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Old 3rd October 2006, 04:50 PM   #1
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Question Heathkit W-5M rebuild

Greetings from a newbie,

I have a question concerning rebuilding a pair of Heathkit W-5M's that I recently purchased. One amp sounds very good - neat and clean assembly but still has the original caps. The other amp is a mess - all the parts are there but the only thing keeping a number of them from falling out is the bottom plate. This amp needs to be taken apart and re-assembled. It looks like a very unskilled monkey did the soldering.

Now for the question - I have the layout and parts list for a power supply capacitor board that replaces the 2 large can capacitors and most of the large axial caps. I also have an AudioXpress article that details amp/power supply updates using parts available from Antique Electronic Supply - this just replaces existing parts with a few minor upgrades.

This is brand new territory for me. I sure there are pros and cons for each approach. Advice/opinions are needed and welcome.

Kevin, aka firenewt
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Old 3rd October 2006, 05:46 PM   #2
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Hi Kevin,

Since you claim to be new at this, here is what I recommend. Repair the bad amp back to normal using the good amp as a model standard. Don't be concerned about updating this and modifying that just yet. Get it working correctly and see how you like it. Listen to it as it originally was. They were pretty good amps to begin with. Once you're familiar with them, then you can consider making changes and modifications. My 2

Victor
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Old 3rd October 2006, 09:25 PM   #3
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Hi Victor,

That's a really good idea. I have a tendency to jump in the deep end and then check if I can swim. I am retired (not by choice) so I have plenty of time on my hands. Besides it will be a good learning experience.
I became interested in tubes about a year ago after being a solid state kind of guy for the last 35 years. I purchased and assembled the S-5 Electronics stereo amp - assembled, not built since all it took was soldering components to a board. A small simple amp but that was all it took to make me rethink my ways.
Since then I've picked up a Heathkit AA-141 preamp and a AMC CVT 2030 power amp. Didn't take much to get them working - listening to them as I type.
You will no doubt see many more questions from me, BUT only after I search previous postings.

Kevin
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Old 3rd October 2006, 10:32 PM   #4
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Hi Kevin,

I totally agree with Victor, but if you mean that you have built solid state amps for the last 35 years you are not new to building techniques and what goes on. If that is the case you might as well check the electrolytics at the outset. They must be quite old (if originals) and if you are comfortable with it you might invest in new ones from the outset. (I presume you are aware of safety measures for high voltage!)

You might also consider (now or later) replacing the 5U4 rectifier tube with a 5AR4/GZ34 (direct replacement) with advantage. It generates less heat and has the advantage of a slow turn-on, avoiding high peak d.c.voltages on the power supply capacitors. This is not so much a "design change"; the GZ was simply not around when this design came out.

It so happened that I was asked the same question just a week ago by a local friend, making my first aquaintance with the W-5M. Perhaps the mentioned article is the one also showing an under-chassis picture, which will further enable you to trace if anything has been changed also in your working amplifier. One of the pictures will also show how original components were changed for more modern ones in a rather neater layout - that for later then. This is a version of the classic Williamson amplifier and well worth having. (Many of us cut our teeth on that design.)

Best wishes!
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Old 4th October 2006, 07:25 AM   #5
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Hi Johan,

Never built a solid state amp from scratch but have put together a number of amps using available modules, boards etc. I also have had the "pleasure" of diagnosing and repairing some. Matter of fact, I have a pair of Sony ES home theater amps awaiting some attention. Picked them up at an auction - got them cheap. Don't think I will be working on them for awhile - not near as much fun as tubes. I got a copy the Heathkit W-5M assembly manual in the mail today so I'll not flying blind.

Kevin
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Old 4th October 2006, 02:26 PM   #6
wa4htz is offline wa4htz  United States
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Kevin,

My suggestion would be to CAREFULLY take the bad amp apart and completely rebuild it (my first suggestion was going to be to get the manual but you already thought of that!). If it's as big of a mess as you indicated, this could give you a few advantages:

1. You could check the value of each of the parts against the parts list. Carbon composition resistors have a nasty habbit of changing value when they get this old. Measure with a decent DMM. Remember, you only have to be within the tollerance of the original value.

2. You could eliminate some wiring errors all at one time. If parts are actually falling off, it may have been worked on several times and the quality of workmanship sounds iffy at best. It also sounds like you can solder better than whoever built the amp, so you would eliminate a lot of potential bad solder joints.

3. After you have disconnected all of the parts, you could unmount the transformers and choke and perhaps give them a fresh coat of paint. It's amazing what a can of Rustoleum spray paint can do for the look of a ratty transformer! You could also wash the bare chassis and get off years of dirt.

4. And last but not least, you will have the fun of building a complete Heathkit! Many other kit manufacturers came close to matching Heath's throughness in assembly instructions but no one was ever really as good as Heath.

Your idea of replacing the electrolytic capacitors to start with might not be a bad one. When they get this old, they can either just stop working or give you some exciting pops and bangs when you power it up.

Good luck and keep us posted. It is great to see folks reviving these old amps instead of just throwing them away.

