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Hoffman Amps Forum image Author Topic: Please help with 2ch 50w build - Schematic supplied  (Read 22586 times)

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Offline Meat_And_Beer

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Please help with 2ch 50w build - Schematic supplied
« on: June 12, 2013, 05:08:58 pm »
Hi There! First post, lots of lurking.

There are some amazing people on here, and I’m hoping someone can help me out on a build I’ve been working on for over a year now. It’s my first, and quite an undertaking for someone with no previous knowledge of any of this stuff!

I feel like I should give all the details I can, so I apologize for the massive length of this thing in advance!

I met a super talented, smart and awesome man through my girlfriends place of work who’s been building tube amps since he was a teen, now in his mid 50’s. This started as just a preamp.. Now it’s this massive two channel, mixable 50 watt monster with an fx loop.  He took my under his wing, and taught me everything I know right now about this art form.

I was strictly told not to publish any of the schematics, or even photo’s of gut shots online or anywhere. I’m at an impass, and I now live about 5 hours from my extended parents. (He and his wife) Even an emergency visit when the problem occurred, couldn’t produce results that got to the bottom of it. So, desperate times, desperate measures…

The amp has two main channels, 5 gain stages each. Channel one, as we’ll call it, is the top row of knobs on the chassis. Channel two, also has 2 buffer/followers (on 2nd & 3rd stages). A switch sends the signal from after the 2nd stage buffer to the PI, effectively giving a Marshall Plexi mode. Neat trick! Each channel has two defeatable tone networks. Channel one has a defeatable additional gain stage, Channel two can select its output from stages 1&2, or 1,2,&3 with a defeatable feature called “Contort”. (A glorified Contour)

Channel one (Stage 5) was crafted from part of an Engl E530 schematic, and heavily modified/developed. (For months I slaved over this channel, and the resulting circuit floored me when I got it right to my ears!!) Channel two (Stages 4&5) is a BK Butler Real Tube RT-902, again, HEAVILY tinkered with. These channels are now very much deviated from the original, but that’s where they started out.

The two channels can be played independently, or summed through the mixer tube at the end. This mixer has a resistor ladder that yields a Hi-Z output, the FX send, and of course to the PI.

I had cross talk issues (Electrostatic coupling) between the channels that I got rid of with the brass shielding that you see, and also by changing almost every signal carrying wire to shielded wire. Another amp builder told me how to completely silence the channel not in use through the rotary selector knob, sending ground to shunt its output. Fantastic! But if I knew that before the build, the rotary would have been at the other end of the chassis, of course…

This was before I had the final values for the FX loop installed. It was working splendidly! Every single aspect and component was in great functionality. (Sans some tweaking that’s always inevitable at the end of a build) I even put it in its case and played it for a few days while I was waiting for my amp tech guy to get back to me on final values for the loop. The day came, and I took it back out of its case, and put it back onto the working jig, and installed the FX loop properly.

I tested it at low volumes, and it seemed super. Then the next day, and I got on the volume a little bit, and something sounded wrong… As I pondered and stared at the guts, a spark, POP! Shot out of the power supply. Weather this was of real consequence, I’m not sure anymore. I never found the crime scene, no arc marks to be found. The inside of the chassis had never really been cleaned/blown out, it very well may have been a foreign object landing somewhere undesirable with the flipping around from jig to case back to jig.  Pretty squeaky in there now though.

The thing that sounded “wrong” was that channel 1 is somehow getting another signal riding on top of it, sounding much like the electrostatic coupling I had gotten rid of. That channel sounds nothing like it’s supposed to now, but I can hear the original signal back there, it’s just getting squashed by this parasite!

Channel two as well, but not nearly as noticeable. Also, its second tone network’s treble is problematic. At zero, there is full volume. As you bring it up, treble increases, but volume decreases.

So I took the emergency trip down so see him for the weekend and figure this out. We suspected something in the power supply, where the spark originated from. (There is now also a nasty ground issue, that hadn’t yet really developed)
« Last Edit: June 15, 2013, 09:33:00 pm by Meat_And_Beer »

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #1 on: June 12, 2013, 05:13:19 pm »
We checked and swapped out for known good;

- All filter caps
- All decoupling caps
- Choke
- Jumping over the FX loop/completely bypassing
- PI cap
- Power/connections to color organ (Yup, there’s one of those in there too)
- Tube swaps
- Bypassing “Plexi Mode”
- Guitars/Cables
- Many other assorted jumping/removal/otherwise disabling things

Through our experimentation, a swirling sounding ground issue had developed. I attached a sound clip of it here. At the visit, (Providence, RI) it was more like RF, radio, and static. At home (Much more rural, not as much city) it’s more just like swirling ugly ground noise. The sound clip is at home, I did not adjust any knobs during the recording, it’s just a swirling pool of madness all on its own.

Originally, I had bent lug 3 of the pots that ground to the bus bar that runs along both rows of pots. This broke/made them iffy, so I replaced every single one with brand new. This ground issue sounds just like it did when a pot or two was acting up. Can’t be one of those now, though, right?

We put a couple 22pf across the grid and plate of some first stage areas, rolling off the top end starting around 15kHz. It helped a bit with the RF.

Here’s how it’s set up mechanically;

- 1st bank of filter caps ground at the center taps with the PT
- 2nd bank grounds on bus strip
- Decoupling caps ground at or near where the stages they feed also do on buss strip
- Buss strip grounds at PT point
- OT common is at the speaker outs only
- Input jacks ground to 1st stage of channel two

PT: Hammond 374BX
OT: Merc Magnetics JCM 900-50-0
Choke: Merc Magnetics MAR100-C

The PT and other gnd’s are to one of its mounting bolts. I know this is not in good practice now, I plan on changing that. I tightened it, poked at it, with no effect. I’ve spent countless hours poking around with a stick, I can NOT find where this crap sound is coming from.

Do I have too much shielded cable in here?

I also attached a picture to see if some eagle eyes can pick up on something. (It was much prettier before all the mod’s, relocating, adding the color organ, and taking everything in and out a bunch of times and putting burn marks all over) I’m already going against his wishes, and would really prefer not to post any schems. I may decide to PM something to someone, but let’s see where we can get with this first.

Pictured parts labled:
1 – 12AX7 - Stages one and two channel 2
2 – 6AV6 – Stage three channel 2
3 – 12AU7 – Buffer for stages 2&3 channel 2
4 – 12AX7 – Stages 1&2 Channel 1
5 – 6AV6 – Stage 3 channel 1
6 – 12AX7 – Stages 4&5 Channel 2
7 – 12AU7 – Stages 4&5 Channel 2
8 – 12AU7 – Mixer
9 – 12AU7 – Phase Inverter
10 – 6AU6 – FX Loop (very fast tube, could use some taming in the upper freq’s somewhere I’m sure)
11 – 5U4 – Rectifier
12&13 – 6L6GC

Caps A-F are 22uf 450V Decouplers (Between 290v-310v supplies)
A - Mixer
B – V5, V7a
C - V4 a&b
D – V10 FX Loop
E – V3b V2
F – V3 a, V1 a&b
G - ~100v supply for V6 a&b
H - ~100v supply for V7 a&b


Any voltage readings or other information, I’ll be happy to give a list. But they’re all pretty much where they should be as far as how it was designed. (And as far as I can tell)

Remember, this amp did work, and quite well. Something has slowly failed/moved out of spec, or has mechanically failed. I’d like to believe it’s one thing that gave out… But obviously I don’t know for certain.

You are a trooper if you read this whole story, and I commend you. Thanks for such a great place guys, any and all suggestions on further troubleshooting this beast is so much appreciated!

