Amp-building: Stringing components by their leads

[Sovereign_13]

I admit I tried searching for this on the Interwebs, but I can't find any information.  So I figured I'd try you guys.  (Apologies to moderators if this is in the wrong spot - it seemed pertinent to amps).

The short of it is that I'm in the process of assembling an amp - slightly-modified Hiwatt DR103 clone, if you're interested - and I'm looking for thoughts on best practices.  Turret board/point-to-point construction.  What I'm curious about is if there's a maximum distance you (as a person who has assembled a P2P amp) would feel comfortable using component leads as wires.

The long of it is this precisely: the leads on the rectifier diodes are pretty beefy, and I don't feel any qualms about bridging two connections with them.  The big 5W power resistors are the same way.  What I'm concerned about are the little 1/2W resistors of which there are considerably more.  Running them from one turret to another seems fine because the turrets are only barely far enough apart to fit a resistor anyway, but what about running them from a turret out across open space to a tube socket?  Sure, they technically reach, but the leads are like 28AWG and not particularly stiff.

Some cases obviously call for external wiring.  I guess my overall question would be when people feel comfortable just using component leads to bridge gaps, and when they'd consider using a small length of wire.

 

[mayfly]

Hi There,

The issue is is that most modern components (which I'm pretty sure you're using) are made for PCBs.  That means that the thickness of the wire on those leads are a lot smaller than what they used to be.  Especially true for 1/2 watt resistors and Mallory 150 caps.

I'll get back to this later with some recommendations- family emergency with 6 year old right now...

 

[Cagey]

Back when I repaired/built/modified on amps, I used component leads any time I could, as they're automatically sized correctly, and most often oversized. For instance, a 1/4 watt resistor can't dissipate more than 1/4 watt without deteriorating or burning up, so the leads will handle at least that much and usually much more. Where I couldn't was usually in cases where I wanted shielding so exposed leads were kept as short as possible, or if there was some risk to the mechanical integrity of the termination. Components out swinging in the breeze (so to speak) can have their leads become work-hardened and break, or develop intermittent connections, which can happen surprisingly fast with solid wire.

 

[mayfly]

OK!

With my amps I always put them on a eyelette board.  This allowed better mechanical stability for components with weak leads.  I know that's not much help for you as you're doing a HiWatt style build (which if done in the traditional HiWatt fashion involves turret strips - not even turret boards).  This style of construction very much depends on the strength of the component leads to make a reliable circuit.  Otherwise he components will move and the leads will (eventually) break. - especially if you intend on treating that HiWatt in the conditions where it was designed to operate (touring rock band where things get dropped a lot).  In my current work, we put our new designs on shaker tables and subject them to multiple G forces for a good 20 minutes while operating to ensure that the design is reliable - imagine your in-air components in that environment. 

So ... Here's your options:

1 - find resistors with stronger leads.  These will almost always be old crufty carbon composite resistors with questionable performance.  maybe not the best option.
2 - go up a wattage size in those resistors.  Yep - use 1W resistors instead of those 1/2 watt jobs.  The leads will be stronger and likely longer.
3 - cover the resistor leads with insulation.  This won't prevent them from breaking, but at least they won't short on anything when they do.
4 - use the weak components and keep the amp in the living room and don't tour with it.  You'll probably have to extend the leads of some resistors to make this happen.  At least use 18AWG for that 
5 - change the design to use an eyelett board to give those components the support they were designed for.  Yea, you probably don't want to do this  :glasses10:

BTW, got any pics for us?

 

[Sovereign_13]

No pics at the moment, I can take some tonight when I get home (or more likely tomorrow) for you guys.

While I am using turrets, the preamp section is on a turret board (I assume you're using "board" to refer to parallel rows of turrets on a single board and "strip" to refer to single-row boards).  I tried to keep components close together, but my chassis (which isn't exactly the same size as the original) required some...creative layout choices to fit everything in.  I did try to keep as true to the original layout (which I got from Mark Huss's amazingly thorough website, hiwatt.org) as I could.  Hopefully, my choices won't cause problems down the road.

I would reaaaaaalllly rather not remove/replace all the components that are already done (nearly everything that's just attached to turrets has already been wrapped and soldered in place).  I plan to keep it in wherever my Designated Area is in the house we eventually move into and possibly take it to a friend's or out to a bar gig every so often.  So no touring for me.  If I find I have a problem with breaking leads even then, I can pursue uprated components.  Most of the small components only span turrets spaced 3/4" apart, and most of the components that span more than that are heftier things like diodes and power resistors with stronger leads.

I suppose I'll give it a shot and see what happens.

I think this will all make more sense with pictures, so I'll try to post some tonight.

 

[Cagey]

The "eyelet" board Mayfly is referring to is what Fender (and some others) used...

instead of the turret board you're using...

They both accomplish the same thing - durabilty, mechanical integrity and high current/voltage/temperature handling capabilities you don't normally get from printed circuits, which are all qualities you want in a tube-based amp. Tube amps create their own awful operating environments on top of what they get exposed to from being frequently and roughly transported, so you want them built like tanks.

 

[Sovereign_13]

I'm at least passingly familiar with eyelet boards.  I was referring to the difference between a turret "board" and a turret "strip".

Basically what I'm using are different sizes of these, with the leads wrapped around the posts.

Sorry the pictures are so small.  I think they're thumbnail pics from Mouser.

