Tube Amp Archive

I jumpered the jacks to chassis ground and all is quiet. I think that I overthink cliff jacks because I keep revisiting that very issue over and over when I deal with them. Thanks all.

Hmmnn, I am using Cliff jacks for the outputs, so they are isolated from ground Ill bet. I wish work could wait.

I feel terrible to lean on you so much. Thank you. I'm late for bed, but I will get them tomorrow after work if you are still interested.

I received some help with voicing and oscillation issues and how I am trying to tackle hum. I started with the EL34 power tubes and all was quiet. I added the 12AX7 phase inverter and the noise came back. Lifting the NFB stopped the hum, so I switched OT leads and reconnected NFB. Now I had hum plus...

I was thinking about using a shielded wire there, as it happens. I didn't want to do it "just because" though so I was going to research that a bit. The weird bit is that I have done as you suggest and put everything to 10 and all I hear is some hum, but it is present even with volumes down, so I am...

I was using shielded wire for that connection, but I see the point about that resistor hanging out there. I ended up bypassing that turret entirely and running a longer shielded wire to the resistor and then to the pin with minimal exposed lead. I did try swapping OT leads while I was waiting for so...

While researching the proper way to remove the low input, I found a thread here that discussed just that, so I used it as a guide. What do you see wrong?

Thanks for the advice. I will make the changes and advise. I have tried another 2x12 cab that I built. It is loaded with Avatar M65s and is closed back. It still has the issue, but the onset is much higher in the volume range and even then, much less serious.

I removed the low input from this circuit, as well as the bright cap. The 470k/470pf treble peaker between V1 and V2 has also been replaced with a 100k resistor. Oscillation was what I landed on after some research, but narrowing down the source is where I have some weakness.

After more experimentation, if I max out the master volume and use the preamp volume to adjust overall volume, at about 1 or 2, I hear a scratch in the pot and things get fuzzy and begin to make all sorts of bad noise.

Hi all, I posted a while back about some problems I had with my newly built (and my first build as well) JCM800 Mini. I built is per Rob Robinette's drawing's (https://robrobinette.com/RR2104_Master_Volume_Micro.htm#JCM800_6V6). Bass notes seem to cause a feedback as the note is struck. It happens o...

Been away for a few days, but I will try these and let you know. Incidentally, is there is there a theoretical reason for the bass early-treble later approach or is it something you have learned from experience?

I hover around 5 at home, but I do spend some considerable time below that when wifey is doing her work form home.

I guess that what I am trying to accomplish is the get the the tone stack set to a point where from zero to ten, it is at least musical. That said, I would welcome any mod suggestions, even if they move away from the JCM800 sound. Ultimately, this amp is a keeper for me, both because it is my first ...

xtain,
As noted above, I removed the peaker and brite cap as well. Also remove the low input. I have never used them. I put a 68k resistor in place of the peaker. Is there a better option there?