SuperBee
2026 posts
May 26, 2014
6:29 AM
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a few snaps:
Last Edited by SuperBee on May 31, 2014 10:19 PM
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5F6H
1780 posts
May 26, 2014
7:13 AM
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Tidy work.
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www.myspace.com/markburness
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jbone
1634 posts
May 26, 2014
8:02 AM
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I'm no amp or electronics whiz but I know quality point to point hand wiring when I see it. I bet that thing will just sing when it's all together!
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http://www.reverbnation.com/jawboneandjolene
https://www.facebook.com/profile.php?id=100000386839482
http://www.youtube.com/watch?v=wa7La7yYYeE
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1847
1818 posts
May 26, 2014
12:09 PM
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i like to hear that with a nice 10 inch speaker
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i get a lot of request when i play my harmonica
"but i play it anyway"
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yonderwall
68 posts
May 26, 2014
12:21 PM
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Really nice work! I'm sure that the time and effort spent on such a clean job will pay off in spades when it comes to the quality of sound you will get (not to mention making any later component repairs/substitutions easier!)
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SuperBee
2027 posts
May 26, 2014
3:42 PM
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Thanks for looking, and kind comments. Especially thanks to Mark and Arne, and Kingley, for help and encouragement at LoneWolf forum. Very generous with time and goodwill.
It's a beginner project. My first crack at assembling an entire amp.
I'm not really pleased with the way I've routed the heaters between the pre amp and power amp sockets, but I'll leave it until I hear how it runs.
This idea started when I wound up with (former forum member) NOD's harpgear2 cab and speaker. Eventually I grew tired of seeing this nice tweed cab sitting around the house, unemployed.
(I had thought perhaps I'd try to emulate the amp which used to be in the cab, but eventually settled for the baby-steps progression of building a fairly standard/common circuit, before I consider how it could've been better.)
So , it will be installed in HG2 cab, with Weber alnico sig8.
At Mark's suggestion I have used 47uF for first filter.
Transformers are from Magnetic Components.
So far I've tested that the PT is running ok, heater connections seem good, and the chassis is earthed. All the grounds test good, through chassis to the terminal on the mains plug.
But, I'm waiting on rectifier tube to arrive. Couple days.
I have a radiotron 5Y3GT on the way. And a Phillips miniwatt 12ax7 for starters. Also a JAN Phillips 5751. For 6V6, I'm not sure, but I have 2 or 3
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Kingley
3583 posts
May 26, 2014
9:50 PM
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Looks great! Superb work SuperBee and damn fine and tidy soldering and wire work. Can't wait to hear it.
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chromaticblues
1571 posts
May 27, 2014
9:40 AM
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Looks nice!
I've built a number these types amps and found that I like the sound better without the bypass cap in the preamp. It sounds a little less fuzzy to me without it and lowers the preamp output (the preamp was plenty of output). I also use a 500K pot instead of the standard 1M. Food for thought!
Anyway after you fire it up try it with and without and see what sounds best to you!
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SuperBee
2033 posts
May 28, 2014
4:15 AM
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Thanks Kingley and chrom'blues. I think Kingley it was your suggestion that started me down the path..
Kevin, i know some folk do run them with switchable bypass caps...i'm interested.
a couple of people have commented to the effect that if one cant get a good sound from a stock tweed champ, hang up the mic. i thought id give that a try..."but what is 'stock' in a tweed champ?". it must be the most copied and messed with amp design ever?
so i decided to start with this "fairly standard" scheme. although i have messed with filter caps already. the original plan was 20-10-10, but Mark suggested i should go bigger on the first one. ive currently got 47-20-10. anyway, just as you say, i want to see how it is as is, then maybe mess with it a little.
tell me more about the 500k pot, please. why do you do that?
i was sure my rectifier would arrive today. wrong. very disappointing.
Last Edited by SuperBee on May 28, 2014 4:17 AM
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chromaticblues
1572 posts
May 28, 2014
8:13 AM
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Yeah your right about what is stock and what isn't.
The 5F1 that you alluded to doesn't have a bypass cap on the preamp cathode resister and that is one reason why that is my favorite champ. The Model before (5C1)and after (silverfaced)had a bypass cap there.
