Amp Build Strategy

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donvan
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Amp Build Strategy

Post by donvan »

I am getting ready to build my first amp. I have experience soldiering and troubleshooting low power circuits but no experience building vacuum tube circuitry. I was thinking that I would do the build in sections.

I will first build the power supply and check all of the voltages. Next, the preamp - I will take the output and feed it to the power amp of another amplifier that I own. Next, I will add the overdrive section and test it also by feeding it to an existing power amp. Finally, I will build the power amp section and test the entire amp.

This seems like a logical approach to me but I guess my concern is that if I build it in stages the power supply and various stages will not be have the same loads that they will have after the entire amp is built.

Do you see any issues with this approach vs. building the entire amp before testing?

Thanks,
Don
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Re: Amp Build Strategy

Post by Stevem »

There's only so far you can go in testing the power supply if you build that first because with no load / current draw on it by means of the preamp and output stage all of your voltages will test out high, but for the bias supply should the amp be fixed bias.

I would build the whole amp carefully and use the Aiken amps start up guide to fire it up.

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Malcolm Irving
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Re: Amp Build Strategy

Post by Malcolm Irving »

^^^ Agree.
But one thing that can be worth testing, at an early stage, is the heater wiring from the power transformer. You can check that heater voltage is getting to each tube socket before you wire everything else up. It will be a higher voltage than usual due to lack of load.

(Or at least, test the continuity of that heater wiring.)
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martin manning
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Re: Amp Build Strategy

Post by martin manning »

I don't see anything wrong with building the complete power supply and testing it. Even if it's unloaded you can learn something. If possible you could then wire up the power stage and load the power supply with that. If everything is on one board that would be difficult.
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pompeiisneaks
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Re: Amp Build Strategy

Post by pompeiisneaks »

Yeah I agree that building parts at a time shouldn't be a major problem, just make sure you understand that adding each stage will change voltages, the power tubes will drop voltages when conducting, and then again the preamp tubes will as well when conducting. This just means in each phase you'll have different performance, but so long as you're aware of that and expecting it, it should still make sense.

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romberg
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Re: Amp Build Strategy

Post by romberg »

Malcolm Irving wrote: Tue Jun 27, 2017 5:53 pm But one thing that can be worth testing, at an early stage, is the heater wiring from the power transformer.
This is great advise. You can even install the tubes at this stage and watch them glow. If they don't you will want to fix things before adding anything else as re-wiring heaters in a mostly finished amp is at least 100 times less fun than doing the heaters the first time. :)

General steps I follow when building an amp:
  • Build the amp virtually first. By this I mean print a copy of your layout and schematic. And go over everything with a highlighter. If the layout has grounds that just connect to a ground symbol figure out where you will run a wire. Draw it on your layout. The end result is a layout that you have verified matches the schematic. In doing this you may find you have questions you did not have before doing it. Ask them. :)
  • Build a light bulb current limiter if you don't have one. Do, this first. You will want one when you start things up and it is way too easy to talk yourself into not needing one with a finished amp ready to go. :)
  • Dry fit everything. Mount all of the components such as the board, transformers, pots switches, jacks and anything else that mounts to the chassis. See if you have any clearance issues. If you need to enlarge a hole or move things a bit this is the time to do it. Like the heater wiring these adjustments are painful at later stages.
  • Mount the PT, mains switch, fuse and tube sockets. Wire up the heaters. The heater wiring can be tested at this stage. Make sure to use wire nuts or some sort of insulator to cap off the windings on the PT you have not connected yet.
  • Wire up and install everything else a layer at a time. Working from bottom to top and from the outside in. So, do things like pots, cap cans switches and stuff that may later be more difficult to do. Make a new copy of your schematic and highlight stuff you have connected as you go. I generally install boards last.
  • Before starting up a completed amp, I go over everything again by using a whole new schematic to highlight.
  • Follow a start-up guide such as the one mentioned above. I generally keep the high voltage winding on the PT disconnected (and capped with wire nuts) from the main rectifier. Then test the bias supply (if it is a fixed bias amp). Then connect the high voltage leads and test the main power supply (no tubes and using a current limiter).
  • Install the tubes. Current limiter is still used.
  • Remove the limiter and test the signal path.
Mike
donvan
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Re: Amp Build Strategy

Post by donvan »

Thanks everyone! This is all great information. I'm so glad that I asked the question.

Don
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Re: Amp Build Strategy

Post by tubeswell »

Build a simple amp like a tweed champ or deluxe for your first amp. Less stuff to have to learn to troubleshoot all at once. YMMV
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mhartman
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Re: Amp Build Strategy

Post by mhartman »

I've built some experimental power sections (with PI) first and then plugged rack preamps like an ADA MP1 into the loop. The voltages will be high, but you can confirm the power section is working. Probably no need for this if you're building something standard.
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RJ Guitars
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Re: Amp Build Strategy

Post by RJ Guitars »

Here is something that I posted elsewhere but still is what I consider one of the better approaches to tube amp building:

Occasionally I am asked for a build guide for putting together the amp packages I sell. Historically I have avoided calling my offerings as "amp kits" since there are a lot of implications and expectations that go with that designation that I can't always deliver on. So consider this as an effort to pass along some of the tried and proven tricks and methods I use for my own builds but consider yourself as the master of your own destiny in your DIY guitar amp build.

FWIW - I typically tackle the build in stages and for now I will avoid getting too far into the details but try to define the stages.

But First - An Important Notice you must read before you start a DIY guitar amp - Tube type guitar amps create lethal voltages that can potentially kill you. If you don't know what you are doing and take the necessary precautions, you are at risk of giving yourself an unpleasant if not lethal electrical shock.

1) Step 1 - Gather up all the parts and do an inventory. Verify that you have a correct schematic and a layout to work from.

