Route to happiness: a 5f2a, a Surfyverb and a Makita

Discussion in 'Shock Brother's DIY Amps' started by Paul-T, Aug 22, 2019.

  1. King Fan

    King Fan Poster Extraordinaire

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    Paul, catching up on this thread. Nice work. I like the way you’re figuring things out by wide reading, not just collecting an opinion or two here and there. Rob is always a solid source, and you’re clearly figuring out who else has it sussed.

    Clever way to hang the diodes below the socket lugs. Did you ask about your solder technique? Maybe a little on the dry side; you want a smooth flat blob of solder, not just capillary action around the lead. But tidy, which is good.

    Keep the descriptions and pics coming... not just for us. I find my build threads help me later if I have problems or want to make changes.


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  2. Paul-T

    Paul-T Tele-Meister

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    Good advice on the solder, thanks, I will be more generous in future. the stinginess probably reflects the long drive to pick up more solder, as I'm running out.

    I am learning everything here. The electronics I'm supposed to know about (studied it a long time ago) but have forgotten if I ever knew. It's the hardware side that is the big learning area - as I will doubtless show when I start attempting to use the router for box joints.

    Using a drill press is the big new area for me. I am learning to drill and hit exactly the right location, which is no doddle - the drill wiggles in the holder and it doesn't have a lock switch for on, so I need to improvise a wooden chuck for the trigger to avoid needing three hands. Managed to get clean-ish holes and deburr semi-competently.

    The cheapo Chinese chassis seems to take drilling fine with no flaking of chrome.

    I know I can't avoid having one OT bolt under the circuit board. But am I allowed to have the bolt inside and nut outside? I see the Prof's built he has much shorter bolts, I don't have any short one and worry about damaging the thread if I attempt to cut them shorter, if I could even think of a better way than hammer and cold chisel.

    (For future builders, if you're using a 5F1 board in a 5F2 chassis like me, you could avoid this by placing the board far right, opposite end to the PT, which was where I had it at one point, but moved towards the middle for shorter cable runs. Now of course I would have to rewire all the connections and rework the chassis holes, so I think I'll live with it as others have before).

    The bolt shown from inside is 10mm from my mounting hole for the board. OT transformer hole.jpg OT in position .jpg interior bolt.jpg
     
    Last edited: Sep 15, 2019
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  3. Paul-T

    Paul-T Tele-Meister

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    I simply hacksawed the bolt down and it all threads ok.

    Now, oops and double oops. Why did I not notice there was a reason why folks didn't solder the valve bases on the card template?

    Hopefully my embarrassment will be someone else's education. As I start to desolder, I'll leave this here for my mortification - and to remind me which connection is which, for soldering the bases in situ.

    (and for anyone as ignorant as me... the valve bases mount from outside the amp, not inside ). Valve bases soldered. TOo soon. .jpg
     
  4. Paul-T

    Paul-T Tele-Meister

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    ahem. Valve bases soldered properly now. Although annoying, my mistake of soldering them in the cardboard guide meant they were orientated in the correct direction which probably made it easier to solder in the chassis.
     

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  5. Paul-T

    Paul-T Tele-Meister

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    Input sockets and valve bases all in.

    (black cable in first photo isn't connected, it's for my power amp ground)

    inside 2 all in .jpg input sockets .jpg
     
  6. Paul-T

    Paul-T Tele-Meister

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    Heater wiring, pots and inputs completed.

    I am taking my time and following the established layouts carefully - but of course I am very capable of making a stupid mistake. So all comments are really appreciated.

    Tone pots in. I can't see many Princeton pots wired up on here but followed the 5F3as I've seen.

    Pots.jpg input.jpg



    Then finally the heater wiring. Again, the most comprehensive threads seem to be The Professor's and King Fan's. But there wasn't too much detail on orientation of the heater wiring. I have tried to keep power supplies at 90 degrees to signal, as suggested in this post. But I've only imperfectly understood. Does this look reasonable?

