KT66SE

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Re: KT66SE

Postby TomMcNally » Mon Dec 16, 2013 7:13 am

An inverter is possible. The schematics I've googled are push-pull with a center tapped 24 volt primary. It would have to be pretty heavy current, probably 20 amps or more. It would probably be easier and cheaper to run the mobile amplifiers filament string from 12 volts directly, and use a commercial inverter capable of decent clean sine wave, into a normal high voltage transformer.

I just looked up the 6384 ... sounds like it's a a heavy duty 6L6GC (different pinout) ... there are quite a few on eBay, prices all over the place. Is that what you'd use in the car?

I thought about a car amp a few times, but the space and current requirements make in impractical for me.
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Re: KT66SE

Postby EWBrown » Mon Dec 16, 2013 9:41 am

The 6384 is the Bendix Red Bank, guided-missile-high-g-forces rated version of the 6AR6 and 6098. Weird pinout, it is otherwise like a 5881 on steroids.
The supports and spacers are ceramic, not mica, the warm-up time is fairly long,45 seconds or more to reach full emission. Hard borosilicate glass, and the
inside elementsare VERY securely supported.

Image

They work well in triode strapped mode.

Gary Kaufman built one here: http://www.the-planet.org/audio.html

http://frank.pocnet.net/sheets/131/6/6384.pdf

Heathkit W5M KT66 PP schematic:

Image


/ed B
Last edited by EWBrown on Sun Jan 05, 2014 6:53 pm, edited 4 times in total.
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Re: KT66SE

Postby 6B4G » Mon Dec 16, 2013 10:17 pm

Tom I get what you are saying that room for a tube amp is limited especially when you are some what forced
to own a small car by the government (Greece). When living in Australia there was no issue with room due
to the cars I had. It's a classic to see guys here with subs etc that leaves no room for a spare tire LOL
I would use 6384's on a car amp as they seem to be bullet proof, I don't think anyone would be able to
break a tube that is rated at 500G and also with a 10,000 hour life they most certainly will give you value
for money. I absolutely love the EL37s but there cost is just to high, I have built two amps with the EL37s
one PP and now one SE and they sound fantastic. If the 6384s come close I would be happy.
Ed I have found that link before and unfortunately he doesn't say anything about the sound quality, I would
suspect that he is happy with it as he states " Fortunately I picked up a few before Vacuum Tube Valley wrote an article on Bendix tubes"
My first attempt will be after Xmas, I'm not sure on the opt as Gary Kaufman is using a 5k. I will be ordering a set to be made with
a build time of 4 weeks.



Has anyone seen the amp used with the new Samsung TV's? They are using tubes..............


Regards
Greg
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Re: KT66SE

Postby AmadeusMozart » Fri Dec 27, 2013 2:15 am

Have not read through the whole thread but if the only problem is that you have a 400-0-400 transformer and need 300-0-300 then instead of using C-L-C smoothing go to L-C-R-C smoothing. It will be easier on the rectifier tube and on the transformer (lower peak currents). Use Duncan Amp's PSU Designer II to play around with values and see what ripple you get. No big dropping resistors required and less heat!
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Re: KT66SE

Postby 6B4G » Fri Dec 27, 2013 6:27 am

Hi AmadeusMozart and Merry Christmas.
The 300-0-300 is the way to go, even though I built a SE EL37 with 400-0-400 (that's what I had on hand) and the help of azazello.
The amp is running a small slow fan on a heat sink with the resistor mounted on it.
The 6384's run up to 750v (max DC) so would I still use the 600vct transformer?
Ok just had a look at the specs again and for max life 300vdc is stated also Grid resistance is 25k
excuse my ignorance, but, would that be the resistance for the opt?
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Re: KT66SE

Postby kheper » Fri Dec 27, 2013 9:23 am

6B4G wrote:Hi AmadeusMozart and Merry Christmas.
The 300-0-300 is the way to go, even though I built a SE EL37 with 400-0-400 (that's what I had on hand) and the help of azazello.
The amp is running a small slow fan on a heat sink with the resistor mounted on it.
The 6384's run up to 750v (max DC) so would I still use the 600vct transformer?
Ok just had a look at the specs again and for max life 300vdc is stated also Grid resistance is 25k
excuse my ignorance, but, would that be the resistance for the opt?