-Chris

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #2 on: June 12, 2013, 05:14:21 pm »
More pics, trying to figure out how to post a sound clip too...

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #3 on: June 12, 2013, 05:19:40 pm »

Offline DummyLoad

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Re: Please help me with my creation!
« Reply #4 on: June 12, 2013, 05:31:52 pm »
very complex; perhaps overly so. schematic as built would be of most help as would anode, cathode and screen (where applicable) voltages for each element annotated. 

--pete

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #5 on: June 12, 2013, 06:35:43 pm »
Voltage readings as requested. I knew I should have just posted em…

Again, I really would rather not post the working schem, I gave my word. Besides, the final (Minus power stage) is about a 3x1.5 foot piece of paper. Cripes!

V1a
Plate: 169v
Grid: 4mv
Cathode: 1v

V1b
Plate: 1601v
Grid: between -1 and 15mv…
Cathode: 1v

V2
Plate: 94v
Grid: -10mv
Cathode: 608mv

V3a (1st buffer)
Plate: 268v
Grid: 160v
Cathode: 164v

V3b (2nd buffer)
Plate: 294v
Grid: 93v
Cathode: 104v

V4a
Plate: 171v
Grid: 1mv
Cathode: 1v

V4b
Plate: 175v
Grid: 5mv (fluctuates up and down quite a bit)
Cathode: 1v

V5
Plate: 105v
Grid: -36mv
Cathode: 604mv

V6a
Plate: 62v
Grid: -284mv
Cathode: 3mv

V6b
Plate: 56v
Grid: -169mv
Cathode: 3mv

V7a
Plate: 30v
Grid: 2mv (up and down)
Cathode: .8v

V7b
Plate: 33v
Grid: .4mv
Cathode: .9v

V8a (mixer)
Plate: 189v
Grid: 79v
Cathode: 93v

V8b (mixer)
Plate: 188v
Grid: 79v
Cathode: 93v

V9a (Phase Inverter)
Plate: 150v
Grid: 39v
Cathode: 50v

V9b (Phase Inverter)
Plate: 150v
Grid: 39v
Cathode: 50v

V10 (FX Loop)
Plate: 100v
Control Grid: .6mv
Cathode: 1.8v

V11 (Rect)
Plate (Pin 4): -81mv
Plate (Pin 6): -80mv
Filament (Pin 8): 422v
Filament (Pin 2): 422v

V12 (6L6#1)
Plate (Pin3): 421v
Screen (Pin4): 419v
Control (Pin5): -44v
Cathode (Pin8): .5mv

V13 (6L6#2)
Plate (Pin3): 420v
Screen (Pin4): 418v
Control (Pin5): -44v
Cathode (Pin8): .6mv

Offline sluckey

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Re: Please help me with my creation!
« Reply #6 on: June 12, 2013, 07:19:59 pm »
Quote
Again, I really would rather not post the working schem, I gave my word.
That's too bad.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #7 on: June 12, 2013, 07:31:43 pm »
Sluckey, I know. Thing is, it worked, and now this issue. (I've tried changing it back to when the FX loop wasn't working, same deal. Meaning something bit the dust and I have to find it) I want to see if anyone has any leads on it before I go and divulge it all.

I know this place is very respectful, and an incredible wealth of honest knowledge. To most of you veteran builders, I'm sure nothing in my schematic will make you jump out of your chair. You've most likely seen much more sensitive material than my schem could even hold a flame against. I do realize this.

Do we have any suggestions? I've seen many issues resolved in these threads with less information than I've given here. I'm going to do what it takes, and this thing will make it across the finish line. That is a fact. :)


 :anyone:
« Last Edit: June 12, 2013, 07:52:42 pm by Meat_And_Beer »

Offline tubenit

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Re: Please help me with my creation!
« Reply #8 on: June 12, 2013, 09:17:41 pm »
Quote
Again, I really would rather not post the working schem, I gave my word.

Quote
That's too bad.
  +1

I can appreciate a man keeping his word.  That counts in my book. And if you have given your word, I think you should keep it.

However, it's truly a shame that you're confined to asking for help within that frame work on a forum that shares schematics so liberally and graciously with others.  But again, I can appreciate keeping your word.

Seeing the schematic may have been useful in us helping you.   

Respectfully, Tubenit


Offline Glennjeff

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Re: Please help me with my creation!
« Reply #9 on: June 12, 2013, 09:24:36 pm »
Part of that noise sounds like parasitic oscillation, as you have observed, which causes all sorts of weird things to happen. like pots working the wrong way around.

Do you have an oscilloscope or someway of signal tracing. Even then, hyper sonic oscillations is like radio, it transmits out and gets into everything. The fact that it was picking up radio transmissions in urban areas suggests this also. Check each stage and make sure that their response is rolled off beyond audible frequency range( I think that is putting a few pF between anode and grid for valves but DO NOT TAKE MY WORD FOR THAT) .

Supersonic oscillation can also overload power supplies and blow transformers/speakers.

Quote
V4b
Plate: 175v
Grid: 5mv (fluctuates up and down quite a bit)
Cathode: 1v


Grid: between -1 and 15mv…  ?????

Grid: 2mv (up and down)...  ???????


Those Grid voltages needs super sleuthing. It appears to be talking to itself i.e. hypersonically oscillating. Can you supply Grid CURRENT values, maybe problems with grids latching and drawing current.

Have you tried shutting down logical blocks and then re animating in logical block - like computer programming.

Example/Explanation;

1.Remove tubes and B+ - maybe even coupling caps between stages from everything except PI and Power Amp Stage -TEST,IF faulty  FIX (is it PI or PA???), IF ok NEXT

2.Connect first input stage (V1a, V1b) - TEST, if faulty FIX, ELSE NEXT
(OR work backwards from PI/PA, one stage at a time getting it going and stable.)

etc etc

Have you had a drumstick in there tapping around for microphonics and testing lead dress for changes in the symptoms.

I'm new here and not very familiar with valve electronics, but that amp looks like a radio transmission waiting to go on air. You may need to do a lot more shielding with copper plates to get it stable. (I was a marine radio technician at the end of the tube era, early seventies)

Sparks shooting out is really as bad as it gets, at least it didn't blow your house fuses/breakers.

If that sort of advice is not going to help then the good folks here will need a schematic, if it's a trade secret - well - you're on your own really. I mean that in a down to earth factual kind of way - no hurt intended. Maybe convince your tech buddy to let us have the schematics.

Best of Luck.



« Last Edit: June 12, 2013, 09:37:39 pm by Glennjeff »

Offline PRR

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Re: Please help me with my creation!
« Reply #10 on: June 12, 2013, 10:00:12 pm »
29 knobs, years in the making, multiple fathers, secret schematics, mystery sparks.....

I dunno what to say. Not even where to start.

My personal opinion is that it is "over built", in the sense of "10 pounds of sausage in a 5 pound bag". Actually most of the chassis is quite clear and neat, but that front panel...  :huh:  :huh:  :huh:

Stare at it. Imagine you are the signal. Where do you go? Where can you go that ISN'T good?

Offline plexi50

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Re: Please help me with my creation!
« Reply #11 on: June 12, 2013, 10:06:52 pm »
I would get lost with all the knobs or controls. At one time i was into building amps with all kinds of bells and whistles.
At the present time for me a simple schematic and layout with little insertion loss is what i like best.

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #12 on: June 12, 2013, 11:35:41 pm »
Quote
Again, I really would rather not post the working schem, I gave my word.

Quote
That's too bad.
 +1

I can appreciate a man keeping his word.  That counts in my book. And if you have given your word, I think you should keep it.
Tubenit,
Thank you so much for seeing it as I have to also. Believe me, I want to lay the whole thing out for everyone, as I know that will get it down to the delicious meat and potatoes. I mean no disrespect to anyone here by withholding info. But without this guy that has taught me, spent countless hours calculating and drawing up schematics for me, teaching and showing me why the hell this does that or how it affects the other, I’d just be buying amps and wishing I could get my tone.

