Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: silat on October 16, 2015, 02:45:16 pm
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I have tried everything and cannot get it to work right no sound from my speakers. I took loose all four of the speaker Jacks and only left one for testing to see if maybe I had something shorted.
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I am posting more pics it said my file sizes were to big .
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:dontknow:
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> no sound
Not even a faint hiss or hum?
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Nope! Maybe a slight hum.
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Start here and report back after your have finished
http://el34world.com/Forum/index.php?topic=17701.0 (http://el34world.com/Forum/index.php?topic=17701.0)
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EL34, I am printing out that layout now to check against mine. I wrote down my voltages and it looks pretty weird especially at the rectifier. but aI have got some problems here.
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When you test for sound, makes sure your speaker is plugged into the jack with the switch on it. Otherwise, the switch shorts the speaker output to ground.
Was that really -122v on pin 5 of the output tubes? Or was is -12.2?
You should also be clipping your meter's black lead to the power transformer secondary center-tap (Red-Yellow), which ideally is grounded at the same place your 1st filter cap is grounded.
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It was -122 which is pretty weird.
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Yeah I know about having my speaker plugged in I do not want to burn up my OT! :BangHead:
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It won't damage your OT, you'll just get little-to-no sound from the speakers.
-122v seems unlikely from your amp's bias circuit. Check that you have the wire from bias circuit to output tube 220kΩ connected to the correct eyelet (not the one the bias diode is sitting in), and that you have a ground from the bias filter cap - & 56kΩ. If those were wired correctly, I'd expect the bias voltage to be divided down to the ~ -40-50v range.
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Give us more information about the amp. Is it built from a kit? What transformers did you use?
It appears you have a fault in the heater wiring to pin 9 of the first preamp tube. It should be the same as the other two, not zero.
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Do you have the input jacks wired correctly? Plug instrument cable into hi input and clip your DVM leads to the tip and sleeve of the cable.
You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K -144K.
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It is a tweed bassman kit. the transformers are from weber Pt W0227898 Int and the Ot. I Have new voltages.
V1 V2 V3 V4 V5 V6
P1 192 61 291 0 0 N/A
P2 0 4 16 2VAC 2VAC 500
P3 1 3 50 506 519 N/A
P4 2VAC 2VAC 2V 504 507 -0
P5 2VAC 2VAC 2VAC 0 0 N/A
P6 215 359 281 500 506 -0
P7 0 359 15 0 2VAC N/A
P8 1 356 50 78 88 501
P9 2VAC 2VAC 2VAC
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I checked my wiring and had the 6L6's wired together on pins 8 instead of pin 6 it was my dyslexia.... :help:
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weber Pt W0227898 Int
No such PT. Maybe you mean W022798INT instead??? Did you get the standup bell covers for this PT?
V6 pins 4 and 6 should have a BIG AC voltage, more than 300VAC. I suspect this is correct since you show 500VDC on pins 2 and 8.
V4 and V5 shows 0V on pin 5. Yesterday you said you had -122V. Correct reading should be about -40v to -50v.
V4 and V5 pin 8 should be zero volts.
There are multiple bad voltage readings on all the little tubes!
Your filament voltage readings for all tubes is only 2VAC. That should be 3.15VAC.
I don't trust many of your voltage readings. Either your meter is lying or you are not checking voltages correctly. The DC voltage you read on pin 8 of V6 should be the highest DC voltage in the entire amp, yet you show higher readings on V4 and V5. What meter do you have?
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Sluckey, Yes I did make sure I got the standup bells for the transformer. Ok somewhere something is not right it sounds like. I have a craftsman volt meter.
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Can you take a better focused picture of the PT/rectifier area? It's tough to see what's going on there. Also, a clear, full length shot of the guts would help.
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Yeah, I will try to get some pictures my laptop went down I am borrowing my wifes.
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More pics
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:sad2:
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:BangHead:
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I was told my file size is too big when I uploaded the pics, but I thought it was the same as I used before. So I have posted them individually.
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In the last picture there's a hole in the eyelet board on the far left side and it doesn't look like you have the blank insulator board underneath the eyelet board? :dontknow:
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I do not because the chassis makes the pots too close and hit them so I put a thick carpet tape. I bought a cheap chassis and i am not very happy with it.
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Ok as long as nothing is shorting out to the chassis under the eyelet board?
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OUCH! There is 500VDC on that board. I would never use any carpet tape I've ever seen as an insulator for even 12V. If it's not a problem yet it will be.
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What do you suggest Sluckey? I have zero clearance... if I use the blank board it pushes the board tight against the pots. It is a very narrow chassis.
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Looking at your earlier pics it looks like you have plenty of room? The blank board is only, what a 1/16"?
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Ok I will put it under the board I do not want future problems to go along with my non working amp at the moment. I thank everyone for helping out. I hope you all stick with me on this and be patient with me?
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I know it's a pain to take pic's while you build an amp, but it is your documentation and only reference of confirmation of what you have done to look back on for any errors we all make at times when building an amp. I spend more time taking pic's to confirm my work than it does to build the amp. In the end it will save you a lot of grief and quess work.
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Alright, I replaced the tape with the blank board while I was there I noticed I had a wire in the bias circuit in the wrong place. I moved it to where it belonged and rechecked both my pins 5 on the two 6l6's and I now come up with -38 which is a lot better. But I have yet to get any sound. Any suggestions. I think it might have been plexi50 that suggested I do that. Thanks Plexi for that! Or whoever it was that thought of that.
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It was Hotplate Blues that came up with that! So Thank you ! :think1:
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Recheck voltages on all filter caps and on every pin of every tube socket. Post the results. Double check your wiring. You just found one error. I'm betting there are others. Hang in there!
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Are you double checking your wiring with the what's in the link that Doug posted in reply #5 of this thread?
Best way to double check that I know of.
