First Build Problems- KLD kit Build

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I have a 22k resistor I’m going to try when I get home. I’ll pull r55 and toss it in there. Hopefully that will get us in range better.

[jammied]

Oh ok


My experience with that transformer is it will be about 395v to 400v b+. Ofcourse depending on consistency in manufacturing

[jammied]

I just went and measured my kld jtm25 (I suspect same transformer)


B+ is 399v with the tubes installed. Been meaning to change the bias resistor in it but my 6l6'S are marked 6l6gb being 19watt tubes. If infact the markings are correct. 

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Ok, awesome! I’ll compare those readings to mine when I get home.

[2deaf]

I have a 22k resistor I’m going to try when I get home. I’ll pull r55 and toss it in there. Hopefully that will get us in range better.

Don't do that.  According to Reply #13, the stock bias already has the 6L6's near cut-off.  Replacing R55 with a 22K resistor will only make it worse.

With the tubes installed and the amp warmed up, note the voltage on pin 3 of the power tubes.  Take the number "21" and divide it by the voltage on pin 3.  Adjust the 20K Bias pot until the voltage on pin 8 equals the quotient.  Now check the voltage on pin 3 again and repeat the process.  Note the resulting bias voltage at the junction of R51, R55, and C54 then post that voltage here along with the voltage on pin 3.

[jammied]

The number 21 being 70% dissipation of a 30watt tube?

[2deaf]

The number 21 being 70% dissipation of a 30watt tube?

Yes

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Yes sir! I’m on it right after dinner!!!

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I have absolutely no voltage on pin 8 of the power tubes. I’m trying to troubleshoot it now...

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Please excuse my ignorance. Clearly you must be talking about mV. I’m going to bust out my analog meter and get those readings. My apologies.

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My results are ambiguous to me. I don’t know how to interpret this. With the 20k bias pot all the way down pin 3 is at 396vdc. Divided by 21 I get 18.857. However, when I set my analog to mA I barely get any needle movement. Please tell me what I’m not understanding. ( Realizing, of course, that may be so much information no one has time to explain it all to me! )

[2deaf]

21 divided by 396 equals 0.053.  Adjust the bias pot until you have 0.053V on pin 8.

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My humble apologies. My meter can barely detect that. I believe I’m set there currently, or, as close to it as I can read on the needle.

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Ok, I’m there. The junction is at -38.4vdc, and pin 8 is currently set to 0.053v. Sorry for my confusion.

[jammied]

Out of curiosity what is your b+ voltage? And what is you pin 3 voltage now?

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B+ is at 380vdc, and pin 3 is 398.2vdc Jammie.

[jammied]

Hmmm I would think the 398 would be b+ AND 380 would be pin3

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I’m currently playing it and just took a reading 383.7 on B+ & 397.4 on pin 3. On a side note. There’s an incredible volume difference between the normal and lead channels. Is that normal for yours?

[jammied]

Mine is a jtm45 so it has a normal and a bright channel roughly the same volume.


The master volume marshall models have a high gain and low gain channel.


When the master models are setup correctly they can get a huge clean blooming tone. That's how alot of the greats ran them with a pedal in front

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Clearly mine is far from right.

[jammied]

   part of the tone search.


What speakers are you using?


Still red plating and humming?

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I’m in it boss. I was hoping to make a neat amp on the cheap by buying this kit. Clearly I underestimated the complexity and concept of kit, and cheap.

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I’m running a 6.5” eminence in a custom cab, and a 10” celestian also in a custom (ahem...) cabinet. And yes, if I crank it she’ll red plate. Post rewire of the pentode/triode switch there’s an intense hum of I switch to pentode. Like I said before, there’s also no volume on the normal channel. Not no, but low, I guess. It sucks cause the clean is very clean at mid vol and gain. But if I pull my fingers off the fretboard she buzzes, which I’m assuming is grounding.

[jammied]

That sucks! Personally I wired mine up originally without the penrose tried switch and without the send and return loop. Just to save trouble shooting. If needed.


But mine is a point to point. And it doesn't like to be grounded anywhere except through the pots with the shielded cable. Then its quiet.


There bbn is a video on YouTube of a kld jcm25. And that one seems to sound pretty good.


