NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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 Posted: 13 Oct 2016, 17:21
 Project Author

Joined: 06 Jun 2008, 18:23
Posts: 5188
Location: Australia
Peter W. wrote:
gofar99 wrote:
Ugh. I have ranted on this before several times. There is no way I would allow such a thing in the house. A single fault in either the house wiring (I found a reversed hot and neutral just last year and we have been here 30+ years) or in the unit itself can place the full line voltage on the chassis and anything connected to it. I figure that as long as transformers are cheaper than headstones, I believe I'll stick to transformers.

Good listening
Bruce

Yeah - at a plate voltage that could be at/around 425V that could hurt. How many milliamps do you think it would take to put more than 1/4 watt of current through a 10,000 resistor at 425V?

I = 425/10000 = 0.025

Or, not many.

Why that equation? A healthy adult human may be substituted for a 10,000 ohm, 1/4 watt resistor. Anything that puts more than that amount of current through 10,000 ohms will cause damage to either unit.

I should have started a new thread. Way back in the postings you will see I used a power tranni. No it's not directly connected to mains. Fabulous amp though, I would recommend it to anyone wanting an excellent sounding amp and only need a few watts.

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 Posted: 16 Oct 2016, 12:53

Joined: 12 Jun 2009, 15:43
Posts: 87
Location: College Station, Texas
thehoj wrote:
mwhouston wrote:
Geek wrote:
*GASP!*

At least maybe have back-to-back filament trannies to give some isolation?

Strangely I do have a filament tranni with dual windings.

I was wondering.. How dangrerous / feasible would it be to build an entirely transformerless amp.. OTL 6AS7, with mains and filaments direct off of AC

I only just saw this, and apologies if this is reverting to an obsolete aspect of the thread, but I just wanted to give a response to thehoj's question. I built a 25W OTL amplifier that is along the lines of what he was asking about. It uses 6082 tubes rather than 6AS7 for the output stage (modified Futterman); these are essentially equivalent except for having 26V heaters, which are ideal for forming the bulk of a heater chain for direct 117V mains connection. There are no transformers at all in the amplifier, and the main B+ and B- supplies for the output stage come from half-wave rectification of the mains. US 117V mains is much more practicable, and safer, than European 220V, for direct mains connection, and is ideal for the rather low HT voltages needed by the OTL output stage (+150V and -150V.) My amplifier is rather close in concept to the classic 1954 design by Dickie and Macovski. It weighs 8.4 lbs only. Here's a picture:
Attachment:
otl1.jpg

About safety: Chassis is connected to 3rd-prong ground. Signal ground, on the other hand, is connected to neutral. (Means a floating signal source is needed, but that's not a problem; most CD players are floating.) There are massive 35A back-to-back (anti)parallel rectifiers that ensure signal ground can never deviate from true ground by more than + or - 1.5V. If the amplifier were ever to be plugged into one of the dreaded reverse-wired mains sockets, it would trip the breaker at the fusebox instantly. (And yes, I found one mis-wired socket in my house, with neutral and line interchanged. I found it when checking sockets before I first plugged the amplifier in.)

I think people sometimes over-state the case about the dangers of direct mains connection in comparison to equipment with transformers. For example, geek said in an early comment on this thread, "I can plug in a 250V transformer and grab any one of the HV leads and be just fine. Can you say that for sticking your finger in a wall outlet?" Yes, with the conditions precisely as stated by him it is true, that touching one secondary terminal of the 250V transformer, if the secondary is entirely floating, is much safer than touching the line terminal of a 117V mains outlet. But that is not a realistic comparison. Once the transformer is wired up in an amplifier, touching the 250V secondary terminal is at least as dangerous, if not more so, than touching the live mains wire. The maximum current available from the transformer may be a lot less than the current available directly from the mains, but it is still way more than sufficient for a lethal shock.

I would not give my transformerless amplifier to anyone else to use. And I know that in my house no genie is going to visit in the night and interchange the live and neutral wires in the power socket where I plug it in. I grew up in the UK in the 1960s, messing around with direct 240V mains-connected TVs and the like. I don't think the risks with this transformerless amplifier are particularly great, if one follows sensible precautions.

So why did I build it? It's not my regular, everyday, amplifier, although I do use it fairly often. Partly, I built it just as a sort of homage, I suppose, to the rather remarkable design by Dickie and Macovski from 60 years ago. And partly, perhaps, to show that it could be done, and that with some sensible precautions it is really not as dangerous as is sometimes claimed.