My tone is right here, inside of this misbehaving contraption. I just need some outside help.


GlennJeff,
Your advice sounds like an excellent idea! “Logical blocks”... I would’ve never thought of that. I have a little pot/resistor network I use to clip onto a stage in my amp, and it’s fed it to a known good amp on clean to listen to what’s going on from the test amps input to that mentioned point. Bad news is that it starts from stage 1 on both channels.

BUT, if I check each individual stage, or “block”, that will tell me something else altogether. Thanks, I’ll try that!
I do have a scope. My generous amp father leant it to me before I left the last time I was down there. I need to fashion a grid for it, the “divisions” that is. But it’s still very useful for checking for ghosts and other junk on a signal.

I checked the squirrely grids for current, zero.
I’ve tapped and poked and pried at every conceivable connection and component. Just a little action at the first stages, which should be expected anyway, no?

I have fully ruled out that it is the power amp, or the FX loop. If I plug my guitar into the FX return, it’s a beautiful sparkly awesome clean signal that I could listen to for days. The return pot has tons of headroom to boot!
FX send sounds like the sound file attached, as does the Hi-Z out.

I’ll close with this,
Nothing anyone says about my wire dressing, overall build quality, or anything else is going to hurt my feelings. Please, be frank with me. I know there are a million ways of doing everything concerning these builds. Mine does look a bit ugly. (See all the LED’s behind each tube, and their corresponding wires. Those, are the ugliest. Ignore them if you can, I plan on addressing that.)
This is my first actual build. Each channel was built independently in a prototype chassis and developed. They looked MEGA ugly. The power amp also had its own proto chassis. Again, not at all pretty. (I have pics, if you guys want a laugh!) But when I plugged them all together, not only did they work like the dickens, holy mother of god was it splendid…

I’m getting better. I’m not going to drop this craft, I am VERY ambitious, determined, and a bit sharp. This is not to be confused with stubborn, fat headed or conceded. All criticisms are welcome. Thank you so much for the responses so far, looking forward to delivering good news in the near future!!!!

PS, I see a couple of new posts that I’m eager to converse about. Give me just a few minutes, gentlemen. :icon_biggrin:


Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #13 on: June 13, 2013, 12:13:02 am »
My personal opinion is that it is "over built", in the sense of "10 pounds of sausage in a 5 pound bag". Actually most of the chassis is quite clear and neat, but that front panel...  :huh:  :huh:  :huh:

Thank you for recognizing all this can in fact fit in here. It is, after all, the biggest chassis that Dirty Dawg Amps makes. Being that it's all clear and concise, but just the front panel is confusing, well, I'll just thank you at the moment. I'll explain below!

I would get lost with all the knobs or controls. At one time i was into building amps with all kinds of bells and whistles.
At the present time for me a simple schematic and layout with little insertion loss is what i like best.

Boy and how. I agree! I mentioned in the beginning that this started out as a simple one channel PREAMP. How did it end up to be this thing?? Well, months and months of education, trial and error, and he thought I was ready for such a challenge. Sir, I promise you, this thing is a go. Have you any direction as to what is failing in my amp?


Now, I will address the pile of chickenheads on the face.

Has anyone had to work front of house at just about any kind of event? You have a mic, a board, some outboard gear, a power amp and speakers. (The typical scenario anyway)

You have to set the mic gain on the mixer just so, so that you're under clipping, usually, so you can set the mixers fader at unity without having to memorize about 10 tracks of where everything wants to be. Then there are aux sends, don't over-feed them either!

Weather your outboards are getting fed with the aux's or the main outs, no difference for this, it would get too technical with all of the sub out possibilities and everything. Just picture it a linear venture from mic to speaker.

If you have a return signal, or if your outboard effects have a send, you have to watch those also, again, to avoid clipping, or any other kind of undesirables. Within just this small set of equipments, you can greatly affect the tonal quality of what gets delivered to the power amp. Don't forget, you cant have THAT set too high or you'll overpower the speakers, or if they're set too low you'll be trying to pound your signal into them from the board and that wont sound too pretty either.

Here it is;

Gain staging. It's all about how you set the gain from one stage to another. If I want to hear the first tube pound the proverbial snot out of the preceding stages, I'll dime that pot. But I don't, so I don't do that. Next in line is how much do I want out of that first tone net? Do I even want the first tone net? I usually do, but there's a simple switch for yes or no, and accompanying pots because of load differences.

The more I increase the first input pot, directly influences how much of the tone net I will hear in the end. (If it's engaged, or it's just straight gain/volume) next is how I want that 2 stage pile to affect the rest of the mess. Next up, depending on which channel, is an optional thing. (Either the "more" on channel 1 which is just more gain, or the "Contort" on channel 2 which is a stage w/ contour really) You can include it, play with its tonalities, or ignore it.

THEN, there is the, "how much do you want to let that thing in..." Pot. It's the end, you can EQ that too, or not. Up to you. In the end, the switches you flip, determine the number of pots you have to play with.

This amp is an almost limitless tone machine. It's actually very simple. BUT, remember, I just asked for a preamp.

The more you play with this amp, the more and more easy it is to understand. It's really not as crazy as it looks. A lot of the pots are there for when you want them. Or, they can be all there at the same time. Up to you.  :laugh:

Offline Glennjeff

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Re: Please help me with my creation!
« Reply #14 on: June 13, 2013, 12:17:33 am »
Quote
Bad news is that it starts from stage 1 on both channels.

I take it you mean that noise, which is in it's own way beautiful, starts from stage 1 on both channels. Signal tracing is probably not going to be helpful then, it's likely parasitic oscillation.

The initial outbreak of this oscillation could have taken out lots of things. Have you checked all resistors for appropriate values, caps for short. Check valves individually in a working amp)

Logical Blocks, this approach might save a little time;

Completely disable power to all channels and disconnect signal feeds except Channel 1. (How many channels are there ?)
Also disable any "side add-ons" that can be switched in, switch them out. Adjust gain structure for clean sound.
Good or Bad? Fiddle with knobs. What happens?

Disable/unpower Channel 1 and disconnect signal feeds.
Reconnect signal and power channel 2
etc etc

Basically, You had it working but it was faulty in the sense that it was unstable. You not only have to repair it, you also have to find underlying problems in it's engineering, which appear to be related to unwanted feedback paths which, as PRR pointed out, most likely come from the front panel wiring and pots.

Another BLOCK you could tackle;
Get as many of those front panel pots that are not necessary for "bare bones", "most basic" operation disconnected at the feed point on the PTP circuit board and unselect them with their switches, unwire their subsection on the PTP board. They, and their feed wires/shields, are antennas.

Otherwise, get it going one valve at a time. As your PI/PA is ok you should be able to use it as signal tracer once you've got rid of that "ethereal angelic music" that we call noise (by disabling sections). Using the internal PI/PA might detect anomalies that an external "signal tracer" amp would not.

This project was never really finished and it is going to be a big job to get it finished.
That is what makes projects fun though, in a masochistic sort of way.

I'm not the best person to ask, but, once you get it stripped down and working in "bare bones" mode I will be happy to TRY and tackle the radio engineering problem that the front panel poses.

All the best.



« Last Edit: June 13, 2013, 12:41:39 am by Glennjeff »

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #15 on: June 13, 2013, 01:06:51 am »
Quote
Bad news is that it starts from stage 1 on both channels.