You'll get it. Just got to keep trouble shooting

[jammied]

Also I'm 99.9% certain that you have 2 wires backwards. Plate voltage should be higher then pin 3


Mine is showing b+ of 399v and pin 3 is 388v.

Did you measure b+ at the standby switch? Or where it says b+ 2 on the board

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On the board bub. I’ve been looking at the schematic trying to figure out how to rewire without the switch. It was a cool idea, but I’d rather have an amp that’s loud when cranked, but sounds great, than an amp that’s sounds like crap, but is bedroom playable!

[jammied]

Ok


Take a measurement at the standby switch

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I will bro, in the am. Thanks for all your help. Means a lot to me. From everyone. Means a lot.

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So, today B+ is reading 404.8vdc and pin 3 is real near to that. I really want to do away with the pentode/triode switch, but I’m afraid I’ll blow the amp up. It looks straightforward on the schematic, but I’m unsure.

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One major mess up figured out. The arcing in my pentode triode switch was a poorly executed solder joint that id covered up with heat shrink. The solder had contacted the switch chassis tab and was grounding out! I fixed all the joints and re heat shrunk everything. It’s not as pretty as when first done, but it’s sounding much better. At low volume and gain the cleans are down right clean!! Nice glassy tones, with good chime and some warmth to boot. However, the pentode setting has considerable buzz in its own right, add any amount of gain and all bets are off. The sound goes in the toilet- gritty, muddled, and just downright awful. I’m assuming the buzz is unfound ground issues. My real question surrounds the gain. Should I be looking more at the preamp section for that type of gain issue or at the power side? I’ve switched out the tubes in both sides with little appreciable difference, so I’m tentatively ruling that out for now. I’m not sure how to proceed with my troubleshooting at this point.

[jammied]

Still red plating?


To bypass the pentode/triode switch take the yellow and green wires and hook one to where p1 is marked on the board and the other to where p2 is marked on the board. Then both p12 and p2a hook directly to where b+b is marked on the board ( r30&r31 junction)


Also double check all of the shielded wire connections. The line all of the way through the circle is the conductor/inner most wire and the line on the outside circle is the shield/bare wire.


Also be sure that when soldering the shielded wire that loose strands didn't short/make contact with the conductor. Or that when you soldered the shield and or conductor didn't melt through the insulation of the inner and cause a short

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Copy that!!! I may redo all the shielded sections with better quality wire. I’d suspected perhaps that was a weak link for some time now. Thx bub!!!!!

[jammied]

If its still red plating or if the pentode tried switch makes a notable difference in hum/buzz. I would just bypass it until everything else is worked out. Then come back and try and get it working properly.


Not going to be alot of volume difference between pentode triode. SPL at 1 watt 1 meter . If the speaker is 97db at 1 watt 1 meter then 12 watts or so is still going to be 97db. To me it is more of a tonal difference then volume difference.


The shielded wire in jtm25 was actually pretty good quality.

[2deaf]

To bypass the pentode/triode switch take the yellow and green wires and hook one to where p1 is marked on the board and the other to where p2 is marked on the board. Then both p12 and p2a hook directly to where b+b is marked on the board ( r30&r31 junction)

Remove all of the wires from the Pentode/Triode switch.  Remove the wires connected to P1, P2, P1A, P2A, and B+B on the board.

The yellow wire from the OT goes to P2 on the board and the green wire from the OT goes to P1.  P2A on the board connects to P1A and then P1A connects to the junction of R30(10K), R31(2.2K), and C16(47uF) aka B+B on the board.

[jammied]

Yeah I just figured he already had the wires from p1a and p2a routed to the switch so just take both from the switch and connect to b+b .  And the green and yellow wires may need to be swapped around. If oscillating is happening (mine did have to be swapped). Could unsolder the wires at the switch and just hardwire the b+b and p1a and p2a together and leave them full length.




But your directions are much clearer and easier to understand. For sure!

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You guys are awesome!! I have to repair our dryer today, so I’ll get on this after. You two are the best!!!!!