I believe Mayfly is referring to the single-row units as strips and the double-rows as boards.  I don't even know if you can buy blank eyelet boards that aren't made for a specific layout.  I suppose I could buy the board and eyelets and make my own...

 

[Cagey]

I prefer turret boards, myself. I like a rigid board I can mount on standoffs. Where single rows or less ambitious groupings are required, I'll typically use screw terminal or standoff terminal strips...

 

[Sovereign_13]

I don't know that I'm too worried about turret boards vs eyelet boards.  I'd like to get to the point of "functional amplifier" before I start addressing potential failure points.  And if it becomes that much of a problem, $150 worth of new components and some eyelet boards wouldn't be that hard to do (although it would set back other projects).  The nice thing about these older amps is the relative simplicity.  Sure there's like a hundred-odd, through-hole-sized components.  A digital amp probably has thousands, if not millions of tiny little SMD parts.

If I can at least know that all the circuits are complete and functional and nothing is failing, that's a better place to start from in my opinion.  If I'm not convinced of the integrity of some components, then at least I'll know swapping them for something beefier should still result in something that works.

 

[Cagey]

Right. No sense in "fixing" something that isn't broke.

 

[Sovereign_13]

I will subtly redirect you to the flavor text under my profile picture...

Which I stole from a coffee mug my wife gave me, given as the "Engineer's Motto".  I wish it were more inaccurate.

 

[Sovereign_13]

Pictures as promised.

Progress so far.  Turret boards mounted and fully populated.  Power tube sockets mounted, rear panel stuff mostly mounted.

Top view.

Front panel.  Bass pot is missing because of a stud that needs ground down in that location.  Rooster-head knobs for show purposes.

Heyboer transformers

Loose components.  Can capacitors and preamp tube sockets (they have shields, they're just not pictured).

Rear panel view.  This one didn't come out very well.

I'll keep taking pictures as I make connections.  The finished thing will get some glamor shots with a better camera than my phone.

 

[mayfly]

for the most part I don't think you'll have a problem with the distance you're running those resistors.  Possible exception being the one that you have in the air around a turret, terminated by the adjacent turrets.  If this were my amp I'd put some insulation on the leads of that one, and any similar ones.  I'm also not a fan of that radial electrolytic in the air like that.  Might want to address that one as well.

 

[mayfly]

BTW - is this meant to be rack mounted? did you do the lettering yourself on the front panel?

I'd personally be a bit worried that a 1RU rack holding up the weight of those rather large transformers - unless you've got a different support mechanism in mind. 

 

[Cagey]

BTW - is this meant to be rack mounted? did you do the lettering yourself on the front panel?

I'd personally be a bit worried that a 1RU rack holding up the weight of those rather large transformers - unless you've got a different support mechanism in mind. 

I wondered the same thing, but it could be mounted at the bottom a head enclosure. If it's meant for a rack, a rear rail attachment would spread the load so it wouldn't be an issue, kinda like they do for servers and power amps.

 

[Sovereign_13]

It is meant to be rack-mounted, however, I don't plan on letting all the weight of the amp rest on those ears.  It's probably close to 40 lbs with the transformers and all.  Mostly I went rack-mount to avoid having to build/find/custom order a head cabinet.  The whole thing will sit in a 4U case, and I plan to add a rack fan unit on the backside for cooling.  For support, I'll either look at rear rails or possibly some kind of feet to support the weight.

I did not do the lettering myself, no.  The chassis and front panel come from a company out of Canada called Protocase, which does custom electronics enclosures and rack mount chassis.  They're not cheap, but they do good stuff and I don't have the capability to do what they do.  Eventually, maybe.  They offer digital and silk screen printing, in addition to powdercoating.  Ordering a one-off is always more expensive, but I'm pleased with the result. 14ga galvanized steel with seam-welded corners (I was morbidly afraid of the transformers warping the chassis, and it didn't cost more to use thicker gauge material).

I made the mistake of populating the turret boards before I had them assembled in the chassis, so there's definitely some things that I already plan to redo.  Including the two power resistors that sit kind of on top of each other, and that radial cap that's suspended.  For some reason, I didn't stop to think where that cap goes and ordered a radial because all the other electrolytics were radial.  I might do beefier 220k resistors for the ones that go between the turret board and the power sockets too.

 

[Cagey]

I might do beefier 220k resistors for the ones that go between the turret board and the power sockets too.

That's a good idea. 220K is 220K, whether it's a 1/4W or a 5W, and you don't have production quantity cost considerations.

Although, I think I read on The Gear Page that the wattage of the resistors affects the tone... :laughing7:

 

[mayfly]

I've never heard of protocase!  Might have to give them a try.  What side of the country are they on?

 

[Sovereign_13]

They appear to be in Sydney, Nova Scotia?  Google Maps says it's about as far East as you can go in Canada.

 

[Cagey]

Good ol' Nova Scotia. Where they know how to play road hockey on skates, eh?

Two American tourists were driving through Nova Scotia. As they were approaching Shubenacadde (shoe-been-ack-id-dee), they started arguing about the pronunciation of the town's name. They argued back and forth until they stopped for lunch.

As they stood at the counter, one tourist asked the blonde employee, "Before we order, could you please settle an argument for us? Would you please pronounce where we are... ver-r-ry slo-o-owly?"

The waitress leaned over the counter and says, "Tiiimmmmm Hoorrrrttooonnns"