The initial outbreak of this oscillation could have taken out lots of things. Have you checked all resistors for appropriate values, caps for short. Check valves individually in a working amp)


Eesh, I really hope I don't have to individually test each component. To answer, no I have not tested all of the resistors. Do you have a logical guess as to where to start?

Check valves in a working amp? Do you mean some of my tubes might be bad? If so, I've tried a myriad of tubes in different locations, I have a good collection of 12A_7's. (And the others) Also a tester, but they don't really matter in these occasions. I'm sure it's not a tube.

There are two main channels, one has a little trick that sends what is essentially a Marshall Plexi circuit to the speakers. Other than that, its just two, with a lot of yes or no switches and knobs along the way.

Thank you for your many ideas to narrow this down, I have a lot of work to do, and you to thank if anything comes of it. I'll keep everyone posted!

Offline tubenit

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Re: Please help me with my creation!
« Reply #16 on: June 13, 2013, 04:54:54 am »
Quote
This was before I had the final values for the FX loop installed. It was working splendidly! Every single aspect and component was in great functionality. (Sans some tweaking that’s always inevitable at the end of a build) I even put it in its case and played it for a few days while I was waiting for my amp tech guy to get back to me on final values for the loop. The day came, and I took it back out of its case, and put it back onto the working jig, and installed the FX loop properly.

Quote
I tested it at low volumes, and it seemed super. Then the next day, and I got on the volume a little bit, and something sounded wrong… As I pondered and stared at the guts, a spark, POP! Shot out of the power supply. Weather this was of real consequence, I’m not sure anymore. I never found the crime scene, no arc marks to be found.
Something happened in between these two that you will have to figure out?  You're stating it worked splendidly and then it didn't. I'd go back and undo everything added beyond working splendidly.  And I'd probably replace everything around the area where the spark was in the power supply.

With respect, Tubenit

Offline Glennjeff

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Re: Please help me with my creation!
« Reply #17 on: June 13, 2013, 06:37:05 am »
Components probably ok if PI/PA survived. What I was trying to convey is "develop some sort of strategy that is systematic and thorough" I guess. Doubt you'll get a "wave the magic wand" solution on this one.

Blue flames and Mushroom clouds (Mystery Sparks) are really a sign that something has been badly compromised so do what tubenit suggested first even though the power supply appears to be OK. Put the oscilloscope on the high tension B+ and make sure it is fairly ripple free and that the "hum/oscillation" is not getting onto the supply (or measure for AC on the DC supply with a DMM). Check around the terminals and plastic seals of the filter caps in the power supply for any sign, leaking goo, slightly buckled cap bases etc.

Also, as tubenit suggested, remove the prior modification that you did just before the problem developed. If that doesn't resolve the problem then its probably the long hard road.

Spend some time on it, implement tubenits suggestions and then get back to us. One step at a time.

By the way, I really like the front panel artwork, how was that done.

All the best.
« Last Edit: June 13, 2013, 06:40:07 am by Glennjeff »

Offline tubenit

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Re: Please help me with my creation!
« Reply #18 on: June 13, 2013, 07:24:50 am »
Quote
374BX 200VA, 375-0-375 @ DC ma 175, 5VCT @ 3A, 6.3VCT @ 6A.

You have 10 preampish tubes .......... so I'm thinking maybe around 30 ma total or more presuming a LTPI?  

The 6L6's will be drawing maybe 140ma?

Your PT is 175ma.

I am wondering if your current draw is at the max or exceeding the specs?  That's probably not it but without a schematic,  we're really grasping at straws trying to help you.  It's kind of like diagnosing a car problem without knowing what kind of car it is other than having a V6 engine.
 :dontknow:

With respect, Tubenit
« Last Edit: June 13, 2013, 07:31:31 am by tubenit »

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #19 on: June 13, 2013, 12:12:15 pm »
Thanks guys,

I have swapped/subbed the entire area the spark occurred with known good parts.

I have already tried to undo what I did in the FX loop to where it was beforehand, that didn't work.

When I plug into the return of the fx loop, its a beautiful clean signal. (Telling me that everything from that point to the back end is good) If I send it to another device from the FX send, I get the noisiness.

tubenit, I asked my amp tech about this very thing, "Are we pushing this PT too much with all these tubes?" He said I was just about maxed out. Do tubes draw a specific amount of current depending on their type, or does it depend on things like what voltage you're running them at etc?? I'd like to actually know what I'm expecting from the PT also, and if this expectation is out of line.

I'm sorry, LTPI? I did a quick search and still didn't really get the gist of it. It's very easy to stump me on random things still.

I like Glennjeff's suggestion of breaking down all the blocks and searching that way. I'll start implementing that strategy next.

And thanks, the front panel was a lot of work! I found a font I liked, and plotted out the face of the amp on a program called Flexi 7. It's kind of like a CAD drawing program for sign shops that do decal and lettering work. Tried to match the yellow to the knobs with a shops in stock stuff, and had them run me off a few. I stuck them onto the chassis that was wet sanded and ready for clear. Had it cleared over the decals with automotive.

I know this power amp is essentially a Marshall with very little done to it, if at any. There are some parts of the schem that wont bother me to share, and this is one of them. As far as I know, all is good in the world of the power amp. This thing is a tank, it worked perfect with no issues both times that I built it.

Do I have an LTPI?...



Offline Glennjeff

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Re: Please help me with my creation!
« Reply #20 on: June 13, 2013, 12:27:44 pm »
Long Tail Phase Inverter, V8 and it's bias components.

Read about it here http://www.valvewizard.co.uk/acltp.html. I found it a bit of a brain tease.

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Re: Please help me with my creation!
« Reply #21 on: June 13, 2013, 01:31:42 pm »
Maybe Sluckey or HotBluePlates or PRR or Dummyload or someone who actually knows can verify this ............ Do 12AU7's draw more current than 12AX7's?  I am thinking they can handle more current?

I do think that the PT current capability could be an issue?  Can you pull around 3 or 4 12A_7 tubes and still play thru it?  IF so,  try that and report back.

Do you know how to safely jumper over sections?   IF so, try running V1a directly into the return of the FX.  Does that work?  Then add V1a & V1b into FX return. Does that work?  and so on

Your goal by jumpering and bypassing sections is to locate which section creates the problem?   And again, it may be there is too much current draw on the PT?  I don't know.

BE SAFE!!

With respect, Tubenit
« Last Edit: June 13, 2013, 01:51:10 pm by tubenit »

Offline tubeswell

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Re: Please help me with my creation!
« Reply #22 on: June 13, 2013, 03:31:59 pm »
What tubenit said. Eliminate parts of the circuit (one part at a time) with a high voltage .1uF capacitor to ground to try and see where the problem is occurring.

Other than that suggestion, I really aren't prepared to guess whats going on without being able to see the (entire) schematic.
A bus stops at a bus station. A train stops at a train station. On my desk, I have a work station.

Offline tubeswell

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Re: Please help me with my creation!
« Reply #23 on: June 13, 2013, 05:55:50 pm »
Do 12AU7's draw more current than 12AX7's?  I am thinking they can handle more current?

Both tubes draw the same filament current, but the tube current depends on the load. 12AX7s have more plate resistance and work better with larger plate resistors, and should not be used with less than about Ra = 47k, because the maximum plate dissipation rating is lower than a 12AU7. 12AU7s have lower plate resistance, and a higher plate dissipation rating, and therefore are capable of conducting more tube current. But if you use Ra = 100k with a 12AU7 triode, it won't conduct much tube current at all.
A bus stops at a bus station. A train stops at a train station. On my desk, I have a work station.

