Currawong

the thermionic watercooler

Re: Currawong

Postby soundbrigade » Thu Sep 07, 2017 1:11 am

Tom, I haven't made a final descision of OP transformers. I think I can use a pair of Edcore XPP from a retired 6AQ5-amp, else I am considering any of these:
http://en.uraltone.com/electronic-components/transformers-and-chokes/output-transformers/all-output-transformers-as-list/inmadout-output-transformer-tu84m18c.html
Or a Hammond 125E.
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Re: Currawong

Postby EWBrown » Mon Sep 11, 2017 7:00 pm

I have a pair of Hammond 1609s as well as three 1608s, that I purchased (or traded for) about 10 years ago.
TBD on the power trannie, I have several options to choose from.

The board and parts was a nickel short of $36, and I have all the tubes on hand, both in 6.3 and 12.6V filament voltages.
12V would make it simple, I'd just use a 12V 4 A SMPS "brick" and thusly eliminate any 60HZ from the board -
or I could use 6.3V tubes and wire them in series, in pairs.

Or, I I could go back to the method I used in my 13EM7 SE amps, use one of the Trafomatic toroids, and use 12.6V filaments in series pairs.
I think 700mA at 26VDC should be sufficient to meet the requirement.

So, there is no additional monetary expense necessary, just have to ramp up the enthusiasm and start building, after a few years' hiatus.

/ed B in NC
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Re: Currawong

Postby soundbrigade » Tue Sep 12, 2017 12:29 am

I feel I need some distance before giving the Currawrong another go (I replaced the blown fuse). Instead I have anothe rproject for 6L6s that a little resembles the 6V6 a little. The single input/splitter/driver tube, 12AT7. Picked this one beacuse of its simplicity. The CCS is a LM317 but got inspired by a build of the OddWatts in another forum to pick the K-version (TO3) as that would fill a hole in my chassis.
The only place in Sweden stocking 317K's wanted almost 10 bucks/each whereas I got five of the (two working hopefully :/ ) from Chian for half that sum.

PP6L6.jpg
PP6L6.jpg (41.04 KiB) Viewed 131 times


The hole and the ordinary LM317.

6L6-31.jpg
6L6-31.jpg (137.68 KiB) Viewed 131 times


OOOPS!!!! I had apperantly planned to use the holes for tube VU-meters ....

6L6-46.jpg
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Re: Currawong

Postby EWBrown » Thu Sep 14, 2017 2:58 pm

I like that one, very elegant in its simplicity, no floobydust, blue flashing LEDs or embryonic baby cattle required ;-)

And if one truly desires to have NFB, it is a simple matter of injecting a wee sample of the 8 ohm output back into the top of R5. [:)

I'd use 10M45S in place of the LM317, just because... *) (b) (y)

Approx 8 mA per 12AT7 triode, that is a good plate current for these, makes them really perform!

Even though I have a plethora of 20 year old LM317s on hand, I like the 10M45S as a current source or sink. And have LOTS of them.

Six of one, half a dozen of the other. $)

Or when truly high voltage ratings are required, 10M90S (900 maximum DC volts (666)


/ed B in NC
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Re: Currawong

Postby soundbrigade » Thu Sep 14, 2017 3:05 pm

So here we don't go tuberolling. We go regulatorrolling!!!! (banana)
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Re: Currawong

Postby soundbrigade » Fri Sep 15, 2017 1:44 am

I just dug up a pair of 10K, 15W transformers when I was vacuuming our flat. Well they stood on a shelf and I have been looking at them every now and then, but considered them to be single ends.

How much will gain/loose using them instead? I get it that I will have less power but lower distortion, but still; are they suitable for the 6V6s?
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Re: Currawong

Postby EWBrown » Fri Sep 15, 2017 7:52 am

10K is just about perfect for 6V6s in cathode-biased operation. 8K is better for fixed-bias, but either value is OK.

For 6L6s, 6.6K A-A is a good value.

/ed B
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Re: Currawong

Postby soundbrigade » Fri Sep 15, 2017 8:43 am

I did ordered a pair of Hammond 125E's. Maybe use them in the Currywrong. ;)
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Re: Currawong

Postby soundbrigade » Wed Sep 20, 2017 1:03 am

I may have a need for a gain stage to both the 6V6 and 6L6 pushpullers. I had an idea of using as´pensize tube hidden in the chassis, something like this:

Hybrid-2sk1058-.gif
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Re: Currawong

Postby EWBrown » Wed Sep 20, 2017 9:08 am

One must always utilize the Triode of Improved Reliability! [:) $) :/ O:) (banana)

https://frank.pocnet.net/sheets/113/6/6S31B.pdf
Last edited by EWBrown on Wed Sep 20, 2017 9:34 am, edited 1 time in total.
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Re: Currawong

Postby soundbrigade » Wed Sep 20, 2017 9:25 am

No need. I always find it much better to go skydiving without parachute. (y)
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Re: Currawong

Postby EWBrown » Wed Sep 20, 2017 9:32 am

No parachute necessary - :[ just use a really long bungee cord ;-) =:o (stop)
It's not the fall that kills, it's the sudden stop at the bottom :))
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Re: Currawong

Postby soundbrigade » Sat Sep 23, 2017 11:07 am

It's not the fart that kills, it's the smell. Guess I have given you this Swenglish expression before, where 'fart' is 'speed' and 'smell' is 'crash'.

Here's another smell:
I am updating my website. I more or less list all projects, show some pics or many pics, link to some on-line info and present some diagrams. I have just finished the short info on my Russian Priboi amp, which, built on rather crappy dual-tetrodes (6R3S-I) was modified into something rather different. Same tubes but trioded, running on lower voltage and fully in class A. I suddenly got the GREAT idea of scrapping the amp boards, restore the PSU and use some RTR boards for 6CA7 or KT88 or maybe even 6L6 and GU50. Found a lot of boards but many VERY expensive, many populated and then, in China I noticed this one: http://www.jjjaudio.com/en/products/el34-pp-pcb-board.html.
Ridiculously priced ten bucks, I couldn't resist and have just ordered it but what the 17 have I bought. EL34/6CA7 - thats obvious but what amp is this board based on? My guess is a 12AX7 as input tube and a 12AU7 as driver OR vice versa.


(What about the Currawong? Dunno, have to try to short out relays and turn-on delay and see if I can make the amp work without shooting fuzes.)
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