New Amp Builder question

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New Amp Builder question

Postby black_dog on Mon Jan 06, 2014 6:43 pm

Hi,

I'm new to amp building and have started by modifying an AC15HW - replacing caps, OT and choke, along with some resistors. I'm looking for some tips about soldering and adding components. In particular, how sensitive are components like caps to heat from soldering or bad wiring?

For example: I had replaced components and the amp was sounding really sweet. I then decided to change the stock tube socket for V3 (preamp 12ax7) for a belkin type. In the process of wiring up the new socket, I mistakenly soldered the heater wire to pin 8 instead of pin nine and fired up the amp. No sound of course, so I realized my mistake, moved the heater wire to pin nine. Now I have sound, but the sweet sound is gone! Or at least I think it is. Could one of the caps have been damaged by wiring the heater to pin 8. Is this even possible? Sorry but I am just learning about amps and have little understanding of how to trouble shoot.

I need a method (besides my ears) to conclusively test the amp before and after adding components.

Any advice would be most welcome.
Thanks very much.

-James
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Re: New Amp Builder question

Postby Unit_1 on Wed Jan 08, 2014 4:44 am

pin 8 is the ground from that side of the triode - hooking 6.3vac up to it shouldn't have an effect on anything except maybe the tube - not really sure what that would do

try a different tube and see if it sounds better
OH, and welcome to the forum black_dog :cheers:
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Re: New Amp Builder question

Postby black_dog on Wed Jan 08, 2014 5:39 am

Thanks for the reply. I installed the stock tube socket and now everything sounds great again. Since I have no trouble shooting methods I can only think that it must have been solder joints and not the belton socket itself. For now, amp building seems mysterious and full of chance. Well, if it aint broke don't fix it seems like a good rule.

Replacing the filter caps with vintage values and also the signal caps improved the sound of the amp so much. However, the amp is not as lound. I personally do not care since I'd rather have good tone than volume for this amp.

Thank you also for the kind welcome. This seems like a cool forum with knowledgeable members. I'll be back with more comments and questions for certain.

-James
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Re: New Amp Builder question

Postby Unit_1 on Wed Jan 08, 2014 6:02 am

ah, it was probably a connection that didn't have metal to metal contact, which is easy to do on tube socket connections

i always apply solder with one hand and use the iron with the other for the initial solder, and then immediately drop the solder and grab the wire. i reflow the solder and gently tug on the wire to be sure it has good metal to metal contact as the solder cools.

solder does not conduct as well as direct metal to metal contact

and yup, don't fix what's not broken!!!
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Re: New Amp Builder question

Postby ThisLifeILead on Wed Jan 08, 2014 7:19 pm

Welcome to the forum Dog!!
When i first started amp tinkering i was ancy to get working and created a whole mess of things.
Too much heat is bad.period.
Take your time, dont rush, do your homework and things will work out. :jam:
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Re: New Amp Builder question

Postby Unit_1 on Wed Jan 08, 2014 7:56 pm

ThisLifeILead wrote:Welcome to the forum Dog!!
When i first started amp tinkering i was ancy to get working and created a whole mess of things.
Too much heat is bad.period.
Take your time, dont rush, do your homework and things will work out. :jam:


it also depends on the type of cap. the .0047 orange drops are particularly sensitive to heat and should be soldered with a heat sink to avoid heating the cap

paper in oil caps are seriously heat proof and you'd be hard put to ruin one even intentionally

resistors create their own heat and are built to take it

when i'm soldering i keep the heat on until i see the flux evaporate in a puff of smoke and i know it's not a cold solder, and not too hot.

remember to let the tip of the soldering gun get wet with solder, and just touch the surface to be soldered. don't use pressure, the wet solder will transfer heat hundreds of times faster than a dry tip and loads of pressure.
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Re: New Amp Builder question

Postby black_dog on Wed Jan 08, 2014 11:20 pm

Great soldering info. Thanks.

On this particular project I had much desoldering to do - since I was modding a stock amp; the production solder was lead-free high heat. Since the board is turret type, there is a lot of metal to sink heat and it took quite a bit of heat to a) melt the lead-free solder and remove it with a solder sucker, and b) repeated attempts to clean the turrets. This board has connections on sides of the board, so heating a turret to extremes can damage the connection on the other side. Then also there are adjoining (turret to turret ) connections that transfer heat to adjoining components.

The components I replaced were the signal,coupling, and filter caps. Signal and coupling caps are mallory/sozo and atom,the filter caps are atom. Since I was paranoid about heat, I used a heat sink when installing these.

What I am hearing from you guys is that the quality of solder joints affects the tone of the amp.... and it is possible to have solder joints that carry a signal but introduce noise.... Is this correct?

I have checked and resoldered bad looking joints on both side of this layout board.
However, when can I rest assured that the amp is sounding as it should with components installed, and not being affected by bad solder joints or possibly damaged components? The amp sounds good now, but I am not convinced that it is healthy (since I did the work!).