Offline DummyLoad

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Re: Please help me with my creation!
« Reply #24 on: June 13, 2013, 10:24:29 pm »
about the PI posted - in this case, Ib is around 7.6mA & the balance is wonky - about 28% out. R anode of inverting amp should be around 68K to maintain reasonable balance - IF this is truly a 12AU7 driven LTPI.

with 450V B+ one would expect Vbias to be in -53 to -55V range.

interesting NFB insertion point. usually it's inserted under the tail R.

have you tried disconnecting NFB loop? made sure secondary of OT is grounded properly? 

--pete

Offline PRR

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Re: Please help me with my creation!
« Reply #25 on: June 14, 2013, 12:45:49 am »
He's probably not overloading the PT. PT current-ratings are not drop-dead blow-up points. 200mA in a 175mA PT will sag and run hot. Life may drop a bit. It's not today's problem.

*milli*Volts on tube grids which "should be zero" are un-important. There's always some grid current, in or out. Tenth-volts are not uncommon. Worry when stray grid voltage becomes a noticable part of grid-cathode bias voltage. For typical g-amp circuits with 1V-3V across a cathode resistor, a tenth-volt is "huh?" but probably not a problem. A hundredth-Volt (10mV) stray grid voltage is beneath notice.

He states "ruled out that it is the power amp, or the FX loop. If I plug my guitar into the FX return, it’s a beautiful sparkly awesome clean signal". Therefore speculations on 28% unbalance in the phase splitter are "probably" off the mark. (However I have seen old filter caps +plus+ a 50% unbalance excite motorboating due to large unbalance in output stage sneaking back into input stages.)

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #26 on: June 14, 2013, 12:55:35 am »
I was going to work backwards from the mixer tube to see which stages I could reconnect before I got to the undesirable sound. The sound is there with channel 1 disconnected, as well as channel 2 disconnected. I did not pull tubes or B+ for this...

Dummyload;
It's been determined that the power amp, PI, and FX loop are known good. That is different about the NFB location, I agree. I'm not the actual creator, to I don't have an explanation for you. OT common is to the speaker jacks only.

I've also determined that this disgusting sound is inherent throughout the preamp, both channels.

Why is my standby switch loudly thumping when turning it into the OFF position occasionally?

New tonight, the color organ now hums like hell when turned on. It was always VERY quiet while in operation....

I was going to go through and make sure nothing above a nice ~15k rolloff was getting into the tubes. Only problem is I packed up my sig gen already. Somewhere. I'm moving at the end of the month, so this is going to have to take a back burner pretty soon.

I'll be up to some amp shenanigans this weekend, hopefully I at least get some sort of solid clue soon...

Thanks everyone, I appreciate all the help you've been giving me, even though I'm an outcast that isn't allowed to share much.

Who knows, I might break. But it'll be a while.

Offline DummyLoad

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Re: Please help me with my creation!
« Reply #27 on: June 14, 2013, 01:00:38 am »
Therefore speculations on 28% unbalance in the phase splitter are "probably" off the mark.

i made no statement that was the culprit, and for the record, it IS very unbalanced; i was simply pointing that out.

my thoughts are that this amp has RF/ultrasonic instability in the output stage. since reading the last post, he seems to have made some headway by isolation of the pre-amp ckt.

i should have know better than to chime in...  :dontknow:  

--pete

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #28 on: June 14, 2013, 01:18:04 am »
DummyLoad;

Never feel that way. I have actually noted your observation and it now exists on a list of tweaks and things I plan on doing/modifying/addressing after the amp gets restored to its former functionality. I appreciate it, thank you!

Offline Glennjeff

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Re: Please help me with my creation!
« Reply #29 on: June 14, 2013, 02:30:46 am »
DuumyLoad - It's probably got some really nice even harmonic distortion :icon_biggrin:

Meat_And_Beer - Disconnect the colour organ (whatever that may be). Forget about it, very secondary to the immediate situation.

Pull all the non PI/PA tubes except the one immediately before the last known working OK tube. Is that FX send, FX return or PI at this stage?

Standby switch may need a little thump filter on it. Not knowing how or where it is wired is a bit of a problem, but I'll get you some diagrams in a few minutes.

One simple step at a time.

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #30 on: June 14, 2013, 11:39:52 am »
There is actually a harmonic distortion characteristic at about 9k that's undesirable to me, think the two may be cause/result somehow?

I had the color organ (Blinking LED light ckt) disconnected for a long time while working on this problem, I cut its power and signal feed. It didn't make a difference, but I also don't know its there (Aurally) when its connected and in the "off" position.

I was wondering, how many tubes is OK to pull at once? Isn't that not a good idea to have all the pre's out at the same time for supply/load reasons? I could very well be worrying about a non-issue, also.

If I pull the mixer tube, V8 (PI is V9, FX is V10) everything goes dead silent. Flatline. Any other tube I pull one at a time (Aside from PI/PA) will usually drop its volume, but otherwise no effect.

FX Loop is the return, Send comes from a resistor ladder after the mixer.

Here's the supply. I thought the .1 across the switch was supposed to do that? Or would that be more like a 4M7 to gnd?
« Last Edit: June 14, 2013, 11:52:07 am by Meat_And_Beer »

Offline silverfox

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Re: Please help me with my creation!
« Reply #31 on: June 14, 2013, 01:31:58 pm »
Dear Swirling in Providence,

Your problem is not with the amp. Your problem is with the Guru! I'll let you in on my experiences and offer a solution to your enigma.

Having never spent much time in the learned halls of academia and like you pursued the dross-less path to Jedi-Tube-Sorcerer, primarily by way of self study, I would at times find myself enamored in the presence of that mystically speaking, (on purpose to enhance mystism), curmudgeon of knowledge that frequently is fall out of the corporate world due to the fact that: They don’t get along very well with others. The all knowing "Guru of Tube Nirvana"

Smart as H*ll they are very appreciative of your presence for reasons including, someone recognizes them for their brilliance-

My personal experiences with Gurus are basically positive but they definitely have their quirks and eccentricities. After a time you wake up one day and realize two things: The bizarre aspects of their behavior tends to drive you away- (The use of profanity is a common trait with them when they begin to diatribe their favorite injustices upon, presentation of a simple query). The falling out begins as your knowledge advances to the point of asking questions that result in long-winded answers ending with- I don’t know; either said or left to the interpretation of the hearer. Your experience may be different.

In reading your post you state the design is a secret and the Guru can’t fix it, paraphrased. In passing I wonder first if G. intends to build and market it or does he just want to keep it a secret? Big difference.

By the way- unless a product is doublesealed in epoxy and encased in a welded self destructing chassis the design will be fathomed in a matter of days upon release or by a technician that loses his authorization because he can’t pay the $10,000 service department license fee. There are no more secrets- Just ask the NSA.

Here’s what I think has happened and how to attempt to resolve it or ethically break free from your commitment to keep it a secret should resolution fail.

G. Doesn’t know how to fix it. Something has crossed the boundary of logical flow in the circuit. If G. won’t commit to fixing the design he got you to spend all the time and money on and G. won’t let someone else try to fix it and G. doesn’t intend to profit from the design of it- He should let someone else fix it. Has G. ever mentioned profit sharing if it became a smashing hit?

G. has an ethical problem.

I’m very busy cause we may have a nuclear war any minute so I’ll cut to the chase:

Go to your Guru and have a serious talk. Tell him diplomatically you have an expensive broken amp that he goaded you into building. In the process your going to find out what kind of integrity this person has; and the vibrations here will tell me some things too.

If, as you imply he is a close friend of yours he should either offer to fix it some way or let you divulge the schematic so that others may attempt to do so. What does it say if he won’t do either and your stuck with a white noise generator instead of an amp.

The amp concept you have placed before us is not unique and even an amateur as myself has already figured out what the gist is. A couple of posts ago someone else created a similar- Space Age: Tube Amp Design Laboratory. You’d have to be from the 60’s or so to get that one.