2) Step 2 - Make certain you have all the tools you'll need including a good soldering iron, a digital multi-meter, a good set of small wire cutters and also a set of needle nose pliers.

3) Step 3 - I start with the chassis prep work - this includes adding any extra holes to punch, drill or thread. After that I clean the chassis with warm water and dish washing soap - this works really nice for aluminum chassis'. I have always thought it would be great to be able to run them through the dish washer but my wife has no sense of humor about that idea. Once the chassis is clean you can do any painting, powder coating, or anodizing. If you want any labeling done by laser etch or silk screen, this is the final step in chassis preparation.

4) Step 4 - This begins the fun. Mount these items in the following order:
a) Any internal standoffs, ground tabs, terminal strips, or other items that mount directly below the transformers or circuit boards.
b) Transformers
c) IEC socket
d) Fuse holder
e) Impedance switch
f) speaker jacks
g) Faceplate
h) Pilot light
i) input jack
j) On/Off and Standby switches
k) potentiometers
l) terminal strips and ground tabs
m) surface mount components (chassis resistors etc.)

5) Step 5 - Wire the Power transformer beginning with running the safety ground wire from the IEC socket to a ground point on the chassis - this is the only wire that uses these two terminals. Do not use this ground point for a signal ground connection. Then continue wiring the AC socket, on/off switch, pilot light. In a traditional TrainWreck amp the neutral wire is also switched.This is not considered a "best practice" in modern electronics, but is typical in a traditional Wreck build. Once the AC wiring is finished, tie all center taps to ground as appropriate, and heater wires to either a terminal strip or the first tube they feed, whichever is appropriate.

6) Step 6 - Wire the secondary of the output transformer to the impedance switch and any other connections that can be made before the power supply is created. Don't connect the B+ wire or any other wires to the primary side of the OT yet.

7) Step 7 - Wires the tube heaters. This is usually one of my least favorite tasks, especially on a Liverpool or Rocket type of build because they have so many tubes in them. I prefer to use two colors of #18 stranded wire for the tubes. I twist the wires together by taking about 24" of each wire and clamping on end of the pair in a vice, then the other end I put into my electric drill... you can figure out what to do next... you'll never be tempted to use a loose sloppy twisted pair if you do this. from the length of twisted pair I cut the correct length to go from one tube to the next, always using the same color wire on the same pin for each heater in any given type of tube.

8) Step 8 - At this point I suggest some electrical testing. Make sure you put a fuse into the fuse holder. Do a visual inspection and make sure every hot wire is connected to a safe and proper place and/or is properly insulated or isolated to avoid an electrical shock or short. The most important wires to verify are the high voltage taps from the power transformer secondary... make sure again that they are completely insulated and isolated from touch each other, the chassis, and you. If you have properly wired things up to this point, the light should come on and power transformer will create the appropriate voltages. Using an insulated connection you can measure the high voltage coming across the secondary B+ taps. You can also measure the heater voltages across the heater taps, and then to each individual socket. If all this goes well, verify that everything is again insulated and isolated and you can put a tube into each socket and verify that the the heaters light up... this often gives me a great feeling of accomplishment.

9) Step 9 - I will trivialize this for now by saying"wire up the power supply". This will require more information and detail later. After it is wired up, make lots of measurements and recognize that at this point you have energized the filter capacitors and they are carrying potentially lethal voltages. After you unplug the amp from the AC mains power, you will need to short them to ground before sticking your fingers into the amp to do any further work.

10) Step 10 - Install the preamp board. Some folks prefer to mount the components before they put the board in, other do it with the board in place. I've done it both ways but which ever way you choose, make sure you have all the wires and connections complete on the back side of the circuit board before you mount it in there. Hook up the B+ connections and grounds to their appropriate locations.

11) Step 11 - Install and wire the components to the power tube section, including the connections back to the preamp board. Again, I have trivialized this and details will need to be filled in later.

12) Step 12 - Wire the phase inverter between the tube and the preamp board. Details needed...

13) Step 13 - Wire the gain stages in descending order, between the tube sockets and the preamp board.

14) Step 14 - Wire the input jack.

15) Step 15 - Wire the volume control and tone stack.

16) Step 16 - Verify that everything matches the layout and agrees with the schematic.

17) Step 17 - Power up the unit... if you feel the need and want to be cautious, you can use a light bulb limiter or other forms of circuit protection. In modern amps with modern components, the filter caps do not need to be "formed". This only is needed with very old caps and I don't suggest you use them.


18) Step 18 - put in tubes and hook up a speaker or some sort of load on the output. Tube amps do not like open circuits on the output section and it can ruin your output transformer if you don't attach a speaker cabinet. I always use a shorting jack for the speaker output so that if you forget to hook up a speaker, the amp is shorted to ground - this protects the output tranny.

19) Step 19 - If all is well, then your amp should sound great... if not then it is time to read the trouble shooting guide (which has not been written yet).
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donvan
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Re: Amp Build Strategy

Post by donvan »

More great tips. I really appreciate it!
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MakerDP
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Re: Amp Build Strategy

Post by MakerDP »

That post should be "stickied" RJ... good stuff.
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pompeiisneaks
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Re: Amp Build Strategy

Post by pompeiisneaks »

I agree, but I think it may be best done as a new thread just with that content, imo, RJ, if you'll copy and paste that outstanding info into a new thread, name it what you will, I'll sticky it so the knowledge is right there for anyone to see quickly ;)

~Phil
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MakerDP
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Re: Amp Build Strategy

Post by MakerDP »

yes that's what I meant... just that bit he typed up.
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RJ Guitars
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Re: Amp Build Strategy

Post by RJ Guitars »

You guys are generous... thanks, I'll do that.
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