/diy/ - Do It Yourself

[Anonymous No.387885]

Hey guys. I have a 60's Heathkit EA-2 amplifier my grandfather put together that I've been using for a while. I have it hooked to a giant GE monitoring speaker from the '40s that came out of my grandfather's radio station.

Recently, the amplifier has created a popping sound when I turn on light switches and it intermittently has a heavy crackley static sound after it gets good and warm.

I don't know a lot about electronics, but from what I've read its either a capacitor going bad, corroded posts on a tube, or RF interference.

I took the cover off and saw that one of the power transformers (I think thats what it is) appears to be leaking. Could this be my culprit, or is this just some sort of melted resin coating?

Should I take the bottom off and visually inspect for bloated caps or just replace them all on principle?

[Anonymous No.387903]

if any of the caps are bloated, replace them, and re solder any if all solder points , if that don't work then also replace main amps.

[Anonymous No.387905]

I took the bottom off and I don't see anything obvious.

There are a jillion soldered joints. Should I go ahead and reflow them all?

Which part are the "main amps"?

[Anonymous No.387906]

Picture of the guts on the bottom.

[Anonymous No.387922]

sorry but just posted thinking of newer electronics, but check and see if tubes "heat" up and if anything looks too brown ie burned.

[Anonymous No.387923]

resolder is always good, as blackouts drops in ac voltage tend to crack solder points.

[Anonymous No.387925]

>>387922

All the tubes seem to work. The amp does work as-is, it just gets really static-y after about half an hour or so of run time.

I don't see anything obvious, but I'll go ahead and relfow the solder tonight and see what happens.

[Anonymous No.387927]

>>387922
The only burn mark is a brown spot on the cover from where the round metal thing between the two transformers touches.

[Anonymous No.387937]

try adding a high flow 120v fan in it too, sounds like a heat problem, tubes do heat up a lot, solder and high flow fan should do the trick, replacing what ever is under brown "spot " on top cover is also good, after you mod a 120v fan on it.

[Anonymous No.387941]

also make sure the speaker watts is not more then amp output, (12 watts) try smaller speakers watts

[Radiofag No.387953]

Replace all wax/paper capacitors. All it takes is a tiinnnyy bit of moisture to throw them outta wack.

On my Heathkit DX40 transmit, I had a 420v capacitor that was +/- 100v.

The one I replaced it with was 418v, +/- 3v.

Simply put, the old components are no match for modern components.

Check the resistors too, they sometimes go bad, although not as commonly as caps.

[neckbeard_the_pirate No.387966]

>>387885
Pic related. Have fun.
http://www.vintage-radio.info/heathkit/

[Anonymous No.387968]

>>387953
guitarampfag here, and I got a little hard looking at your amp there.
radiofag's right, but I'd suggest saving up a little, going to angela.com or other old electronics place and replace straight across. Those caps will be +- 20% stock, and they'll have drifted substantially by now. Your tubes have most likely started to go as well.

[Anonymous No.387996]

Will a crappy multimeter from harbor freight be enough to check the resistors? I still have the factory assembly manual so finding their original values will be easy.

Ill just plan on replacing all the caps. Will modern ones from radio shack work? Just match the values and solder in, right?

[Radiofag No.387999]

>>387996
I have the Centech one that does capacitance and transistors too It works fine... I think I paid $9.99 for it?

It won't be 1% accurate, but that doesn't matter. It'll be consistently inaccurate, which is good enough.

[Radiofag No.388001]

>>387996
Oh, and don't go to radioshack.

They likely won't have high voltage capacitors.

I buy mine from Allied Electronics. It takes about 2 days to receive a package from them, UPS ground. Expect to spend $2.50 per capacitor.

While you're at it, I'd go ahead and switch the power cord out to a grounded 3-prong. You can order that from Allied too.

[Anonymous No.388002]

>>387937
What do I wire the fan into? Directly into the power coming in?

[Anonymous No.388008]

>>388001
Ill probably order from them tonight then. What part of the amp do I solder the grounded wire of a modern plug to? The chasis?

[Radiofag No.388010]

>>388008
Yep! That way, if something shorts, it shorts to ground and not to you.

You may also that it improves the audio quality of the amplifier, as it removes a floating ground issue (common problem with EM applications).

[Anonymous No.388022]

>>388010
The shitty house im in now isnt grounded but I put in gfci outlets. Would it still do any good?

[Anonymous No.388062]

>>388022
yea, it's pretty easy to do, will prep the machine for later use, and will still at least shunt the zap to the wall instead of your finger.
a sginer for the band the Yardbirds died by getting shocked by his amp, as have probably many, many more. Star ground is a good thing.

[Radiofag No.388072]

>>388022
Audio wise, you would still have a floating ground.

Safety wise, the GFCI will pop as it shorts, protecting you.