Chris

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 Posted: 16 Oct 2016, 17:08
 Project Author

Joined: 06 Jun 2008, 18:23
Posts: 5188
Location: Australia
I thought the same thing that the secondary from a HT tranni will deliver more than enough current to kill. The idea of a direct mains amp is still on my mind. I have thought of using a non-conducting chassis e.g wood. I would use a small mains power filter and a filament transformer. We are on 250V here so rectifying it will produce a high HT which can be limited with a resistive network. Selecting a tube which uses a high HT would work best here. Also ensuring a well selected fuse both on the mains side and DC HT side to limit current into the amp would add to safety.

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 Posted: 20 Nov 2016, 00:04
 Project Author

Joined: 06 Jun 2008, 18:23
Posts: 5188
Location: Australia
I've been on the Tripath Class D and non-Tripath Class D trail for some time now and built way too many. Fortunately all sold except one. But I have one 1500W monster to build. My latest T3 Tripath monoblocks http://www.diyaudioprojects.com/Forum/viewtopic.php?f=10&t=5724 sold within a few days of completion and my thoughts were to build another. It was extremely good.

While searching for some tubes for another I noticed I had some NOS Trigon "London" black glass 6V6 I may have never used. So along with an early NOS Sovtek 6SN7 I swapped out the tubes in my Black Lace. Sounds good and now I'm not missing the T3. Just need 50hours of play to run the tubes in.

With my Beyma 15" speakers I only need a watt or so to deliver better than good volume. Looking forward to the tubes running in.

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 Posted: 22 Nov 2016, 06:38
 Project Author

Joined: 06 Jun 2008, 18:23
Posts: 5188
Location: Australia
Enjoying this amp with the new tube compliment. Has anyone ever heard of the company Trigon??

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 Posted: 22 Jan 2017, 18:47
 Project Author

Joined: 06 Jun 2008, 18:23
Posts: 5188
Location: Australia
For a couple of years now a fellow Melbourne Audio Club member has been asking me if he could purchase my 807 amp which Suncalc design. Finally I gave in and have lent him the amp to see if he really likes it.

The 807 got a lot of use in my system II with FM radio and my DIY 2-way bookshelf speakers. Always nice to listen to classical and always more than enough volume. Since the 807 is away I dropped in my Black Lace 6V6 amp (another Suncalc design and with split PS). Well surprise, surprise, the 6V6 sounds even better. Much better.

If the amp doesn't sell I may try on eBay or whatever. The 6V6 just sounds far more detailed and brighter. Wished I'd swapped it out sometime back.

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 Posted: 22 Jan 2017, 20:39

Joined: 20 Feb 2014, 10:35
Posts: 59
Location: NZ
mwhouston wrote:
Enjoying this amp with the new tube compliment. Has anyone ever heard of the company Trigon??

Yes, quite common over here. There were a UK valve re-brander like many others (Haltron, Zaerix, etc).
Valves were sourced from different manufacturers so you never know exactly what you might get, but you can get lucky as they re-labeled Mullards, Philips, etc also.

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 Posted: 24 Nov 2017, 20:43
 Project Author

Joined: 06 Jun 2008, 18:23
Posts: 5188
Location: Australia
Take a look at some distortion graphs for Black Lace here; http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5731&p=52175#p52175

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 Posted: 24 Apr 2019, 19:30
 Project Author

Joined: 06 Jun 2008, 18:23
Posts: 5188
Location: Australia
Never tried my Black Lace 6V6 SE UL amp with these horns. 1.9W compared to the usual 180W class d amps is a big drop. But I can play just as loud as before. Speakers are about 92db efficient. Even up loud there appears no strain or distortion. Bass not as d tended but good down to 50hZ. All tube setup now.
Attachment:
A9D00097-A406-49D2-9854-AAC32C87CF5A.jpeg
Attachment:
0A66CAF4-C67D-4A62-8057-AC19D14B7342.jpeg

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 Posted: 26 Apr 2019, 19:10
 Project Author

Joined: 06 Jun 2008, 18:23
Posts: 5188
Location: Australia
Though I think the 6SN7 in my 6V6 power amp is a good one (NOS red base RCA) I have ordered a Chuguang CV181-Z for my amp. I have enjoyed the CV181-Z in a recent preamp and thought it would make an improvement in my power amp.

I mentioned the eBay purchase on another forum and was questioned how I would ensure or prove the “new tube” is a new tube. I have a tester and said I would expect emissions to be very high. But then what of Gm. I know emissions aren’t everything but it’s all I can test.

Is there a very simple setup you can apply to a tube to test Gm or any other specification of a tube. With transistors etc. tying the base to the emitter then a 100k resistor on the collector with a 9V battery and measuring current through the 100k will give you some idea of the hfe of the transistor. This way you can roughly match transistors. Is there a tube equivalent?

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