Unloaded b+ low
Moderators: pompeiisneaks, Colossal
Re: Unloaded b+ low
I know it's not a thing of beauty but it seems the more I try to improve it the worse it gets...
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Re: Unloaded b+ low
Wow! Quite a hodge podge mess you have made. I understand your dilemma. I don't understand why you would throw all this stuff together, especially for a first scratch build. My sympathies to the guys at 18watt.com.
Re: Unloaded b+ low
I haven't scrutinized your build much, but it is clear your grounding scheme does not follow your schematic. It is usually good practice to separate your preamp ground buss from your output section ground scheme. You seem to have it all on one buss wire. Your schematic shows your PI cathodes grounding through the PI tail resistor circuit to your OT secondary ground, but you have this connected to your preamp buss wire. Try clipping the buss wire between that PI tail resistor and the preamp tube cathode capacitor ground and develop a second ground point for your PI/output section.
Your power supply also shares a single ground point with both plate supply and screen supply caps as well as your dual PT cathode bias caps/resistors. An expert will need to opine, but I'm not sure those should all be connected at the same point. AFAIK, you would normally share the PT plate supply cap ground with the heater center tap (artificial CT 100R resistor grounds) and the HT secondary center tap, and have a second isolated ground point for the screen supply capacitor.
[EDIT: A bit more looking---Your turret board places the power rail at the bottom edge of your board. Your plate and cathode wires pass directly over this to get to your tube sockets. Usually you would separate the plate supply rail away from the signal wires as much as possible, usually by hiding the power rail underneath your turret board in the middle of the board and extending your plate load resistors from there to the bottom edge of the board for dressing leads to your tubes. Your layout makes that difficult.]
Your power supply also shares a single ground point with both plate supply and screen supply caps as well as your dual PT cathode bias caps/resistors. An expert will need to opine, but I'm not sure those should all be connected at the same point. AFAIK, you would normally share the PT plate supply cap ground with the heater center tap (artificial CT 100R resistor grounds) and the HT secondary center tap, and have a second isolated ground point for the screen supply capacitor.
[EDIT: A bit more looking---Your turret board places the power rail at the bottom edge of your board. Your plate and cathode wires pass directly over this to get to your tube sockets. Usually you would separate the plate supply rail away from the signal wires as much as possible, usually by hiding the power rail underneath your turret board in the middle of the board and extending your plate load resistors from there to the bottom edge of the board for dressing leads to your tubes. Your layout makes that difficult.]
Just plug it in, man.
Re: Unloaded b+ low
Hodge podge mess. It has got rather like that. I only just added the recto switch to see if the valve rectification was causing problems. I had real problems with diagnosing problems as they were very intermittent. I eventually realised my ac supply was VERY bad and I'm now running off an always on ups. By that time I'd done a lot of wiggling components about and chopsticking and resoldering. I thought I'd followed 18 watt best practice ground scheme
https://www.18watt.com/viewtopic.php?f=4&t=25372
I think my pi and pre sections are on one ground bus going to ground with the inputs.
I've made more space between the wires crossing and the ht rail. I didn't want anything under the board just in case the amp didn't work first time...
https://www.18watt.com/viewtopic.php?f=4&t=25372
I think my pi and pre sections are on one ground bus going to ground with the inputs.
I've made more space between the wires crossing and the ht rail. I didn't want anything under the board just in case the amp didn't work first time...