Ken
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Old 4th October 2006, 08:43 PM   #7
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Ken,

The amp is really as bad as I stated. I'll take a picture of it before I start the disassembly. I remember back in the early sixties a good friend of my dad got a pair of the W-5M's. I thought they were the coolest things. My amps are in good physical condition - no rust on the transformers or choke. The paint isn't bad either. Only down side is one of the cages has been drilled and 5-way posts and a headphone jack added. I am pretty good with a soldering iron and can read schematics with the help of my cheat sheets. Also found an online resistor calculator - just plug in the colors and presto, the value is displayed.

I have some questions/concerns regarding replacement parts.

1. I have a bunch of NOS carbon resistors. From what I have read here, a carbon resistor tends to drift with age. Also, from what I can tell there is a number of camps as far as which resistor type is best. - carbon, carbon film, metal film etc. I'm thinking at this point of using carbon film or metal film. Which ever I use will eventially be used in the other amp. Opinion?

2. I have a lot of NOS Sprague Atom caps. They test good on my cap analyzer so is there any reason not to use them? Again, whatever I use will ultimately be used in the other amp. Opinion?

I think I will start the controlled destruction tonight - can't wait.

Regards,
Kevin
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Old 5th October 2006, 04:50 AM   #8
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Hey Kevin,

Regarding resistors and capacitors:
The discussions about these componets has raged on for many years with as many opinions as there are brands of amplifiers, resistors and capacitors combined. Add to this plenty of dogma spread around by advertising hype and extreme viewed writers. There are a few guide lines that you can use, but in short, your ears will have to be the judge of what is best for you.

In fourty plus years of being an audiofiend (I mean phile...heh-heh) I've had my share of discussions on the sound of things and what is and isn't best. When someone claims that old carbon resistors and paper capacitors are bad and should be upgraded, I always ask them this. Why do so many audiophiles roll their eyes and swoon over the sound of those marvelous old Mercury Living Presence and RCA Living Stereo shaded dog recordings when they were made with electronics that were infested with those very same parts?

I don't think I've ever gotten a satisfactory answer to that. And it isn't just microphone placement. And why are Sprague Vitamin-Q capacitors so coveted and sought after? They're just paper and oil in a hermetically sealed can. Check out the price of NOS Allan-Bradley carbon resistors on eBay. Unbelievable! Albeit they are the best of the carbon comps.

Truth be known, all resistors are subject to drift with use. With wire wounds being least affected. Some characteristics to consider are that carbon composition resistors will withstand an overload without burning out quickly. For this reason alone, they would seem to compliment tubes. Film resistors can't take an overload and were designed for RF and higher frequency circuits do to their surface resistance. Of course they can be used for audio too, and where you need close tolerance for RIAA values.

Plastic dielectric capacitors (I'm using that term broadly) may give you a little more frequency extention if you have the output transformer (or ears) to hear it. But they are not always a good thing. In the case of a circuit that has any equalization designed in using paper capacitors, the response will be altered if plastic capacitors of the same value are substituted.

Remember, audio amplifiers are not compelex devices like some RF and microwave circuits that require the ultimate in stability from componets. Some folks will apply RF practices to audio where it serves no real advantage forgetting that audio is the bottom basement of the spectrum.

I would say to use what you've got to start with. Then experiment with different type later.

Victor
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Old 5th October 2006, 05:37 AM   #9
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Quote:
When someone claims that old carbon resistors and paper capacitors are bad and should be upgraded, I always ask them this. Why do so many audiophiles roll their eyes and swoon over the sound of those marvelous old Mercury Living Presence and RCA Living Stereo shaded dog recordings when they were made with electronics that were infested with those very same parts?
Well, those parts werent old when they were new. They hadnt had 40+ years to absorb water, become leaky, and drift. Whether they were good in the first place is another question. Water is the bane of PIO caps, some PIOs are hermetically sealed because of this.


Using a generously speced (thermalwise) resistor should reduce drift, whatever the type.

Some recommend mildly baking resistors (of some types) to force thier drift, then measuring them for use.
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Old 5th October 2006, 07:06 AM   #10
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Hello Tweeker,

To say that fourty year old parts drift and become leaky will get no argument from me. They sure do. Especially those old "bumble bee" capacitors with the stripes. (more on that below)

However, Kevin was asking about using using new old stock parts verses brand new modern parts. And it was in that context and mindset that I was responding. Certainly one would not use fourty year parts to rebuild an amplifier. (or would they?) With the exception of electrolytic caps, resistors and most capacitors age very little on the shelf. This is assuming they were kept in a good environment and physically undamaged. So it was a question of how much better were the newer style verses the old.

Quote:
Using a generously speced (thermalwise) resistor should reduce drift, whatever the type.
Agreed.

To bake resistors to force them to drift is something I have no experience with. I've never tried it. I tend to think it would have more to do with current flow over time then outside temperature. But not being a manufacturer, I have no intimate knowledge of their compounds and behavior.

Bumble bee capacitors. I never cease to be amazed at the price some people will pay for these old dogs. Even obviously used ones that, by their age, are surley leaky. Search eBay's completed items for "bumble bee cap*" and you'll see what I mean. Here's an example" Unbelievable!

http://cgi.ebay.com/Sprague-022mfd-4...QQcmdZViewItem

Victor
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