First Build Problems- KLD kit Build

[shooter]

(Assuming in a known good amp)
probably, B+ is a missing element
I like to monitor while playing hard since PP tends to go somewhat current crazy when pushed, so what "appeared" ok at idle might be to much at full roar


for this thread, i'm still not convinced the test equipment, or methods, isn't a contributing "issue", besides the issue with V4

[imgumby001]

(Assuming in a known good amp)
probably, B+ is a missing element
I like to monitor while playing hard since PP tends to go somewhat current crazy when pushed, so what "appeared" ok at idle might be to much at full roar


for this thread, i'm still not convinced the test equipment, or methods, isn't a contributing "issue", besides the issue with V4

Look, I couldn’t agree more! There’s no arguing I’m a complete rookie. I appreciate the “schooling” I'm receiving from you guys. There’s no possible way I could have figured any of this out without y’all. That being said, I’m trying real hard not to be an idiot, and I genuinely want to be good at this and fully understand how to do this on my own. Hell, I’d like to one day be good enough to help other rookies!! Tonight I’ll take a photo of all my test equipment so you can see what I’m using. As far as the implementation of the tools, user error is definitely a reality.

[jammied]

Something has gone afoul. Maybe retention and clean the tube sockets?


IF the 387v on pin 3 (the plates) is correct?


Here are 70% numbers for bias


6p3s= 36.2ma
5881 23watt=41.6ma
5881 26watt=47ma
6l6gc 30watt=54.3ma


Just trying to learn something. So a true 6l6gc shouldn't red plate? Or a 5881wxt+ 26watt tube. According to his measurements. But a 20 watt tube very well could be?

I'm not doubting Sluckey he for sure knows what he is talking about. I'm trying to understand how increasing the negative voltage is going to stop the red plating? The plate voltage and ma across the 1ohm resistor is showing they should be within range. Or maybe on the cold side?

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The more I think on it, it seems to me my initial mistake was not identifying the correct tubes in the first place. I’m going to order a set of GC’s AND a set of EL’s and see where we land. I think Slucky’s real point was it’s time to do SOMETHING different as we’re not really getting anywhere at this point with the current setup. Makes sense in my head anyway!

[2deaf]

So a true 6l6gc shouldn't red plate? Or a 5881wxt+ 26watt tube. According to his measurements. But a 20 watt tube very well could be?

I'm not doubting Sluckey he for sure knows what he is talking about. I'm trying to understand how increasing the negative voltage is going to stop the red plating? The plate voltage and ma across the 1ohm resistor is showing they should be within range. Or maybe on the cold side?

Let's say an amplifier is running at 400V and it has an OT with a 4K primary.  With the proper screen voltage, a 30W 6L6GC will work fine in this amplifier.  It will operate above the maximum dissipation for part of the positive signal swing, but not that much above and there is plenty of time when it isn't above maximum dissipation. 

Installing a 20W tube and leaving the idle at 21W will cause that tube to run above its maximum dissipation for the entire positive signal swing and to exceed the maximum by up to 20W.  If the tubes are borderline red-plating, decreasing the idle current can give them a little more time under maximum dissipation and just might hold off red-plating.  Or not.  Idling clear down to Class B is not a viable solution and it might not prevent red-plating, anyways.

The real problem is that the 20W tube needs a higher OT primary impedance and/or a lower HT voltage so that the time spent above maximum dissipation and the magnitude of the excess is reasonable.


 

 

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Let's say an amplifier is running at 400V and it has an OT with a 4K primary.  With the proper screen voltage, a 30W 6L6GC will work fine in this amplifier.  It will operate above the maximum dissipation for part of the positive signal swing, but not that much above and there is plenty of time when it isn't above maximum dissipation. 

Installing a 20W tube and leaving the idle at 21W will cause that tube to run above its maximum dissipation for the entire positive signal swing and to exceed the maximum by up to 20W.  If the tubes are borderline red-plating, decreasing the idle current can give them a little more time under maximum dissipation and just might hold off red-plating.  Or not.  Idling clear down to Class B is not a viable solution and it might not prevent red-plating, anyways.

The real problem is that the 20W tube needs a higher OT primary impedance and/or a lower HT voltage so that the time spent above maximum dissipation and the magnitude of the excess is reasonable.


 

 

Thanks 2deaf! Some 6L6GC’s are on the way, along with some EL34’s just in case the 6L6’s don’t sound to my liking. The pn3p tubes were an inadvertent mistake.

[jammied]

So if the voltages were as advertised on the power transformer 360v b+ that may have ended up with 350v or so on the plates.


Then the 20watt 6p3s  may have worked fine?


