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    Building a pair of new MKIVs and need some help


    Posts : 6
    Join date : 2011-08-17
    Location : East Coast

    Building a pair of new MKIVs and need some help

    Post by HiGHFLYiN9 on Thu Aug 24, 2017 11:19 am

    I posted this over on DIYTube a couple weeks ago but that forum is unfortunately in deep cryo-stasis now that Shannon has retired from offering boards. I was gathering parts for a pair of MKIVs, I first asked VTA but they aren't offering MKIV boards currently. I was very fortunate to get a pair of Poseidon boards that Tom McNally had spare. Now, between the Poseidon board and the Classic Valve Cap board, I'm a bit confused about how things are configured as the documentation on the cap board is a little nebulous (at least for a non-engineer).

    Here's the schematic and images for the Poseidon: Poseidon Manual

    This is the Cap board and schematic:

    These are the two transformers:

    ...and this is what I have so far:

    So some questions regarding the cap board:

    1. Would the "rectifier output" connection be pin 8 on the 5AR4?

    2. Assuming "power ground output" means the black wire on the A-470? ... would this also be run to the negative speaker terminal?

    3. For Transformer Bias Tap, would that be Red/Black on the PA-135?

    4. For Transformer Center tap, would that be red/yellow on the PA-135?

    5. Where do eyelet #6 and #8 correspond on the Poseiden?

    Sorry for all the rudimentary questions. While I can make assumptions, I want to ensure everything is exactly correct and consulting the experts is always important! Smile
    Bob Latino

    Posts : 2639
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Building a pair of new MKIVs and need some help

    Post by Bob Latino on Sun Aug 27, 2017 8:39 am

    The answers to your questions 1 through 4 are yes. As to your question 5 about eyelets 6 and 8 and what would they refer to on the Poseidon board, I am not sure? I suggest you Email Shannon and/or Classic Valve for an explanation of what is connected to those eyelets.


    Posts : 1435
    Join date : 2008-11-30

    Re: Building a pair of new MKIVs and need some help

    Post by tubes4hifi on Mon Aug 28, 2017 8:00 pm

    if you look at a Dynaco MK4 schematic you will see where eyelets 6 and 8 are, but those are on the original Dyna board, NOT on the new Poseidan board, so they wouldn't be used in your case.

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    Re: Building a pair of new MKIVs and need some help

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