AmadeusMozart is suggesting that you run the 400-0-400 transformer with a choke input filter to obtain a lower B+, rather than dropping it with a resistor. (A good idea) You would get about ~345Vdc, but you need a high quality choke for this to work without producing hum. If you lower the B+, you could increase the bias current. (Also good for an SE Class A amp)

The "Grid resistance" is just the resistance of what the control grid of a 6384 will be at 300Vdc, not the opt's resistance.
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Re: KT66SE

Postby AmadeusMozart » Fri Dec 27, 2013 1:28 pm

Sometimes you have a voltage between the optimum for either capacitor input or choke input. You can then start playing around with some R-C-L-C input and the values of R and the first C can be used to manipulate the final voltage. The first capacitor will have a large ripple which may reduce life expectancy. Sometimes it is best to use two in series (lower voltage across the cap will make the capacitor last longer).
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Re: KT66SE

Postby 6B4G » Tue Dec 31, 2013 12:52 am

Thanks for that
A quick one, can I run a GZ34 or any other tube without a load, apart from the caps and the and choke without damaging the tube?
Or in other words I would like to work on a power supply live and add or subtract components with no damage to the tube.
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Re: KT66SE

Postby AmadeusMozart » Fri Jan 03, 2014 1:33 pm

I've mentioned it elsewhere - Duncan's Amp has the PSU Designer II (free) that will allow you to mimick a PSU. Load will change voltages so getting voltages right without load is not going to be very helpful.

PS I thought about the KT66 / 6L6 design in the first post before designing and building my 6L6-GC. My design is on audiokarma (same moniker as here) and used good iron (James). The KT66 and 6L6 series have been specifically been designed for push-pull operation in ultra linear mode and although I got around 8 watts out of it I was not impressed.For SEP I like the EL84 and have started gathering parts for the Budgie. I've been informed that the 6V6 in SE UL is very remarkable too.
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Re: KT66SE

Postby 6B4G » Fri Jan 03, 2014 11:37 pm

I'm running EL37's on the this schematic and it sounds fantastic, dead quiet. I haven't checked what power output yet I'me running it in, I also have used James opt's but these were picked up over 7 years ago and they were made for someone that didn't take them all. I regret not getting more.
I'm thinking of getting opt's from http://www.ogonowski.eu/transformers/single-ended/ with c-cores but I can't find anyone that has used them.
If there is anything I can help please tell me.
Now the thing I am looking for is a great preamp schematics to build.
Re PSU Designer II I have it.
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Re: KT66SE

Postby johnf » Sat Jan 04, 2014 11:14 am

Have a look at the SRPP line preamp at: http://diyaudioprojects.com/.
The build forum thread is at:http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=2448
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Re: KT66SE

Postby AmadeusMozart » Sat Jan 04, 2014 1:32 pm

I've build a 6L6-GC SE with James iron and was not that overly impressed. I suspect it may have been the Schade (plate-to-plate) feedback that I used, recently I did read some reasons why manufacturers moved away from it and switched to GFB. Personally I've started to lean towards little feedback plus a design using the most sold types (12AX7 & EL84) reasoning that going from approx. 3~4 watt to 7 ~8 watt is not worth the cost (plus the weight is more than double from what I will make now).

I have over the last few months also read some alternative views on potted transformers and remember a late friend who moaned when he had to redo QUAD II transformers (mainly power but also the odd OPT) which were potted with pitch. I suspect motor rewinders will be around for a long time (at least longer that I'll be around) so I am using Transcendar's OPT and the Classic Hammond Power and choke.

If someone is interested in an amplifier doing about 4 - 5 watt with high feedback I have a Dutch design in PDF with EL84 that has 40dB feedback and was highly regarded. It is in Dutch but it has the chassis and component layout. Drop me a PM if you want the PDF.
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Re: KT66SE

Postby 6B4G » Tue Jan 21, 2014 2:45 am

Sorry for the delay in replying I'm not using any feedback plus I'm using EL37's and I am impressed
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