Again just something to be aware of and try because it does make a difference. Once you try it you will like one way or the other probably. Just another way of dialing in your sound.
I wasn't referring to the power caps.
I agree with Mark the original value caps in the power supply of those amps isn't anywhere near enough.
Any Champ like amp from the 50's and 60's.
They make great amps to modify using techniques that people have figured out in the last 20 30 years.
Doing what your doing is even better. Building from scratch with high quality materials.
I only build single ended amps now. I love em'!
The biggest down fall is they hum. That is why Mark told you to that.
As far as the volume pot goes, remember it's just a grid load resister! The higher the value the less signal is going to ground and the "hotter" the stage is going to be. If I'm using a twin triode preamp I use 500K volume pot. If I use a 6SJ7 or 6AU6 I use 1M.
The 6AU6 is an excellent preamp tube for harp.
I love it! I've built a few of them.
Right now I'm building a 5Y3, 6DG6 , 6SJ7 2 1/2 maybe 3 watt amp.
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SuperBee
2035 posts
May 28, 2014
3:20 PM
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Thanks Kevin
About the preamp cathode bypass cap. I even almost grasp the concept of how that works to increase gain and affect tone.
I've read a few peoples' ideas on it. Seems even though it's not present on the fender schematic, it's become such a standard inclusion (I guess it's a modification by definition, as not on the published schem) some people think of it as an error on the schem! I've also read assertions that it was included in most of the factory-built amps. Personally, I have no idea if that's true. But as it was included in most of the builds I looked at, and I had the part, I went with it for starters.
The concept you've introduced me to here is about the volume pot as a grid load resistor. I think that's an important thing for me to work out, so thanks!
Last Edited by SuperBee on May 28, 2014 3:32 PM
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SuperBee
2044 posts
May 30, 2014
6:24 AM
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Electricity seems ok on the power tube. I calculate 13.4 watts plate dissipation, 1.4 watts screen dissipation, with B+ 373 volts.
Amp sounds good to me, but does hum, louder as volume is turned up. Dead quiet with volume at zero. Not really too noticeable with the harp mic plugged in as volume only gets to 6 on the dial (input no. 2) before feedback. But beyond that point up to 10 it's irritatingly loud, in a quiet room. Quietens down a little beyond 10..
I would like to build that out if I can.
Sound like a grounding issue?
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chromaticblues
1576 posts
May 30, 2014
7:34 AM
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Try a few different lower powered preamp tubes.
Also try removing the preamp cathode bypass cap I mentioned earlier. That's just crating unneeded gain which can cause hum.
Look at it this way if you have an amp that starts feeding back while your playing at 4 on the knob. Does the preamp need to be that powerful? NO! The more gain a single stage has the more radiant energy it gives off which will create the type hum your talking about.
Your is circuitry hum because it is quite when you turn it on. If it was the power supply it hum 10 seconds after you turned it on.
Hope this helps!
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5F6H
1781 posts
May 30, 2014
2:41 PM
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Try regrounding the volume pot ground tab direct to the input jack, one wire.
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www.myspace.com/markburness
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SuperBee
2045 posts
May 30, 2014
11:15 PM
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Tried 12ax7, 5751, 12ay7. No appreciable difference in hum. Not much appreciable difference in sound either. 12ay7 perhaps brighter.
5751 perhaps clearer.
Moved preamp grounds. Left plate and screen filters grounded at PT bolt with high voltage CT. Preamp is grounded at input jack. Cathode from stage one has it's own lead, everything else is via the vol pot then single wire from vol pot to input jack. Thought initially it had quiet ened down a bit, but really can't say. Still quite hummy. Not a problem for the harp.
I'm gonna leave the bypass cap for a while. I'll move the heater wiring first, because I think that's dodgy anyway.
Last Edited by SuperBee on May 30, 2014 11:18 PM
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SuperBee
2046 posts
May 31, 2014
1:09 AM
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That didn't make any difference.
I reckon it's about the volume pot/switch/lead to pin 7...
Might cut that lead free a fly a shielded one over the top..
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SuperBee
2047 posts
May 31, 2014
5:34 AM
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moved the lead between wiper of pot and preamp pin 7, so that it runs around the pot on the side away from PT/AC leads. this did reduce the noise somewhat. the lead is tight against the pot...maybe some extra length on that lead...
i built a 6v6 board for a valve junior earlier this year. that build dispensed with the valve junior DC heaters, but even with AC heaters it is very quiet. thats what id like with this one. not there yet.