-James
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Re: New Amp Builder question

Postby Unit_1 on Thu Jan 09, 2014 12:15 am

yeah that lead free solder is for the birds, so hard to work with and it doesn't last forever like lead solder. a bunch of network equipment made with the first batches of the stuff a few years ago didn't last long at all. all the wire-heads at a company i used to work with were just constantly changing out failed equipment.

one other important thing to do is be sure you use a clean sponge, use distilled water, and clean the tip before each and every single solder - this keeps carbon and other contaminants which can degrade the signal out of the joint.

always use fine steel wool to polish the leads of all components before soldering and be sure none of the little bits of steel wool stick to the leads. it only takes a second and it gets rid of oxidation which can also degrade the signal, as well as the plastic coating some mfgr's apply to leads to keep them from becoming oxidized.

if not removed the plastic coating can burn and again, contaminate the joint. some people just use alcohol, but i prefer seeing those little polished leads gleaming in the light and i know it's the best it can possibly be.

do NOT use sandpaper. steel wool polishes, sand paper will remove the tin. not good!

on a health issue note, always wash your hands for 20 seconds after handing solder whether it's lead or not. NEVER eat while soldering. heavy metal poisoning is a nasty way to die.

speaking of eating, i was eating while i wrote this - no solder involved. just had a home made cheese/chicken enchilada with a side of quinoa, and a big glass of yin yang huo tea. color me full and HAPPY! :mrgreen:
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Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
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Re: New Amp Builder question

Postby black_dog on Thu Jan 09, 2014 12:31 am

Damn! Now I am convinced that every solder joint I added is f'd. ha ha ha! I used tap water, did not wipe iron every time, did not clean, use alcohol. I think the only thing I did correctly was not eating while working....

Is it really worth taking the time to remove, clean and carefully redo my solder joints? Yikes... I'll do it if it means better sound.

Cheers!

-James
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Re: New Amp Builder question

Postby Unit_1 on Thu Jan 09, 2014 12:45 am

lol....

if it sounds good to your ears, then let it be!

you can always use these techniques on your next kit amp

btw, i get wholesale prices from Mojotone so if you ever want one of their kits i can save you a bundle and just have it drop shipped to you.
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Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
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Re: New Amp Builder question

Postby black_dog on Tue Jan 14, 2014 3:26 pm

This VOX HW amp uses a post type board - and the post is hollow with hole at top. The production components are soldered into the hole at the top. I have done the same with replaced components -- could soldering this way introduce noise into the amp? Is it better to wrap the posts and then solder?

Finally, how do I know that my amp sounds the way it should sound based on components installed? Are there some standard voltage tests I can do to check? Such as tube bias and so forth?

Thanks!

-James
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Re: New Amp Builder question

Postby Unit_1 on Tue Jan 14, 2014 7:30 pm

the posts, i.e. turrets, are pretty standard for british amps, and fender used eyelet boards

i prefer turrets myself

all you need is one good point to point connection for turrets. many times after you solder one end, the other end will lift up off of the turret on the other side.

when this happens, i first solder it, then immediately drop the solder and pick up any tool that's handy and use that to push down the side that lifted up while i reflow the solder until that side drops down in direct contact with the top of the turret and then i hold it in place until the solder cools.

don't try this with your fingers you'll get burnt !!!

i've not a vox expert, and have never played one. maybe if you make a short recording/video of how it sounds and post it to youtube someone you knows more than i can comment on whether it sounds the way it should. and maybe post that in a new thread in the VOX forum "does my vox sound right?"
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Re: New Amp Builder question

Postby black_dog on Tue Jan 14, 2014 9:14 pm

Thanks for the turret soldering tips. I think the soldering is ok.
As for the sound, well it sounds like a vox, but I'm listening for nuances. Characteristics of the amp such as stiffness, roundness of tone and richness of harmonics. It all comes close, but not quite ideal for my ear and playing style. I'll keep working on it! At this point I am not sure I have not made a mistake that adds noise, harshness, etc. Like one bad solder joint or a bad component. Thanks again....

-James
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Re: New Amp Builder question

Postby Unit_1 on Tue Jan 14, 2014 11:44 pm

black_dog wrote:Thanks for the turret soldering tips. I think the soldering is ok.
As for the sound, well it sounds like a vox, but I'm listening for nuances. Characteristics of the amp such as stiffness, roundness of tone and richness of harmonics. It all comes close, but not quite ideal for my ear and playing style. I'll keep working on it! At this point I am not sure I have not made a mistake that adds noise, harshness, etc. Like one bad solder joint or a bad component. Thanks again....

-James


what tube do you have in the V1 position in the preamp? this is the most critical position for a good tone.

maybe time to go to eBay and get a nice bugle boy 12ax7?

http://www.ebay.com/sch/i.html?_sacat=0&_from=R40&_nkw=bugle+boy+12ax7&_sop=15

p.s. i would not trust any of them that don't have the writing on the tube as the lowest priced one in the above search does. kinda also looks like it was made dirty on purpose to make it hard to ID.
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Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
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Re: New Amp Builder question

Postby black_dog on Wed Jan 15, 2014 12:03 am

Hi,

Running Tungsrams for the el84s, nos mullards for the 12ax7s, RFT rectifier. So these are the ideal tubes for a vox. Can you tell me how to check bias on the el84s or where I can learn, to be sure they are not running too hot? I think this has to do with the value of the cathode follower cap... right

Thanks!

-James
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