New issues on my JTM45 build while testing tubes.

[gtrplayr1976]

I started a new thread since these are issues that showed up after I had selected tubes to use in my JTM45.

1: As stated in the previous thread ,I had experienced some audible noises when I removed tubes from the amp after it sat unplugged overnight. Never had that happen even after an hour. Was said to be leftover voltage in caps.
2: After I had settled on tubes to use for awhile I had set the bias ,and left it there for about 30 minutes. It was steady ,so I turned it off ,and left it overnight. The next morning when I powered up to check it again the bias was slowly increasing ,but when it settled it was more than 10mA off. I adjusted again to where I had set it before. As I was increasing it I could hear a little puttering until I got near what it was then it stopped. I left it there for about 30 minutes ,and it was steady.
3: When I switched from play to standby there was an awful bunch of noise ,and as soon as I switched back to play it was fine. Every time I did this I got the noise. Bad switch, cap, choke? I only tested the switch continuity with a meter. Seems fine. Checked the filter cap attached to the switch with a capacitance meter ,and was within spec. ( I have an ESR meter on the way).
I have a few more things I want to check ,but I'm leaning toward bad standby switch since I know they aren't designed to handle high DC.

Had the wrong layout. THIS Triode is what I used.

[The Dude]

......The next morning when I powered up to check it again the bias was slowly increasing ,but when it settled it was more than 10mA off......

Are you saying the bias supply voltage was slowly increasing or the bias current? The bias was 10mA off, was it too much current or too little?

[gtrplayr1976]

Are you saying the bias supply voltage was slowly increasing or the bias current? The bias was 10mA off, was it too much current or too little?

I was using a bias probe. Had it set at 39mA ,and it was 29mA. That seems to be ok for now. I think I need to reroute some wires. I believe when I removed the PPIMV ,and put the control grid wires back I may have them in a bad area. I also twisted them together. Not sure if that's advisable? I may just bypass the standby altogether.

[Helmholtz]

I don't see the 0.05µF cap in the layout that connects from the rectifier output to ground (before the standby switch). It should be rated at least for 630V. It helps to reduce the turn-on surge current for the GZ34.

[gtrplayr1976]

I don't see the 0.05µF cap in the layout that connects from the rectifier output to ground (before the standby switch). It should be rated at least for 630V. It helps to reduce the turn-on surge current for the GZ34.

Yes I noticed that none of the layouts I have from different makers have that cap. The Marshall ,and Fender Bassman schematics both have it. I will either add that cap along with a new switch ,or just bypass the switch.

[gtrplayr1976]

Found AN issue. Three of four points on the wires from my bias pot to the circuit were broken ,or probably just nearly broken. When I moved the wires a little they all snapped. Got that fixed ,and reset the bias ,and the standby switch isn't making noise now? I'm going to play around with it some more ,and see what I can find.
One thing I saw that confused me, when I was reading voltages on the control grids of the power tubes I noticed on one when I put the lead on it i could hear a rising noise ,and the bias was going up. Could that have been because I had that tube sitting in a bias probe socket ?

[Helmholtz]

One thing I saw that confused me, when I was reading voltages on the control grids of the power tubes I noticed on one when I put the lead on it i could hear a rising noise ,and the bias was going up. Could that have been because I had that tube sitting in a bias probe socket ?

Try to pull the PI tube before you repeat the grids measurements.

[gtrplayr1976]

Try to pull the PI tube before you repeat the grids measurements.

Speaking of the PI ,what voltage can you typically expect here where the two resistors meet?

[Helmholtz]

Speaking of the PI ,what voltage can you typically expect here where the two resistors meet?

Around 350V. What are your PS voltages?

[gtrplayr1976]

Around 350V. What are your PS voltages?

That's what I thought. It looks very low ,but I think I'm just getting a bad reading because the plates are 240-250.

[Helmholtz]

That's what I thought. It looks very low ,but I think I'm just getting a bad reading because the plates are 240-250.

In your other thread you mentioned a plate voltage of 450V. What happened?

[gtrplayr1976]

In your other thread you mentioned a plate voltage of 450V. What happened?

Power tube plates yes. This is the PI plates.

[Helmholtz]

I see, but what's your problem?

but I think I'm just getting a bad reading because the plates are 240-250.

I don't understand this. What is a bad reading?

[gtrplayr1976]

I see, but what's your problem?



I don't understand this. What is a bad reading?

I was getting a bad reading on the meter at the point where the two PI plate resistors meet. Plates are good ,so it was just a funky connection between my meter ,and that point.

[Helmholtz]

I was getting a bad reading on the meter at the point where the two PI plate resistors meet. Plates are good ,so it was just a funky connection between my meter ,and that point.

Now what's the good reading? Do you need further advice?