Mini Valve amp transformer

Discussion in 'Shock Brother's DIY Amps' started by Asmith, Jan 13, 2020.

  1. Asmith

    Asmith Friend of Leo's

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    Hi there,

    I am looking for a suitable PT for a mini valve amp.

    Running 4 (i will settle for 3) preamp valves (2/3 12ax7 for the preamp and PI and a 12au7 PP output). I'm not particularly fussy about the B+ as Im looking for anything from 250v to 300v after smoothing and I dont mind dropping it if its higher than needed.

    I would like a toroidal though since they have so many magical properties such as low noise, heat and space especially since these mini amps have a rep for noise without a choke.

    My google-fu failed me this time, I found one that can power 3 which i would jump on but the guy selling them is on a sabbatical which has extended its self.

    So im wondering if anyone has any alternatives?

    And to make things worse i live in the uk
     
  2. EmWeAh

    EmWeAh TDPRI Member Ad Free Member

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  3. Squawker

    Squawker TDPRI Member

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  4. Asmith

    Asmith Friend of Leo's

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    Perfection!

    • Pri: 0-120-230-240 V (black-yellow-purple-red)
    • Sec 1: 200 V @ 0,1 A (red)
    • Sec 2: 6,3 V @ 1,5 A (green)
    • long leads ca 200 mm
    • h=35mm d=70mm
    275V @100mA after smoothing
    1.5A on the heaters

    Should do about 5 dual triodes so nice to be slightly over spec.

    And shouldnt cost more than £35 to acquire. Thanks a bunch Ive been on and off for a week, I bet that European comma rather than the full stop was the reason I couldnt find anything a 6.3V heater supply.

    The amp is based on an AC15, Ive been sat on this design for a year so I cant wait to finally pull the trigger on the parts.
     
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  5. EmWeAh

    EmWeAh TDPRI Member Ad Free Member

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    Cool, sounds interesting. Please make sure to start a build thread to keep us other addicts updated.
     
  6. Dacious

    Dacious Poster Extraordinaire

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    Get two filament transformers and run them back to back, cost $20 from Mouser. I built a very successful single tube 6BM8 amp using them and a line transformer as the output.

    You can get 130-140 volts B+. Enough to drive a preamp tube. Voltage doubler if you want more.

    Here in Oz mains is 240v so I got almost 300 rectified volts.
     
  7. Asmith

    Asmith Friend of Leo's

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    I will try but im not great at keeping track and my builds arent pretty. Drawing and testing a schematic is easy when you know how to use LTspice but putting it on a turret board is just tedious and can take up 'unnecessary' space. So if I build an amp (or a pedal with a small part count), I go point to point, Im even planning on cap cans as well so I can save even more space.

    My last amp (well my first amp) has two channels and is all p2p except for the power supply which is on a tagboard.
     
  8. Asmith

    Asmith Friend of Leo's

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    Trouble is with mouser and the uk is that its not worth the £12 delivery, the 20% VAT and the royal mail £8 handling fee before youve put anything in your basket your already £20 out of pocket. And by the time youve spent enough to get free p&p your still £20 out on tax and handling fees.

    So as much as I like mousers selection unless its my only option its my last option.

    Since were still in the eu (just) I can still get that other one from germany without import tax. And it does everything I need while taking up less space, this amp is going to be seriously small. Burnt finger tips and extremely stressful debugging here I come.
     
  9. Dacious

    Dacious Poster Extraordinaire

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    Ok - didn't realise you were UK but that's even better. Just go to your electronic components store - Dixon's? - where you buy resistors and caps and glass fuses. They will have them for not quite pennies. You have 240 volts too!

    You connect mains to one, 6.3 to 6.3 on the second and you now have 240vac unrectified HT. Take your heater wires off the 6.3 v junction.

    http://www.electrojumble.org/equipmen1.htm
     
  10. Squawker

    Squawker TDPRI Member

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    Shouldn't be too bad even after Brexit. There are systems coming into place to pay the local VAT at the point of sale, so if you buy from Germany they'll take off 17% German VAT, add back 20% UK VAT and whatever the postage is (should still be the European rate). Then there should be no more royal mail fees and VAT on import since it's already paid. That only works for participating merchants, but looks like most decently sized ones will. We're watching this closely from Norway as we've been subject to Norwegian VAT and ridiculous handling fees (£15) on any parcels over approx. £32 - now they removed the £32 limit so everything will be VAT-able, but as long as the merchants play ball it should work smoothly with no stupid fees.
     
  11. Asmith

    Asmith Friend of Leo's

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    The only general electronics parts suppliers I can think of are rscomponents and farnell (both similar to mouser but no way near the size). I use both but rs does free delivery sometimes I definitely take the piss (forgot to order the opamp for that pedal go to rs.)

