Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: timbertoes on March 11, 2017, 08:20:45 pm
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:icon_biggrin: :icon_biggrin:
OK Stout TMB it is then ! maybe with an extra hole or two on the chassis for "something else" :)
Today the chassis was drilled, dremel-ed, cussed, dropped and fought over.
here is a pic, with obligatory other cool things in the pic, lol.
(https://photos.smugmug.com/Guitar-Amp-Builds/i-JPBTV2m/0/L/20170311_174308-L.jpg)
One change is using 1n4007's instead of a tube rectifier. made a little board for those and the first filter cap. Will mount on side wall next to power xformer.
Have the terminal board cut, mounting holes drilled. but that is all I have for now.
Think I will kick back and listen to Music on you tube. BTW, it is really neat to watch the Hoffman amp you tube videos :icon_biggrin:
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progress :icon_biggrin:
(https://photos.smugmug.com/Guitar-Amp-Builds/i-bKrc66n/0/M/20170312_212156-M.jpg)
(https://photos.smugmug.com/Guitar-Amp-Builds/i-bVnh5cS/0/M/20170312_214559-M.jpg)
(https://photos.smugmug.com/Guitar-Amp-Builds/i-jd3KSgS/0/L/20170312_215003-L.jpg)
(https://photos.smugmug.com/Guitar-Amp-Builds/i-bvMmK72/0/L/20170312_215051-L.jpg)
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Looking good. Keep the pix coming.
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I am considering adding a Presence pot to it. perhaps start with it AC coupled across the existing R19.
installed some parts on the turret board. Waiting for 600v rated wire to arrive and yet more things from mouser. No hurry, but with some luck might get sound by next Sunday.
I got two new books on Amp desing. reading.. eventually I woud like to work backwards through the design, to get a proper understanding. Just takes time.
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neat job !
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1n4007's are fine. But why not using a diode bridge? For a buck you get a 5A diode bridge (with a hole in the center) that you can bolt on to the chassis. Remember though, you must not use the minus leg,( I cut them ) the pt center tap is your minus.
Colas
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I had a bag full of 1n4007's, not so much any hi voltage bridges :)
Got a few wires tacked down on chassis wiring last night. But Guitar practice was calling... ;)
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Would it be useful to add a switched bypass cap (or series cap/res) to the cathode of V2 for tone via gain change, etc ? your thoughts please :icon_biggrin:
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For that question the answer is "do you want to try?" it won't hurt anything, many gain stages don't have a coupling capacitor at the cathode, for that reason, being able to switch it in and out would be good, but you may get some popping (I can't recall the easy fix to this, something like a high value resistor in the right spot stops the pop). If you don't like it, remove it, or re-purpose it for some other good use like a bright switch etc.
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indeed :) it is about some experimenting.
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Dang it. I *conveniently* neglected the large V drop across the design's tube rectifier... so I get to un-wire, remove, re-do - add a Zener, and change the first filter cap to handle the higher voltage at the diode rectifiers output etc. And I work in the power supply industry... major duh moment. :laugh: :laugh: :dontknow:
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I had a lot of hum in this amp after it was built. Certainly due to differences in construction.
now the hum is virtually gone.
Rewired by: First removed the ground buss bar from the pots, since this made a second chassis ground.
Added a 3 terminal strip next to V1.
Removed cathode resistors and bypass caps from the turret board. Wired those parts direct from tube socket to the terminal strip.
Common ground tie point for those parts on te terminal strip (not chassis) , input jack ground, tone, volume pots. Took that common gnd tie point to the single chassis stud with 16ga wire. Then on the turret board, changed ground path of R12. Much happier, its a lot of fun to practice on! both my Gretsch and Schecter love it!
Look forward to the next one hehe.
(https://photos.smugmug.com/Guitar-Amp-Builds/i-6kN5PQX/0/M/20170327_190549-M.jpg)
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Looks great dude. Thanks for sharing what you did to rectify your hum issues, all of us new builders appreciate finding out what has caused issues before!
-Brett
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Excellent looking build, did you like how the different value for the bright switch turned out?
~Phil
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thanks :icon_biggrin:
Bright cap switch, etc. - I have not added anything to it.. except bypass the cathode on V1-B as part of the hum fix. lol.
More time needed to understand the amp, and heck even improve my playing....(there is that)
Overall I am happy enough for now, just to complete it, and get a decent, fun sound out of her !
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I'm referring to the fact that you didn't have a 100pF cap for the bright switch and were going to use a 250. I'm wondering if it sounds 'right' to you, that's all.
~Phil
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lol, I don't think that was me... I have lots of Caps!!
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Would it be useful to add a switched bypass cap (or series cap/res) to the cathode of V2 for tone via gain change, etc ? your thoughts please :icon_biggrin:
Sorry confusing your build with someone else's... this is what I was asking about... did you implement this and how does it sound lol!
~Phil
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hehe :icon_biggrin:
I have a 10uf cap soldered there now.
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What I have not done...
is have not put it on the bench, with sig gen, speaker or resistive load, and scope through it, take numbers...