5W 2A3 SET AMP

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happyrabbit

5W 2A3 SET AMP
« on: 26 Nov 2020, 12:58 am »
310V @ 65ma based on the JJ 2A3-40 driven by a 6n7. Coleman Filaments with Intact filament supplies. Monolith RS-3 output transformers.  Built by Oliver Sayes. After living with a SS amp for the last 10 months, feels lovely to own a SET amp again !

Dwight











« Last Edit: 26 Nov 2020, 03:05 am by happyrabbit »

JakeJ

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Re: 5W 2A3 SET AMP
« Reply #1 on: 26 Nov 2020, 01:43 am »
Congrats!  Looks lovely.  Nice black walnut frame too.  Curious, I see some thin little L brackets in the top of the chassis just above the handles.  What are thier purpose?

Enjoy,
Jake

happyrabbit

Re: 5W 2A3 SET AMP
« Reply #2 on: 26 Nov 2020, 01:52 am »
I own a 4 year old.. the mount for a tube cage  :green:




« Last Edit: 26 Nov 2020, 04:14 am by happyrabbit »

JakeJ

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Re: 5W 2A3 SET AMP
« Reply #3 on: 26 Nov 2020, 01:46 pm »
Good on ya.  My big VAC amps are cageless free-range tube amps and could be dangerous to child or pet.  Fortunately my cat has zero interest in stereo gear but she does come listen occasionally when I'm in a Jazz mood.

It still looks good with the cage on and I'm betting you are like most of us and listen with your eyes closed for the most part.

richidoo

Re: 5W 2A3 SET AMP
« Reply #4 on: 26 Nov 2020, 02:14 pm »
Beautiful amp!

Is 5W enough for those speakers in the picture?

What is that rectangular component between the power tranny and the 2A3? Thanks

poseidonsvoice

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Re: 5W 2A3 SET AMP
« Reply #5 on: 26 Nov 2020, 03:24 pm »
Beautiful amp!

Is 5W enough for those speakers in the picture?

What is that rectangular component between the power tranny and the 2A3? Thanks

The rectangular component is most likely an oil filled non E-lytic capacitor. Pretty typical for the style of building. Moreover, the horizontally mounted transformer (nearest to IEC) is most likely the power transformer while the black unit next to the rectangular capacitor is most likely a choke. But it could be a filament transformer too.

The cardinal component however are the uber expensive Monolith transformers from Belgium. Drool worthy.

Best,
Anand.

happyrabbit

Re: 5W 2A3 SET AMP
« Reply #6 on: 26 Nov 2020, 05:23 pm »
Poseidon,

Correct on all counts !   A good potion of the undercarriage is dedicated to the 2a3’s filament supply. DHT’s are a pain in da azz  :D. Attached a pic of the capacitor in question.  It’s definitely very big for 10uf...  I will have to ask Mr Sayes @ it.  My old 45 SET would not drive the Electric Studio’s (91db) but this amp will.  Also , it’s not a huge room either.  This amp will also accept the EML 2a3 solid plate.  The 6n7’s are filtered by a pair of tentlabs mec-50 ( next to the big blue caps ).   We were running out of room , and I wanted decent filtering for the driver supply.   The big blue caps are part of the ground reference for the Coleman Filament Supply.  The link for the Intact filament supplies : http://www.intactaudio.com/fil.html



« Last Edit: 27 Nov 2020, 03:06 am by happyrabbit »

Jon L

Re: 5W 2A3 SET AMP
« Reply #7 on: 26 Nov 2020, 11:23 pm »
This amp will also accept the EML 2a3 solid plate. 

I run EML 2A3 solid plates, but they won't make 5 watts in this amp like the JJ 2A3-40, correct?

happyrabbit

Re: 5W 2A3 SET AMP
« Reply #8 on: 27 Nov 2020, 02:59 am »
Yes !  the EML 2a3's will make ~ 5watts in this amp just like the JJ 2a3's.    A standard 2a3 will not last long @ 310V / 65ma.  A standard 2a3 can handle a Plate Dissipation of 15w.   An EML 2A3-S can handle ~28w and the JJ 2a3-40 @ 40watts according to the data sheets.   This Amps Plate Dissipation is ~20W (310 x 0.065) . Not much higher than a standard 2a3 but enough to make a standard 2a3 unhappy  :oops:      I am a big fan of the EML 2a3-s !   Its a better tube than the JJ, just a bit more expensive..  I will be ordering a pair in the near future.

Standard 2a3
http://www.r-type.org/pdfs/2a3.pdf

JJ 2a3-40
https://www.jj-electronic.com/en/2a3-40

EML 2A3-S
http://www.emissionlabs.com/datasheets/EML2A3-S.html

I am no expert on this subject..   please forgive if I am in Left Field :)

Dwight

richidoo

Re: 5W 2A3 SET AMP
« Reply #9 on: 27 Nov 2020, 06:42 pm »
Thanks Dwight and Anand for the info and pic

Docere

Re: 5W 2A3 SET AMP
« Reply #10 on: 27 Nov 2020, 10:44 pm »
Some nice elements to that design Dwight and both Intact and Monolith do good stuff. Tidy, compact build. Good to see the TentLabs mini eChokes getting a run - almost designed them into my next build and I’d like to use them in future. Is Jac warranting his tubes for use with the more recent versions of the Coleman Regs? What is the configuration of the 6N7 twin triodes - paralleled plate, single plate used (able to alternate plates), other?

A 2A3 running at “classic” operating points (250V/60ma/2K5 load) will make 5W, albeit at roughly 7% H2 distortion, before the grid swings to 0V and the sound can get a bit nasty; at 3.5W the 2A3 is generating an estimated 5% H2. I don't see the RS-3 transformer on the Monolith site, but I assume something like a 3K to 3K3 primary, which at the operating points shown for this amp and not drawing the lines, should produce around 5W at around 5% H2 distortion with a bit of available headroom.

I run EML 2A3-S as my daily drive; the JJ 2A3-40 sits in cupboard in case of emergencies.
« Last Edit: 6 Dec 2020, 08:06 pm by Docere »

happyrabbit

Re: 5W 2A3 SET AMP
« Reply #11 on: 28 Nov 2020, 01:42 am »
Here is the info on the RS-3.. sorry for the poor res !   I guess I will wait on the EML’s.  Looks like paralleled. Ha !  It has a common cathode. Very Cool tube !  http://vinylsavor.blogspot.com/2011/02/tube-of-month-6n7.html









« Last Edit: 28 Nov 2020, 02:21 pm by happyrabbit »

Docere

Re: 5W 2A3 SET AMP
« Reply #12 on: 28 Nov 2020, 01:58 am »
Thanks Dwight. Quality, solid performing output transformers you have there. Running the 3K5 load, I assume? Should be a fine sounding amp. Enjoy!

happyrabbit

Re: 5W 2A3 SET AMP
« Reply #13 on: 13 Dec 2020, 04:27 pm »
This is the preamp I designed for the 2A3 - https://www.audiocircle.com/index.php?topic=173838.0
« Last Edit: 13 Dec 2020, 08:56 pm by happyrabbit »