[Anonymous No.388081]

The transformer is fine. That is just the coating they put on it. The crackling sound when you flick the switch is a result of a capacitor across the switch going bad. It is a common problem that I have read about.

As for the crackling after it heats up, no clue. But like the others have said, replacing the obvious parts may help.

[Anonymous No.388087]

Filter caps going bad = random noise.

[Anonymous No.388097]

Sounds like caps are going bad
Death Caps gonna kill you because its not a properly wired 3 ground plug

Good Luck
https://www.youtube.com/watch?v=UZyy7uICKPI

[Anonymous No.388115]

>>388081
Good to know its just the coating as I suspected.

I'll go ahead and replace the cord, won't hurt to have it ground to the gfci socket instead of me.

Sounds like I just need to replace all the caps, reflow the solder, test the resistors, replace the cord, and get some extra tubes and I should be set.

Did I miss anything? Thank you everyone for the help so far!

[Anonymous No.388657]

Ok, I'm back. I dug out the manual and found the parts list. Which of these caps do I replace? All the ones that say "paper" or ALL of them?

Also, I assume the 30-20-20-20 is the big metal can. Does it need to be replaced as well?

Also, I found that the part leaving a burn mark on the bottom casing is a 100 ohm hum control. Is it normal to get hot or is it bad?

[Anonymous No.388663]

>>388657

Try electrolytic capacitors first.
Yes, 30-20-20-20 is an aluminum can. It's the power filter cap.

[Anonymous No.388664]

>>388657
And this is the 30-20-20-20 electrolytic cap. Its about 4 inches tall. Is this the filter cap? What do I replace it with? I've seen some videos of people using modern Marshall parts to replace ones that look like this.

[Anonymous No.388666]

>>388664
captcha ate my pic

[Anonymous No.388668]

>>388663
So just the big can and the two 10 ufd 25v caps? I've read that the paper ones need to be replaced too as they tend to absorb moisture over time, which throws off their values.

[Anonymous No.388697]

>>387941
That is incorrect.

[Anonymous No.388718]

>>388657
Is the correct replacement for the 10uf 25v electrolytic?

http://www.alliedelec.com/search/searchresults.aspx?dsNav=Ntk:Primary|electrolytic%20capacitor%20axial%2010uf%2025vdc|3|,Ny:True,Ro:0&dsDimensionSearch=D:electrolytic%20capacitor%20axial%2010uf%2025vdc,Dxm:All,Dxp:3&SearchType=0

[Anonymous No.388727]

Is this the correct replacement for the 10ufd 25v electrolytic cap?

http://www.alliedelec.com/search/productdetail.aspx?SKU=70079659

[neckbeard_the_pirate No.388738]

>>388727
I'm sorry, but I didn't see any 25V capacitors in the schematic. The cap should have the info printed on it, and those tall tube capacitors actually have more than one capacitor inside. Those are normally replaced with individual capacitors.

[Anonymous No.388741]

>>388657
I'm going off this list. Its the second cap from the bottom.

[neckbeard_the_pirate No.388762]

>>388741
The cap you've chosen will replace that one nicely. Have you gotten replacements for the main filter cap?

[Anonymous No.388771]

>>388762
The main filter cap is the big metal one, right? I've been looking around but have only found one available and its about $50 shipped.

I've seen some videos on youtube about gutting it and replacing the internals with several smaller newer style caps but I don't really know if thats the best way to go.

[neckbeard_the_pirate No.388781]

>>388771
Yep. The main filter capacitor is the tall metal can. Inside that can are the guts to 4 other capacitors. The most common thing to do is to replace the single can with multiple capacitors (like they did on YouTube). Previously I posted a schematic, but the schematic doesn't have the voltages. The thing you'll probably want to do is to hook up a voltmeter to the cap, turn on the power, and measure the voltage. Get a similar cap with a higher voltage rating and maybe higher capacitance. Actual capacitance values aren't needed for filter caps. Bigger is better.

[Anonymous No.388792]

>>388781
The manual says its a 30-20-20-20 ufd electrolytic. Would that mean its four caps, one being rated for 30 ufd and the others at 20 ufd for the capacitance?

I have the OEM manual so I'll look and see if any other schematic lists the voltage. If not, I'll have to dig around for a dmm to measure it.

[neckbeard_the_pirate No.388795]

>>388792
Yep. Four caps in one package. A 30uf and three 20uf. I forgot you still had the manual. If the manual doesn't list the voltages, it probably has a troubleshooting section that tells you what voltages you should get while testing. Also, look at the imprint on the can. If you can't find the voltage ratings or are able to measure the voltage under test, I'm quite certain a 400V part will be more than adequate. It's only a 12W tube amp. It shouldn't have any of the real high voltages needed to push the higher currents. I worked on a 1kw amp that had 1.5kv as a plate voltage. Yours is probably around 150v to 300v. Using a higher voltage than needed cap is safe. The uf rating can also be higher, just don't go past 100uf. The inrush current could possible blow the rectifier tube.