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SuperBee
2049 posts
May 31, 2014
10:26 PM
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i popped out the the pot and re-routed the wire from the wiper.
From this:
To this:
 
Thats all it took to change this from a noisy amp to a quiet-running amp
and now it looks like this:
  
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Barley Nectar
402 posts
Jun 01, 2014
6:43 PM
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WOW, Nice build there Supe. Excellent job susing out that hum.
I would like to suggest a speaker swap after you play that for a while. IMO a Weber 8F125 will blow that Sig away! Bigger, fatter, cleaner, punchier, louder! The Hepner big mag alnico (cheep on Ebay) from an organ will work well. The Eminence 820H may be an option also.
I'm sure you will find the perfect setup in time.
Nice amp...Goose
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puri
149 posts
Jun 01, 2014
8:40 PM
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Lovely looking amp and very neat wiring job! Congrats superbee! @goose, I've been curious about 820h for a while is it worth trying and how would you describe it's tone, thanks.
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arnenym
289 posts
Jun 02, 2014
12:13 AM
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Nice work. It's amazing that a small change like this could change it from a humming amp to a quiet amp.
Last Edited by arnenym on Jun 02, 2014 12:14 AM
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SuperBee
2050 posts
Jun 02, 2014
2:57 AM
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Thanks BN, Puri and Arne. you all have helped educate me and inspired me to have a go.
BN, i have a few different 8"s to try but not many 4 ohm. my OT does have an 8 ohm tap though. i have a 4 ohm 2 x 8" cab with 8A100s
i'm fairly happy with the sig 8 at the mo', but interested in others. speakers are exxy to import to australia though...the twin webers cost as much to import as an extra speaker
Hi Arne, yes i moved grounds and heaters and nothing made a difference..
something about how the hum was less from 10 to 12 made me think the problem was around the pot...then i noticed the signal lead hard across the AC leads...
its an even smaller change than appears from the photos. before i resoldered, i had pushed the wire to the same side as its now on, and the amp still hummed. if that lead was on the black part of the pot it would buzz.
that bit of troubleshooting took nearly as long as assembling the amp, but i probably learned as much or more from chasing it down.
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bonedog569
911 posts
Jun 03, 2014
9:23 AM
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Don't think I could do work that neat if my life depended on it. I like that trouble shooting and fix you did on the hum issue. An inspiration- that shit drives me nuts.
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1847
1843 posts
Jun 03, 2014
11:14 AM
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An inspiration- that shit drives me nuts.
don't worry bone dog....
it's a short drive.
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i get a lot of request when i play my harmonica
"but i play it anyway"
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SuperBee
2054 posts
Jun 04, 2014
1:29 AM
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Hi Bonedog,
I was keen to be as neat as I could, it may not bear close inspection quite as well as it seems in photos, but I'm quite happy with how it turned out.
As for troubleshooting, I must say it totally distracted me for Friday night,all Saturday and Sunday morning. I couldn't leave it alone until I found the problem.
If I could be that obsessive over practicing scales...
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SuperBee
2180 posts
Aug 31, 2014
9:22 PM
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I clipped the cathode bypass cap from the preamp. I think I prefer it this way. I'm running 12AY7 and even so, the amp was delivering a broken-up sound fairly early on the dial. Now I can turn it up a little more, but more importantly there's a greater range of tone available. I'm sitting in with the band at the blues club tomorrow; I think I should be able to give it a run there...
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Barley Nectar
507 posts
Sep 01, 2014
6:58 AM
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Break a leg Supe. Thanks for the update...BN
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SuperBee
2184 posts
Sep 02, 2014
5:58 AM
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Thanks BN. It was the 'best gig ever'...but I used my Princeton reverb :/
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Greg Heumann
2819 posts
Sep 02, 2014
7:42 AM
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Very clean professional work - looks great!
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
Bluestate on iTunes
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HawkeyeKane
2597 posts
Sep 02, 2014
7:53 AM
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Lookin good Dave! Kudos!
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Hawkeye Kane - Hipbone Sam
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