    Rs do a 20VA 6.3V transformer cheap and will do 5 heaters but again its not toroidal and id have to get another transformer for the B+ and I definitely wouldnt want another 2. I dont mind spending up to £50 all in if it means i get something as compact and low noise.

    I thought the uk was bad, at least the new system looks good, I mighy even wait just a little longer (next pay day) before springing for it.
     
    Last edited: Jan 13, 2020
  12. Dacious

    Dacious Poster Extraordinaire

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    Farnells is great. I buy stuff from them it's so cheap.

    I'll post a pic of what I built when I'm home. The three transformers cost about 15 GBP.
     
  13. Asmith

    Asmith Friend of Leo's

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    £15 is really good for 3 of them, Ill probably have a look at them for another project. I really like building amps and Id probably build one a month if it didnt cost so much, Im lucky to get one a year. But there are so many things I want to try, at the top of the list are paraphase phase inverters (high gain and beautifully simple), true pitch shifting vibrato and bias vary trem. So anything to that could make the opportunity more accessible is very welcome.
     
  14. Paul-T

    Paul-T Tele-Meister

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    For reference:

    https://sklep.toroidy.pl/en_US/index?fbclid=IwAR3QO-7W_470YDvERJm7vXOOenfbDXrEIHfmy7hjrowmkHDxoTXUAr7DNYA


    I guess you're talking about that cool little Ampmaker toroidal. Have you tried emailing him to see if he will tell you the supplier?

    Haven't looked recently but any of these any use?
    Primary Windings site

    All that said, I went with the tubre-town for my Micro deluxe. Their postage comes out pretty low, too.

    WHereabouts in East Yorkshire are you? Have you been to Birkett's for your valves?
     
    Last edited: Jan 14, 2020
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  15. tubelectron

    tubelectron Tele-Holic

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  16. Asmith

    Asmith Friend of Leo's

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    Thats the one, the picture on the site indicates its a dagnall though. But they usually deal with bulk/manufactures, Im sure they're in some marshall's but Im far from an expert in that regard. They say on their site they keep the specs of previous customers secret and design around your needs. Basically spelling out expensive for an individual to buy a singular PT. Assuming theres a design fee, a machine setup fee and then a fee for the for the actual product. Plus the tube town one will let me use a dual triode with 2 inputs, rather going for a depletion mosfet like I would have with the ampmaker one.

    Im going for the OT that primary windings offer but I'll be checking out tube-towns options first.

    I havent heard of birkett's before, I normally go for wattford valves. All just standard JJs but I havent bought many valves, I can list every one of them and why.

    And Im in Beverley and incase anyone is interested heres a partial schematic with the mosfet input. Its missing the ss bridge rectifier B+ is V1 (280V) in the top right of the schematic. Next to V1 is R16 and R19 and they are a filter cap drain/heater elevation (60V). V2 is the input on the bottom left.

    AC15 Micro Schematic.png
     
    Last edited: Jan 14, 2020
  17. Asmith

    Asmith Friend of Leo's

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    Honestly that is largely my inspiration, Ive read about the build on your site. Im just going for a head for this build, as cool as a combo that size is, this is a gift for my sister. Its going to be her first proper 'toob' amp and want to pair it with a 10" cab. She currently has a small SS marshall that isnt great.

    She's got to point now where shes realised its not that great. Shes into indie rock like myself and wants the jangly cleans and bright crunch and even I cant get her setup to do that. So I thought a classic vox circuit ought to remedy the issue.

    Anyway Im hoping to get this as small as possible just because of the novelty factor. Buying the trannys first so I can plan the enclosure around them.
     
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  18. Paul-T

    Paul-T Tele-Meister

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    My parents live in Beverley and when I drive to see them I often try to drop into Birkett's in Lincoln, it's where i got most of the resistors for my Micro Deluxe plus new old stock valves. He's out of ECC83 now although he does have the 5751, I think it is, the slightly lower gain version (which has its own fans). Plus the ECC82/12AU7 for micro output valves. Bits from Jack 1.jpg

    Details here.
     
  19. Asmith

    Asmith Friend of Leo's

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    And all i thought Lincolnshire had to offer was farm land. :lol: It looks like a real gem! I dont drive though, I'm gutted, I would love to see a place like that (I didnt even know they were still a thing).

    At least Im not particularly bothered about NOS/vintage for this one, my sister can tell that her cheap SS isn't ideal but she still has a way to go before her technique and ear will appreciate it. So Im sorry to say its all going to be modern transformers, metal film resistors, poly not PIO, etc.
     
  20. Paul-T

    Paul-T Tele-Meister

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    In case this search comes up again, the ampmaker transformer (120/240 primary, 6.3V @ 1A, 240V @30mA), which is a fair bit smaller than my tubetown, and cheaper, comes from a uk supplier, Carnhill, who also have their own website, so it's probably available direct from them ?
     
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