If the Guru won’t do any of the above, I think in the process you will learn something about his character and with a clear conscience you could probably send a copy of the schematic to one of our "Trusted Gurus" here for further analysis- In strict confidence of course.

Then, at least if they can't help you, at the end of it all, they'll tell you to bring it to a local service technician, i.e. Amp Guru.

Crazy as a Silverfox.

Offline Glennjeff

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Re: Please help me with my creation!
« Reply #32 on: June 14, 2013, 01:39:06 pm »
Usually there is a resistor in parallel with the capacitor on the switch, typically 220k on the ones I've seen.

In most circuits pulling the tubes shouldn't be a problem. The voltage to the output tubes might increase a bit but no dramas USUALLY. I would not have expected this to be a whole new way of hooking up tubes. WAIT for one of the more experienced folks here to confirm but I think you have to  do it.

OK, here is a step you should be comfortable with.

Remove the final tubes before the mixer in each channel, That is only removing two tubes, the last tube in channel 1 before the mixer and the last tube in channel 2 before the mixer. If you  pull these two tubes and the noise is gone, you have eliminated the mixer stage as a problem, one step in the right direction.

Everything going silent when you pull the mixer tube (I assume it mixes channel 1 and channel 2 together) is perfectly expected if the amp is ok when you bypass the pre-amp via the FX loop, because pulling the mixing tube does exactly that,  bypasses the preamp.

I do hope you are turning the amp off, removing the power cord from amp and discharging the caps with a 2k resistor on insulated clip cables with each step. Never be complacent when it comes to safety procedure. I got bitten by a charged cap a few weeks ago whilst doing some paid work for a studio. Left hand also. Not nice, not safe, I was concentrating on one section of the board and touched a power transistor that was waving it's little metal tag in the air where I was not looking.

Hope you enjoyed the lively rant from Silverfox as much as I did.
« Last Edit: June 14, 2013, 02:04:54 pm by Glennjeff »

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #33 on: June 14, 2013, 02:04:40 pm »
Silverfox,

You touched on some very valid points.

I've PM'd a couple people on here asking if they'd like to go over the schematic with respect to privacy. One very respectfully declined, another very nicely stated that I should go to hell because I wont post it publicly to the world. I can live with that, I have no hard feelings.

I've also contacted someone semi-local to me pertaining to this repair, awaiting his response.

We don't swear unless it's called for, but I know exactly the type you speak of.

The tech in question gets along great with others, is a super humble, honest man, has amazing academic credentials, not to mention a few amps in particular that would make some of you "Jimi Hendrix" fans wet yourselves and melt immediately afterwards. But I digress, and don't mean to overly defend him. But the dude is a total sweetheart.

It's not that he can't fix it, we just didn't have enough time for the problem at hand. We crossed many, MANY things off the list. Again, the amp WORKED, and something has given out or weakened. It's a search party for the faulty component(s), not an erroneous design.

Yes this is actually a simple build, thank you for realizing that. A lot of people get confused easily when there are too many colorful and shiny parts close together. Hell, I would too not knowing any better. This is my first build, you could say this is what I was brought up on so I'm none the wiser.

We have discussed producing these as one off's for those so inclined. Myself, personally, doubt that will ever happen, however.

Thank you for clearing the air on some of those things, I like your eloquence!  :thumbsup:

Glennjeff,

Yes, the mixer does just that. Mixes the two, or when they're in single mode, they signal passes through just one half of the tube.

I just tried pulling both last stage channels tubes. It's still there, so shall we suspect Mr. Mixer??? I saw a ckt VERY similar to the mixer in my amp in the RCA receiving tube manual. My book is in a box somewhere, so I can't double check it, but I'll throw the schematic for the mixer in my amp up here tonight when I get home from work in about 9 hours from now.

Thanks again folks!

Offline Glennjeff

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Re: Please help me with my creation!
« Reply #34 on: June 14, 2013, 02:16:27 pm »
Unfortunately, this is not sufficient evidence to press charges against Mr Mixer. Had the noise gone with that test it would mean Mr Mixer was definitely innocent. Now he is just a more likely suspect.

Are you in a position to measure all valve 8 resistors, measure/ replace capacitors, examine the socket and solder joints there.

If I were in that position I would then turn the amp upside down, ensuring that it was stable and could not topple and then, with those two valves still out, I would switch the amp ON and tap Valve 8 socket, pin/wire side, with a drumstick, sockets do go faulty.

I'm not suggesting that you should do this of course.

I still think you should pull all the valves prior to the mixer and see if Mr Mixer is culpable. V1 - V7 - GONE. Better make sure you know which ones go where, I can only count to five before the intense desire to start juggling them kicks in.

All the best.
« Last Edit: June 14, 2013, 02:49:28 pm by Glennjeff »

Offline sluckey

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Re: Please help me with my creation!
« Reply #35 on: June 14, 2013, 03:29:13 pm »
I've PM'd a couple people on here asking if they'd like to go over the schematic with respect to privacy. One very respectfully declined, another very nicely stated that I should go to hell because I wont post it publicly to the world. I can live with that, I have no hard feelings.
I guess the one that respectfully declined is Tubenit. That's just the way he is. He would never tell you to go to hell, or even express that about you when talking to someone else.

So that leaves me as the accused one that stated you should go to hell??? Well, I'm surprised you got that from my short, direct response to your PM request. Maybe you're just lying about that part. In my defense I'll just quote our entire PM conversation...

Hi Sluckey,

I sent Tubenit a pm asking if he'd be willing to look over my schematic if he thought he might be able to shed some light for me. He recommended I ask you.

My amp tech has been less and less apt to get back to me in the last few months. He has cancer, doesn't eat or sleep much. (He also smokes a lot ) I worry about him all the time. I thought it might be time to get a fresh outlook on this, so I came here.

I don't want to give you a sob story, I just would like to ask you if you'd be interested in seeing what's actually under the hood of this thing. Questions like, am I asking too much from my PT?, and, is the 6AU6 introducing oscillation because of its design characteristics? are some of my main concerns.

Of course, as I've mentioned, I'm still very green. About 1 and a half years experience is nothing, in the grand scheme. I try my best, I have good fabrication skills and hands, I am a quick learner and all, but I have a looong way to go.

I mean no disrespect at all withholding information that would surely expedite this resolution that will surely come eventually. These are his wishes, and I owe it all to him, I'm just being honest and trying my best to keep my word. On that note, if you agree to look over the schematic, all I ask is that you please just keep it to yourself.

I know there are a lot of very trustworthy and super knowledgeable people on here, and I'm ready to expand my horizons. I'm in this for the long haul, I just starting out is all.

Thank you in advance, I look forward to hearing from you. All the best!  

Chris

And I quickly replied...
I do this stuff as a hobby. But I only do it in the open forum.

You have asked this public forum to help you, but you can't provide the single most important piece of info that might fix this Rube. Without a schematic, everyone would only be making wild ass guesses and blindly shooting in the dark. When PRR says "I dunno what to say. Not even where to start.", that pretty much sums it up.

I think you may have to fix it yourself. I suggest you put on a blindfold and start probing.
« Last Edit: June 19, 2013, 05:56:14 am by tubenit »
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline tubenit

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Re: Please help me with my creation!
« Reply #36 on: June 14, 2013, 04:10:31 pm »
Chris,

Sluckey has been one of the most generous and gracious individuals on the forum in helping others. He is superb!  I consider him a friend and he has extended a remarkable kindness to me personally for yrs over this forum (and in person when I met him once)

He easily holds the record for helping me with both real (within normal limits) challenges in amp building and finding my total goof ball mistakes. Sluckey has always been forebearing and patient with me.

