Blown C5 Cap

2nd harmonics for the masses

Postby TerrySmith » Sun Mar 02, 2008 9:21 am

Lift the ground from the IEC connector, give the amp a try. Also try different input cables and source if possible.
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Postby 77seriesIII » Thu Mar 06, 2008 12:01 pm

Ok I did alot of work over the weekend, removed the old bus and redid the set up. In a re-cap when I shorted out the rca inputs dead quiet. I re did the ground bus, much better now, neater, etc. I re-tested it last night with shorted out rca and no sound. OK so I didnt screw anything up but not sure yet if I made it better. I took the shorts off and connected the RCA connects and connected wife's iPod, in short alot of work and I didnt fix it, same loud racket. When I disconnected the rca's (in frustration...think ripping and ideas of tossing out window) from the ipod it got quieter, hum there but at a level what I would expect if the connects were open. So I changed the cable, and did a re-do, same results as the other cable. I wonder if my rcas are crap or the wires/connections/solder joints that make up the RCA connectors/wires are bad. I'm looking to do a re-do on the RCAs just need to get good ones that are a bit longer and can be mounted on 1/4" wood.

On the orginal bus I used a 3mm solid core copper wire and my solder joints were HORRIBLE. I switched to a 1.5mm wire and my solder iron was able to cope. I did promise a few pictures and will see if the wife is up for it. still hunting for ideas but I think I am getting closer.

Thanks for all the help!

/e
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suspect the 'pod first...

Postby EWBrown » Thu Mar 06, 2008 12:55 pm

I'd suspect that the i-pod cable is the most likely cause of the hum problem, the shielding can't be very good, if indeed the cables are, in fact, even shielded at all... interfecing the "pods" to tube amps can be challenging.

The "fatman" brand i-pod tubed amps use a docking adapter / connector so that no external cabling is needed. Most other ipod amplified speaker sets also use the docking adapter approach.

One "trick" I learned (if there is no volume control) is to connect the input tube's grid resistor across the input RCA jack, then run shielded or twisted pair wire to the VA tube, and use a 1K CC grid stopper resistor connected reasonably close to the grid pin on the socket. This is another neat "humbuster" method which works for me.

The 'pods were never intended to play well with tubes, so YMMV at best...

It's best to run the 'pod or any other "portable" source off its batteries, and not using the charger, the latter is a recipe for ground loops and hum insanity Yellow_Light_Colorz_PDT_09 :o Yellow_Light_Colorz_PDT_09 :o

/ed B in NH
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Postby 77seriesIII » Thu Mar 06, 2008 1:14 pm

ed thanks on ideas. I did run the test with my laptop as well with the same results, both iPod and laptop were operating on battery, no wall power. I just find it very odd that everything worked well before the cap blew but after blowing they system has become very sensitive.

wiring for a volume control, good place to look for schematic? I have a spare CD/DVD player that would completely eliminate a need for a computer/iPod or the ilk.

thanks

/e
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Postby EWBrown » Thu Mar 06, 2008 1:58 pm

Connect the "high" end of the volume (I usually choose 100K, audio taper) control to the RCA center, the "low" end to the RCA jack ground and circuit ground, and the wipers (ceenter) goes to the 6SL7's grids.

I usually place the RCAs on the front and have the volume control fairly close, but any normal physical layout will work fine.


gotta run for today, back Friday AM

/ed B in NH
Last edited by EWBrown on Fri Mar 07, 2008 12:59 pm, edited 1 time in total.
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Postby 77seriesIII » Fri Mar 07, 2008 12:03 pm

Ed, going to show my ignorance. The center goes to "the grid"...could you help a brother out? What is the grid ;)

New RCAs are on order so we shall see.

/e
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Postby Shannon Parks » Fri Mar 07, 2008 12:25 pm

77seriesIII wrote:Ed, going to show my ignorance. The center goes to "the grid"...could you help a brother out? What is the grid ;)

New RCAs are on order so we shall see.

/e


J1-1 and J2-1 go to the grid. The triode's grid.

What happened to the pictures you were going to take? You can email them to me and I'll host them here. Inside, close up shots would be wunderbar.
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Postby EWBrown » Fri Mar 07, 2008 1:03 pm

(Hmmm, strange server bug, I just hit "reply" and it brought up Shannon's last message to edit. I backed out and started again, this time it came up as an empty slate).

I clarified my previous postings, the volume control wipers go to the 6SL7's grids connections on the PC board, the pot acts as an auxillary grid resistor in addition to volume control. You can leave the original 470K grid resistors in place on the board, it will not noticeably affect anything.

HTH

/ed B in NH
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IT'S ALIIIIIIIVVVE!

Postby 77seriesIII » Wed Apr 16, 2008 9:02 am

I must say big THANK YOU to all the folks that helped me get the wee beastie up and running again. It was a nasty ground loop that somehow manifested itself after the 300B's decided to check out.

I ordered new female rca connects and used shielded cable to connect them to the PCB. Next I purchased a high grade shielded interconnects for going from a minijack (computer iPod...) to the amp.

Went through the whole battery of tests no noise. so I felt froggy connected everything and waited and waited oh yeah turn it on helps. Then I waited...NO NOISE!!!! so then I hit play on the iPod and no FREAKIN music..what th...plugged that in and I had MUSIC!!

Works like a champ, thanks again for all of the help

/e
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