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V1 V2 V3 V4 V5 V6
P1 184 346 288 0 0 N/A
P2 4.8 1.2 23 2.9VAC 2.9VAC 512
P3 3 2.9 54 514 512 N/A
P4 280 250 277 510 510 -0
P5 4.9VAC 2.9VAC 2.9VAC -38 -38 N/A
P6 280 350 277 510 510 -0
P7 0 350 17 2vac 2VAC N/A 22UF filter caps 512,512,510,421
P8 1.3 348 54 87 45 512
P9 2.9VAC 3VAC 3VAC
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Are you double checking your wiring with the what's in the link that Doug posted in reply #5 of this thread?
Best way to double check that I know of.
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Your voltage readings are still severely messed up! For example, V1 pin 4 is 280. V1 pin 5 is 4.9VAC. Well, pin 4 and 5 should be connected together and read the same voltage. That voltage should be 3.15VAC.
You either have major wiring errors, or your meter is lying to you, or you don't understand what you are doing and don't have an idea what the correct voltages should be.
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I am being honest. 4 and 5 are tied together and I just put the meter on them and got 3 vac. I might have touched 3 and 8 tied together and did not notice it.
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I Got it working at least but it is really low. I took the four speaker jacks loose and only hooked up one.
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I Got it working at least but it is really low. I took the four speaker jacks loose and only hooked up one.
Do you have more than one speaker jack connected at all? If so, plug into the one with a switch (that is, the one with 3 lugs).
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Yeah that is the one I am plugged into.. I turned off the Normal volume pot and have the guitar plugged into the bright channel and it got loud like a bedroom amp but that is full blast. So I am getting there.
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If you are 100% certain that the underside of the board wire connections are correct then you should find the problem shortly on the top side. But if you have any reservations about the board underside then just get it out and flipped over and take some pic's.
If you cant find the problem on top then you really have no choice but to pull it out and conquer that puppy.
That's part of the fun in knowing for certain and ruling out any doubt. Pull the board and you will be glad you did it sooner than later.
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plexi50, I pulled the board a couple of nights ago and put the blank board underneath because i had carpet tape sluckey had said it would not last so while I replaced that board I looked it over and took a picture.. I did not want to wonder about it. I have sound but it should be where i could not stand it full blast. I cannot figure what else is wrong unless I have a wrong resistor value or a short or bad solder joint somewhere..
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staying tuned to the same bat channel and...waiting to see what happens next!? :icon_biggrin: (sorry no time to help, heading out for sushi & will check back later) I love trouble shooting-capades...
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What are your cathode voltages on each of the preamp tubes?
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V1 Pin 8 pin3 V2 Pin 8 pin 3 V3 Pin8 pin 3
1.4 1.4 358 2.1 53 53
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V2 Pin #8 358 volts dc?
Do this:
Pull V2 preamp tube. Measure all 9 pins and tell me what each pin is reading.
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pin 9 pin 8 pin 7 pin 6 pin 5 pin 4 pin 3 pin 2 pin 1
2.9 VAC 0 401 401 2.9VAC 2.9VAC 0 0 400
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Ok lets start all over. Why do you have two different colored leads coming from the choke? I see the customary black lead connected with the OT CT and connected to the first (2) 20uf filter capacitors. But then i see a white wire connecting to the 4.7k supply resistor. What is the story with that? It should be the second choke lead and black as well.
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It is a universal choke I got from Weber . I thought it was weird too because usually you have only two back wires. But this choke has black and white wires... I bought one just in case for a 6L6 But I did not put it in yet.
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Some chokes have 2 different colored fly leads, I think some hammonds are made that way.
1 is the start and the other is the finish of the choke wind.
I think it's like with a coupling cap where the outside foil (finish) of the cap gets hooked up to the lowest Z side or to ground and acts as a shield.
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We can get this amp working tonight after a few questions here.
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Ok i understand now. Now i want you to unplug the amp and lets do a continuity check first from the other side of the 4.7k and over to the 100k/82k PI junction. Continuity?
I am looking for a problem before or at the 10K PS resistor feeding V2 pin #6
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V1 Pin 8 pin3 V2 Pin 8 pin 3 V3 Pin8 pin 3
1.4 1.4 358 2.1 53 53
V2 Pin #8 358 volts dc?
You have a resistor mounted on the socket for V2, running (I assume) from pin 6 to pin 1, and pin 6 is connected to power supply voltage. This resistor should be 100kΩ (Brown-Black-Yellow); measure its resistance. I think you have a 10kΩ (Brown-Black-Orange) or 1kΩ (Brown-Black-Red) in there instead.
That would cause the stage gain before the cathode follower to be very low.
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It seems I have continuity from the 4.7K to the 10K but not over to the 100k
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you know what to do, get 'er done!
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it is Brown black yellow silver 100kOhm
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So what do you think continuity problem somewhere? Possibly from the 10k over?
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it is Brown black yellow silver 100kOhm
Don't go by just the colors, double check to confirm by measuring it.
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I have got continuity over from the 10k over to the 6 Pin on V2
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it is Brown black yellow silver 100kOhm
Don't go by just the colors, double check to confirm by measuring it.
I confirmed it with my meter.
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What's the resistance you measure from V2 pin 8 to ground? Use your power supply filter cap negative terminal as your ground point for this measurement.
I'm asking because you have essentially the full B+ at the cathode of one section of V2 (and across the cathode follower load resistor, which appears to be pin 8 in your amp), and too-high voltage on the plate of the other section of V2 (which appears to be pin 1 in your amp). The V2 pin 3 voltage with V2 installed looks reasonably correct. So for there to be too-high plate voltage at pin 1 means too little voltage drop across the plate load resistor on V2 pin 1; that happens with either too-low current through that tube section (ruled out by the good cathode voltage reading) or a too-small plate load resistor.