    I am guessing folks just do it then chopstick anyways, but if I've made any grievous errors I'd appreciate thoughts. Especially as I'll be wiring the main transformer in this weekend!

    6V6 socket first, then the 12AX7, then finally the configuration of the interior. 6V6socket.jpg 12AX7socket.jpg

    Interior.jpg
     
    Last edited: Oct 19, 2019
  7. Paul-T

    Paul-T Tele-Meister

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    Ok, while waiting for folks to comment, thinking about heater-current inducted hum, I looked at rob's and merlin's comments on heater centre taps.

    I will try putting an artifical centre tap in, but only have 100W 1/4 watt to hand. Is the power rating crucial?

    Am I fine running two series pairs, to give me effectively 200Ohm 1/2w?

    Update: I tried it, but I'm not happy with the 1/4W resistors, the wires are too flimsy so I have no confidence they'll stay in place. I'll leave for now and redo after my next trip to Lincoln for bits. Yes, I did burn some of the insulation but it's still intact.

    tap.jpg
     
    Last edited: Oct 19, 2019
  8. Paul-T

    Paul-T Tele-Meister

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    Sorry if I'm asking the same old questions. I've done lots of site searches here and it's surprising hard to find clear photos.

    My hammond 290CAX power transformer has two nuts, with little nylon washers. I assume I leave one nut in place, as shown? It feels like I need to do so to hold the assembled together. But is one nut on the inside enough to hold? It's surprising tricky to tighten the damn things. Unfortunately Hammond don't supply locking washers.

    I'm finding it hard to tighten the 2 pole mains switch, too. Even though it's the sturdiest one from my vintage stash, I might have to swap it for an uglier one with a hex bolt.

    IMG_1111.JPG IMG_1112.JPG IMG_1117.JPG
     
  9. King Fan

    King Fan Poster Extraordinaire

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    Hi, Paul. Looking good. I’ve been offline and have to rush out now but in haste let me say I think your heater wires look decent given that fat stiff wire. Merlin has the best pictures to guide this and yours seem like they should work. Many amps work ok even when their wiring around the heaters is 'wrong' as Merlin admits.

    You’re right to leave the inner nuts on the transformer bolts but the outer nuts that clamp them to the chassis really need to be either keps nuts or tightened down on a metal star washer. Even then you should also add some thread locker.

    I’m not quite sure what problem you’re having with the switch but the outside looks good. Am I missing something?
     
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  10. Paul-T

    Paul-T Tele-Meister

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    thanks so much @King Fan . It's a big relief to know that's how the transformer fits - I will get some star washers though.

    The problem with the mains switch was tightening it - in the end I wrapped a wrench in gaffa tape to avoid scratching the (already scratched) chrome while tightening and it 's holding up great.

    I spent today working up a temporary speaker cab and will update once that's aok.
     
  11. King Fan

    King Fan Poster Extraordinaire

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    Yeh, some tape and needle-nose pliers are a common approach. Sometimes even just latex / nitrile gloves give you enough grip.

    Not sure you can source 'em in the UK but Stew Mac sell this "Multi Spanner" for knurled tighteners of "jacks, pots, switches and tuners."

    [​IMG]
     
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  12. Bill Moore

    Bill Moore Tele-Afflicted Silver Supporter

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  13. King Fan

    King Fan Poster Extraordinaire

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  14. Paul-T

    Paul-T Tele-Meister

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    thanks, gents, both those suggestions re really helpful. Yes I realise I need a nut cube.

    I picked up a couple of 1930s radio extension speaker cabinets on eBay, sold one of them, and re-shellac'd and rebuilt the other, with a new baffle board from scraps. This is for testing until I build the 5f2a cabinet. I went for a 4 ohm Italian Jensen.

    I actually got into this via a plan merely to have an extension speaker for my 54 Champ. From there the project seems to have grown. I blame the internet.

    Once I'm done I'll find a lighter vintage speaker and try making a bluetooth extension speaker in the same cab . spkrfront.jpg spksback.jpg
     
  15. Paul-T

    Paul-T Tele-Meister

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    Drilled for all the earth bolts etc. This is just a note to myself so I can find the correct earthing scheme.