[neckbeard_the_pirate No.388797]

>>388795
..."the voltage ratings or aren't able to measure..."
Sorry for the typo.

[Anonymous No.388811]

>>388795
Went and looked at the can. It conveniently had everything listed. Here is what it said:

ASTON
25-63 (week-year production code?)

30 MF - 450 VDC (bell-shaped symbol)
20 MF - 400 VDC (square symbol)
20 MF - 350 VDC (triangle symbol)
20 MF - 350 VDC (slash symbol)

I assume this means I could use 4x 30uf @ 450v caps or slightly higher and still be in range?

[OP No.388813]

>>388811

I assume the symbols have something to do with the caps positions marked on the bottom tabs somehow. They're currently obscured with *suff* in the way.

I'm glad I have the manual and all the poster-sized blown diagrams. My grandmother was a hoarder when it came to reciepts and manuals and my grandfather was very meticulous when he put it together so its got everything checked off and a little note here and there.

[neckbeard_the_pirate No.388819]

>>388811
I'm glad you didn't go ahead with my "400V" suggestion. That would have been messy. If you want you can use the symbols on the can to figure pinout, but since you're replacing it with 4 separate caps I wouldn't even bother trying to decode it. You can replace all caps with a 30uf. It'll just filter out ripple on the power better. The schematic I posted had the symbols.

[OP No.388823]

>>388819

Can I use the same cap for all four positions? That would keep me from messing up if I mixed them up.

I see the symbols on the schematic now, they make more sense. I have the same schematic in the manual as well but I think I'll be saving this thread and printing it out to put in the manual for future reference.

[neckbeard_the_pirate No.388824]

>>388823
Yes. The highest voltage is 450V, and the highest capacitance is 30uf. You'll do fine.

[OP No.388825]

>>388819
Looks like only one was over your 400v guess, but it still could have been bad. Would going ahead and bumping up my cap to 500v be ok?

Having a bit of wiggle room never hurts, I would think...

[neckbeard_the_pirate No.388827]

>>388823
...Just get the polarity correct. Electrolytics have a "plus" and a "minus". The common connection (found as the connection that surprisingly enough goes to the speaker wire named "common") is the "minus" side.

[neckbeard_the_pirate No.388829]

>>388825
500V is fine. The voltage rating is the maximum voltage it can take before it lets the magic smoke out.

[OP No.388836]

>>388829
I found these, but they're about $10 each. Ouch. Do cheaper parts exist or do I just suck it up and get them? I don't mind investing extra if the quality is worth it.

http://www.alliedelec.com/search/productdetail.aspx?SKU=70102489

[OP No.388837]

>>388827
I'll keep that in mind. Unless I can use bi-polar parts to keep me from messing up, but somehow I doubt that it would be suitable.

[neckbeard_the_pirate No.388846]

>>388836
That isn't an electrolytic. It'll probably fail on DC after a while. The cheapest I can find are in the $10.00 range. Don't use bi-polar caps. Much like your first selection, bi-polar caps might fail under DC.

[OP No.388850]

>>388846
Ooooh, ok. Makes sense.

[OP No.388853]

>>388846
This better?

http://www.amazon.com/JJ-Electronics-Electrolytic-Audio-Capacitor/dp/B00564MF3U/ref=sr_1_1?ie=UTF8&qid=1359863355&sr=8-1&keywords=electrolytic+capacitor+30uf+500v

[neckbeard_the_pirate No.388854]

>>388853
Nice catch! I missed that. That should work fine.

[OP No.388858]

>>388854
Awesome. Heck, I may see if I can find the others on Amazon from the same seller to save some on shipping.

Anyway, so I need 4 of the 30uf 500v caps and two of the 10uf 25v caps for sure.

Do I need to replace any of the caps marked "paper" or "ceramic"? I've read the paper ones can absorb moisture and messes up their values. I've read the Ceramic ones are pretty stout and are probably OK and that any resistors are probably OK too, but they're worth checking with a DMM.

[neckbeard_the_pirate No.388863]

>>388858
Sorry if this wasn't made clear. Replace all caps. Even the non-electrolytic ones. In old tube equipment they used capacitors with a paper insulator. The paper gets moist with humidity and start going wonky. The newer caps don't have this problem. The 10uf 25V caps are for the self bias on the 12AX7 and help filter out hum. All the other caps are non-electrolytic and you can use bi-polar or non-polarized capacitors (ceramic caps are a good replacement).

[OP No.388866]

>>388863
I think someone else further up said to just start with the electrolytic so I wasn't sure. Are the existing ceramic caps ok or should those get replaced too?