Find and fix your error with V2 and you'll be closer to the amp working.
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I confirmed it with my meter.
On a lot of the newly made R's the colors can vary a lot and are not easy to read. The old R's seem to have had deeper, more clearly readable colors.
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What's the resistance you measure from V2 pin 8 to ground? Use your power supply filter cap negative terminal as your ground point for this measurement.
I'm asking because you have essentially the full B+ at the cathode of one section of V2 (and across the cathode follower load resistor, which appears to be pin 8 in your amp), and too-high voltage on the plate of the other section of V2 (which appears to be pin 1 in your amp). The V2 pin 3 voltage with V2 installed looks reasonably correct. So for there to be too-high plate voltage at pin 1 means too little voltage drop across the plate load resistor on V2 pin 1; that happens with either too-low current through that tube section (ruled out by the good cathode voltage reading) or a too-small plate load resistor.
Find and fix your error with V2 and you'll be closer to the amp working.
360 PIN 8 to ground pin 1 60 I am at a loss. I am going to my grand-daughters B-Day party so I will be out for awhile.
I will check back later and get right back looking for the problem. I changed somethings on my input jacks and no longer have any sound. I also changed one of the pots that was supposed to be 1 M as it was 10K no I have nothing.
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This is a pretty simple circuit and build so it'll get resolved eventually and is a good learning situation for you silat. However you photos are a bit too close up to get an idea of things in better perspective. Plus things like the photo below also don't help much cause we can't see where things are going very easily...? You really need to be sure on all of the part's values you are using before installing them in the future. It's good practice to always measure resistors & capacitors ahead of time. Believe it or not, you'll have a few experiences where you or the part is not always correct. I also double check all voltages and heater contacts at all sockets before installing components (where applicable) because I've found what looks like a great good solder job actually had a bad heater connection one time that was verified by my meter. A simple re-touch up of the joint saved me time & frustration later on. It's just called doing your due diligence aka "a stich in time..."
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Like others have said do not go strictly by the color code on your resistors. Use your meter to verify their values.
Be certain that you have your power supply capacitors going to each section of the amp as in the schematic.
You do essentially almost have the entire B+ voltage on V2 pin 8.
Re-check each power supply filter caps grounds and perspective B+ connection points.
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What is the plate voltage on V1 PIN 1 & PIN 6?
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What is the plate voltage on V1 PIN 1 & PIN 6?
V1 pin 1 pin6
185 196
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Are you 100% certain you have the power supply capacitors and 10K resistor feeding V2 wired correctly?
Look again if you have to. There is no way you should have anything near 300VDC on the cathode pin 8 of V2.
You have to have the 10K resistor and power supply cap wired wrong. There's nothing else that would or could be putting any voltage over 190VDC max on V2 cathode.
Are you certain you have the 100K resistor on V2 going to pin #1 #6 & #7? Not #1 #6 & #8
Check again:
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I have looked it over and it looks right. I have to be missing something somewhere. I took a picture of the back of my board and it looks right.
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Are you 100% certain you have the power supply capacitors and 10K resistor feeding V2 wired correctly?
Look again if you have to. There is no way you should have anything near 300VDC on the cathode pin 8 of V2.
You have to have the 10K resistor and power supply cap wired wrong. There's nothing else that would or could be putting any voltage over 190VDC max on V2 cathode.
Are you certain you have the 100K resistor on V2 going to pin #1 #6 & #7? Not #1 #6 & #8
Check again:
It is going to 1- 6 and 7
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Well your gona hate the answer but your going to have to go through the amps part values and wiring as if you were building it all over again. Pull your rectifier tube and turn just the power switch on. Measure the (2) red leads soldered to the rectifier socket. Ground the black meter lead and touch each red wire at a time. What are your AC voltages for each red wire lead?
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393 VAC 385
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Just to be perfectly clear about that resistor on V2 socket... The resistor connects between pin 1 and pin 6. There is just a piece of wire between pin 1 and pin 7. It's common practice to just loop the resistor lead through pin 1 and double it back to terminate at pin 7.
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And that is just what had done 1-6-7
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And that is just what had done 1-6-7
It doesn't look like it in the photo below? See photo and remarks. But again, your supplied photos aren't helping us much here. Please take a few better shots for us as this is tedious without your continued help in showing us your amp's interior better.
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Just to be perfectly clear about that resistor on V2 socket... The resistor connects between pin 1 and pin 6. There is just a piece of wire between pin 1 and pin 7. It's common practice to just loop the resistor lead through pin 1 and double it back to terminate at pin 7.
I had it looped behind from 6 to 7 so I changed it
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Just to be perfectly clear about that resistor on V2 socket... The resistor connects between pin 1 and pin 6. There is just a piece of wire between pin 1 and pin 7. It's common practice to just loop the resistor lead through pin 1 and double it back to terminate at pin 7.
I had it looped behind from 6 to 7 so I changed it
Show us another picture that clearly shows exactly what V2 socket looks like now. We need to be able to clearly see what is connected to each pin. If the pic is too large to post here and you can't figure out how to get the file size down, then post it somewhere else and just post a link to the pic on the forum.
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I hope you can see this?
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Here is another.
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Do you have some wire ends going to the sockets center hub?
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Do you have some wire ends going to the sockets center hub?
No......
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Need pic's like this/ Looking down at the tube pin and socket. This is V2
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Need pic's like this/ Looking down at the tube pin and socket. This is V2
You switched triodes! That's really gonna be confusing. :icon_biggrin:
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I am sorry I do not have a good enough camera but here they are anyhow.
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One more.
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One more.
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look at the pic, not sure if it's your issue now but it will be.
nib off the "tail" from the blue wire, clean out the solder splatter from the other circle
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Shooter your pic is looking mighty hungry! It doesn't eat amps does it?