Well I ordered a pair of the 6p3s to try. But I have been using the 8k primary classic tone 18watt marshall transformer

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I don’t have the schematic in front of me, I can’t remember what the it’s primary resistance is. The 6n’s will still serve me at some point, I didn’t hate the sound coming out of them. I’d really like to finish this project, I’ve got four more right behind it!! ;)

[jammied]

Supplied transformer is 3.4k


My gut instinct thinks your going to have to swap bias resistors to get above 50% with the el34's or 6l6gc.

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That just seems crazy to me that they would mess the schematic up that bad. The only real test is to do it and see. Got nothing better to do tomorrow. I’ll swap them in the am and post my voltage results.

[jammied]

Dont know if I would get crazy just yet the may be fine.


I was just blabbering my thoughts.


I have 2 sets of nos 6v6's one rca and the other jan sylvania I think? And 2 sets of 6l6gc, a set of el34's and a set of 6l6gb


The 6l6gb's biased fine stock as did the jan 6v6's. All the others I had to change the bias resistor.

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You blabber away bubba, it helps me get my schemes in order!!! I’m going to try it just to see. I won’t have the other tubes until the end of next week. Besides, it’s no big deal to put back whatever I change!!

[jammied]

Right on


Just remember to be careful with those pcb traces. All master model Marshall's that I know of had PCB's out of the factory but they were a little more forgiving

[Raybob]

V4-34mA
V5-48mA

Those are take with the little meter.

Ok I'm trying to learn something here so dont get me wrong .


If the bias meter used here is reading correctly.   Shouldn't these numbers be within range for 6l6 tubes?

No.  -34v is not in the range you were given by Sluckey earlier.

[2deaf]

No.  -34v is not in the range you were given by Sluckey earlier.

That's pretty funny and everything, but I don't really think that it's cool.

[jammied]

I understand that. I was saying 34ma or 34mv across the 1ohm resistors.


2deaf cleared the matter up with the graph and explanation.


Normally a 20watt max tube such as the 6p3s would be completely fine at 400v and 34ma dissipation 400v and 48ma bias and a 20watt max is over max.


As stated 2deaf cleared up why the 20watt max tube could still be red plating while still operating within it's safe dissipation range.


I respect sluckey and know he knows what he is talking about.


I wanted to know why it would matter. Give a man a fish and you feed him for a day but teach a man to fish and feed him a lifetime..... I wanted to learn how to fish so to speak.


Now after 2deaf give the example I'm getting some bait.

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This morning a paralleled in a resistor with R51 to see what difference I could get on the red plating front. It made a definite difference, I just chose too low of a value for a significant parallel adjustment. I also pulled all the low grade shielded wire off the inputs and pots and replaced it with some nicer coax. I triple checked all the values of the components on that board, and they all checked out good. The presence pot still does nothing. The really sounds terrible at high gain/volume. The red plating is present still, but dramatically reduced. I’m hopeful, but really not happy with the job I’ve done so far. At least I’ve learned a lot.

[jammied]

Still v4 red plating? Even if swapping tubes?

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I didn’t swap today, but, as of last test, yes. The order from nesstube won’t be here till probably Wednesday, so, I’m working with the 6n3p’s still. Side note, I’m very lucky. I wasn’t aware, as in I didn’t know, that 6L6’s could be a problem if they’re actual 6L6’s. My Sylvania brand tube is an actual 6L6. I’m lucky in that I didn’t melt it down.

[jammied]

Have you tried swapping the green and yellow out put transformer wires?


Maybe unhook the presence control wire. Or retention the tube sockets. They may not be making good contact.

[jammied]

Ok ..... my 6p3s tubes arrived . The one tube did the blue electron glow also.


So I did the sluckey mod by swapping the resistors. Now mine had a 22k in it instead of a 27k.


Now I get a range of -47.8 to 59.3


Haven't tried the tubes again that was with no tubes in the sockets.


I believe sluckey was shooting for -40 to -55 range.

[jammied]

I didn’t swap today, but, as of last test, yes. The order from nesstube won’t be here till probably Wednesday, so, I’m working with the 6n3p’s still. Side note, I’m very lucky. I wasn’t aware, as in I didn’t know, that 6L6’s could be a problem if they’re actual 6L6’s. My Sylvania brand tube is an actual 6L6. I’m lucky in that I didn’t melt it down.

I dont know anything about ness tube but on there website they show nos sovtek 6l6gb's and state they cant be used in a 6l6gc amp. But the picture is clearly of 6p3s tubes!


So I looked at their new production tubes and they have ness 6l6gc's again the picture is clearly a 6p3s.


I have been running the 6p3s with bias resistors in normal positions with the following voltages and no red plating.


Pin 1= 35.2mv


Pin 3= 384v


Pin 4= 355v


Pin 5= -33.5


No red plating at all. But have the blue glow. Now I studied that on the net and. It seems that it may very well be fine. Dont know? But that's the word on the net

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How does it sound?

