My new build ,high volyage readings

[danman]

If you use the light bulb limiter with the power tubes installed, the bulb will glow because of the current draw of the power tubes filaments. It should not glow intensely but it will stay lit because of the filaments's current draw. Don't be surprised if the amp doesn't sound great either because the light bulb will starve the amp. Just check to see if the amp plays ok and then you can unplug from the limiter and plug it in normally. Then you will be able to take a plate voltage reading and do the math to set the bias. Be sure to always have the amp plugged into a speaker cab anytime that you have it on with the power tubes installed.

The voltages that I mentioned checking should be listed in the instruction manual for your amp. You will want to check the plate voltage (DC) on pin 3, the screen voltage (DC) at pin 4 and the negative bias voltage (DC) at pin 5 of each power tube socket. It would also be a good idea to check the AC heater voltage on pins 2 and 7. Keep in mind that if you check these without power tubes installed, all of your voltages will read 10-15% higher than expected. If you do not have a voltage chart handy, just take the measurements and post them here.

[fixer2]

I put in the power tubes and with the dim bulb test with a 200 watt bulb in it .just a dim light up then out then slowly light alittle not even a 20 watt bulb bright after two minutes I got 59.2 volts I have three settings on this kit of the feedback circuit like a jtm 45 ,1987 plexi,and a fender bassman . So I got 59.2 volts 124 volts and 82 volts so were Iwas before getting 111.4volts Inow am getting 59.2 volts.they say plus or minus 10 volts .Notransformers got hot no smell and Ileft it on for 20 min.I need to test the other pins of the power tubes ,what are the voltage readings I don't have any chart or info on this.

[danman]

It sounds like everything is ok with the power supply but did you get a chance to play the amp to see if it was functioning correctly? I cannot give you an accurate voltage chart for your amp because I do not know what type of power transformer was supplied with your kit. The plate voltage (pin 3) on Marshall amps varied anywhere from 370vdc up to over 500vdc depending on the year and type of circuit. Since Tube Depot supplied a voltage chart for the preamp tubes they should have also provided a list of expected power tube voltages that would correspond with the power transformer supplied with the kit. If you cannot get the info from them, check the Metroamp JTM45 instructions for a list of voltages. You can find it online pretty easy with a simple Google search. Keep in mind that it may differ slightly from your amp because of the transformers used in the kit.

[fixer2]

Thanks I will have to try that (plugging in ) And also get the reads so you all know.

[fixer2]

Hi I tried it with a guitar ,and got no sound so now I am starting oving threw every thing neating up too.I also notice no light in the pre amp tubes.And from the ground to the one wire on the pres. pot I get a continuity ?.Well I know now That I have a lot to check so when I can I will get the voltage readings to post,them .But still any Ideas I will listen to.Thanks.Also I was not getting any signal or dc voltage to the speaker jacks?

[danman]

Are you positive that the preamp tubes are not lit? Some tube's filaments glow pretty bright while other hardly glow at all. Do they get warm after a few minutes with the amp on? You will need to verify that you are getting filament voltage to all pre and power tubes before the amp will pass any signal to the speaker jack.

[fixer2]

Hi I have been doig a lot of looking into this amp I mean tracing my work and trying to see what I did wrong .So far I have come up with nothing I am very new to this so I do not know.I did pit back together what I took apart and plug it straight into the wall full voltage and turned off all the lights in the room an d I did see very dim little lights close to the base of the tubes on the pre amp tubes no were near as big and bright like the power tubes .I did do some meter testing last week with ,continuity test and I get a beep when I put the one probe on the chassi for ground and any one of the points on the choices of speaker out puts or were the filament wires from the transformer hook up to the board and on a few pins on each tube Iam getting no sound and it seems like I am sending the sound off to the ground and going no were . What is the path of the singal from the in put to the first tube to the board and to the second tube ??????? Or am I send the power to the ground and that's why I am getting such a high reading on v3 pin #8 111.4 volts instead of 35 volts.Where do I start looking ,I will take it back apart and redo if that's what it takes.

[fixer2]

Question where are the heater wires ,what pins on the tubes I think this is where it is messed up I think Iam getting a ground read here to the body of the chassis because after a few minutes after powering it up there is no voltage left in the capictors the big ones I mean do yo bleed them off by grounding out pin number one on V1 ???????

[danman]

On page 13 (drawing 5.5b) in the Tube Depot JTM45 instructional pdf, it has a detailed drawing of which pins to connect the heater wiring to on the power and preamp sockets. It is normal for the filament wiring to show continuity to ground because the filament center tap on the power transformer is connected to ground. Whats more important is that you check each socket for the proper AC filament voltage. Without the proper voltage for the heaters, the amp cannot pass a signal. As for the filter caps bleeding down their voltage after turning off the amp, it can be normal depending on the circuit. You mentioned earlier that the light bulb in your limiter did not glow when powered up so it doesn't seem that you have any shorts to ground in the power supply. It is possible that your signal voltage is going to ground and this may or may not be why the amp produces no sound. We really need a full list of all voltage readings at each socket to help figure out the mistake. To get started, set your meter for AC voltage, on the preamp tubes place one meter lead on pin 9 and the other lead on pins 4 and 5 (they should be connected with a small piece of wire). What voltage do you show with the amp powered up and on standby? Now place one lead on pin 7 and one on pin 2 of the power tube socket...what voltage reading do you get?

[fixer2]

When you say stand by on you mean in stand by mode not play mode ,so the stand by is letting the amp heat up and make no sound that is if I where to have a guitar plug in just want to make sure .Thanks

[danman]

Correct...in standby and just warming up. In standby mode you should have AC voltage to the tube's heaters but no high voltage DC (B+) should be getting to the tubes yet. When you take the amp out of standby mode, the B+ will reach the tubes. I just want to see if you have the proper voltage at the heaters right now.

[fixer2]

just been busy with work havent have time to get all the readings but I soon will have them .Have to get ready for a show this week end first

[fixer2]

Hi I tested them just how you ask me to and I got a reading of 006 volts

[danman]

When you measure across the two pins on the power tubes, you should see a reading around 6.3vac. When you measure across the preamp tube pins, you should see around 12.6vac. From the measurement you listed above, I cannot tell if you just don't have your meter set correctly or if that is the actual reading. Does your meter have an auto-ranging function or did you set it for the proper, low voltage AC scale? Your reading of 006.v may be correct for the power tubes if you have it set on too high of a scale but that reading would be to low for the preamp tubes. I took a look the instructional pdf for the kit and it has very good instructions on how to set the meter and where to measure the voltages for the heaters and other parts of the circuit. Since this kit is a little different than the normal Marshall style layout, it may be best to follow the testing procedures they list in the instructions.

[fixer2]

I think I had the meter set for ac volts I do have another setting I will look .I will look the meter up for more imfo on it I am using a friend on mines meter so I do not have any book on it but it is a good flluke meter.sorry about that.