Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SILVERGUN on December 08, 2012, 10:21:28 pm
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I am completely addicted to building, so I wanted to challenge myself....
Build something quick,,,don't overthink it,,,dont re-draw the layout 20 times,,,use some parts that are laying around and do something I've always wanted to do-----re-pay an old debt with an amp that I build
In my early 20's I had a close friend who's family owned a local Italian Restaurant, and who loved blues and great guitar players......he would get us tickets to go see everyone who ever came through Phila., from Albert Collins to Buddy Guy, Larry Carlton, Robben Ford, Brian Setzer, Duke Robillard, Steve morse, many more......without him, I would of missed most of that
He also gave me the freedom to walk into his restaurant at a moments notice (with or without a date), and eat for free.....feels like it was a hundred times....(best lasagna and meatballs on the planet)
One of the last memories that I have from that time is of his wife giving him a Gibson ES-175 for Christmas :huh:
He didn't play much before then, but I have a feeling he has picked it up since......I moved away, lost touch, and now I'm back, and ran into his wife who has extended me an open invitation to the Sat. night ritual card game (just show up after midnight !?!?)
So in an attempt to repay him for some of his kindness and generosity, i wanted to build him an amp that i could be proud to give to him......I took a chance on this schematic and it payed off big....this thing sounds better than i ever could've expected for such a simple build......
I had picked up 2 Valve Jr. chassis from eb*y a while back, and a used Hammond 269ax that is only enough power for a 2 tube build, so my path was clear,,,,,and after 2 nights staying late at work, i finished it, plugged it in, and much to my surprise have 0 issues to resolve.....it just works!!, and does a great clean to mean with a twist of the volume control.....I really like it with the neck single coil in my Warmoth Strat, but the JB in the bridge really pushes it hard and makes it a low watt contender to my original T-wreck stock build......very cool
I still have to touch it up, power switch is temporary, and it needs some graphics to cover up that Valve jr crap!
Merry Christmas guys.....remember, it's never too late to do the right thing :thumbsup:
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Cool!
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Yeah cool man, he's gonna love it.
Just a couple questions
Why the 150R resistor between the diodes and first cap?
What's the B+?
What OT did you use and why the 600R cathode resistor when most champs use 470R?
I too am an addict. Picked up a VJ too and want to do something with it.
Thanks, keep on buildin'
Jeff
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Nice Job :thumbsup:
The 150R is a SAG resistor, isn't it ?
May be not, as in SE amp there isn't really need of it
so is a resistor to drop a bit B+ ...........
SILVERGUN which was your real intention ?
K
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Why the 150R resistor between the diodes and first cap?
Honestly,,,because it was on the print......I'm still a slave to the schematic, BUT, it serves both purposes, sag resistor that drops a little B+.....nothin fancy (B+ is 395 with 122 Vac input)
I didn't overthink it, and just trusted that someone smarter than me had designed and tested it...
What OT did you use and why the 600R cathode resistor when most champs use 470R?
OT is...5W.....7K primary.......4+8 ohm sec......standard Blackface champ spec. (1--6V6)
The 600R cathode resistor brings the plate dissapation into spec........I originally put the 470 in there and checked the #s, and it was high----16 watts
I checked the math and 600R will bring it down to about 14W.....better
I left the 470R in there, because I don't have a 600R in stock, and amp sounded great, with no sign of red-plating, BUT I imagine that 6V6 is not happy with me...I'll put a 600-680R in there and change out the power switch before I give it to him..
Amp has more gain than you'd expect from a Champ, and I thinks it's a great little platform to test different tube types....
Volume control is clean until 3, gritty up to 5 and after that has no effect on perceived volume, just doubles the OD by the time you hit 10....I mostly ran it at 6 and used the guitar vol. to control dirt.....Tone control is useful and provides a nice sweep, from 0 being totally rolled off highs and 10 being a little nasally and sharp with a lot of bite,,,,I liked it best at around 6-7
I currently have a Sovtek 7025 and Tung Sol new production 6V6 in there
On Sat. I went up to a local music store looking for a speaker to try, and I know the guy that works there....he let me take and try a used Celestion 10" (made for Fender),,, it made the amp sound terrible compared to the 4x12 that I was using prior to that, and it also sounds good through a std. 12" Celestion test speaker........pick a good speaker!!
I'll probably build another one for my bench as a tube tester :thumbsup:,,,and I wouldn't hesitate to recommend this for your next 2 tube build...plenty of room in that Valve Jr. chassis.
As always,,,thanks for the nice comments guys......I'll post a clip as soon as I can get some damn recording done... :embarrassed:
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Very cool thing to do!
With respect, Tubenit
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Yes, very nice. Merry Christmas.
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Big Tone in a small package. Great job!!!
I'd like to hear it!!!