Conveying that he politely told you to "go to hell" just doesn't fit who Sluckey is or the generousity of his time, help and information.

A number of us have commented on the extreme and even severe difficulty in helping you without a schematic. And we've supported you keeping your word to not share the schematic.

The norm is people post schematics and as a community we try to help the poster.  You've asked something extraordinary in wanting help within the confines of no schematic.

You've excercised limits in what you can bring to the table so how about honoring the limits that others bring in what they will or will not bring to the table?

I suggested you contact Sluckey because he is waaaaayyyyyyyyy smarter than I am and I wasn't sure I could help even with a schematic. 

It is perfectly reasonable and appropriate if Sluckey sets limits for private help & is willing to only help thru a community effort.  That's his choice and I don't think he should be portrayed as being unkind for a very reasonable and legitimate choice. 

With respect, Tubenit

Offline Willabe

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Re: Please help me with my creation!
« Reply #37 on: June 14, 2013, 04:42:13 pm »
And I quickly replied...
I do this stuff as a hobby. But I only do it in the open forum.

That's not telling you "go to hell".   :laugh:

Sluckey has been one of the most generous and gracious individuals on the forum in helping others. He is superb!  I consider him a friend and he has extended a remarkable kindness to me personally for yrs over this forum (and in person when I met him once)

It is perfectly reasonable and appropriate if Sluckey sets limits for private help & is willing to only help thru a community effort.  That's his choice and I don't think he should be portrayed as being unkind for a very reasonable and legitimate choice.


All of what Tubenit said in his last post IMO is right on the money. Sluckey just want's everyone here to benefit as a group and that's more than fair.

You have 29 knobs and 15 switches on that amp and you say;

Yes this is actually a simple build, thank you for realizing that. A lot of people get confused easily when there are too many colorful and shiny parts close together.

So the guys are confused because they need a road map for the 4 miles of wire and component connections in your build?    :w2:

Sorry but you painted yourself into a corner with your guru. I don't see how it's fair to ask help with fixing a top secret design that has 29 knobs, 15 switches with out a schematic.

And they still tried to help you.


               Brad     :l2:    
« Last Edit: June 14, 2013, 05:17:32 pm by Willabe »

Offline TIMBO

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Re: Please help me with my creation!
« Reply #38 on: June 14, 2013, 05:19:15 pm »
Hi MAB, "PLEASE HELP ME WITH MY CREATION" is your REQUEST of this FORUM and HELP is here to be given.

I will not RANT at you as I am not I a position to do so, I am a carpenter with NO electronic training at all but I have a passion for music and old electronic stuff and this is my driving force behind my "cupboard of it almost worked" builds.

There is a lot of stuff in there because the builds I have been doing are usually bits and pieces of other amps that are CUT and PASTED to make a SCHEMATIC and me thinking that this will work  :dontknow:

I was pointed in the direction of this forum by the guy's at TUBEDEPOT and I have never look back.

After being on this forum for a some years now some of my creations are still not flying but the one thing that stands out is that with EVERY build that I do I am getting closer to the "ONE" the "ONE" being the amp that will make my CRAPPY guitar playing sound as good as my FAV player, Mr. Gary Moore.

When you talk you leave me  :w2: because you sound like you have a good grasp on this electronic stuff, far more than i'll ever have.
You are lucky the have this guy to bounce stuff off and to have a PLAN for the "ONE" and I assume that this is the "ONE".


DO you PLAY guitar??????

You are the one that is outlaying the money and time to this amp and if you play guitar you really should be building or learning to build the amp that will serve you and perform to YOUR needs!!!

I have built some of the creations born on this FORUM and once built they sounded great BUT they were not to MY liking or style of playing. I was not bummed by this as these builds are a platform for other builds not only when it comes to the actual circuit but EVERYTHING that goes into building VALVE AMPS and there is a lot.

AS for your SCHEMATIC, I too believe that it should be kept under wraps as requested by your friend. You just might hold the secret that puts the amp building world on its ASS (Please don't that that comment as being derogatory)

AS I said I pick parts from other amp builders (mainstream builders Marshall, fender etc.....) because they work but by plugging each bit together doesn't mean it will work without some considerations and what they are depends on everything  :think1:

I even looked at some local builders as their builds relied on what parts were on hand and some ideas they had were really OUT OF THE BOX or were they  :dontknow:

What I am getting at is that i'm sorry if I say the wrong thing but I don't think that what you have on paper is in any way NEW, VALVES have been around for a very long time and it think that they have been USED AND ABSUED in every way possible.

This is what you should DO,strip it back to a basic amp with preamp(one channel that you are most likely to like and delete any bells and whistles) PI and power amp. This is the basis of all amps and tweak it and play it to see if you like it and if there is no problem then build onto it in stages.
I would think that the base amp is nothing new so posting a schem should be ok if there is a problem.

I wish you luck on this build and I hope YOU get what you want out of it, because this is what we are all here for.  :icon_biggrin:

Offline Willabe

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Re: Please help me with my creation!
« Reply #39 on: June 14, 2013, 05:35:21 pm »
I was looking at your photos and with the amount of shielded wire you are using you could have easily melted the insulation for the inside conductor and it's shorting out to the shield. It has happened before to the best of them.

Does the shield have clear insulation on it or is it bare? If it's bare it could have shorted out something.


                  Brad        :think1:

Offline HotBluePlates

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Re: Please help me with my creation!
« Reply #40 on: June 14, 2013, 05:43:46 pm »
... We crossed many, MANY things off the list. Again, the amp WORKED, and something has given out or weakened. It's a search party for the faulty component(s), not an erroneous design.

It's very rare for a new build to have any part that "gives out".

I just tried pulling both last stage channels tubes. It's still there, so shall we suspect Mr. Mixer???

Quote from: Meat_And_Beer
If I plug my guitar into the FX return, it’s a beautiful sparkly awesome clean signal that I could listen to for days. The return pot has tons of headroom to boot!

I agree at this point with Glennjeff that the problem is probably between the mixer input(s) and the grid of the output tubes. I looked at the "Two-Channel Audio Mixer" in the RCA Tube Manual and note that there is a chance that the way it's connected to the new FX loop may be an issue. Really, the mixer is a little over-built for what you're doing.

As for the spark/pop, you have to assume a stray piece of wire got in somewhere, or there's unintended contact from a high voltage point to a "groundish" voltage.

In a future build you may want to stay away from the Gibson-style shielded wire, as the bare shield offers an excellent opportunity for unintentional short-circuits.

I think you'll also agree that it's easier to visually troubleshoot an amp for a wrong connection (the cause of maybe 90% of new build problems), and make good connections in the first place, if the layout is not so dense in areas.

But before you think I'm jumping on you, I must congratulate you on the fact the amp worked at one time! My first electronics build was an over-complicated distortion pedal that never did make a sound other than motorboating.  :l2:

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #41 on: June 14, 2013, 11:52:45 pm »
The first words out of my mouth is an apology. Sluckey, I didn't mean to pose you as a bad person at all. I surely wasn't about to call you out as such openly, either. What I got from your "That's too bad" regarding my not having permission to post the schematic as, Ohp, well tough $#*&, kid. Your quick, short response to my email also felt very sour. This is how I came up with what I said, judging by my intuition, and reading between the lines as they say.

Suggesting I put on a blindfold and start probing is pretty mean, just for the record.

I don't know you, and I may have taken these statements the wrong way, and even way out of context. If I have, I do sincerely apologize. I have certainly made bigger mistakes in my life and unfortunately it wont be the last.

