Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Blind Lemon on February 23, 2022, 01:41:01 pm
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Hello Gentlemen, doin another one of these for a good friend of my son's. Had a little trouble with the last build, distortion in the PI. Don't really think the problem was completely cured, but I think it was mask fairly well. :dontknow: I am very interested to hear if this build has any of the same issues. I would love to hear from anyone that has built this layout and how it turned out for them.
Link to previous thread. https://el34world.com/Forum/index.php?topic=28060.0 (https://el34world.com/Forum/index.php?topic=28060.0)
I am starting with a blank BF Bassman chassis this time instead of a Twin chassis. Amp will end up in a head cab.
A few pics. I am a little farther down the road than these pics, so I'll post a few more post to get caught up. Been meaning to start a thread on this but got a little behind.
BL
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Got the chassis punched and drilled , transformers mounted and tube sockets installed.
Figured how big of board I could get away with and how the circuit would line up with the tubes to keep the wire lengths as short as practical.
Board and layout.
BL
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Board drilled and turrets set.
BL
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Board populated.
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My computer doesn't like your pics. Are the pics those crazy Iphone proprietary "multi frame" pics that show motion when viewed?
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They were converted to JPG from HEIC file.
Can you not see them?
Maybe I need to repost them?
BL
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I can see the pictures with no issues, looks nice!!
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They were converted to JPG from HEIC file.
Can you not see them?
Maybe I need to repost them?
BL
I tried four image programs on my windows 10 PC. Nothing works for me.
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sluckey, can you see them in the first post now?
I am on a Win 10 machine also and I could see them, but they weren't showing as thumbnails.
BL
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I can see them fine.
I agree,like good.
What’s the best way to punch the chassis for your power receptacle ?
Seems hard for me to grasp how to punch a shape into steel other than round? Such as the receptacle you have, or the spot for the strain relief, or sometimes fuse holes are flat on the sides not round.
Ive looked at Greeley punches but never saw any other shape but round.
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Then you have to ask yourself - how do manufacturers do it? I'd like to know.
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sluckey, can you see them in the first post now?
Yes, but I was hoping for the original size. Cannot see any of the others.
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I can't see any photos other then the first two ..
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I can't see any photos other then the first two ..
Same here.
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see them all now I'm liking that red board too. I just built a 5F10 circuit with it..
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Swapped all the pics out. :icon_biggrin:
VT - I have a Greenlee punch, it's not the perfect size but with a little filing it works. I watched ebay until one came up that I thought would work and jumped on it.
BL
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Hell now all the pics are sideways. :BangHead:
BL
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Finished up all the hookups, will do the start up tomorrow.
BL
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Couple more......
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Still sorting a few things out, but here are the voltages.
BL
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That's not one of my boards.,
I don't use Red board material
I am assuming Hoff is Hoffman?
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Just giving credit for one of your layouts.
I''ll try to edit that out.
BL
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Was able to edit my post.
Sorry for any inconvenience.
BL
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So I wrestled with this alligator today and it ended up sounding pretty good. Had a few dumb hookup mistakes on my part but after straightening them out I had the same gravelly sound on the notes as I did with my last build of this type. I jumped straight to to PI where I experienced trouble before. I put in a jumper from V1-B6 to before the .001uf cap at the PI, bypassing the effects, trick I learnd from local hero. The distortion was still present so I scoped it before and after the PI and the fuss was present after the PI. Put a 300pf across the 220k resistors after the PI and it pretty much filtered the fuzz out. The only way I can hear anything of it is if the amp is really loud, but there will be a certain amount of distortion anyway.
So I guess the question is, what can be causing the distortion in the PI? And what exactly is the 300pf capacitor filtering out?
Schematic here: https://el34world.com/schematics.htm#Hoffman_AB763_One_Channel_