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Silat don't give up and get feeling bad. We all have had our share of going through similar issues.
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Yep. :icon_biggrin:
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I tell you I feel like giving up. But I appreciate everyone being positive for me.
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That's what make this forum so great! You have a lot of help and eventually the problem will be found. It makes you learn and understand what all the component do and there function. It takes a little time to grasp all of the possibilities.
Did you get your input jacks straightened out? Volume pot? What king of A/C DC meter are you using?
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You never said if you tried double checking your amp with our host Doug's method?
It works great, we've seen a number of guys who couldn't find what's wrong use Doug's method and find it.
Here's the link again if you haven't tried it;
http://el34world.com/Forum/index.php?topic=17701.0 (http://el34world.com/Forum/index.php?topic=17701.0)
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I am going to start tracing soon.(Using Doug's little handy dandy method) I am given myself a little break now for a few hours. so I will be bothering you all again soon enough when I begin again.
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If this helps this is the underside of my board wiring.
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Thank you Plexi!
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It doesn't eat amps does it?
:l2:
Don't think so, but I did give up on photography and moved on to oil paints!
that "tail" looks like a spark-gap waiting to fire though.
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Ok Silat lets get going on this. Whats the latest news? I want to hear it working. I myself cant wait to hear what the problem was.
I have myself done some silly things in the past. And looking back you wont forget them once found. I used to expect the Fn worst. But 9 times out of 10 it usually turns out to be something so simple that it makes you feel dumb.
Keep going. No rest for the weary.
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I have myself done some silly things in the past. And looking back you wont forget them once found. I used to expect the Fn worst. But 9 times out of 10 it usually turns out to be something so simple that it makes you feel dumb.
Keep going. No rest for the weary.
I just want tosay ditto. I just finished my 5f6a build and made a super simple mistake and replaced nearly every component and it turned out to be the simplest thing. You will get it.
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I still have not found the problem.... I spent some time on it. I reheated up some suspect looking joints but have nothing... I moved my cap-board on the outside of the of the chassis instead of the inside so I could see better. I am at a loss....
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I think I may replace the tube sockets and see if that may do it.
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Silat i really believe that you have it wired wrong under the board at the 10K - 8uf filter cap junction that is feeding V2 which is also why V1 plate voltages are way higher than they should be. I wage a virtual 12AX7 tube on it.
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Ok I will look again. I have looked several times, but that does not mean I did not miss it somehow. Thanks for all your help.
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I am going to start tracing soon.(Using Doug's little handy dandy method)
Did you do this?
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Silat i really believe that you have it wired wrong under the board at the 10K - 8uf filter cap junction that is feeding V2 which is also why V1 plate voltages are way higher than they should be. I wage a virtual 12AX7 tube on it.
I took it off and it is not wired wrong. I looked it over really close. I took a yellow marker to my layout and put my fingers on the component as I was tracing it. I have no sound at all but maybe some white noise now.
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I took a yellow marker to my layout and put my fingers on the component as I was tracing it.
Not just the components, wires too. 1 at a time.
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I took a yellow marker to my layout and put my fingers on the component as I was tracing it.
Not just the components, wires too. 1 at a time.
When I say components I mean wires also.
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Do you have the input jacks wired correctly?
Plug instrument cable into hi input and clip your DVM leads to the tip and sleeve of the cable.
You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K.
What are your readings. We must know to help rule out other issues.
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Do you have the input jacks wired correctly?
Plug instrument cable into hi input and clip your DVM leads to the tip and sleeve of the cable.
You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K.
What are your readings. We must know to help rule out other issues.
7.17, 7.56
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Your inputs are wired wrong. Have a pic of them?
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I really do not think so but at this point I will try anything.
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If the red circle on the jack is the sleeve ground lug and that wire is going to 1 of the 68K grid stopper R's than it's wired wrong.
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Drawing from Doug's Tube Amp Library of information, link for it can always be found at the bottom of any page on the forum.
They should be wired like this, G=ground, S=switch contact, T= jack tip/hot input.
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That got me some sound! Although very faint and very distorted where I am putting a speaker up to my ear to hear it.
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Do you have the input jacks wired correctly?
Plug instrument cable into hi input and clip your DVM leads to the tip and sleeve of the cable.
You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K.
What are your readings. We must know to help rule out other issues.
Now try this test from Plexi50 again to confirm it. :icon_biggrin:
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Do you have the input jacks wired correctly?
Plug instrument cable into hi input and clip your DVM leads to the tip and sleeve of the cable.
You should read 1Meg just + or -. Then plug into the low input. You should read roughly 134K.
What are your readings. We must know to help rule out other issues.
Now try this test from Plexi50 again to confirm it. :icon_biggrin:
1078, 1076
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That's still wrong. It's either wired wrong or your meters lying or messed up or it's not set right?
Sometimes guys get false readings if the meters batteries are low. Try a new set of batteries and then check some spare R's you have laying around and see if it's reading correctly.
If good then try the input jacks again.
(I just measured 1 of my amps that has Fender type hi/low input's and it read just like Plexi said.)
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Plexi right that it's the input jack wiring as you can see. Get that fixed and you may have a working amp. :icon_biggrin:
It's very good that you did hear a little sound through the speaker. That may be because the rest of the amps working.
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Get your jacks lined up and it will make more sense. Solder the (2) center tab terminals together (upper jack & lower jack) and then add the 68k wires to each one as shown.
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Plexi, I am sorry but I m not understanding what you are saying here? Could you be a little more specific?
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Read again. Look at pic.
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Read again. Look at pic.
Sorry, you had a different picture of the tube sockets and it was confusing...
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YEAH I PICKED THE WRONG PIC FOLDER FOR A SECOND.
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Get your jacks lined up and it will make more sense. Solder the (2) center tab terminals together (upper jack & lower jack) and then add the 68k wires to each one as shown.
