jtm 45 high voltage readings

[elmo]

This is my first build. I am reading 246vdc pin1 and 324vdc pin6 on v1 all the heaters are around 3.5vac without any tubes. any suggestions of where to start. I only put the tube 1 and 6 in just to check these voltages I didn't want to ruin anything is the reason I only used the two tubes. I'm using a heyboer PT, any help would be appreciated . Thanks

[danman]

Welcome to the forum! You will really need to have all of the tubes installed to get a proper voltage reading. Without the power tubes loading down the circuit, your readings on v1 will be high. If this is your first build it may be a good idea to use a "light bulb current limiter" for the first power up with your power tubes installed. This device is easy to make and will help to prevent any damage from a wiring mistake.

[vh junkie]

Lets get a full tube chart of voltages like in the metro amp instruction with just the rectifier tube and the (3) preamp tubes in. Do not put the power tubes in yet. What is your AC wall voltage?

[elmo]

Thanks danman and vhjunkie I do have a current limiter [uncledoug style] my wall voltage is 124vac. I was trying to follow the chart from the instructions my readings seemed high. I will get the tubes in Wednesday and repost then, work is all ways getting in the way of my hobbies, but it does help pay for them. Thanks for your patience

[elmo]

Here are the readings with v1,2,3 and 6 installed.
v1 pin 1: 228.3 2: 3:1.8 4:3.51 5:3.51 6:251 7: 8:1.8 9:3.50
v2 1: 202 2: 3:1.25 4:3.51 5:3.51 6:354 7:202.5 8:203.6 9:3.50
v3 1:280.6 2: 3:46.6 4:3.51 5:3.51 6:259.6 7: 8:46.5 9:3.51
v4 1: 2:3.51 3:493 4:486 5:-41.7 6:487 7:3.51
v5 1: 2:3.52 3:484 4:487 5:-41.7 6:487 7:3.53
v6 1: 2:495 4:363 6:363 8:495
standby is 363vdc and power supply is 121.5vac
If these are acceptable should I put the 5.6k resistors at pin5 of v4 and 5 or wait to see if the squeal/ motor boating happens.
Thanks

[danman]

If I am reading your voltages correctly then nothing unusual jumps out at me. When you do fire it up with the power tubes installed, your current limiter will flash brightly for a second or two as the caps charge up. It should die down to a soft glow after a moment, but this will depend on what wattage bulb you choose to use. If everything looks good with the limiter, you should be ok to plug in normally and give the amp a trial run.

It would be a good idea to install the 5.6k's on pin 5 now. There was a fellow here last month that was having issues with his new build. After Neikeels suggestion of adding the grid resistors the amp performed perfectly. Be aware that if you do get a loud squeal or horn blast after installing the resistors, you may need to swap your OT's primary leads at the power tube sockets.

[elmo]

Thanks danman I will finish up tonight and post an update tomorrow. I appreciate the help greatly

[elmo]

danman I installed the 5.6k grid resistors put the kt66's in plugged in on the treble input put the tone stack in the middle volume on 2 to sounds good!!! Got one problem I used a y cable went to flip the standby and got lit up [shocked]. where should I look for the bad ground the input grounds are together at the pot buss Thanks for all your help

[vh junkie]

Make sure you did not inadvertently connect the HIv to one of the junctions of the 68k resistors near the inputs. This connection might be under the board. Check the Vdc at the junctions of the 68k resistors.

[elmo]

I had bent the 470 over and believe it was touching pin seven and the standby switch was a little loose I checked several times for voltage on the switch and had no problems played about 2hrs today it sounds sweet loud enough to break up. Thanks again Danman

[fixer2]

Hi I just finished m first amp build a clone of a JTM 45 and I put the rectifier tube in and three per amp tubes,no power tubes yet I plug it into my light bulb dim tester I got a light but only for a very short while ,like one second or less.no smoke no smell nothing hot to the touch like transformers just the tubes.On v3 on pin number 3 the chart said I should get 35 volts with 116 wall volt coming into the amp I have 114 volts on the wall coming onto the amp and on pin number t36 on v3 pin #3 Iam getting 111.4 volts .What could be wrong ,what do I need to check so you guys can tell what is wrong .I have build five pedals before this buid so I have done some small work like a delay pedal ,etc. using a good flike meter (and have lokked over every joint with a fine tooth comb )