm glad I didn't go with the cut control I was thinking of adding.
Up between about 9 and 10 on the bass control the volume drops a bit, and that weird drop is affected by where the treble control is set. I don't know exactly why it's doing that, but it's not a problem. Just weird....it may be the bass pot itself because I used a 500K instead of a 1M. I may get a 1M and stick it in there and see if that's the issue.
There are no weird ghost notes/strange harmonics, pops, beeps, burps, or that horrible frying bacon noise we've all heard.
The humdinger works a treat. There is a little residual hum and a little bit of hiss (more than normal for my builds), but I'll fiddle with lead dress and see if that changes things. I used no carbon comp/film resistors, so I know the hiss is not due to that. I'm not expecting much improvement after messing with lead dress because this is built point to point with no marshalling boards. I guess if it's gonna look like a bowl of spaghetti, there's gonna be extra sauce in there.
I played through a 2x12 open back cabinet and it rattles the windows in a lovely way. It can get very loud and stay clean with the volume maxed and the gain control brought up to about 50%, and with the gain dialed up it grinds really well and sounds like a screaming AC30. Very responsive to changes of the guitar's volume control too.
Overall I'm very happy with how this project turned out. It's not the best amp I've heard, but it's a good one, and I learned a ton of stuff on this project.
Thanks again Pete for all your advice.
Geno
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Post by Pinetree on Mar 28, 2023 19:31:30 GMT -5
That sounds like how the treble control on a Mesa Boogie acts.
Still waiting for the video.
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Post by Peegoo 🏁 on Mar 28, 2023 19:50:18 GMT -5
That sounds like how the treble control on a Mesa Boogie acts. Still waiting for the video. I had a Mark III for a few years and I don't remember it affecting the bass control like this. I'll record a short vid with sound samples. |
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