The 2 center tabs/solder lugs?
Here this might be better to see, it's rotated like it should be in the amp.
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Get your jacks lined up and it will make more sense. Solder the (2) center tab terminals together (upper jack & lower jack) and then add the 68k wires to each one as shown.
The 2 center tabs/solder lugs?
Here this might be better to see, it's rotated like it should be in the amp.
Yeah i messed up saying to solder the (2) center tab lugs. But as i have it anyway as the jacks are positioned.
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But as i have it anyway as the jacks are positioned.
Yep. :icon_biggrin:
Your the guy who sniffed out the input jacks. :icon_biggrin:
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His input grids have been shunted to ground all along. But theres another issue with 350+vdc on V2 8 that bothers me.
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His input grids have been shunted to ground all along.
I think your right.
But theres another issue with 350+vdc on V2 8 that bothers me.
Agree, I think Sluckey brought that up too?
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His input grids have been shunted to ground all along.
I think your right.
But theres another issue with 350+vdc on V2 8 that bothers me.
Agree, I think Sluckey brought that up too?
Yes Steve did. Think about this: If the 10K & 8uf filter cap were wired correctly and the B+ was passing through that 10k on to pin #6 then there is no way there could be 350+ on V2 pin #8 or V1 @ 190+
But i am assuming he is using a 325-0-325 PT
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I'm looking at the schemo and I agree with you.
I know you have built this amp and know it well. :icon_biggrin:
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Silat: Following V2 pin #8 wire to the board,slope resistor,treble peak cap & 100k resistor.
Is the 100k from that junction across and through that resistor to the other side of the 100k lead grounded?
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Silat: Following V2 pin #8 wire to the board,slope resistor,treble peak cap & 100k resistor.
Is the 100k from that junction across and through that resistor to the other side of the 100k lead grounded?
Yes the 100K is grounded.
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I myself have somewhat of a hard time wiring up 2X hi/low input jacks.
I need to have a very clear drawing in front of me to get it right. (Switches are also another thing that can be difficult for me.)
It's been said MANY times before here and else where, 'divide and conquer'.
So......
Get the input jacks wired up correctly 1st. No input, no output. You can confirm (and need to) that their their wired up correctly by testing them with your meter as Plexi posted.
THEN if the amp still isn't working, go to the V2 dcv problem.
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I think I might have found the problem as to why my voltages were so high on V2. My Power transformer (W022798 INT) shows 720 V Center tapped that is what I had. I switched to the red and white wire and that gave me 330-0-330 or 660v it brought my V2 down to Pin8 161, pin 7 156, pin6 356. Still the sound is very faint and distorted.
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First answer the question about your input jacks. What do they read on the high and low jack inputs.
We need to know if you have fixed them before going onto any other issue.
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Yes you need to use the two red/white trace wires to the rectifier socket pin 4&6
That is why i asked you to pull the rectifier tube earlier in this thread and give us the voltages of each lead to the rectifier socket
Every step of the elimination process and questions asked have to be answered or we can only guess. Guessing can get you killed with high voltages like this. We want to hear success as bad as you do.
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First answer the question about your input jacks. What do they read on the high and low jack inputs.
We need to know if you have fixed them before going onto any other issue.
When I measure a 1 meg resistor I get 1014 But I get 538 and 131 on my input jcks but I wired them just like the drawing showed that you all gave. Unless my meter is messed up. It must be right.
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This is what you have to have for input jack readings + or minus a little.
Low input top pic/
High input bottom pic/
If not they are not wired right. Again please be more specific. Is the 131K (not ohms) reading your low impedance jack? That would be fine.
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1069, 141 I have no other way to set from that. That is what I have and the only reading I can get from my meter.
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Ok that's beautiful and all good. That is on each channels inputs (both high and lo jacks)?
What is your B+ plate voltage measurement on pin#3 of each power tube.
I am assuming you are using 6L6GC tubes
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Ok that's beautiful and all good. That is on each channels inputs (both high and lo jacks)?
What is your B+ plate voltage measurement on pin#3 of each power tube.
I am assuming you are using 6L6GC tubes
475, 476, yes I am using 6L6's
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Ok the plate voltage on each tube is even. But you may still have a problem. What is you bias grid voltage on pin #5 of each power tube?
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Ok the plate voltage on each tube is even. But you may still have a problem. What is you bias grid voltage on pin #5 of each power tube?
It did not move it stayed at -38
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Ok what is your bias resistor value in the amp now?
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Ok what is your bias resistor value in the amp now?
15k
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Change that resistor to 56K. MINE WAS ACTUALLY CHANGED TO 47k SO YOU MAY HAVE TO DO THE SAME . WE NEED TO SEE -48 VOLTS ON PIN #5. YOUR PLATE VOLTAGE WILL COME WAY DOWN AS WELL WHERE IT SHOULD BE. 475 IS TO HIGH. My typing sucks/
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STOP!!!!! The 15K across the (2) bias capacitors stays. Change the bias resistor that is connected from the 15K side going to the positive capacitor leads. That's the bias resistor/ What is that resistors value?
Pay no attention to the yellow wire on my bias system. I am not using a diode. You are.
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STOP!!!!! The 15K across the (2) bias capacitors stays. Change the bias resistor that is connected from the 15K side going to the positive capacitor leads. That's the bias resistor/ What is that resistors value?
Pay no attention to the yellow wire on my bias system. I am not using a diode. You are.
I figured that out... No worry's I stopped to eat a bite. I do not have any 47K's to try though.
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Ok no problem. Throw a 56k in there. You will wind up with 48.9 --50 volts. I want to hear this amp working tonight!
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What is the bias resistors value in the amp now??
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STOP!!!!! The 15K across the (2) bias capacitors stays. Change the bias resistor that is connected from the 15K side going to the positive capacitor leads. That's the bias resistor/ What is that resistors value?
