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Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


    I rebuilt my ST35 with FPE - with mistakes.

    corndog71
    corndog71

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    I rebuilt my ST35 with FPE - with mistakes. Empty I rebuilt my ST35 with FPE - with mistakes.

    Post by corndog71 Mon Jul 27, 2020 4:34 pm

    I love EL84 amps.  There’s just something about them that makes them fun to build.  I built one similar to this a few years ago for my brother.  It turned out so well that I decided to replicate it for myself with a few changes.  For the earlier one I drilled all of the holes in a 12x10x2” Hammond box.  This time I designed a plate on front panel express and used the power supply pcb from Dave Gillespie with built in EFB (enhanced fixed bias). http://tronola.com/html/daves_store.html
    I went with the same 12x10X3” box that I used for my power strip.

    Unfortunately I screwed up some of my measurements.  

    1. The hole cut for a filtered IEC jack was too small
    2. Three of the holes for the pcb were off by a few millimeters.
    3. There are 3 screw holes which I can’t even remember why I added them.
    4. Two screw holes for terminal strips were based on the wrong part.

    Fortunately I got most of the holes right and am now living with my mistake.

    It’s completely noise-free aside from a very slight transformer buzz.

    I rebuilt my ST35 with FPE - with mistakes. 50160337361_3f938ecb49_c Custom ST35 w/EFB v5

    I rebuilt my ST35 with FPE - with mistakes. 50159790168_df36bf25d0_c Custom ST35 w/EFB v5

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    Earl
    Earl

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    I rebuilt my ST35 with FPE - with mistakes. Empty Re: I rebuilt my ST35 with FPE - with mistakes.

    Post by Earl Tue Aug 04, 2020 8:44 pm

    I would have tried to mount the two output transformers closer together. Laughing Laughing

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    wantech826

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    I rebuilt my ST35 with FPE - with mistakes. Empty Re: I rebuilt my ST35 with FPE - with mistakes.

    Post by wantech826 Mon Aug 17, 2020 11:22 am

    how can you get those lettering ?
    thanks

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    rustybutt
    rustybutt

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    I rebuilt my ST35 with FPE - with mistakes. Empty Question from ignorance

    Post by rustybutt Mon Aug 17, 2020 12:50 pm

    I'm going to ask a question about something I know nothing about.  That's why I'm asking it.

    One of the things I've noticed which seems to be standard on stereo tube power amps is that the output transformers are typically on opposite sides of the amp chassis from each other, with the power transformer in between them.   This amp has the output transformers smack dab up against each other.  I've never seen that before.

    Under the assumption that the mag field of the transformers aren't confined to their physical form, wouldn't they impact each other?  Is this a potential problem?
    corndog71
    corndog71

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    Post by corndog71 Mon Aug 17, 2020 1:23 pm

    rustybutt wrote:I'm going to ask a question about something I know nothing about.  That's why I'm asking it.

    One of the things I've noticed which seems to be standard on stereo tube power amps is that the output transformers are typically on opposite sides of the amp chassis from each other, with the power transformer in between them.   This amp has the output transformers smack dab up against each other.  I've never seen that before.

    Under the assumption that the mag field of the transformers aren't confined to their physical form, wouldn't they impact each other?  Is this a potential problem?

    Well, the sound quality I'm getting leads me to think they don't. Another upside of this layout is both inputs and outputs can be placed far away from the power transformer. Another thing you might not know is the output transformers produce no heat at all. Only the power transformer and tubes get hot.

    Also, I'm not the only one who thought of this.

    I rebuilt my ST35 with FPE - with mistakes. ATLA32BLACKMED


    Last edited by corndog71 on Mon Aug 17, 2020 2:17 pm; edited 1 time in total

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    corndog71
    corndog71

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    Post by corndog71 Mon Aug 17, 2020 1:32 pm

    Lettering is cut into the panel and filled with paint.
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    Wharfcreek

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    Post by Wharfcreek Mon Aug 17, 2020 3:38 pm

    So I note that not only you, but also in your example of the 'close output transformers' unit, both these amps have the 12AX/12AU driver set-up vs the stock ST-35 Driver tube (7247). I've built a few of these myself, and I used the same 12AX/12AU, as copied from Shannon Parks' circuit. I'm just curious if you did the same, or if you just used the 'stock' ST-35 schematic and divided up the two triodes yourself? I'm pretty sure the distinctions are minor, but just wondering, as I'm also quite delighted with how my units have turned out..... Also, how 'bout posting a pic of where you mounted Dave's PS board? I'd thought about adding one to one of my units.... but truth be told, they sound so damn good 'as is' I just haven't seen the need. Maybe next time........ WC
    corndog71
    corndog71

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    Post by corndog71 Mon Aug 17, 2020 5:03 pm

    It is derived from Shannon's circuit.  I kept his feedback circuit as well.  What can I say? It works.  

    Here's the gut shot.  Mind you I had to improvise the power cord connection because I couldn't fit an IEC jack in the hole.  I'll probably come up with a more secure version of that in the future.  

    Power supply caps are Nichicon Muse.  
    Coupling caps are Solen for feedback and Miflex copper for outputs.  
    Input resistors are Vishay Z Foil.
    Input RCA jacks are copper based Vampire.  
    Binding posts are copper based Mueller.  
    Most of the wiring is Kimber TC.  Heater wiring is Belden 8450.
    I added a ground loop breaker circuit.
    I'm currently using all new Tung Sol tubes with a 5751 as the VA.

    I rebuilt my ST35 with FPE - with mistakes. 50238467802_8abd789f89_c ST35 v5
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    buchela

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    Post by buchela Mon Aug 17, 2020 7:07 pm

    Placing the output transformers that close and with the very same orientation is something I would not do, even if others would, as there is nothing to gain from that. There might not be enough MF to cause any disturbance but the MF gremlins are there. Sound great ? hey that's what counts. I have to say the lay out looks very nice, and so is the symmetry. That is a lot of work. Cheers
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    Wharfcreek

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    Post by Wharfcreek Mon Aug 17, 2020 8:19 pm

    Nice! BTW, what is 'FPE"?
    corndog71
    corndog71

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    Post by corndog71 Mon Aug 17, 2020 9:36 pm

    Wharfcreek wrote:Nice!   BTW, what is 'FPE"?  

    Front Panel Express. They offer free software for designing your own panel. That’s where the top plate came from.
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    Wharfcreek

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    Post by Wharfcreek Mon Aug 17, 2020 9:55 pm

    Gotit! Thx

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