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Old 16th June 2013, 03:46 AM   #11
lexx21 is offline lexx21  United States
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Join Date: Mar 2011
Location: North Carolina
A few questions.....

1) Specifically what version of the 6l6 are you using?
2) What is your schematic? Post it, it will help.
3) Did you modify the schematic at all during your build?
4) What plate voltages are you running on your driver tubes, the phase splitter (if you have one), etc...
5) Do you have anything at all shorted to ground?
6) What kind of output transformers are you using?
7) Do you have the output transformers isolated from the case? Do you have the power transformer isolated from the case? Do you have the choke isolated from the case if you are using one?
8) Do you have one leg of the output transformer secondary grounded? It will sound like crud if you don't.
9) What are you considering ground? Explain what you have for ground.
10) please post along with the schematic detailed pictures of your wiring. Be verbose with this because we are sort of guessing at what you have.

As a suggestion here.... you said that you were getting the popping sound on the output of your input tube. Check your wiring VERY carefully. Trace every wire and mark it on your schematic after you do.
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Old 16th June 2013, 09:09 PM   #12
ba3jar is offline ba3jar  England
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Quote:
Originally Posted by lexx21 View Post
A few questions.....

1) Specifically what version of the 6l6 are you using?
2) What is your schematic? Post it, it will help.
3) Did you modify the schematic at all during your build?
4) What plate voltages are you running on your driver tubes, the phase splitter (if you have one), etc...
5) Do you have anything at all shorted to ground?
6) What kind of output transformers are you using?
7) Do you have the output transformers isolated from the case? Do you have the power transformer isolated from the case? Do you have the choke isolated from the case if you are using one?
8) Do you have one leg of the output transformer secondary grounded? It will sound like crud if you don't.
9) What are you considering ground? Explain what you have for ground.
10) please post along with the schematic detailed pictures of your wiring. Be verbose with this because we are sort of guessing at what you have.

As a suggestion here.... you said that you were getting the popping sound on the output of your input tube. Check your wiring VERY carefully. Trace every wire and mark it on your schematic after you do.

1. specifically a CED 6l6GC
2. schematics of the amp and the modification is in the first page already post them again i post them below

https://taweber.powweb.com/store/lauren_schem.jpg

ef86 preamp
https://taweber.powweb.com/store/ef86_schem.jpg

3. yes i did make the modify during the build not after
4. the voltage on the driver tube which is in the schematic is defined as V1B plate voltage = 172v
on the V1A plate voltage = 320v
on the ef86 plate voltage = 281v
5. i dont understand what u mean by shorted to ground , everything that needed to ground i did wire
6. the output transformer is weber WSE25 single ended 5k primary 25watt
7. yes they are isolated
8. yes the output transformer secondary is grounded
9.everything that shown in the schematics wire with a triangle wired to the ground
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Old 16th June 2013, 09:53 PM   #13
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I'm a little vague why a website should use a secure https connection to show me a schematic diagram, so I'm following my browser's advice and not looking at the schematic on powweb.
The point of the pop in the speaker test is to focus your eyes on where the problem is. You work back from the output stage to the input, finding out where you don't have any response. If you do have response all the way back to the input, and you have the expected DC voltages on the plates pentode grids and control grids, then you move on to AC analysis. I would get a battery (ungrounded) FM radio, tune it to a rock station, wire the headphone output to a couple of .47 400v caps (hot and ground). Then pull the driver tube of the output tubes, connect the radio (caps outputs) to the control grid and the ground, see if music comes out. Okay? turn off, put the driver tube back in, pull the next tube back out (the one driving the driver tube), connect the radio to the control grid and ground of the driver, turn on. Got music? great. Not, whynot?
I got my battery radio out of the trash, one channel was dead and the slide pot was ****, so I put a fixed resistor in for the slide pot and only need one channel to debug amps with it. Cost $1.50 for two AA batteries, and a dead headphone I cut the plug off of. You can determine you are tuned to a rock station by listening with a good headphone before you put the test headphone plug in. The reason for rock music, you can see the beats on an analog VOM to discriminate music from possible RF oscillations caused by bad solder joints or wiring errors.
Note I don't use a tube tester, usually if the bias voltage on the grids are right by the tube datasheet, and the AC voltage in is a volt or two, music will come out the plate capacitor (or transformer for the output tubes). If you have an analog AC voltmeter (not a slow DVM) with a 2 VAC and 20 VAC scale (use capacitors to couple the +) (or a scope with a 10 x probe) you can measure the AC voltage in the control grid, the AC out the plate cap, divide by the plate plus cathode resistance, and figure the transconductance of the tube (which is on the datasheet). Transconductance out is current out (v/r) divided by voltage in.
Leaky gassy tubes will have low plate voltage compared to the print with the control grid bias voltage right due to too much current flowing through. Your tubes are new, so not very suspect, but shorts do happen in the first hour of tubes sometimes. Also some tube manufacturers have the reputation of not rebuilding their vacuum pumps often enough. Most new amateur amp builders have cold solder joints, or miswires, more commonly than tube or part failures.
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Last edited by indianajo; 16th June 2013 at 10:05 PM.
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Old 19th June 2013, 10:39 PM   #14
ba3jar is offline ba3jar  England
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before i connect the radio and try it the way indianajo explained i just replaced the 6l6 with a KT88 and i did measure the voltages on it and the driver and preamp tubes section so these are details for the voltages
KT88
plate = 417.5v
cathode = 24 v
screen = 296.5v
cathode R= 300 ohm