Pay no attention to the yellow wire on my bias system. I am not using a diode. You are.
It is 56k...
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And you have -38 ? Are you using a Digital Multi Meter or Analog Meter?
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I am using digital.
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What resistor values do you have on hand? Try a 33K. Or take a 33k and 10K in series and you will have 43K.
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I did it took down to -32
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I did it took down to -32
You did what to take it down to -32 volts?
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The 33 K resistor took it down to 32 I can take a picture if you like?
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What is the voltage on the Red & Blue trace bias lead in A/C volts going to the silicon diodes anode? Where the silver band on the diode is.
Should be 45 volts a/c
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What is the voltage on the Reb&Blue trace bias lead in A/C volts going to the silicon diode?
+46 AC
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Ok you say you have a 33k bia r in there now. Check the plate voltage again on the power tubes and tell me if the voltage went up or down.
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Like I said I put in the 33K and just now checked and it is at -32 it has not moved. It was - 38 with the 56K
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Check the plate voltage again on the power tubes and tell me if the voltage went up or down.
No, the PLATE dcv on the power tubes.
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Voltage on Pin 3 of the power tubes again?
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473,474
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Something is very wrong here. Tack a 82k or 100K in the bias resistor spot. Turn on the power but leave the standby off. Do not power the amp full on. What is the pin 5 voltage reading?
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He changed the -bias but the plate voltage only changed ~1dcv.
Think maybe the power tube K's aren't hooked up to ground?
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He changed the -bias but the plate voltage only changed ~1dcv.
Think maybe the power tube K's aren't hooked up to ground?
I know. This is weird. My next question is are the positive leads of the bias caps going to ground side.
Think maybe the power tube K's aren't hooked up to ground?
I guess were going to find out.
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-44 with 100k in the bias and standby off.
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Ok -44 is going in the direction we want. We want -48. Are your bias capacitors positive leads going to ground?
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He changed the -bias but the plate voltage only changed ~1dcv.
Think maybe the power tube K's aren't hooked up to ground?
I know. This is weird. My next question is are the positive leads of the bias caps going to ground side.
Think maybe the power tube K's aren't hooked up to ground?
No they are going the right way with the ground pointed toward the diode and the 15Kr like it shows on the layout.
I guess were going to find out.
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No the question is are your bias capacitors positive leads going straight to ground.
Additionally are your power tube pins #8 grounded to the chassis?
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No Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis. I have no idea what you are talking about with the ground on the bias caps the 2 -8 UF caps if that is what you are talking about?
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No Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis.
Aha!
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Major revelation!!!!!!!!! :worthy1: :worthy1: :worthy1: :worthy1:
You must run a wire from pins #1 & #8 straight to the chassis. They must be grounded. This is the cathode of the power tubes and what turns the power tubes ON. That why we don't have a bias of -48 volt give or take. Put the 56k bias resistor back in place and turn the amp on after you have grounded pin 1 & 8 of each power tube
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No Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis.
Aha!
Well it is nice you are having an aha moment but you will have to help me? I did have them(The 6l6's) grounded to chassis but they red plated my power tubes. I never thought anymore about it....
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He probably doesn't have a big enough iron to solder that steel chassis, he needs to us a solder lug that get's bolted to the chassis with 1 of the power tube socket bolts.
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I did have them(The 6l6's) grounded to chassis but they red plated my power tubes. I never thought anymore about it....
What do you mean exactly?
We are trying to help you, nobodies making fun of you.
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The power tubes red plated at that time because the bias resistor value had to be wrong. And you also at that time had the PT wired using the 720 Volts CT leads.
Turn your volume down Silat cause you about to hear a loud amp. Check the bias first and look for -48.9 --50 volts using a 56K bias resistor.
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If you disconnected the power tubes cathodes (K's) from ground to get the power tubes to stop red plating that will do it. But then they will not be able to draw any current.
Like Plexi just said they were red plating because the -bias was wrong.
More -dcv = less current.
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If you disconnected the power tubes cathodes (K's) from ground to get the power tubes to stop red plating that will do it. But then they will not be able to draw any current.
Like Plexi just said they were red plating because the -bias was wrong.
More -dcv = less current.
I want to hear this working tonight. OR HEAR THAT I HEAR IT IS WORKING WITH THE RIGHT VOLTAGES TONIGHT.
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He might have killed the PI tube, he had 500+dcv on it early on.
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Eureka! I have sound and it is good and loud but my bias voltage is still at -38... :worthy1: :worthy1: :worthy1: :worthy1:
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He might have killed the PI tube, he had 500+dcv on it early on.
Maybe. I think 380 is insane for a 12ax7. Ive seen that on more than one occasion.
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Eureka! I have sound and it is good and loud but my bias voltage is still at -38... :worthy1: :worthy1: :worthy1: :worthy1:
Ok check the plate voltage now and tell us what it is. Don't leave the amp on for long becasue we still need to get the bias set right.
Your power tubes will red plate again until you get the right bias resistor in there and obtain -48 + volts
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No Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis. I have no idea what you are talking about with the ground on the bias caps the 2 -8 UF caps if that is what you are talking about?
Are the positive leads of each bias cap going to the chassis ground? The positive leads. Not the negative leads
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Eureka! I have sound and it is good and loud but my bias voltage is still at -38... :worthy1: :worthy1: :worthy1: :worthy1:
Ok check the plate voltage now and tell us what it is. Don't leave the amp on for long becasue we still need to get the bias set right.
Your power tubes will red plate again until you get the right bias resistor in there and obtain -48 + volts
plate voltage is still 438 on both pins 3 on the 6l6's
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plate voltage is still 438 on both pins 3 on the 6l6's
That's much better.
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438VDC is excellent and will be 425VDC or less after the bias is perfect @ -48 volts. Please re-read and answer the bias capacitors question.
