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Heathkit W5M rebuilds

Yes, indeed, I haven't seen too many other amps with 1uF output tube coupling caps that are 1uF in size!

Here are some shots of the completed driver tube socket connections. Here you can clearly see the .1uF driver tube coupling caps. They do look rather small compared to the 1uF caps. The 6CG7 sections have their cathodes tied together and biased via a 2.4K resistor. Currently this is unbypassed.

The next shot is of the completed input tube voltage amp/phase splitter. Again, all that was basically done was to reconfigure the replaced socket to use a 6CG7 and premium components.
 
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Back to the power supply

Let's go back to the power supply. We left off with the 110 ohm resistor dropping network. This is filtered by two 100uF 450VDC caps in series to ground to form an effective 50uF 900VDC cap. The original value here was two 20uF caps to form a 10uF filter. Since this is buffered by the resistance of the choke and the 110 ohm network, I'm not worried about any turn-on strain on the power transformer. The voltage output from this node feeds the 6CG7 tubes via additional dropping resistors and caps. A rock solid and well filtered voltage here is desirable.

You can also see where the elevated signal ground was extended via some solid copper wire. This helped with grounding the additional caps.
 

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I have a buddy with a pair of W5s that I helped retube/recap a few years back. At the time we were a bit stumped by it's use of that pair of 40uf caps in series.(effectively 20uf and bridged by a 200K bleeder load) Since the secondary was center-tapped it wasn't a doubler type and the caps were rated to 450VAC and since there was a maximum of 475VDC on the plates, it's seemed adequate- so it didnt really make sense.

Anyways not putting 2 and 2 together we replaced it with a single 40uf/575V cap we had on hand and were greeted by a horrendous "light show" within the 5R4GY upon power up. What we ended up determining was that the 5R4GY rectifier was not very tolerant of higher than 20uF on the first filter capacitor. (in fact IIRC the tube data sheet lists 4uF as maximum)
So we assumed that the circuit might have been originally designed for a different rectifier tube and the capacitors "doubled up" in the filter to rectify (pun intended) that. After adding another 40uf in series (and dropping the total capacitance to 20uf) everything was fine...
WopOnTour
 
Yeah, sometimes you can get away with exceeding the maximum uF rating for a capacitive input tube rectifier filter setup.....for a while......
 
Shown below are the two power supply nodes for the input 6CG7 tube. Both caps are 100uF 450WVDC. These supply about 100 volts DC to the first triode section and 250 volts DC to the second triode section. The original capacitance values were 20uF for each section. This just about completes our rebuild of the W5M!

And a shot of the bottom of the amp, now ready to be powered back up after who knows how many years of storage!
 

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Power Up Time!

And now for my favorite part after a total rebuild: Powering it up for the first time!

I checked and double checked everything, connection to connection.

Step 1: Plug it in with no tubes installed and turn it on! 910 volts AC on pins 4 and 6 of the rectifier socket. That sounds about right.

Step 2: Install some junker test tubes and power it up, look for smoke, check for sound. Hey, whatya know, it works!

Step 3: Install the real tubes and make some measurements. In went the KT-66's, NOS 6CG7's and 5R4 rectifier. The schematic says 475VDC on the plates of the KT-66's. I measured 481VDC. Close enough. No hum, either!
 

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great thread! I have a w-5m pair that I am planning on slowly rebuilding (they are fine but wanted to update the parts), I found a source via another thread here for the can caps and wanted to be sure I am not missing something or to see if anyone has any comments on the source

according to the website they are:

Made in the USA on Mallory's original machinery.
-10%, +50% tolerance
85° temperature rating
1-3/8" diameter x 3" tall

I plan on buying (from tubesandmore)

20/20/20 µF @ 525 VDC
40/40/40 µF @ 525 VDC

to replace

20/20/20 450v
40/40 450v

My assumption was that the higher voltage rating was fine on the replacements?
 
Yes, you are correct. The higher voltage ratings of your intended replacement caps is fine. It's also a good idea as your safety margin is increased.
 