    I am assuming the green/yellow lead on @Rob's diag is a heater centre tap. Hammond's wiring is similar enough... just to confuse (no heater centre tap).

    Initially, I will try wiring the secondary centre tap/earth (red/yellow) to the power amp earth bolt, rather than C3's earth, as the latter is cramped under the tone pot and, knowing me, I'm likely to fry it in the process. Hopefully there won't be much difference in potential along the inch or so of wiring between C3 and the bolt.


    [​IMG]

     
    Last edited: Oct 24, 2019
  16. Paul-T

    Paul-T Tele-Meister

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    Been out and about getting final washers, bolts, etc.

    Getting close. Reading this.

    limiter.jpg
     
  17. Paul-T

    Paul-T Tele-Meister

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    Had a lovely week where I managed to take a couple of mornings out to pick up timber, and bits.

    I found my favourite woodyard is closing to make way for housing. They will plane all my timber down to 18mm for £4 or so, as well as cutting it to size, so I think I'll get stocks in over the next month.

    All Londoners should check out Cricklewood electronics. Great for small bits online, but even better in person. (It's also round the corner from Mick'n'Keef's flat, where they first started writing together. Most of my money was spent on solder, a big roll with lead. Then I also also visited Clerkentwell screws and bolts. The kind of place where you can buy 50 3mm toothed washers plus other bits and only part with £2 or £3. So everything in this amp is now held down securely, plus I have lots more little bolts for the valve bases etc I've stocked up on.

    And now the real business. This is the theory:

    290CAX.jpg

    And this is the reality. So...

    transformer.jpg

    Brown and white wires connected together in connector strip, bottom left (white looks dirty), wrapped in red insulating tape, below transformer.
    Live wire (brown) coming in goes to fuse, then to left of (DPST) mains switch.
    Neutral (blue) coming in goes to right of mains switch.
    Earth (yellow/green) coming in is bolted to chassis, via longer lead.

    The mains cable is temporary. I'll wrap the neutral connection with insulating tape once it's permanent.

    PT primary, orange and black, is connected to output of mains switch.

    Centre tap is to power amp earth.

    315 outputs are sealed off with cable tie, bottom left.

    First test is to check mains switch, and that I have earth continuity. Both heaters, secondaries not connected as yet. I'll disconnect red/white B+ DC out from the rectifier before I connect the secondaries.
     
    Last edited: Oct 26, 2019
  18. Paul-T

    Paul-T Tele-Meister

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    Tidied up that loose bit of wire on the bulb. No glow from the limiter. Glow from the 6.3v zindicator as expected. No shorts at the moment. 293 volts unloaded at both secondaries.


    light.jpg secondary v.jpg

    2: filaments wired. No shorts again so far. Showing 3V from earth to filaments, and 6.3V across the filaments which I recall is right.

    (Even though the mojotone guide seems to suggest 6.3v to ground).

    3: rectifier heater wires. Reads 5v across the connections, but zero to ground. Assume this is normal.
     
    Last edited: Oct 26, 2019
  19. Paul-T

    Paul-T Tele-Meister

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    4: wired up the rectifier, which is not connected to C3etc, and I'm getting 253V DC at Pin 8. Seems very low.

    Secondaries are measuring the same 293 DC as before. Thoughts?

    Took out bulb. 299V ac at pins 4 and 6, and 271V DC at pin 8. They seem sometimes to momentarily register 360V then go down to 271. Seems awful low..

    I know the 5Y3GT works because I took it out of my Champ.
     
    Last edited: Oct 26, 2019
  20. Paul-T

    Paul-T Tele-Meister

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    Turns out that "DC" measurement was mostly AC, as the filter caps aren't connected. I missed the Sluckwy line "There are no filter caps at this time, so readings will be low."

    These things are so obvious when you know them and so hard to suss out when you don't!

    Wired up C3 and I get 410V now.
     
    Last edited: Oct 27, 2019
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