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 Post subject: Re: 6EM7 power amp
PostPosted: 22 Oct 2011, 17:24 
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Joined: 06 Jun 2008, 18:23
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Thanks Matt but I may have a new case with a bit more room. More to follow.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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 Post subject: Re: 6EM7 power amp
PostPosted: 25 Oct 2011, 23:20 
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I have had the most trouble I have ever had deciding how to case this amp. Part of the problem has been open frame exposed OPTs and chokes. The other part of the problem is there are two of everything. Two power trannies, chokes and rec tubes. I do have a power tranni larger enough to power both channels but then I thought "dual mono". This it will be.

In this high timber base I can hide the open frame OPTs and chokes in. This base has a front and back plate. No need for top mounted RCAs and speaker binding posts. Also I am including a single stage preamp (front tube) so the amp doesn't need a seperate preamp. I also have a remote control volume control I may use. See picks.
Attachment:
6EM7Layout4_IIIss.jpg
Attachment:
6EM7Layout4_IIss.jpg
Attachment:
6EM7Layout4_Iss.jpg


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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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 Post subject: Re: 6EM7 power amp
PostPosted: 27 Oct 2011, 15:43 
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Matt/forumers: I realise I have to use a limiting resistor in the HT path to bring the HT down to the 260V mark. Is it best to put this before or after the choke. It is my intention to use this resistor to form part of the filtering network. My question is should the resistor go before the choke or after. Should the filter network be C-R-C-L-C or C-L-C-R-C.

I know the first cap coming of the rec tube should be no more than 30uf but what is the best order (if the is a best) to set-up the network. The base in the last photo was the forth set-up I tried. Now the plates have been marked and ready for drilling. Tonight I hope to have all the drilling complete and the primer on. I'm yet to decide on a colour for the top plate etc.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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 Post subject: Re: 6EM7 power amp
PostPosted: 27 Oct 2011, 21:18 
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Quote:
My question is should the resistor go before the choke or after. Should the filter network be C-R-C-L-C or C-L-C-R-C.
The best rule to follow (in general purpose amplifier power supplies) in a cascaded filter design is always LC stages first, RC stages after. So C-L-C-R-C.

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 Post subject: Re: 6EM7 power amp
PostPosted: 27 Oct 2011, 22:15 
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Thanks

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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 Post subject: Re: 6EM7 power amp
PostPosted: 28 Oct 2011, 06:47 
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I like to use the drill press outside with the birds and bees but rain threatened so I set-up in the car port. Got all of the top drilled. I forgot to mark the bottom plate.Tomorrow finish marking the bottom plate then drill the rest out. 60% of the drilling is in the top plate and this is done.

Tomorrow: finish marking the bottom plate, drill the rest and prime the lot. I have picked my colour for the top, bottom and smaller pannels for the amp. Stay on your meds, it maybe a shock.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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 Post subject: Re: 6EM7 power amp
PostPosted: 28 Oct 2011, 20:30 
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All the time spent carefully marking and I forgot the speaker binding posts. Does a power amp really need speakers??

The idea was to keep every connection on a back plate in the base. The plate has been marked and drilled. Now there is no room . So the speakers will reside on the top plate at the back. More marking and drilling to go.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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 Post subject: Re: 6EM7 power amp
PostPosted: 29 Oct 2011, 23:01 
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I was anoyed by getting behind with this project so after a big effort: Plates and base are sprayed and before the end of the week I shoud be able to start assembly. The colour is called Sungold. Some might say "yellow". The shop had yellow but I thought this a little more tastefull. I did warn you about the colour but I have had this in mind way before building this amp. The paint and primer are Epoxy Enamel and dry hard but it stakes about three to four days.

I could have picked hammer tone but with the black trannies it may have all looked too dull. I have some nice black screws to hold down the top plate, so with the black trannies and screws on a the Sungold coloured top plate the amp should look good. Or interesting or different.
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BaseI.jpg
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BaseII.jpg
Attachment:
BaseIII.jpg


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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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 Post subject: Re: 6EM7 power amp
PostPosted: 30 Oct 2011, 11:40 
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Joined: 07 Feb 2010, 15:42
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Location: England
I have to say I'm a big fan of the colour. Is this going to be a recurring theme? Blue on your 6AS7 amp, Yellow (or rather 'Sungold' ) on the 6EM7 and perhaps a Red on a future build's top plate? :D

Lewis

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 Post subject: Re: 6EM7 power amp
PostPosted: 30 Oct 2011, 16:05 
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Location: Australia
I used a Woodlands Grey on the silver dragon. It's more about making the amp being interesting on a number of levels. This amp only has 2W of power so to make it a little more impressive, from a visual stand point, the brighter colour. I have used a beaten copper, black and reds in the past. As stated above I wanted a colour that would work with the black trannies. The Sungold top plate with black screws and black trannies should provide colourful relief.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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