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Old 29th October 2012, 05:08 AM   #1371
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Oh and BTW check these guys out Tube Amp Chassis DIY 13x10x2 Aluminum Project Box Enclosure Stereo Amp Preamp | eBay Been using their chassis for quite some time now.

What I do is to pull all of the parts from the Conn amps (transformers. fuse, sockets, resistors, diodes) and install them to the new chassis. Then new caps and modern input/output terminals and an IEC power entry A decent set of 6L6's will do about 25-30 WPC with the self biasing circuit. Upgrading to a fixed bias and a 5-20 front end ups the power to 50WPC and will give a Citation 5 fits in a shootout at a fraction of the cost.
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Old 29th October 2012, 11:16 AM   #1372
AJT is offline AJT  Philippines
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wow, those are nice looking chassis....myself use 1.5mm(0.063) aluminum sheets.....
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Old 3rd February 2013, 07:49 PM   #1373
mfaughn is offline mfaughn  United States
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Default First power on...not quite there yet.

I powered up my amp for the first time today and I've got problems. I am fairly new at this and could use some assistance. When bringing up the bias to a reading of 400mV I get a loud hum out of my speakers long before I get all the way up. The hum increases the more the tubes are balanced (hum decreases when tubes are unbalanced). This happens in both channels.

My amp is a mostly stock build using 6GV5. The divergence from stock is in my OPTs. They are from Knight kit integrated amplifier that used a 5-20 type circuit.
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Old 3rd February 2013, 09:05 PM   #1374
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We will need to know some of the DC voltage levels with no input shorted to ground and no feedback to start to help you. The amp should be DC stable, take the schematic and do a voltage map on one side.
Is the 6.3volt for the heaters center tapped? and connected to about 50V?
Did you populate the correct resistor positions for the 6GV5 ( 6JM6) not 6JN6?
B+=350V G2 Screen =150V Neg bias around-60V
Both plates on the input tube about 110 to 130V?
What does it do with the input tubes removed?
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Old 4th February 2013, 12:35 AM   #1375
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Quote:
Originally Posted by mfaughn View Post
I powered up my amp for the first time today and I've got problems. I am fairly new at this and could use some assistance. When bringing up the bias to a reading of 400mV I get a loud hum out of my speakers long before I get all the way up. The hum increases the more the tubes are balanced (hum decreases when tubes are unbalanced). This happens in both channels.

My amp is a mostly stock build using 6GV5. The divergence from stock is in my OPTs. They are from Knight kit integrated amplifier that used a 5-20 type circuit.
Since this design includes gNFB, it looks like Mr. Murphy wired you up for positive feedback, not negative. You might want to try reversing the plate connections to the primary of your OPT. If that doesn't fix it, more details please.
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Old 4th February 2013, 06:06 AM   #1376
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I agree with Miles, having bought that t-shirt before. w/ positive feedback, I would call it an 'earth sharttering OMG my speakers are going to die' noise rather than a hum.

./e
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Old 4th February 2013, 11:32 AM   #1377
mfaughn is offline mfaughn  United States
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Originally Posted by 77seriesIII View Post
I would call it an 'earth sharttering OMG my speakers are going to die' noise rather than a hum.
./e
That isn't far off the mark. Luckily I am A) using cheapo goodwill speakers that will can handle a lot of abuse and B) encountered it while bringing up the bias so I could just back it off when it started.


Thanks for the rapid input folks. I'll rewire and give it a shot as soon as I can...which isn't always soon between work and the lil' ones going to bed at 7pm. Yowling amps in the night don't make the missus real happy :-)
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Old 5th February 2013, 02:50 AM   #1378
mfaughn is offline mfaughn  United States
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Yep, that was it. Thanks again. I'm am soooo happy that this thing is finally going. I bought my board 51 weeks ago. It has taken me a long time to get this far. Next is to see how it sounds with speakers that are good for anything other than testing. Now I have some tidying up to do and to make a pretty box for it to live in. I've got a nice piece of chechen (aka black poisonwood) that I think will do nicely.
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Old 5th February 2013, 10:46 AM   #1379
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I've not seen that choice before. so I looked and it should be very nice with the grain. I have a plank of South American Rose wood that is lightly grained that I found for my amp and preamp set. amp will set on the preamp and the grain will flow between them.
chechen pic attached for example.
You will enjoy the amp and have a hard time working on it when you are too busy listening to it!
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File Type: jpg chechen.jpg (19.0 KB, 290 views)
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Old 5th February 2013, 08:51 PM   #1380
mfaughn is offline mfaughn  United States
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Hooked up to a set of Snell A/iii now. Sounds very good...more and more so with each passing minute. There is a bit of a hiccup though. When playing music with ridiculous amounts of low bass (e.g. Santigold - Fame) things get rough. I get distortion throughout the spectrum. When the bass hits the vocals warble. I am guessing that this is some sort of interaction with the speaker because when I bi-amp the speaker so the DCPP is getting the full signal but only handling the mid/tweets then everything is fine. While the DCPP does make a spectacular boom I am just fine with the bi-amp situation (400wpc of iron-fisted Ashly). I'd still like to understand what is going on here for sure though.
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