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AC30/6 About to Begin

Discussion in 'Shock Brother's DIY Amps' started by mjcyates, Dec 1, 2020.

  1. mjcyates

    mjcyates Tele-Meister

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    So I have been commissioned by one of my previous customers to build an AC30/6. I have never built a Vox circuit and this looks like its going to be quite a challenge. He has sourced the chassis and tagboards and has an original cabinet. Going to be interesting. If any of you guys have tackled one of these before any info you can provide would be greatly appreciated.
     
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  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Subscribed.

    So you still need to find the transformers?
     
  3. mjcyates

    mjcyates Tele-Meister

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    Yes I do, any thoughts or ideas? I haven't even made it that far yet.
     
  4. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The AC30 1960 schematic shows a 280-0-280 160mA PT.
    Hammond suggests the 290NX. 290-0-290 262mA.

    I think that would be a little too much voltage. It starts 10 volts high and the 262mA rating would not let the voltage drop much.

    The Hammond 290MX looks better. 275-0-275 230mA. I am not sure if the chassis is designed for a lay down PT though.
     
  5. JamesAM

    JamesAM Tele-Meister

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  6. gusfinley

    gusfinley Tele-Afflicted

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  7. gusfinley

    gusfinley Tele-Afflicted

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    Triode has ClassicTone Power,Output and Choke still listed, but I don't know if they are actually in stock.

    Tube Depot has the ClassicTone Choke and Output, but the Power is sold out.

    Mercury Magnetics is always an option, but its hard to know specs on them. They should be a drop-in fit.

    Mojotone sells the power and output transformers, but I can't verify that the power transformer has the right dimensions.
     
  8. David Barnett

    David Barnett Doctor of Teleocity

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    Unless something has changed in the past few years, Mercury transformers for Vox have primaries for 115V AC, and voltages will run high with the ~125V AC we get these days.
     
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  9. gusfinley

    gusfinley Tele-Afflicted

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    That seems to be what I remember, too. Of course, if MM is what is desired a voltage reducing box could also be match the voltage to the output transformer.

    This is the sad thing about ClassicTone going out of business - They seems to make very good modern equivalents of vintage transformers. Or, in other words, You could get vintage Power Supply voltages using modern AC mains voltages.
     
  10. Wally

    Wally Telefied Ad Free Member

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    Mercury has a number of options. One has HT at 270-0-270.
     
  11. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    That was the issue with a couple alternatives from Hammond that I almost suggested. Seriously, who still gets 115V from a wall anymore? :rolleyes:
     
  12. gusfinley

    gusfinley Tele-Afflicted

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    Luckily Hammond seems to have wised up and added 120V primaries to many of their transformers - especially those for guitar amps.

    Now, If only they would make chassis for common amplifiers, they could be an even larger asset to the DIY community.
     
    Last edited: Dec 2, 2020
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  13. Dennis Perusse

    Dennis Perusse Tele-Meister

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    If you're going to do it old school then get the book "A Service Engineer's Guide to the Vox AC-30 Valve Amplifier" by Stephen Grosvenor. His book is an eye opener on what you'll be doing should you go that route. :)
     
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  14. mjcyates

    mjcyates Tele-Meister

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  15. gusfinley

    gusfinley Tele-Afflicted

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  16. mjcyates

    mjcyates Tele-Meister

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    Thanks for the link. I came across that before and that is the layout that I am going by. I also found a legible schematic that I am using to cross check the layout. I am actually creating my own version in DIYLC. I like to build amps virtually before I do the physical build. I find that I get most of my questions and issues resolved prior to diving in. The same person providing the chassis is also providing the tag boards, tag strips, terminal block, and hardware. His name is Stuart Castledine of Castledine Electronics. Regarding the faceplate I think the person I am building this for has one but not sure about that yet. I was wondering about the voltage selector, I haven't tried to find one yet.
     
  17. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Take this for what it is worth. I am not familiar with the original Vox transformers.

    From the above layouts, I see no Center Tap for the HT. Also an artificial HT CT is not indicated. I assume the HT CT may be grounded with the chassis of the PT.
    The schematic shows the HT CT ground and the PT chassis ground separately. It is hard to judge the actual physical layout from a schematic.

    Should you use a vintage PT, I thought you should be aware as some older PT's did have the HT CT connected to PT chassis ground.

    So... Don't be alarmed if the HT has continuity or low resistance with the PT chassis if a separate HT CT wire is not present.

    When I use the term *PT chassis ground*, I do not mean the amplifier chassis.
     
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  18. mjcyates

    mjcyates Tele-Meister

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    Duly noted. Thanks for the info!
     
  19. mjcyates

    mjcyates Tele-Meister

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