Chris

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #42 on: June 15, 2013, 12:30:20 am »

So the guys are confused because they need a road map for the 4 miles of wire and component connections in your build?    :w2:

Sorry but you painted yourself into a corner with your guru. I don't see how it's fair to ask help with fixing a top secret design that has 29 knobs, 15 switches with out a schematic.

And they still tried to help you.


               Brad     :l2:   

       

When I said, yes, this is actually simple, I picture it all out in my head easily. I've been dripping sweat and solder over this amp for a while now. I mean no degradation to anyone by saying that! I knew it was going to be taken wrong, and it's completely my fault for wording it that way. Imagine a single channel 50w amp with 5 gain stages. Not too bad, right? Well this one has another preamp shoehorned in there, and you can switch em. A mixer gets them both going simultaneously if you want, and there's an FX loop... And some other crap..

Okay. Its complicated.  :lipsrsealed:

I certainly hope I haven't painted myself into a corner, I'm trying to do the exact opposite, break out and get feedback. The little info I've given so far has already gave way to possible anomalies that could be upgraded. ie, the PI being 28% out of whack as previously mentioned.


When you talk you leave me  :w2: because you sound like you have a good grasp on this electronic stuff, far more than i'll ever have.
You are lucky the have this guy to bounce stuff off and to have a PLAN for the "ONE" and I assume that this is the "ONE".


DO you PLAY guitar??????


Timbo, the only reason I have anywhere near the grasp I have on this stuff (And please believe me when I say it is VERY limited) it's because of the man I started interacting with regarding this build. I am beyond grateful, and hope to attain much more knowledge in the very near future. I will not stop working on these things, "hooked" isn't even the term for it anymore!

I have been playing the guitar for JUST shy of 20 years, I'm 32. Going into this project, each preamp channel, and the power amp were prototyped. The pre's were developed, mulled over, messed with, they shocked the shit out of me numerous times because I'm a newb, and I almost killed an ocilloscope with the headstock of my guitar when I let go. They've been played into with a million guitars, out to other power amps and speaker cabs.. That's it, I'm going to post pics.

I finally got my million dollar sound. MY sound, to MY ears. It's in the top row of this amp, and I cant wait to show it to everyone. The bottom row, is amazing also. Voicing is different, spectrum & versatility is in a totally different direction than the other. This is what MY ears told me, this is when I said, "OK, we have a final schematic for this bad boy."

And I never would have gotten to where this thing is, without help, and extreme determination.

Offline Glennjeff

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Re: Please help me with my creation!
« Reply #43 on: June 15, 2013, 12:42:40 am »
So Meat_And_Beer

Have you pulled tubes 1 to 7 and tested the sound yet.

Given that you have most inadvisably had the shit shocked out of you on a number of occasions I take you have learned safe operating procedure. Oh, by the way, you have to be careful with older tech oscilloscopes, they have a floating ground so if you have the test lead ground at a point on the amp that is high tension, you can get shocked by touching the oscilloscope.

NEVER work on the amp with a guitar strapped on - NOT EVER.
« Last Edit: June 15, 2013, 12:58:37 am by Glennjeff »

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #44 on: June 15, 2013, 01:45:08 am »
Hi Glennjeff!

I just pulled all tubes before the phase inverter. Leaving in the PI, FX loop, 5U4 and 2x 6L6. The unstable ground swirl is still there. Engaging the FX loop actually gets rid of it to a degree, but it still exists, but in a much more minor degree.

With FX tube pulled and FX loop switched off, it's still there in the "minor degree" present. With it switched to "on", there is nothing. Though, I could only assume that to happen anyway.

 :icon_biggrin: Yes, I have learned and re-learned the safe practices in these big voltage meanies. Thing is, when you learn something, it really takes it coming into actual reality why you should remember it in the first place! Or conversely, (Hopefully) just a reminder. The headstock almost into the scope incident was a first time learning for me... I didn't factor in that my hand on the strings connected me to ground. The "One hand rule" was out the window, little did my other hand know....

I like your last line!

So Meat_And_Beer
NEVER work on the amp with a guitar strapped on - NOT EVER.

In other business, I mentioned earlier, accusing the mixer. At work, of course, I was thinking about it all night. As well the post from SilverFox because that was excellent, and makes me chuckle just thinking about it..

A previous test previously mentioned, If I feed stage ONE to a known good amp. I hear the unhappiness of something somewhere. Now that is without disconnecting coupling caps or supply's. If I get unhappiness from stage one, and also so from the mixer, then I suspect anything from either channel, stage 1 and beyond to the PI. But c'mon!

WHAT could be cross-talking/leaking signal/causing ground insanity.  :BangHead:

Offline Glennjeff

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Re: Please help me with my creation!
« Reply #45 on: June 15, 2013, 02:33:19 am »
Great, we've made some progress. This is a pretty sure sign that there is something wrong in either FX, PI, PA or PS.

Leave all preamp tubes out and fix the problem as it now exists and you may be in luck.

Remove the cables that "sent to" and "receive from" the FX loop from the main circuit board, remove the FX tube and make a jumper from the board between "send to" and receive from", in other words temporarily get the FX circuitry out of the way, as if it was never there. Then retest.

I am assuming that the signal goes to FX before it goes to PI. It would be really weird to have the FX send after the PI. If the FX is after the PI, which your description kind of implies, then get back to us before you try that.


« Last Edit: June 15, 2013, 02:52:41 am by Glennjeff »

Offline Meat_And_Beer

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Re: Please help me with my creation!
« Reply #46 on: June 15, 2013, 02:39:18 am »
As promised, here is the mixer CKT. I'm tired. But, tomorrow is amp day for me.  
« Last Edit: June 15, 2013, 09:52:16 pm by Meat_And_Beer »

Offline sluckey

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Re: Please help me with my creation!
« Reply #47 on: June 15, 2013, 04:55:36 am »
Suggesting I put on a blindfold and start probing is pretty mean, just for the record.
Not mean. Just plain stupid. How in the world could you possibly work on a complicated piece of gear that you cannot see?

Oh wait a minute. That's what you asked the forum to do!
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline tubenit

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Re: Please help me with my creation!
« Reply #48 on: June 15, 2013, 05:53:52 am »
Chris,

Sluckey is a very good hearted guy and you significantly misunderstood him.  He is not unkind, just straightforward.

Regarding your mixer ........................

I've never seen anything like that before. IF you had given me the entire schematic, I think I would be at a loss to know whether something was designed correctly or not.

Try this ...................  use two 470k mixing resistors as a way to mix those two channels and bypass the "mixing tube".
See if that resolves the problem.  IF it does, then the issue is the mixing tube.


With respect, Tubenit
« Last Edit: June 15, 2013, 06:01:08 am by tubenit »

Offline HotBluePlates

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Re: Please help me with my creation!
« Reply #49 on: June 15, 2013, 06:58:19 am »
As promised, here is the mixer CKT.

Regarding your mixer ........................

I've never seen anything like that before.

I hadn't either, and had to look twice at it because I expected something different. What I think I see is a fixed-bias unity-gain mixer, using the grids of a dual-triode to isolate the two input circuits while mixing their outputs at the shared plate load.

But... if that is correct, then there should be no bypass cap across the 47kΩ cathode resistor; that's because the only valid reason to make that resistor so large is to insure the mixer provides a gain of just less than 1, or said another way a stage that only mixes.

What I thought you referred to was the below circuit from the RCA tube manual. It is cathode-biased and uses the grids of a dual-triode to keep the two input channels from interacting. However it uses resistive mixing at the output. Like Tubenit showed, you could skip all that and just use the resistive mixing, which is the approach used in the overwhelming majority of guitar amps.

In the end, at least this mixer may be "too clever," as a lot of unnecessary parts are present providing many extra opportunities for something to go wrong.

 


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