[neckbeard_the_pirate No.388873]

>>388866
Ceramic caps are normally very stable, so no unless they are bad (obviously cracked, blown, etc).

[neckbeard_the_pirate No.388877]

>>388866
...It's a good idea to start with the "small" stuff (replace the main filter caps), test, and hunt down other problems as they show up. The only reason we're saying "replace all the caps" is because in old tube equipment they're the first thing to go wrong and we're always replacing them. The old cap technology wasn't up to snuff.

[OP No.388882]

>>388873
Thats what I was thinking. I'll visually inspect them, but I didn't see any that were obviously bad.

So I can replace the remaining "paper" caps with ceramic caps? I don't have a problem with replacing stuff that is going to be a problem in the future, preventive maintenance and all that jazz.

I know some things aren't worth messing with until they're obviously bad (like the ceramic caps), but on the paper ones I feel like I might as well swap them out.

[neckbeard_the_pirate No.388894]

>>388882
You can replace paper caps with ceramics if they have the right voltage and capacitance. You can also replace the paper caps with the superior metal film capacitors. They're basically made the same as paper, but use plastic instead of paper, and are better sealed with modern plastic/epoxy.

[OP No.388919]

>>388894
Oooooh, ok. I'll poke around for those then and see what I can come up with. Having the manual with them all listed certainly helps.

This has certainly been a learning curve. I've got another Zenith radio from my grandparents that will need much of the same work that should go a lot faster after this initial learning curve. I really appreciate all the help you've given me thus far!

[OP No.388940]

The manual calls for:

2x .05 ufd paper

Will this suffice? If I'm on the right track then I'll go ahead and select the rest. The only thing I don't get is that the amp has other ceramic caps, if they are better than the paper caps, why weren't they used in the first place?

http://www.alliedelec.com/search/productdetail.aspx?SKU=70079815

[Anonymous No.389244]

>>387906
Replace the capacitors, like you said. Don't go radio shack. You want to match the value and the voltage rating.
Digi-key carries a good selection of capacitors. Usually $1 each.

[Anonymous No.389267]

>>388940

Big high voltage ceramic capacitors are quite expensive even now and in the olden days they were even more expensive. Their capacitance range was also much more limited than now.

Today's equivalent to a paper capacitor would be a plastic (mylar) capacitor. Not that you can't use ceramics.

[OP No.389353]

>>389244
I'll check there.

[OP No.389354]

>>389267
I'll look to replace the "paper" caps with mylar then.

[OP No.389398]

>>388657
Found a great site that has everything I need. They didn't have any .05 caps so I'm using .047 instead since they are close enough.

All the caps and a cord in my cart so far. I'd order a fan too if they weren't out of stock but that isn't a big deal.

http://www.tubesandmore.com

See anything that I'm messing up?

[OP No.390176]

>>389398
I went through all my resistors and found a few bad ones, but most are good.

My last conundrum is the burn marks around the "hum control" that I do not like. You can see black marks next to it on the chasis and a burn mark on the back cover.

Does this part just run really hot or is it fried? If its fried, where do I find a new one? I haven't had much luck finding anything about them online.

[Anonymous No.390189]

>>390176

The size alone tells that it is a relatively high power part. It wouldn't be a surprise if it runs hot.
If you have a multimeter, measure it.

[OP No.390197]

>>390189
I have a multimeter. The manual says its 100 ohms but where do I measure it? It has three pins to choose from.

If its good, I was planning on putting some thermal paste on it where it meets the back cover to help transfer heat to the cover and away from the hum control part itself.

[Anonymous No.390237]

>>390197

Middle pin is the wiper, 100 ohms appears between the two other pins. Resistance between the wiper and one of the end pins should vary from ~0 to 100 ohms when you turn the pot.
You might need to desolder the wires before measuring, though.

[Anonymous No.390242]

>>390237
Ooooh, so its just a big potentiometer then? I'll go check it here in just a few.

[Anonymous No.390253]

>>390237
I couldn't get a good reading with my crappy harbor freight dmm, so I guess I will have to dig out the soldering iron and desolder the wires off it to get a reading.

[Anonymous No.390262]

>>390253
Desoldered one of the wires and it measures 102 ohms, so its good. The middle post measured about 44, not that it matters.

[op No.390394]

>>390262

Bump for any more suggestions or things to change before I go ahead and order my parts. My roommate said he has a couple small computer fans I can use so aside from the caps, a few resistors, and a cord I should be set.

[op No.391697]

>>390394
Put in my order. A pile of capacitors, some resistors, and a power cord with shipping ran me about $54. Ouch.

Oh well, its a lot cheaper than replacing it or having someone else fix it.

Since DIY is slow, I'll post pictures when I make the repairs. Assuming it isn't pruned/deleted before then.

Thanks for all the help so far again!