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yes it is.
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OK YOU HAVE THE 56K BIAS R IN THERE NOW CORRECT? PUT IN 33k AND THE BIAS SHOULD BE JUST OVER -52 VOLTS.
And plate voltage on power tubes should drop to under 420VDC. Confirm this. If not do tell.
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438VDC is excellent and will be 425VDC or less after the bias is perfect @ -48 volts. Please re-read and answer the bias capacitors question.
I do not understand you are going to have to draw picture because I thought but I do not. Sorry plexi50 and Thanks to you and Willabe for sticking with me on this and helping me even in my ignorance but I have learned but have a long way to go.
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438VDC is excellent and will be 425VDC or less after the bias is perfect @ -48 volts. Please re-read and answer the bias capacitors question.
I do not understand you are going to have to draw picture because I thought but I do not. Sorry plexi50 and Thanks to you and Willabe for sticking with me on this and helping me even in my ignorance but I have learned but have a long way to go.
I did put the 56K back in the bias.
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Plexi did it. :icon_biggrin:
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Bias cap positions.
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Plexi did it. :icon_biggrin:
Willabe did it! :worthy1:
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yeah that is just how mine are and I was for sure that was what were talking about on the bias caps but somehow miscommunicated.
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So is it working !?!?
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yeah that is just how mine are and I was for sure that was what were talking about on the bias caps but somehow miscommunicated.
NOTE: Do not think you are finished yet and start playing the amp until we get the bias right. Otherwise your power tubes will red plate again and possibly destroy them. I'm glad you have it working. Now i am going to take a beer bath. Too late for that now. Not recommended.
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Thanks again all! I just need to get that biased right now...
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Do you know how to bias the amp?
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It is fixed so the only way is to put a different value resister or change it to be adjusted with a bias pot.
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Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis.
I did have them(The 6l6's) grounded to chassis but they red plated my power tubes. I never thought anymore about it....
Now that was a BIG missing piece of the puzzle. Kinda like withholding evidence. Would have been nice to know about 200 messages ago.
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Number 8 pins they are also tied in to number 1 on the power tubes are not grounded to chassis.
I did have them(The 6l6's) grounded to chassis but they red plated my power tubes. I never thought anymore about it....
Now that was a BIG missing piece of the puzzle. Kinda like withholding evidence. Would have been nice to know about 200 messages ago.
Hindsight is 20/20... I would have had to brain-storm to remember all that and reveal it. It is easy for you all to think of because you all do this all the time, I am just learning.I apologize but I would have never thought of that in a million years. I was not purposely "with holding evidence" as I am with you and it would have been much nicer to think about it from the start and get it fixed then.... Again Thank you!
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I am glad you have it working. You may try another pair of 6L6GC / 5881 tubes. You may have damaged them during previous red plating and other tubes may resolve your bias problem. -48 is what your shooting for.
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I am glad you have it working. You may try another pair of 6L6GC / 5881 tubes. You may have damaged them during previous red plating and other tubes may resolve your bias problem. -48 is what your shooting for.
Putting new tubes in still gave me -38
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That's where Doug's tracing method is very helpful.
If you take your time and are careful you find/remember things like the power tube K's not being connected. :icon_biggrin:
Glad you have it up and running!
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My 5F6A PT is supplying 59VAC for the bias. Yours is supplying 45-46VAC. I was think you may have to use an odd ball resistor value above 56K. Try the 82K again. Your bias voltage came way up in the -40 range last time you tried that. Your plate voltage will go up though.
I myself went with a 325-0-325 PT and am using a 5U4GB rectifier instead of a GZ34/5AR4.
I wanted my plate voltages to be lower producing and smoother mellower sound.
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My 5F6A PT is supplying 59VAC for the bias. Yours is supplying 45-46VAC. I was think you may have to use an odd ball resistor value above 56K. Try the 82K again. Your bias voltage came way up in the -40 range last time you tried that. Your plate voltage will go up though.
I myself went with a 325-0-325 PT and am using a 5U4GB rectifier instead of a GZ34/5AR4.
I wanted my plate voltages to be lower producing and smoother mellower sound.
I put a 5u4G rectifier in and got it down to 432 but my Bias still remained -38
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That should be because your PT bias tap is putting out 46 volts a/c vs my 59 volts a/c. Try 82k or 100k bias r again.
Some of the Power transformers i have bought are not exactly as advertised. The specs are off a bit sometimes. The current draw is different in some of them under actual working load.
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That should be because your PT bias tap is putting out 46 volts a/c vs my 59 volts a/c. Try 82k or 100k bias r again.
Some of the Power transformers i have bought are not exactly as advertised. The specs are off a bit sometimes. The current draw is different in some of them under actual working load.
I put a 93 k and Got - 43 my pins 3 on the 6l6's went up to 450
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My 5F6A PT is supplying 59VAC for the bias. Yours is supplying 45-46VAC. I was think you may have to use an odd ball resistor value above 56K. Try the 82K again. Your bias voltage came way up in the -40 range last time you tried that. Your plate voltage will go up though.
I myself went with a 325-0-325 PT and am using a 5U4GB rectifier instead of a GZ34/5AR4.
I wanted my plate voltages to be lower producing and smoother mellower sound.
I put a 5u4G rectifier in and got it down to 432 but my Bias still remained -38
Put a 5y3 and got -42 and 424 on both pins 3 of the 6l6's
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I see why it went up, it was not a 5u4... It was a 5AR4/Gz34 I did not look at it close enough. But the 5y3 it likes!
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The 5Y3 will not like it, it can't deliver enough current for a pair of 6L6's in bride bias and will burn up.
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Don't use a 5Y3. It
can can't take that high voltage for long. I think the power transformer you have is not really 5F6A material.
450 on the plates is fine but i better let someone else chime in here and take over on the bias and plate dissipation factor.
