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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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Board index » DIY Audio Forums » Vacuum Tubes / Thermionic Valves

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attenborough
PostPosted: 19 Aug 2012 6:49 am 
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hi can any one help. i have just finished my amp and i have a few issues.
1. when you turn up the amp it sounds like it is distorting and the output valves have a blue glow in them.
2. there is no base. till you turn off the amp and the last few seconds as the heaters and caps discharged you get lots of base.


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HT Performance
PostPosted: 19 Aug 2012 10:22 am 
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Location: Lisbon, Portugal
Hi!

Welcome to the forum!

I checked the tubes datasheet, and your schematic seems OK to me, it should work fine.

Have you tried to disconect the negative feedback to compare the sound?

Is this your first tube amplifier?


Cheers,

Miguel
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gofar99
PostPosted: 19 Aug 2012 8:26 pm 
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Hi there is a high probability that the phase of the negative feedback loop is backwards. try reversing either the wires on the primary side of the output transformer or the secondary ones (not both) this will swap the phase of the output.

Good listening
Bruce

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attenborough
PostPosted: 20 Aug 2012 1:23 pm 
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hi thank you for your feed back. it is my first stereo amp build. but have done mono builds and vintage radio repairer's. i just love the sound and glow of valves. will try to change the feed back and see what happens, and the output txs wires to see if i have crosed them over
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attenborough
PostPosted: 28 Aug 2012 1:11 pm 
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hello an update. it turned out to be the output txs.they were only 30 ome. not the 10K serves me right for buying Chinese.This is why the valves were glowing blue not the correct load on them. i might as well not put a speaker on them!!!!!!.
now she will sound great when i get two new output tx the same. as all of mine are out of old valved radios and none of them have the same winding.
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gofar99
PostPosted: 28 Aug 2012 2:48 pm 
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Hi, The DC resistance of the transformers has little to do with the actual impedance. 30 ohms (DC) might be fine. The blue glow in some tubes is the result of gas being ionized inside the tube. A fairly common thing when ever the voltage is above about 300. About 99% of the time it is not an issue and just pretty to look at. With audio applied it will frequently jump around in time with the sound.

Good listening
Bruce

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Soundbrigade
PostPosted: 28 Aug 2012 4:02 pm 
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Location: Vänersborg, Sweden
I also feels an ECC83 is overkill for driving the EL95. An ECC82 would be better choice and propably sound better. Check and doublecheck ALL your wiring and all your components.

Got any photos of your amp?

I have been building a similar amp för a few years (never get to the end :blush: ) and I fear I can hardly find the recepies.
However I have a special plate for four 7-pin sockets and it would be great to find a good 7-pin driver (6AU6?).

Image

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gofar99
PostPosted: 28 Aug 2012 9:43 pm 
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Hi, How about a 6C4 or a 6AV6. one low mu and one high mu. In the 6AV6, just tie the diode anodes to the triode cathode. The 12 volt versions of the tubes are fine as well and particularly the 12AV6 is rather common. It was used in nearly all 5 tube AM table radios.

Good listening
Bruce

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