ac ripple on screen grids Ultralinear

[loudthud]

Look for an old analog radio. Nothing with digital tuning. A meter probe will act as an antenna so try probing around those output tubes. The normal between station static will quiet down when a nearby transmitter is broadcasting even if the frequency is not in the AM band. At my shop we listen to AM radio so we can tell when the guy next door is welding. Digital equipment gets data errors and internet connection is interrupted.

[Rattler66]

Look for an old analog radio. Nothing with digital tuning. A meter probe will act as an antenna so try probing around those output tubes. The normal between station static will quiet down when a nearby transmitter is broadcasting even if the frequency is not in the AM band. At my shop we listen to AM radio so we can tell when the guy next door is welding. Digital equipment gets data errors and internet connection is interrupted.

Cool thank you. I'm going to do that. It's gotta be oscillation

[Rattler66]

well i relocated the primaries of my ot and now the voltages are steady and i can bias it fine BUT i'm still getting a hum. AC grounding the grids doesn't do anything. i need to turn it on and determine if 60 or 120hz hum. i also shielded the enclosure with metal tape . i need to see if it helped (i didn't get a chance to plug in)

[trobbins]

Do you have an android phone, or a laptop/PC with microphone - there are many free spectrum analyser apps.

[Rattler66]

yes I have an android, let me check it . thanks

[Rattler66]

Okay as i said i relocated the ot primaries and the erratic voltages stopped. I found a spectrum analyzer for my phone and showed 120hz at the first node. I rebiased and reconnected an additional temporary rc filter right before the first node and the hum dropped by about 80% or more. It's so low i couldn't believe it. But i would like to reduce it more. Am i understanding correctly that if i go with a choke that the ripple would be even more reduced?

[pdf64]

Okay as i said i relocated the ot primaries and the erratic voltages stopped. I found a spectrum analyzer for my phone and showed 120hz at the first node. I rebiased and reconnected an additional temporary rc filter right before the first node and the hum dropped by about 80% or more. It's so low i couldn't believe it. But i would like to reduce it more. Am i understanding correctly that if i go with a choke that the ripple would be even more reduced?

That should be the case, but a choke would need to be fairly beefy to be rated for the current draw.
Before implementing mods, it would be a good idea for find out why the stock HT arrangement, which works well, isn't doing so in your case.
Unfortunately the thread is too long to quickly review what's been checked / tried so far.

[Rattler66]

That should be the case, but a choke would need to be fairly beefy to be rated for the current draw.
Before implementing mods, it would be a good idea for find out why the stock HT arrangement, which works well, isn't doing so in your case.
Unfortunately the thread is too long to quickly review what's been checked / tried so far.

Yeah I get what you are saying. The issue with this build is when I first did it, I severly overspecced the PT, it's a beast and I went with an OT that would fit the application, not necessarily the proper one that the design called for. Anyway I've put a crazy amount of effort into this thing over the years (my wife teases me every time I say "I think I found the problem") But yeah your point is well taken but if I can just add a choke for $30.00 and be done with it, I'd be as happy as a pig in mud.

[Rattler66]

Added the choke and the amp is dead quiet. Finally this amp is done. I really learned a lot through this. Thanks guys

[Mandopicker]

The ultra linear amps I have worked on did not include a choke...and from what I understand, running the OT in UL mode does not require such. THey have been very quiet. I would check the grounding location for the main Filter Caps and the HT from the PT. I have always found the careful selection of where to ground stuff, and with WHAT...makes for a quiet amp.

[Rattler66]

The ultra linear amps I have worked on did not include a choke...and from what I understand, running the OT in UL mode does not require such. THey have been very quiet. I would check the grounding location for the main Filter Caps and the HT from the PT. I have always found the careful selection of where to ground stuff, and with WHAT...makes for a quiet amp.

you're probably right but i racked my brain with this amp and the choke solved it and it sounds great, so i'm not touching it anymore.. thanks though

[Mandopicker]

Good deal!