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Discussion in 'Shock Brother's DIY Amps' started by Preacher, Oct 15, 2017.
P8 on the 6V6 or P8 on the rectifier?
By the way I did fire it up with a lightbulb limiter and did not have any shorts other than a bad tube that was shorting. I replaced it and took the reading without the limiter connected.
6v6 p8 to ground
+Check for heater voltages
Out till Wednesday. So any suggestions would be appreciated.
Your layout has voltages for p3 of both the 6v6 then you stated there was no voltage there. I was looking at the readings and must have missed that.
If you do not have plate voltage, this would be the first item to figure out.
Dou you have B+vdc at the OT primary center tap( the red wire)
This feeds B+ to the plates, p3,of the power tubes( blue wire and brown wire)
If you have B+ at red wire and not at the plates, we need to check the windings of the OT primary.
Amp unplugged and caps drained....
Ohm from the red(CT) to the blue wire then from the red to the brown wire. Keep these measurements to later calculate bias.
Let us know what you find. Good luck.
No voltage on pin 8 on either 6V6.
I did P8 on both 6V6s to ground and have nothing.
We need a resistance reading in ohms here from the 6v6 p8 to ground on each power tube. This will check the cathode bias resistor to ground. It should read close to whatever value is stated on the resistor. stock 5e3 is 250 ohms. lots of kits use a larger value. Take this reading with the amp unplugged and caps drained.
The voltage for the heater will read in AC voltage. Measure across pins 2 and 7 of each 6v6 after confirming the bias resistor
If you have a solid cathode circuit and proper heater voltage you may have more socket issues, reflow the connections, ensure the pins fit snugly into the socket
Also... These things here concern me. I would trim the excess leads from the board so that they do not have any chance of touching anything else. Remove that butt connector and add a grommet to the OT through hole.
Pin 8 on the 6V6 to ground is bouncing from .308 all the way up to .647 and everything in between with resistance on the meter set at 2K with the amp off.
2 and 7 on the 6V6 is measuring at 5.7AC with the amp powered on. The extra leads were trimmed. Good catch I am kicking myself over them. And the yellow butt connector was a washer for the OT. I have clipped it as well.
@Preacher , this needs to be a steady solid reading. Im assuming a 250 ohm resistor there, which should read between 245-255 Ohms or .250 on the 2k range of your meter. Reflow solder connections as needed. Once you can get a reading that satisfies, take another round of voltage readings. While probing for voltages set the volume about half way and note any scratch or pop sounds from the speaker. You should hear something probing the grids and plates of the power tubes, plate grid and cathode of the phase inverter, and plates and grids of the preamp tubes. Lack of noise in any one area points to potential issues.
Good luck! You should be rockin this thing soon!!!
Pin 8 to ground still jumping. I used a new battery in the meter and replaced the lead and am getting the same issue.
Amp is off and caps discharged. Probe is grounded to chassis.
I shot the rest of these just resting the probe on pin 8.
Numbers go up and then come back down. I checked the joints at that resistor and they are good. Resistor is measuring at 247.
So I am getting popping through the speaker when I ground pin 8. Accidentally touched the probe to pin 8 and hit the top of the screw that is poking up.
I also checked continuity on the ground to chassis. I grounded my meter like shown above and then I also grounded it to the bus on the other side of the amp. Same results.
Just re ran some numbers and I do not have any current on the pre amp tubes 1 and 6.
How did you measure the current on the plates?
I tried to get the picture to show all I was doing. I grounded one probe to the chassis (also grounded to the bus but got the same result - I have connectivity between the chassis and the ground bus) and then put the other probe against pin #8. That is where the meter is jumping. I then replaced the lead at that point thinking maybe it had a short but I received the same readings. I even went and took a reading directly off the board at the cap and resistor and got the same wacky up and down readings.
I spent a little time yesterday on the amp, but only a few minutes as it was 95 degrees and a little thunderstorm put the humidity through the roof. I did not think working on a tube amp with sweat dripping off my face was a good idea.