Thanks! I was put off by the price of the cans but it looks easier than trying to do an under chasis replacement

By the way, how do the amps sound? I have been very happy with my w-5m pair, I was asking an old tech in a shop that sells cary/rogue/and other tube brands if a parts upgrade would change the sound noticeably, his response was that he hated kt-66/6l6 amps, he said the limitation was in the tubes themselves, he said the st-70 was far superior, that the el-34 was a much more musical tube (he seemed to really hate the w-5m!), anyway, it was sort of a dud to hear that from someone that has been working on tube audio so long, maybe just a matter of preferences?

I was trying to pick some coupling caps and had considered auricap, sonicap, not really sure how to choose, so many choices but it does add up pretty quick, what would your next choice have been after the obligattos?

Thanks!
 
Definately preferences (or trying to sell you another amp) or perhaps the rest of his system revealed something he didn't like about the KT66 amps. Remember, you can also sub the KT66 tubes on the Heathkit W5's with 6L6GC (or similar high plate disipation versions) no problem. In fact, I have some junker 6L6's that I use for just such occassions when I fire up an amp for the first time.

I'm still burning the amps in and making some small tweaks here and there, but they are extremely quiet (a must with 105dB khorns) and stable. The Eagles sound like they are in the living room and I am listening to a performance and not a recording. I'm sure Roy, the owner, will be pleased with them when I am done tweaking.

Most all good quality coupling caps will give good results. I have used Auricaps with complete satisfaction in my 6BG6GA UL monoblocks. No complaints on the Obbligato caps thus far.
 
Wow, the guy really suggested a ST-70 over w5m's? That's interesting. I bet he was trying to get you to sell them and buy something from him. Do they take in vintage gear? He probably wanted you to sell them in so he could have them!
 
I've never sold anything there, they take items in trade and I have bought some used things there (I bought a pair of soliloquy sm-2a3 speakers with iron stands, a creek cd player). This guy just works on stuff and he is this really big old asian gentleman and is very surly (I hear him muttering things about boutique electronic parts and things like that once in awhile), I think he is just old and set in his ways. Anyway, not sure what to think of it.

A friend is offering me a linn sondek lp12 with what I take to be the stock tonearm and a blue point cart (but it has a sansui headshell, yikes), I am not sure if the power supply is valhalla, anyway, $500, that's money I was going to use to buy parts for the w-5m's, hard to pass on that though, this can be an expensive hobby!

I do plan on proceeding with the w-5m's, I really enjoy the idea of replacing parts, not enough background to make any changes or mods but the idea of restoring them is exciting
 
surgigator?

again, nice thread! I've done a W-5M rebuild and am planning another and want to install surigators in both. Neither of mine had them, can you tell me the parts number? vendor and most important, the location. I can not locate it on my schematic.
Thanks
kirk
 
Hi,
I'm starting my second W-5M rebuild. For the first I used a combination of Allan Bradly and Riken resistors and stayed true to the wattage specs. These are getting scarce. I noticed you used Kiwami's and upped the wattage value in several places, ie 270R screen limiter to 5wts (on the schematic its 1/2 wt). since Kiwami's are only avalible in 2 or 5 watts is it ok to up the wattage? I'm getting my parts list together and would prefer to use as high quality resistors as possible.
Thanks,
Kirk
 
Sorry for the really delayed reply. Life sometimes takes control of things.....

It's perfectly fine to up the wattage on the resistors mentioned. As far as the surgistors, I got mine off of Ebay for cheap!
 
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I have a single of these, unrestored. Just curious what another would run me in today's market.
TIA! S.B.
 
If you're planning on ever running a stereo pair, I would get one now. With good transformers, they can go from $100 and up. Why now? They are just going to go up and up in price. Great amp.
 
Thnx!
Just "took a stroll around the grounds". Nothing for $100, some for multiples. Loosing interest fast.
I have an AA-100 in good cdx with substantial looking ultralinear iron. Building something with that someday using obtainable decent beam power toobz appeals more at this point if I don't swap one or the other for something more interesting pre-owned S/S or ? High-End.
S.B.
 
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