V1B the driver
plate = 159.8v
cathode = 1.1v
cathode R = 1k

V1A (preamp)
plate = 280v
cathode = 124v
cathode R = 1.5k

EF86 (preamp)
plate = 245.7v
cathode = 124.2v
cathode R = 2.2k

i dont understand why i have 124v on the cathode in both preamp section
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Old 19th June 2013, 11:39 PM   #15
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I would have to say the driver, preamp and EF86 cathode voltages look very high. I would wonder what the bottom, the ground side, of each cathode resistor was reading. I wonder if the path back to the power transformer is correct.
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Old 20th June 2013, 03:36 AM   #16
ba3jar is offline ba3jar  England
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now i checked the ground and it appears one of the wire is broken so i solder it again
this time i have SOUND !!!!! and its LOUD!!! specially the buzzzzzz , i did measure this time the cathode voltages and here it is
the V1A (preamp) = 1.442v
the V1B (driver) = 1.07v
the ef86 (preamp) = 1.7v
now after i got a sound from my guitar i have last problem the BUZZ , its HUGE BUZZ and even the amp is so much loud for a single ended
one thing i noticed is that when i touch the chassis the buzz become less and when i take my hand it increase but still there is a huge buzz even if i touch the chassis so i need more to check but any ideas what it could be?

thanks by the way
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Old 20th June 2013, 04:50 PM   #17
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Okay, you've found & fixed that soldering error. Hum usually comes from open inputs (control grids) or faulty grounds. One usually finds the bad area by shorting the inputs (control grids) of the following stage. You can't just short the grid of a tube itself to ground, it has a DC voltage bias network that might be damaged. So you short the signal to ground before the DC blocking capacitor to the control grid. You start at the output tubes and work backwards. As far backwards as you get with no hum, the stage before that is messed up. Watch and don't short a plate to ground either, the plate resistor could be burnt by shorting to ground, too.
Checking the wiring after construction is not a visual experience. You get a copy of the schematic, and a buzzer or beeper, and check continuity of each wire in the schematic diagram. You touch the component lead, not the wire, in case the joint is cold. You color them off on the diagram with a yellow pencil as you go. The one that doesn't beep, has a soldering or wiring error. I realize you can't touch the tube pins, but in case you have a tube socket not touching the tube control grid pin, you can pull the tubes out and buzz from the top side of the socket. Old work often has corroded tube socket metal, or tube pins, and they have to be erased and washed with alcohol, or poked out with a sharp pick. (power off, caps discharged to zero). Your amp is new work so I don't really suspect corrosion of the brass or tin is a big issue.
If you actually prepared a wirelist, of wires and where they start and where they end, you can count wires on each point as you buzz it out and any that have extra wires that aren't on the wirelist are an error. A wirelist is a text document that has a start point and an end point for each wire. Each point in the amp has a name. Continuous strings have an origin with one termination, and two entries for each point that has two wires on it. Tube point to point wiring of course, some points can have many wires on them. there is a wirelist entry (source, end) for each wire on the point. Factories that hand build actually use wirelists instead of schematics. The routing matters of a signal, you don't want the solder operators making up the routing without thought. No high level signals parallel to low level signals, no high AC current wires parallel to wires to high gain points (like control grids).
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Last edited by indianajo; 20th June 2013 at 04:59 PM.
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