Heathkit W-5M First Tube Amp Rebuild

thr33p4c

thr33p4c

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I am considering buying a pair of W-5M Mono Amplifiers to rebuild and use in my 2 Channel rig. I have done work on solid state gear and rebuild passive crossover networks but this will be my first time on a significant tube project. I have read through the construction manual and a bunch of threads but just wanted to ask a few general questions before I take the plunge.

1. What is the best way to tackle power switching? I will be getting some WA-P2 preamps on the deal and was thinking about using them as glorified power switches. I also have a power conditioner that can be set up to have a turn on delay triggered by 12VDC or 120VAC. My third option is adding power switches to the AC Mains input but I do not know if these will degrade the amps' value. On the subject of AC... Is there any need to replace the original power cord? If I end up putting in a power switch should I add an IEC socket. (I guess the overall question is: Do I modernize the amps or try to keep them as stock as possible?)

2. I have seen talk of Thermistors and Surgistors. If my amps do not have these should I consider adding them?

3. Are there any "critical" mods that should be considered to improve performance and life. (I keep reading about higher modern Mains voltages and am wondering if I need to make any adjustments to the circuitry)

4. Can I realistically directly substitute anything for the seemingly expensive KT66 tubes with good results?

I am sure more questions will come to mind but wanted to get a start. I will be looking at the amps this weekend and if the transformers check out I will likely pick them up.
 
Some versions of the W-5Ms have an Achilles heel, the power transformer. I've had a number of them over the years and had the PT open up during normal listening. A real PIA! Somewhere I have a Heath service mod that calls for replacement of blown ones with a Stancor 8412 series PT (400-0-400VAC / 200mA).

To turn them on & off is easy. You can jumper them behind the socket so they go on when plugged in and turn them on/off with a power strip. You can replace the preamp socket with a plate and install a switch there. Or you can be non-invasive. I took a couple ice cube octal relays, gutted them, and installed switches in them. Plug & play.

I've never played with inrush current limiters except on my Mac and even then it was just replacing the stock one with another.

Critical mods are power supply, specifically the power transformer. If the ones you are buying have been in use over the last ~20 years they likely have good power transformers in them. When I was buying mine, they were coming out of garages & cellars and had not seen use in decades.

Hard to beat the original Genalex KT66s. Every amp I got had grey bottle ones in it. They sound superb. But, I have to believe there is a suitable modern replacement. Before all the various KT66 clones were available, 6L6GCs were used as the sub.

Lastly, besides the power transformer variants there is also an output transformer variant. One version uses the physically larger Peerless 16458. These are more desirable than the smaller 16309. The 16309s do sound good but there are lots of indifferent to negative comments about them if you dig deep. A lot of that was lost though when the USENET stopped being archived. Unfortunately this is a fraction of what used to be there but still worth reading -

https://groups.google.com/forum/#!search/heathkit$20w5m
 
My W-5Ms had WE350B installed--that makes KT-66 seem much more affordable! I put the WE away and ran SOVTEK 6L6 with pleasing results.

I have the same dilemma regarding IEC sockets on my Dyna MkIIIs. I will probably cut the chassis to install the sockets--but with the knowledge that I can buy repro chassis from www.dynakitparts.com if I want to return them to stock.

If you are thinking that you may sell your Heaths in the future I would suggest you keep the chassis stock.

If you have exotic power cords that you would like to use... you could find some old authentic IBM PC monitor power cables with female IEC at one end. Cut short and wire into your power supply without cutting the chassis. Odd looking, but not permanent and facilitates the use of your favorite IEC cord.
 
soundmotor said:
Some versions of the W-5Ms have an Achilles heel, the power transformer. I've had a number of them over the years and had the PT open up during normal listening. A real PIA! Somewhere I have a Heath service mod that calls for replacement of blown ones with a Stancor 8412 series PT (400-0-400VAC / 200mA).

To turn them on & off is easy. You can jumper them behind the socket so they go on when plugged in and turn them on/off with a power strip. You can replace the preamp socket with a plate and install a switch there. Or you can be non-invasive. I took a couple ice cube octal relays, gutted them, and installed switches in them. Plug & play.

I've never played with inrush current limiters except on my Mac and even then it was just replacing the stock one with another.

Critical mods are power supply, specifically the power transformer. If the ones you are buying have been in use over the last ~20 years they likely have good power transformers in them. When I was buying mine, they were coming out of garages & cellars and had not seen use in decades.

Hard to beat the original Genalex KT66s. Every amp I got had grey bottle ones in it. They sound superb. But, I have to believe there is a suitable modern replacement. Before all the various KT66 clones were available, 6L6GCs were used as the sub.

Lastly, besides the power transformer variants there is also an output transformer variant. One version uses the physically larger Peerless 16458. These are more desirable than the smaller 16309. The 16309s do sound good but there are lots of indifferent to negative comments about them if you dig deep. A lot of that was lost though when the USENET stopped being archived. Unfortunately this is a fraction of what used to be there but still worth reading -

https://groups.google.com/forum/#!search/heathkit$20w5m
Click to expand...

I've heard of guys un-potting those power TXs and using something fairly generic to go back in the can, but for the life of me I can't remember what it was. I want to say it was a Hammond product, but that's all I got. I love the W5s and run 5881 TungSols in mine when I get them out. I have a grey chassis set, and a gold chassis set, and always wondered if the chassis color would tell me anything?
 
