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Heathkit W5M rebuilds

Must be sweet for absolute sure Jim!
I know and respect the velvet hammer that is top end EV. Have a Suzerain stuffed cab up in Michigan (T350 and 828mid and 15W) and NEED another. Passed on one on ebay years ago, wrong color and 1000mi away, but only stuffed with T35 and 15BW so........
I'de love to redo the Corn crosses. I hear it's a must actually. All horns are mounted horizontally.
 
Awesome thread!!! Sorry if I've missed it in this or any other threads, but
can anybody tell me what value fuse goes in a W5M? I just got a pair with
the usual shipping damage that includes tweaked fuse holders & broken
fuses. These are decently recapped/been in recent use, would have
been plug & play but for the shipping damage. However I'm not finding a
PN-based fuse value @ Buss website or even the parts list in Heathkit's original
assembly manual. Much thanks for any help here.
 
Thank you much. All I saw on parts list was "3AG". @ Buss online, that
got me all kinds of amp ratings. 3AG's just a size/form spec, no?
Should I be looking for fast-blow? I should know all this, guess I've gotten
rustier than I thought. :tears:
 
Y'know, it's still dawning on me how stupid big those power transformers are for the rated output - I'm sure it will be an interesting experience. I'm guessing output current will be in no short supply. :ntwrthy:
 
And even with that, remember that they do have a well deserved reputation for being fragile with respect to turn on surge current. Given today's higher line output voltages at the wall socket, I highly suggest modern surgistors on the primary side of the power transformer as discussed earlier in the thread.
 
Thank you Sir. That build was a few years ago and looking back I can see some improvements that can be made in component choices, etc.
 
First rebuild

Jim, I've read through this thread a few times to prepare myself for such a project. I have a W5M on hand and two more on the way (plus a couple of WA-P2 preamps) and would love to have them operational. I haven't checked out the one I have yet, and there is no guarantee on the other two. My tentative plan was to simply go through each one with a fine-tooth comb and compare against the schematic and manual build info. Then find a variac (not sure what to look for here?) and slowly bring up the voltage like everyone suggests.

But after reading your rebuild info, as tedious as it will be, I'm thinking I should just do that on one of them first and see how it goes.

When you do your rebuilds, what are some tips you have for starting out? Do you strip the unit down to the chassis first and then go back up, or do you go one part (or group of parts) at a time?

I used to build Heathkits (ham stuff) back in the day, but Heath had already gone to transistors by the time I started in the mid-70s. I suspect there's not nearly the fragility in soldering issues with a tube unit, correct?

If there is another thread on the forum that covers this sort of stuff, please let me know. Thanks!

Bill
WK6A
 
Interesting Timing

Although this is a old thread, there are always W5s being reworked some where. Today I did my local "amp camp" for my pair of W5s. Annual PMI (preventive maintenance inspection ) just to do a health check, clean, set bias, test tubes, etc. All is well.

There is a point paper available on the net concerning making improvement to the Williamson amplifiers. I would recommend it as a necessary read for anyone who owns a pair of these puppies. IMO the 12AU7 swap out is the first step I would do.

DSCF1944.jpg
 
DanO55 said:
There is a point paper available on the net concerning making improvement to the Williamson amplifiers. I would recommend it as a necessary read for anyone who owns a pair of these puppies. IMO the 12AU7 swap out is the first step I would do.

View attachment 357280
Click to expand...

Where is the point paper located?

I just received the pair of W5Ms I was waiting for. They look to be in fairly good shape although I haven't opened them up yet. The weird thing is that they both have a pair of 6146s instead of KT66s or similar:worried:. I know from reading that some use 6L6s and 807s, but I've not come across a mod for the 6146 (I have them in some old Heathkit ham gear as power tubes). Obviously the circuit has been slightly modified (I'll find out when I open them up) because the plate tap is on top of the 6146 and there is a wire/cap coming from within the chassis somewhere.

I won't mind using these 6146s if they're considered good for this amp, but if not I would likely want to restore it to original KT66 configuration.

Any hints/tips on this?

Bill
 
The 6146 was never intended, nor was it ever a good choice to use in "traditional" UL service (although it can be used when a tertiary UL winding is available). While the tube has similar bias requirements as that of the 6L6 family, it also has many similarities to sweep tubes in that the tube operates with low (in comparison) screen voltages, and high plate voltages. To that point, using this tube in a traditional 6L6 UL application would be very dangerous for the tube, since it has a maximum screen voltage rating of 250 vdc, while most 6L6 UL designs place at least 375 volts on the screen, and some with nearly 500 volts.

Best to find out what's really going on with these before applying power since it appears that they were modified specifically for these tubes (807s use plate caps as well, but require a 5 pin socket). The only "safe" way to use them in a W-5 would be to convert the amplifier to pentode operation, but that would take significant modification if only to provide a suitable screen supply, and in any event, still leaves you with the question: Why?

Dave
 
6146's would NOT be a good fit for these amps.

For one these amps use UL taps, so the screen's at the same voltage or higher then the plate.
The screen voltage rating on the 6146 is much much lower here. (and you need to adhere to it)
 
quick replies

I'm just glad someone's still reading the thread and replying! :yes:

That's good info to start me out. Since I have no idea what these two units have been through, I'll just plan on scoping out the entire circuit in each unit and plan on complete rebuilds with correct tubes. I've read all the subtle and not so subtle changes to the original circuits that have been addressed in this thread, but as long as I can find the parts I'll plan on trying to stay faithful to the original build.

I suppose where I'll run into problems will be in some of the larger caps and the transformers, in which case I WILL go ahead and stray from the original where necessary. For example, I've seen someone who builds a replacement cap board that looks interesting, and I know there are a few non-KT66s that will work with minor mods.

It was strange seeing these 6146s in the two units. My first ham rig was a Heathkit DX-40 that I picked up used in 1963. It runs 75 watts input with a single 6146 for the final stage, and many of the pre-transistor finals in other rigs used a pair of them to get 180-200 watts input, so I suspected it was not a realistic substitute for this particular application. At least a cursory search on the 'Net didn't produce anything.

Thanks again, guys!

Bill:thmbsp:
 
"I'm just glad someone's still reading the thread and replying!"
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Speaking of which, I'm amazed no one's been harassing AB0EZ
for his updated parts list. That I'd like to see.:guitar:
 
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