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Way to go SG, you big softy you! Really, that's a very thoughtful and awesome thing to do my friend. I was thinking about the faceplate cover-up. If you can, check out self adhesive cupboard or wall paper type of material like vinyl, etc. check link http://www.amazon.com/dp/B002TDVPCI/ref=asc_df_B002TDVPCI2293432?smid=A29254BKC7ZMT5&tag=sdcbing8-20&linkCode=asn&creative=395105&creativeASIN=B002TDVPCI (http://www.amazon.com/dp/B002TDVPCI/ref=asc_df_B002TDVPCI2293432?smid=A29254BKC7ZMT5&tag=sdcbing8-20&linkCode=asn&creative=395105&creativeASIN=B002TDVPCI)
I'm in a hurry but sure you could find it smaller/cheaper but it'd be quick and easy.
*also a little note, on singe ended builds it usually helps to raise the heater center tap either by attaching between cathode resistor/cathode point or another way off the B+ w/ a voltage divider & cap. I'll explain later if necessary - see ya!
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I had a disassembled, hacked-up Valve Jr., and a piece of board material that I had drilled for a Hoffman-style board for another project but never got any further with, so I decided to try use them to make one of these amps (which, as Silvergun mentioned in another thread, is actually the R. Hall/M. Huss "Beast" amp).
I used the Valve Jr. PT (rated at 260-0 @ 115v) with a bridge rectifier with an additional 47uf cap, and added a 470 ohm screen resistor just because it looks right on the Hoffman architecture. The heater voltage was a little on the high side, so I used Merlin's trick (http://www.valvewizard.co.uk/heater.html) of adding a pair of big diodes to knock it down.
I included the boost switch, and also added switchable NFB. I got confused by conflicting layouts in old 18watt.com posts, and initially had the NFB going to the wrong side of the 12AX7, which made a nice loud howl. Once I got that figured out, the amp worked nicely.
I was thinking that if the amp actually worked, I would replace the Valve Jr. OT with a decent one. After shopping around a bit, and being stunned by how much all the vendors seem to want to charge for mailing a glorified Champ-type OT to a location right here in the Lower 48 :cussing:, I'm not sure I can stomach it.
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Champsters---try a 12AY7 or a 5751 in that first spot if ya got one lying around.
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:headbang:
Nice project! Thanks for sharing.
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Nice job Drew,,,,I thought this thread was dead, but since you brought it back up, here's a pic of how mine turned out
It was my first attempt at building a head cab, and I tried a couple different stains on a sample board (3/4" solid pine)
This originally got some amber stain and I didn't love it,,,,SO I TOOK A TORCH TO IT, and burnt the pine evenly all the way around.....lightly sanded off the ash and then finished up with a brown/black stain......IMO, it came out pretty cool
I also added a bucking xfmr on the input just to cool everything down a bit (dropped 14vac), and the only noticeable tonal change to me was a decrease in the "ice-picky" highs :thumbsup:
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SG did you use picture frame quatered dowling (or whatever it's called) there on the sides of the faceplate area?
Nice work boys!
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SG did you use picture frame quatered dowling (or whatever it's called) there on the sides of the faceplate area?
Yup...exactly....good eye sir
I glued em in there and broke the first 2 attempts by tring to add a small brad with a nail gun,,,so I adjusted the depth setting on the gun, and it worked, so I sunk them with a nail set and used some filler....
It definitely added a cool little touch and made it look less amature'ish :icon_biggrin:
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Wow cool, I like the look of the cabinet. Nice job.
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Wow cool, I like the look of the cabinet. Nice job.
Thanks,
Here's the process:
1) Stain a couple deep coats amber and let sit and dry
2) Take a torch and burn it black---don't be afraid, but do wear a respirator :wink:
3) Very lightly sand off burnt ash layer with steel wool
4) Wipe on dark stain of your choice (I used black and walnut mix) and wipe off along the grain lines...wipe harder on parts where you want the amber to show through
5) Finish with one more quick coat of dark over everything
Gives a nice "olde time" western bar kinda feel to it :thumbsup:
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This caused me to think back to the days while in school & before driving that I built my own surfboard carrier to get to the waves without carrying it under my arm. When I had to do that I was already too tired to paddle out into the lineup let alone have the strength to compete for waves! So making a board rack on wheels out of wood was ono-awesome but after flame treating it like a baseball bat, it became the ultimate wavetool carrier! Style points count not just in technique or chops and gives the all important street cred ''_\m/'' Shaka on flame treating
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''_\m/'' Shaka on flame treating
Nice jojo,,,,,,made me google shaka.....paste'y white kids from Philly don't surf :wink:
There is a certain Haiwaiian look that this reminds me of as well...........
Damnit,,,,,,, now I want that koa body I've been lusting after
I would trade this faux finish pine for some nice wood any day :icon_biggrin:
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Didn't mean to sway from the topic but this was a pretty old thread. Anyway, now that you mention Koa - here's the backside of my 21 year old koa Takamine featured at the '92 NAMM show when they were really going with the high-end push. Unbelievable quality, playability, and sound on this one. Came w/ a special matching tan case & insides w/ "LTD-1992" pearloid inlay on the highest fret marking noting the occasion. I love wood figuring no matter what type it is.