Recent Posts

91

Other Topics / Re: Music Electronics Forum 2

« Last post by pdf64 on December 05, 2025, 03:28:35 am »

Thanks for the prompt / reminder, I've just emailed him :)

92

Tube Amp Building - Tweaks - Repairs / Re: DC-coupled cathodyne and feedback

« Last post by Merlin on December 05, 2025, 03:12:19 am »

Is it possible that the additional current through the phase inverter afforded by the 15k loads improves its ability to drive large low-frequency signals (it is after all a "bass amp") on the grids of the 6L6 power tubes?

It will slightly improve its ability to drive grid current yes, but not by much.

93

Tube Amp Building - Tweaks - Repairs / Re: Hum and Buzz in Cordovox Build

« Last post by TIMBO on December 05, 2025, 02:21:37 am »

Hey mate,
This is one I did awhile ago
Upstairs, Downstairs Chassis?????
It all came down to earthing the chassis(two) and a grounding associated with separate chassis
So I can imagine three chassis being a grounding headache

94

Other Topics / Re: Music Electronics Forum 2

« Last post by SoundmasterG on December 04, 2025, 11:25:57 pm »

Well I found my way there. Thx for the heads up! :-)

If you know any of the old crew there who hasn't shown up, get the message out. Chuck H is still not on there, but I don't have any contact info for him.

Greg

95

Sound clips / Rough Ride to Nineveh, Huh Jonah!

« Last post by Platefire on December 04, 2025, 10:39:26 pm »

https://soundcloud.com/connie-and-bob-scott/rough-ride-to-nineveh-huh-jonah

96

Other Topics / Re: Platefire Update

« Last post by Platefire on December 04, 2025, 10:18:15 pm »

Yelp, will do! Same to you. I got a guitar picking buddy that wrote and recorded a song titled "Keep on Keeping on"---pretty good tune that I listened to several times lately.

Had some good entertainment today. I don't like the feel of my guitar strap on top off my pacemaker on my left shoulder. So I did about an hour of experimenting of trying to invent a strap arrangement on my right shoulder instead of my left. Of course it kept sliding off?!? So I got an old belt that I could run through the strap to hold it in place. I finally found a combination that worked good by placing the belt right above my abdomen through the strap of the front and over it on the back. Yelp it seemed to work, but it looked really strange as you can imagine.I haven't gave up on the idea, will have to do some more thinking on it

BTW--I can play sitting down, which I have been doing but---I feel to put my full force into my playing, I need to be standing up

97

Tube Amp Building - Tweaks - Repairs / Re: Hum and Buzz in Cordovox Build

« Last post by Platefire on December 04, 2025, 09:51:32 pm »

The only thing that comes to mind after all the checking that has been done is, chop stick it one more time from head to toe

98

Tube Amp Building - Tweaks - Repairs / Re: Dark half-power Hoffman AC30

« Last post by MORE_Guitar_Solos on December 04, 2025, 06:21:47 pm »

On a (perhaps tangentially related) side note:


How does everybody feel AC-type amps should be biased? I'm aware the originals were cranked way beyond design limits, but is 100% dissipation the goal? Something slightly below that? How do you guys set up your bias on these?


I built my first one of these ~20 years ago now, and it was one of those projects that just came together right the first time, so even though I knew it was biased cold I didn't mess with it. Going for a theoretical ideal with this one. I'm at 85% right now (bias-wise).


Thanks

99

DIY Layout Creator and Custom Boards / Re: How to Print Layout Board in Actual Size

« Last post by wsscott on December 04, 2025, 05:56:07 pm »

Thanks!

100

Tube Amp Building - Tweaks - Repairs / Re: Help with modded SFDR bias circuit

« Last post by stratomaster on December 04, 2025, 05:34:56 pm »

Looks like a bias balance arrangement with the small trim pot being an overall adjustment.

Remove the power tubes and measure the negative voltage at the grids as you turn each pot to get a feel for what they do. The large one will shift voltage from one one side to the other while the trim pot will adjust both simultaneously.