I ran voltages from the wall (115.5) and have power through the fuse and the main switch. Through the standby I was getting about 630 (315-315) on the rectifier tube off the transformer and 4.7 on the heaters.
Preamp and power tube heaters are measuring 5.9 also.
Pilot light is on.
I am getting 315V on the rectifier inputs.
Oh and I did the start up procedure with the light bulb limiter and everything went as it should. I then powered up the amp without the bulb limiter and no smoke or sparks!
I am about to the point where I am going to pull this chassis apart again and start over. I would not remake the board but would pull all the resistors and caps and check them over and then re-install. Scrap all the wiring and redo it with some 18GA I have on hand in pretty colors as the 20GA is a little hard to work with.
@Preacher , I don't believe it necessary to start over, your call though. Do you have a clip for your meter probe? Just hanging it there in the chassis hole can produce some questionable readings. With your black probe grounded via alligator clip or such to the chassis, probe every connection in the path of the cathode resistor with the red probe. Start at pin 8, I see a new green wire there, steady reading, no, go to the board at the solder joint, steady, no, take a reading from the resistor leg itself, steady yet? At this point I would reverse my strategy and clip the black lead to pin 8 on 6v6, now continue at the resistor leg, should be o.o1ohms. Now check the other leg of the resistor, steady 250r, yes, go to the solder joint toward the ground connection, steady, yes, move to the next connection and so on until you reach the chassis. You should be able to pinpoint the area in question. Do this with all of your cathodes until you can predict what reading you should have and why. Reference all this to the schematic and take notes.
With your meter in current or milliamps mode you are shorting the plate to ground through the meter so disregard any readings you got that way.
I recommend you do a voltage chart of every tube pin to help us diagnose the problem. Don't give up, we can find the problem(s).
Here are the voltage readings
The numbers are a little light across the board from what RobRob’s site says. I believe that is because my power tranny is pull from a VHT model and it may be a little under powered compared to the 355/355 PT Rob shows.
So I had a little time today to mess with the amp. I took D’tar’s advice and decided that I had a lot of work completed so before I did a total tear down I ran the voltages again with a clipped down negative probe, a new battery and a steady hand. I posted the numbers in the post above.
So after the numbers all showed promise I decided to fiddle around some more. I found one suspect solder joint at the speaker jack so I fixed that and got a little hissssssss out of the ceramic 10” speaker I have for my Fenderish Valve JR project. Oh and I replaced a suspect 12AU7 with a known Good 12AX7 out of my Valve JR also just in case.
So I am getting a little hissssss out of the speaker so I hook up a guitar to high input #1. Nada. Nothing. Well here goes nothing, let’s try all the jacks. Low input on channel 1. Nothing.
Let’s go to high input on channel #2 shall we.
Sweet baby Jesus!
I have guitar sounds out of the speaker! Bad guitar sounds but they are guitar sounds none the less!
Adjusted the volume and tone controls, they were all dimed by the way and it started to sound better. Adjusted the LTD M15 shop guitar and rolled off some treble from the humbuckers and it was reasonable. Dialed a little longer and decided this is what the amp is supposed to do, at least with a cheap 10” ceramic cabinet on the shop floor.
Went back to work on channel #1. Decided to replace the leads, clean up some solder and LOW and BEHOLD SHE LIVES!!!
I actually threw my hands into the air like Rocky when he won his fight against Apollo Creed!
da da dom dada dom dada dom dada dom!!
So the wiring is complete(I solder and shrink wrapped all the wire bits - no more Wichita Lineman for me. All I need to do is put on the face plate and the knobs. And then start work on the cabinet as the 12” speaker is on hand. I have both 3/4” pine and 1” Baltic Birch plywood in hand. I have baffle material and some really nice ostrich skin vinyl in black and burgundy that I was going to build a motorcycle seat out of.
Whoooihoooooo! I am going to have a 5E3 Deluxe!