[jammied]

I like them.


Really brings out that steely wooly sound. And let's the brassy ringing strat bell tone come through. Kinda different not really bright . Hard to explain. Jtm45 is based on the bassman and known to have flubby bass but these tubes tighten that up.


Definitely got that hendrix marshall thing going on. Humbuckers and some knob tuning and its into ac/DC territory.


So they let the guitar sound like the guitar being played. Where the other tubes I tried always colored the tone or exaggerated bass or treble. The only other tube I tried in it and liked better were the old original sovtek 6l6gb(not the ones mess is selling)


I played the heck out of it. And no problems so far

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Just to be clear you DID swap both bias resistors, or no? And, what are the values of those resistors in you amp?

[jammied]

Originally I left them like in the schematic . Where your are 27k and 15k. Biased to 13-14 watts. Had blue glow but no red plating . Then swapped the two resistors around opposite from the schematic and could only get 7.5mv bias. But very little blue glow.


I ended up swapping back to the schematic placement. And left it there and been playing no problem. No red plating. I really like the sweet pick attack on these

[imgumby001]

Copy that. I’ve now swapped mine and get relatively little voltage to work with. Obviously there’s no red plating. It’s late here, and everyone is in bed, so I can’t crank it, but, clean seems very friggin clean at low volume. Dirty is awful. Even at low volume, when I crank the gain to full there’s a terrible noise generated by the speaker, almost a grinding. Is this oscillation? I’ve just swapped all the preamp tubes back to the brand new shuagang’s(sp?). I’m about to do some low volume work and see how that sounds...

[imgumby001]

What I’m noticing is at full gain, at any volume save all the way down with the master, it’s terribly crackly and buzzy, just awful. But if you roll it back just a bit it clears up, and your left with good tone. It’s and alpha pot, but, bad pot maybe? The Chinese preamp tubes sound fine. I guess the real test will be in the morning when I can come out and blast the volume and see if it will red plate. I’m guessing by your (jammied) findings it’ll be a no.

[jammied]

To bias them plug in your bias meter and also take a pin 3 voltage reading .


From your previous voltages it looks like the higher voltage on pin 3 was 387v start at about 32ma.


Be sure to check each tube on pin 3 . If you start getting over 36ma to 37 ma . The chance of red plating increase. So for purposes of this test neither tube with your bias meter should be set higher than 36ma. 14watts is close to 70% of the 6p3s

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I can’t even approach that with the current config. I’m maxing out at about 29ma. Pretty dramatic shift. Here in a bit I’m going to go play it and keep the mA meter attached so I can monitor the max voltages reached. It’s just a curiosity, but I’d like to see where it goes. Maybe it will be playable, I guess we’ll see.

[jammied]

What is the pin 3 voltage on each tube (with tubes installed)? Also are both tubes at 29ma?

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Sorry, I was testing to recall from last night. Standing here fully cranked it’s only producing 20mA to the hot tube(red plater), and right at 10mA to the cool runner!! Pin 3 voltage for v4 is 399.4vdc, and v5 is 399vdc straight up. I’m think what I’m seeing is definitely under powering these, and if I were to want to run them I’d need to swap the 27k now in r51 position for say a 22k-ish. Does that sound right?

[jammied]

R51 should be a 15k and r55 should be a 27k according to the schematic?


That's what they need to be.


But with the voltages the power transformer puts out you dont want anything over about 36ma to 37ma on either tube

[jammied]

If you cant get enough ma on the bias probe with r55 being 27k up it to 33k. And leave r51 as 15k for now

[shooter]

20mA to the hot tube(red plater), and right at 10mA to the cool

I don't think one side should ALWAYS be higher, randomly yes, but consistently over many tubes tells me there's something not right there.


If the amp has NFB remove and retest current
IF no change, leave NFB off and swap OT primary leads and re-test

[jammied]

Guess he could put the tube that is in v4 into v5 and vice versa just to be certain. Whether it is the tube or the socket.


I think the out put transformer primaries need swapped. Just my personal thoughts.


But with the voltages the power transformer is producing. 36ma is way plenty current on the 6p3s.


Even changing to 6l6gc or el34 . The bias voltage isn't going to allow for biasing

[imgumby001]

20mA to the hot tube(red plater), and right at 10mA to the cool

I don't think one side should ALWAYS be higher, randomly yes, but consistently over many tubes tells me there's something not right there.


If the amp has NFB remove and retest current
IF no change, leave NFB off and swap OT primary leads and re-test

Sorry, NFB?

Guess he could put the tube that is in v4 into v5 and vice versa just to be certain. Whether it is the tube or the socket.