Last edited:
jaymanaa said:
I've heard of guys un-potting those power TXs and using something fairly generic to go back in the can, but for the life of me I can't remember what it was. I want to say it was a Hammond product, but that's all I got. I love the W5s and run 5881 TungSols in mine when I get them out.
Click to expand...

I have (2) dud PT's, pr. of 8412s, chokes, a pr. of 16458's, chassis, cages, and finally (2) plastic Heathkit script logos for the cages.

Picked it up here & there; I really should get off my ass on these.
 
I have not seen the amps yet but here is my idea: If they are in decent cosmetic shape I will probably try to keep them as stock as possible. If the paint is really bad and things are starting to rust I will probably strip and repaint. If I am repainting them I will be losing all of the original markings on the chassis and might as well put in an IEC socket and a new RCA plug and power switch.

If I decide to keep them stock, I will probably either jumper them inside of the chassis or make a jumper/switch plug for the socket as suggested. I also thought about making a little remote enclosure that would allow me to switch them on and off by my preamp in my rack.

Thank you for the ideas guys... I will try to keep the thread up to date as I continue.
 
soundmotor said:
I have (2) dud PT's, pr. of 8412s, chokes, a pr. of 16458's, chassis, cages, and finally (2) plastic Heathkit script logos for the cages.

Picked it up here & there; I really should get off my ass on these.
Click to expand...

I never see the cages come up for sale. I have a set of W7s with no cages too, I guess people didn't like the cages.
 
thr33p4c said:
I have not seen the amps yet but here is my idea: If they are in decent cosmetic shape I will probably try to keep them as stock as possible. If the paint is really bad and things are starting to rust I will probably strip and repaint. If I am repainting them I will be losing all of the original markings on the chassis and might as well put in an IEC socket and a new RCA plug and power switch.

If I decide to keep them stock, I will probably either jumper them inside of the chassis or make a jumper/switch plug for the socket as suggested. I also thought about making a little remote enclosure that would allow me to switch them on and off by my preamp in my rack.

Thank you for the ideas guys... I will try to keep the thread up to date as I continue.
Click to expand...

Please do, and wow, 350Bs huh, you can sell those and rebuild these with money left over. As un-elegant as it sounds, I use a power strip to switch my 5s on and off when I use them.
 
i owned a pair of W5m's. never had a power trans issue just an output trans issue. the smaller output transformers are crap, open windings. as far as upgraded power cords go i feel this is a very UN-necessary venture. no improvement will be made at all. i ran mine with a restored Eico HF-85 and a pair of JBL c-38's. the W 5M amp will put all Mcintosh tube amps to shame in the sonic field IMHO
 
I've been thinking about making my W5Ms my next rebuild project too. Is there any reason to stick with the tube rectifier? I have been thinking about putting some hex-fred rectifiers into mine. But it does seem like adding some inrush current limiters would be a good idea if I go this direction.
 
goldear said:
I've been thinking about making my W5Ms my next rebuild project too. Is there any reason to stick with the tube rectifier? I have been thinking about putting some hex-fred rectifiers into mine. But it does seem like adding some inrush current limiters would be a good idea if I go this direction.
Click to expand...

Why not do both? Pre-rectify the AC going in to pins 4 and 6 then keep the rectifier to delay the application of B+ until the anodes get some pre-heating?
 
j beede said:
Why not do both? Pre-rectify the AC going in to pins 4 and 6 then keep the rectifier to delay the application of B+ until the anodes get some pre-heating?
Click to expand...
Because I dislike using tube rectifiers as a general rule of thumb. And because I cant help but suspect that its additional heater load might be one of the factors which tends to eventually push the Heath power transformers over the edge.
 
In something with a marginal transformer, a pair of SS diodes and a dropping resistor will do wonders for shedding heat load. I personally don't mind tube rectifiers but I don't love them so much that I'd bake a trafo to keep one either. Stuff with expensive tube rectifiers also are good candidates for a conversion. You can buy fancy parts and still spend waaay less than those NOS Mullard rectifiers.
 
gadget73 said:
In something with a marginal transformer, a pair of SS diodes and a dropping resistor will do wonders for shedding heat load. I personally don't mind tube rectifiers but I don't love them so much that I'd bake a trafo to keep one either. Stuff with expensive tube rectifiers also are good candidates for a conversion. You can buy fancy parts and still spend waaay less than those NOS Mullard rectifiers.
Click to expand...
That is exactly what I was thinking as well.

It amazes me though that such large power transformers so commonly fails though! It's not like those are dainty little things on the Heaths. My (highly modified) old stereo 70 ran very hard for 30 years on its original tranny before it finally shorted-out on me. And that is a smaller PT, and there are more tubes inside of that amp.

So why do the original heath PTs tend to fail so often?
 
jaymanaa said:
I never see the cages come up for sale. I have a set of W7s with no cages too, I guess people didn't like the cages.
Click to expand...

Funny you say that. There's one on fleabay now, as well as a listing for a pair of nearly mint restored W-7's. If I had the extra cash, I'd buy them.
 
5. When I am replacing jumpers between components what type of wire is best? Solid core, stranded, copper, silver, gauge?
 
I took the plunge... It's not pretty but it should be a lot of fun :) someone swapped one of the power transformers, the can caps are not all matched, I have no name plates, there is a 1/4" jack added to the back of one unit... I guess I will start by pulling out the transformers for testing.
 

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