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Well, that’s done, and it’s a definite improvement. That being said, it couldn’t sound worse. I’m still red plating at 3/4 gain/volume, with the other all the way up. It’s not loud. There’s no way you could play with a drummer. Like, no way. There’s still the extreme difference between the inputs in volume as well. The only thing I can think of now is to reflow every single joint in the whole amp and hope I inadvertently hit that as the issue. I’m not holding my breath. One thing, I finally received my tube bias meter, and There’s a pretty far distance between the power tubes. Any combo of the four I have here at the house is a pretty far span. 7ma is the diff between the matches set, and the other two are 10+ depending which socket or pair I’m comparing. So, ya, booo. But, thanks for everyone’s help, assistance, and patience with me. I’m learning by the day, and hopefully I’ll be able to be a contributor at some point.

[shooter]

received my tube bias meter

your schematic shows there are 1 ohm resistors on the cathodes of the power tubes.
measuring VDC across that R IS the tubes current, no meter and extra things to cause more problems required.

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Yes sir. Copy that.

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Ha! Nobody yell at me, but, and I don’t know why it didn’t occur to me before, I had an dumb-dumb epiphany and remembered I have a bunch of vintage preamp tubes in my upper shop storage. I pulled all new preamp tubes and filled her with vintage. An old jj in v1, a Holland mans mullard from an ao-43 I have in v2, and an unknown origin Sylvania that you can barely read save a touch of green and a severely faded 12ax7. And holy shnikes Batman, she finally sounds good!! Make no mistake, I’m still red Plating at high gain/volume combination, on the lead channel only, but it sounds clear, low to no buzz or hum, and right before she reds up sounds super SMOOTH!! I’m wondering if I can even get 6L6’s to run right in the current configuration. It’s clearly not the tube or the socket, so it must be the general bias limitations of the bias pot and associated resistors/caps in the bias circuit. Maybe a pair of EL’s would do better?!?!

[2deaf]

It’s clearly not the tube or the socket, so it must be the general bias limitations of the bias pot and associated resistors/caps in the bias circuit. Maybe a pair of EL’s would do better?!?!

I thought the red-plating followed the socket. 

If you are going to reflow any joints, start with pin 5 on the socket that red-plates.

[2deaf]

Any combo of the four I have here at the house is a pretty far span. 7ma is the diff between the matches set, and the other two are 10+ depending which socket or pair I’m comparing.

Does the same tube have different idle currents depending on which socket it is in?

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Does the same tube have different idle currents depending on which socket it is in?
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Yes, it sure does!! Also, I went ahead and flowed ALL points on the pcb, both the power/preamp board and the input/pot board. I’m pretty sure it helped with the overall functionality and noise issue. I must have a bias or voltage problem. That’s being said, I’ve gone over and over the component order according to the schematic. They’re all where they’re supposed to be and values have been verified and re verified. Either the schematic is wrong somehow or all my power tubes are garbage!!!

[2deaf]

Yes, it sure does!!

With the Master Volume at minimum and the Bias pot untouched, please post the idle current for each 6L6 when installed in the V4 socket and when installed in the V5 socket.

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V4- nos Soviet #1-393.1vdc
      nos Soviet #2-388.2vdc
      JJ - 391.4vdc
      Unknown 6L6-384.9vdc

V5- nos Soviet #1-389.2vdc
      nos Soviet #2-385.4vdc
      JJ- 395.1vdc
      Unknown 6L6-390.7vdc

The jj and the “unknown” tube are old used tubes I had from buying tube lots. The NOS Soviets I purchased for this build.

[2deaf]

One thing, I finally received my tube bias meter...

What is the make and model of this tube bias meter?

[shooter]

With the Master Volume at minimum and the Bias pot untouched, please post the idle current for each 6L6 when installed in the V4 socket and when installed in the V5 socket.

there are 1 ohm resistors on the cathodes of the power tubes.measuring VDC across that R IS the tubes current,

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Amptata T5 Vacuum Tube Tester EL34 KT88 5881 6L6 6550 Amplifier Bias Current

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Shooter,

I didn’t use that little meter to measure the current readings above, I used my fluke and got actual current readings. I do as I’m told boss!!

[jammied]

Well I'm pretty sure el34's wont fix the problem.


What is the pin 8 to ground voltage? Maybe measure all of the pin voltages and post here. With the readings of just the nos tubes. Then swap sockets with them and post those readings