Edit: changed can to can't as that's what I think he meant? But the real problem is a 5Y3 doesn't have enough current capacity for this amp. Willabe
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The 5Y3 will not like it, it can't deliver enough current for a pair of 6L6's in bride bias and will burn up.
Isn't a 45 volt bias tap on the weak side for a transformer like this?
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Don't use a 5Y3. It can can't take that high voltage for long. I think the power transformer you have is not really 5F6A material.
450 on the plates is fine but i better let someone else chime in here and take over on the bias and plate dissipation factor.
Edit: changed can to can't as that's what I think he meant? But the real problem is a 5Y3 doesn't have enough current capacity for this amp. Willabe
[/quote
I got rid of the 5y3 and put the 5AR4 back in it.
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Trying to bias an amp by the -dcv listed in an old schematic is not a good way to bias it.
Fender got away with it back then because they were using vacuum tubes from the golden era of tube manufacturing. And they were using RCA which were great tubes. They were very consistent in their current draw. So Fender could just pop them in and they were close enough.
Different tubes from different makers will bias up differently, draw more or draw less current with the same -dc bias voltage.
You really should add a 1 ohm R in between each K and ground. Then you can measure for the tubes current draw without messing with hi B+ dcv. Much safer! And it's also good to change the non-adjustable bias that's in that amp to adjustable bias.
Here's the link for information on biasing an amp from Doug's Tube Library of information.
Since the bias of an amp is crucial to keep the amp from burning up you should read the whole thing on biasing.
Further down he tells you how to add the 1 ohm R's to the K's, how to make the bias adjustable and how to do the math for total power tube current draw.
After reading it through if you have any more questions on it post them. :icon_biggrin:
http://el34world.com/charts/fenderservice5.htm :library: (http://el34world.com/charts/fenderservice5.htm)
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Isn't a 45 volt bias tap on the weak side for a transformer like this?
Maybe a little, but a bias circuit doesn't draw much current, only the bias caps charging current so it doesn't sag down like the B+ wind.
45v x 1.4 = 63v
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Isn't a 45 volt bias tap on the weak side for a transformer like this?
Maybe a little, but a bias circuit doesn't draw much current, only the bias caps charging current so it doesn't sag down like the B+ wind.
45v x 1.4 = 63v
Ok i get that. Maybe i will stick a GZ34 after i order one and compare voltages throughout
Those NOS vintage GZ34 's cost a small fortune. I have not decided if i want to spend $150+ yet for a NOS Mullard GZ34.
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Maybe i will stick a GZ34 after i order one and compare voltages throughout.
Be interesting to see, Doug sells a good newly made version. :icon_biggrin:
Those NOS vintage GZ34 's cost a small fortune. I have not decided if i want to spend $150+ yet for a NOS Mullard GZ34.
Too rich for me. :icon_biggrin:
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.
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I have -64 @ the diode.
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Sluckey, is what you just posted backwards?
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I have -64 @ the diode.
That should be able to get you enough bias -dcv once you get the 2 R's adjusted. Or better yet make it adjustable bias.
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I have -64 @ the diode.
That should be able to get you enough bias -dcv once you get the 2 R's adjusted. Or better yet make it adjustable bias.
Yeah I just read those articles and I am thinking about making it an adjustable bias. I bought a little pot just for it in case that was what i wanted later on.
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Yeah I just read those articles and I am thinking about making it an adjustable bias.
Great. :icon_biggrin:
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I just cannot say Thank you enough! Willabe, Sluckey, and Plexi50! You all helped me tremendously. I hated that it took me so long to figure this all out but I learned a lot in the process.
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I just cannot say Thank you enough! Willabe, Sluckey, and Plexi50! You all helped me tremendously. I hated that it took me so long to figure this all out but I learned a lot in the process.
See that's what this is all about. Pulling your hair out struggling to understand why an amp doesn't work or work properly. Just swapping out tubes does not tell you why a tube may have failed. The health of the resistor & capacitor in a bias situation is something you have to ruel out by taking voltage readings. It may seem like we are harsh at times but it's anything but that. So happy you have it working. The rest is minimal tweaking at this point. :icon_biggrin:
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Sluckey, is what you just posted backwards?
Which part? All of it? What do you mean?
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Which part? All of it? What do you mean?
"If it is higher than the voltage you want at pin 5 of the 6L6s you can lower the value of the 15K OR increase the size of the 56K to achieve your desired voltage."
Won't both of those increase the -dcv not lower it?
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Which part? All of it? What do you mean?
"If it is higher than the voltage you want at pin 5 of the 6L6s you can lower the value of the 15K OR increase the size of the 56K to achieve your desired voltage."
Won't both of those increase the -dcv not lower it?
Absolutely. That's the objective here. When I wrote that he only had -38v and plexi was trying to get him to increase it to -48v. Makes sense to me. Maybe I didn't state it clearly?
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I see it now. If the -dcv at the diode is higher than what you want/have at pin 5 then you can get more by changing either/both of those 2 R's.
I misread it as if the -dcv is higher pin 5.
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I first used a 56K that put me @ 418VDC plates with a -49.8 grid
Then i put in a 47K and that gave me 408VDC plate with -48 dead on.
I can live with 430PV if i had to but i wanted the lower plate voltage.
Tired of 460VDC 6L6GC amps. Their just LOUD to me and that's it.
When my GZ34 arrives i will do all voltage comparisons.
The lower B+ for me though really allows for a more musical tone.
I wonder if Silat used all old tubes would he not have this bias issue? Hard to say i suppose.
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That's fine to get your plate voltage down some as long as the tubes won't red plate.
But I would still double check the total current draw on each tube so their not over 70% at idol.
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I wonder if Silat used all old tubes would he not have this bias issue? Hard to say i suppose.
Maybe? :dontknow: