Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: morton on August 25, 2015, 07:01:41 am
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First amp, let me know how it looks. Practiced on a few pedals first. Really versatile amp, makes me glad I sold my Mesa 5:25. Pretty quiet overall, little bit of a main hum with the master above 6, and the bright volume has some hiss when above 5 or 6, normal volume is pretty quiet though. Couldn't have done it without all the documentation on the site.
Thanks,
Gary
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Very nice! Certainly looks better than my first amp.
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Looks really nice. I love it when I see clean work. Nothing worse than an amp all gobbed together. On that hum, try firing it out of the the cab and turn it up so you get the hum. Then using your chopstick, move some wires around and see if you are get rid of some hum issues. I overlooked a few things on a PR with the way I had routed some wiring and was getting some noise too. Once I saw my mistake it was easy to fix.
You should be proud of what you have accomplished.
Cheers
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That looks great!
I agree, the Plexi 6V6 is probably one of the most versatile amps I have.
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Thanks. I did have some 11x17 copies of your build page helping along the way. On the hum/hiss, anything to fret over? Not real loud on lower volume but dimed it's a constant shhhhh- more so on the bright than normal.
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Hard to say without hearing it.
I would have to fire mine up and see what the normal level is
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Very nicely done! Bravo!
With respect, Tubenit
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Very nice! Certainly looks better than my first amp.
Yep, 1st build, looks great!!!!! :bravo1:
Looks great for any build, 10th, 20th.........!
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Thanks all, means a lot to me. A little nervous on the first power up, but no smoke or popping so I figure I did OK.
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A little nervous on the first power up, but no smoke or popping so I figure I did OK.
Do you know about a 'light bulb current limiter'? You use it on 1st start ups on new or rebuilt amps.
Here's a link to Sluckey's web site with instructions on how to build and use one;
http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf (http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf)
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Thanks, definitely make one this weekend. Was thinking about a 5f2a or 5e3 next but with a ppimv, just not sure how to modify the circuit. Either one would be one of the Hoffman kits.
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Wow! No kidding, this looks like a seasoned builder job, not a virgin! You should be proud. As has been said, put one hand in your pocket and chopstick around. Start with the easy things first.
Jim :bravo1:
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Thanks, Doug's build page helped quite a bit. Tried chopstick king it last night, didn't change much. Overall it doesn't get noticeable before the master and volumes are both past 6, by then the amp is pretty loud and gainy so figure it's nothing too excessive. Pretty quiet up till then, even after that not real bad, just a hiss.
Thanks,
Gary
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Put a 47pF cap across pins 1 and 6 of the PI tube (V3) to reduce the hiss. You can easily put it right on the socket or on the board. Mark Huss had one on his original. I used one too.
http://home.comcast.net/~seluckey/amps/6v6plexi/6v6plexi.pdf (http://home.comcast.net/~seluckey/amps/6v6plexi/6v6plexi.pdf)
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Will do. Do I need to worry about voltage rating on the cap?
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Not really. There's little dc across the cap. I used a 500v cap just because they are widely available in small ceramic or silver mica pF sizes. Here's a pic of my cap installed on the board. Your board is different but the idea is the same. Some people even use a 100pF cap in this position. I used a 47pF just because the original Marshall JMP 1987 did.
http://home.comcast.net/~seluckey/amps/6v6plexi/P-6V6_05_big.jpg (http://home.comcast.net/~seluckey/amps/6v6plexi/P-6V6_05_big.jpg)
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Thanks. If I install on the board it should go after the .022 cap but before the 100k resistor?
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The cap connects between the two lugs indicated by the violet arrows. See pic...
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Perfect thanks. Had to order the caps, only ones I had were 50v. I'll let you know how it sounds. Thanks for the help.
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Are you getting the hum and hiss with the chassis sitting out in the open on the work bench like in your photo, or in a cabinet with a strip of flashing or some other kind of metal attached to the underside to complete the shield?
What tubes are you using? Does swapping the preamp tubes around, or trying other 12AX7s if you have any, have any effect on the hiss in the bright channel?
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I have it mounted to a piece of red oak as in the pic. I tried rearranging the preamp tubes, all EH tubes. I have a set of mullards and JJ's that I'll swap out and see if that does anything as well.
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I'm not a fan of all the transformers mounted that close to each other like that and avoid it at all costs whenever possible. Ounce of prevention and a stich in time...that's just me.
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That layout on my Stout chassis has been proven to work just fine :icon_biggrin:
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That layout on my Stout chassis has been proven to work just fine :icon_biggrin:
I'm aware of that Doug and wasn't implying the layout to be faulty, however I stand by my statement all the same.
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Yes, I understand that's what you like
Just throwing out info because people can take things written on the web as the gospel
In this case it is just a personal preference
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Yes, I understand that's what you like
Just throwing out info because people can take things written on the web as the gospel
In this case it is just a personal preference
That's for sure Doug! Take my good buddy Richie200...on his Marshall Major he's a fan of the one wire mod... but when he implements it he uses only one wire I tell ya!? (using Rodney Dangerfield's voice) :l2:
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Do I need to bring up the reading glasses and the music stand at your live gigs yet again... :evil5:
Innocent Jim :angel
:hijack1:
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Innocent Jim :angel
:hijack1:
Yes about as innocent as OJ, Cosby, & both the Clintons combined? :l2: That's a good one (as I crawl from under that bus) but at least mine had some relevance to the thread Dr Jekyll & Mr Hijacker...!
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47p cap installed, helped quite a bit. Thanks everybody.
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47p cap installed, helped quite a bit. Thanks everybody.
Morton,
Have you solved the hiss issue completely?
Just curious of the cause and solution.
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It's not completely gone, but the master has to be maxed and bright at 6 before it's noticeable, normal volume much les. By that time it's pretty freakin loud, so I'm pretty sure it's just the gain in the amp.
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Very nice! Certainly looks better than my first amp.
In your 6V6 folder posted below, where did you get the 6V6's face plates, to fit Doug's Scout chassis, I don't see them on Doug's site.
al
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In your 6V6 folder posted below, where did you get the 6V6's face plates, to fit Doug's Scout chassis
Are you talking to me???
I built my Plexi 6V6 before Doug. I don't have a face plate on mine. I did draw some plates with Visio to fit my chassis but didn't get them built. I just used a Dymo label maker instead. My plates would not fit Doug's pre-drilled Scout chassis.
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Mojo can make plates for my Stout Chassis
They make the chassis