I think the out put transformer primaries need swapped. Just my personal thoughts.


But with the voltages the power transformer is producing. 36ma is way plenty current on the 6p3s.


Even changing to 6l6gc or el34 . The bias voltage isn't going to allow for biasing

Ok, gonna swap the ot leads and retest. Here’s hoping for an awesome outcome!!!

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Swapping the ot leads leaves it sounding lifeless and probably the worst it’s sounded so far. I’m going to go out on a limb and say they were probably landed on the right points to begin with. But, I still have r55 and r51 swapped, so, should I swap them back and retest BEFORE I swap the ot leads back? The mA range seems to have remained the same for both power tubes.

[jammied]

Did the presence control work? I would go ahead and swap the resistors

[shooter]

Easter eggs keep getting added to the hunt, not good for Tshooting.


1st decide if 2X the current is "normal"
IF not
you need to make 1 change and verify, and note what you did (tube A still 2X I)
pull A install tube B (no change)....all tubes 2 X when in V4 position
Move on
swap OT primaries - done


there has to be a logic to the method otherwise it's just monkeys and darts

[jammied]

Agreed 




And it will never stop red plating if running a 20watt max tube at 19 watts idle.


The biggest problem I see right now is improper bias.


Change one thing at a time. Swap the tube from v4 to v5 using the pair he has in it right now

[jammied]

V4-34mA
V5-48mA

Those are take with the little meter.

Then 2 posts later he swapped the tubes between sockets and the v4 and v5 number were the opposite

[shooter]

improper bias.

the bias goes to both tubes from the same "source", but one side is reacting different than "normal"
so bias is probably a symptom of the problem


so set the bias max neg and leave it for now  (guitar playing is down the road)
next verify every tube in both sockets - logically, with labels and notes and currents
then we've eliminated "bad tubes"  (kinda for now)
that leaves "why V4"
output were swapped
so
swap inputs
un-do everything V4 and re-do
.........
10mA at idle isn't the end of the world, actually pretty normal i'm thinking


once that's all checked n verified
then set bias for 12-14W and evaluate with guitar and monitor current
if current is good and guitar sound sucks, Then we move left 

[jammied]

After swap-

V4-48mA
V5-33mA

Values are approximated due to the way the meter is numbered. I think it’s pretty close though.

This post is after the two tubes between sockets. 48ma at the plate voltage is like running a true 6l6gc at 72ma at the same voltage.


It clearly followed the tube in this test.


But yeah eliminate as many variables at a time as possible.


Shooter knows and we are both getting at the same thing only in different ways

[imgumby001]

Did the presence control work? I would go ahead and swap the resistors

Yes, it seemed like it did respond after the ot primary swap.

Easter eggs keep getting added to the hunt, not good for Tshooting.


1st decide if 2X the current is "normal"
IF not
you need to make 1 change and verify, and note what you did (tube A still 2X I)
pull A install tube B (no change)....all tubes 2 X when in V4 position
Move on
swap OT primaries - done


there has to be a logic to the method otherwise it's just monkeys and darts

I’m going to go down shooters list above and try to figure all these aspects- after I return the resistors to the correct placements according to the schematic. Yes?

[jammied]

Good news!

[imgumby001]

Resistors are swapped to schematic. Voltages read as they were. Socket evaluation yielded no issues. Tested all three pn3p tubes in v4&5- original cool tube and replacement tube w/broken key read near identical- hot tube reads approx 8mA higher in both sockets. Did NOT return ot wiring - warmed appropriately and played- max vol/max gain- on lowest bias setting NO red plating, even on hot running tube- volumes seem louder/punchier, despite being very, very over gainy- will swap to vintage pre amp tubes from Chinese high gain tubes after recording all voltages- removing mA meter from power tubes as it seems to be effecting overall tone. Ya...

[imgumby001]

So, I think it finally happened...(sniff, sniff). It finally...


Sounds RAD!!!! Who would have guessed a properly wired, and biased tube amplifier would operate properly??? Looks like the original issue was the improperly wired pentode/triode switch, then the incorrect rewire, and then improperly biasing. My list of thank you’s is very long, but if you helped me on this project I can’t thank you enough. Fortunately for me there’s all of you, UNfortunatley for all of you I have no less than five more amp projects, literally lined up on my bench! So, short story long, I’d like to say, once again, thank you all from the bottom of my guitar loving heart!!!

[jammied]

Good news buddy!


Wish there was a good supplier for matched 6p3s tubes. I have seen any supplier for them yet that actually burns the tubes in and then matches them.


Almost better off buying the cheap bushel basket fulls from Russia then sorting yourself

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I’m going to get a set of the keyway replacements HotPlate recommended in your 6n3p thread. At that point I’ll have a nearly perfectly matched set!