Heathkit w4am rebuild

I just bought two Heathkits w4-am, and the plan is to rebuild them. I'm just starting to order parts and I have the manual, but I want to see if there are any suggestions or improvements I can make to the units. Please let me know. Here are some pictures of the units and their undersides. I removed a capacitor to test it on one of them.

I also want to know if there's anyway to test the transformers.

A couple of things I want add to both of them:

-Volume knobs
- on/off switches

I fixed up and improved a pair a while back, see post #17 here: http://www.audiokarma.org/forums/showthread.php?t=149678&highlight=bricktop+w4*&page=2

^ lots of info from the thread. Also check out the web for paper on improving the williamson amplifier. My pair of model bs have the on off switch above the AC outlet where your's is mounted. Pull it out and put in a simple slide switch there instead of jumping the preamp plug.

Use caution when using the phono jacks for balancing the tubes. Make sure they reconnect (pins)when the plug is pulled back out. Resistors in this circuit are almost always out of tolerance. Use 1/2 watt 1%. Install a CL80/90 too.

You can check the power transformer by pulling the tubes, apply the AC power, and check voltages on the secondary. Secondary is center tapped so you should have close voltages between the center tap and either side of the secondary which are pins 4 and 6 of the rectifier socket (high voltages here!). Also check the filament leads to pins 2 and 8 of the rectifier as well as the filament leads to the other tubes for correct voltages.
Output transformers should have low ohm readings on primary to other primary leads and on secondary from com ground to the 4,8 and 16 ohm taps.

You can also check for leakage on the OPT by removing the leads and using a small voltage filament transformer and a voltmeter, but you need to be careful not to touch any of the leads together.
Good luck with the rebuild. You will have a nice set of Williamson amplifiers when finished.

Good luck with your project - These are fine sounding amps when restored.

Chiffre -- Congrats on your Heath amps!

Besides the good info you've already received, let me add that while your gold unit does in fact appear to to be a W4-AM, your gray unit appears to be an earlier unit (likely a W-4M) that was ultimately updated by Heath into the AM version due to stability problems with the earlier units. If you plan to keep the stock circuit (other than the modifications you mentioned), then you will definitely want to copy the circuit of your gold unit into the gray unit to protect the amplifier and your speakers from any potential instability. This is no small matter, as the early Williamson designs were rather famous (or infamous?) for burning out tweeters, and causing the woofers to "breathe" slowly in and out with no signal present due to such instabilities.

As Dan said, the web is full of information on the Williamson amplifier, and ways to improve it. Frankly, some of the "improvements" offered are of dubious value, while others, like those offered by bricktop, are excellent and directly address the all to common stability and ringing square wave problems.

Like bricktop, I also developed my own feedback and stability modifications, achieving nearly identical results to his (although with a completely different approach), while largely retaining the original circuit (as does his). If you decide to improve your amplifiers beyond that of the stock W4-AM circuit, either of these choices would be an excellent way to proceed.

Good luck with your amplifiers!

Dave

Plenty of good discussions here and about on bringing these up to snuff and ready for another 40-50 years of music.

First, replace all the power supply and coupling / bypass caps to bring voltages back to spec. and for both short & long term reliability. Its a must do. Check the resistor values, too. While you are in there, also re-flow all the solder joints! I have found that these steps will take care of more than 80% of issues.

Thanks for the advice. I'm probably going to gut the w4 and use the newer circuit if I can,but we'll see how it goes. Also anyone have any info on the volume knob?

Those look great! Hope all goes well with the restore :yes:

Chiffre -- The value of an input level control will depend on what you will be driving the amplifier with. If it is a SS device, the level control can be anywhere from about 25K to 100K. If it is tube device, 250K or higher would be more appropriate depending on what the output impedance of that source is. What will the signal source be coming from?

Dave

These amps are worth the effort and costs. As noted, just because it claims to be an improvement doesn't really mean it is. I have read glowing comments about the Bricktop mods, and we all know DC knows his sheet so when he comments it is with confidence backed by years of knowledge and experience. Perhaps we would all benefits by a reposting in layman's terms of what to remove, what to install , what wire to pin change, etc. when restoring these great amps. The W4 doesn't get the respect it really deserves and can be had for a song if you are a smart shopper. Good luck, but you don't really need luck, with your rebuild. I will be following this thread too for improvements I still need to do on my pair. As they sit now, they are in the keeper stack.

The power transformers are "known" for being marginal, and they do fail. I've had this happen to me on fully re-capped and resistored units I have. Part of the problem is our higher line voltage now 120v, used to be 110v. This causes the unit to run hotter.

Williamson Mods

Chimera Labs suggested Modifications for Williamson amps:
Williamson Mod

VERY thorough family history of the design - well worth a read!
Oestex Link

Another interesting page devoted to Williamson:
Linky

Of some interest:
http://www.preservationsound.com/?p=3823

Further Mods & improvements

The Musicians' Amp http://oestex.com/tubes/mus_amp%20.pdf

There is an interesting declassified Navy report from 1953, I think, comparing merits of several hi-quality transformers and circuits. I can't find it right now, the one link does not work I have is saved on some computer...just have to find it.

Edit- duh. found my own tracks... Navy Tests HiFi

Alright just ordered some parts.
With some luck it should be the last order I have to do for this. It was a total of $210 with shipping on everything for the two amps. The most expensive parts were the tube sockets and the two multi-capacitance capacitors. I went through the original w4-am manual and ordered the parts' values listed or as close to them as possible.
Basically I'm replacing all the capacitors, resistors, tube sockets and RCA jacks. I don't know what the 100 ohm control is listed under the resistor category, anyone know this?
I also haven't gotten around to checking the transformers yet, but hope to soon.
I will be using an SS pre-amp for now, so I still need to figure out where to put some switches on these things. Here's a shot of the parts I ordered.
Thanks again for all the advice.

Chiffre -- The 100 ohm pot should be a wire-wound unit of 2 watt rating (or more if desired). It doesn't have to be a wire-wound unit, but it would be hard to get a control of that wattage rating that wasn't wire-wound. The original pot was also a wire-wound device.

Dave

If the balance pot, 100 ohm control, isn't bad, why replace it? I might have a spare if you find one bad.

Studd

Got some stuff in. Not everything, but close.

YeeHa

Now the fun begins. :thmbsp:

Subscribed, I just purchased a pair of these puppies from the auction site and eagerly await their arrrival. Keep us posted on your progress.

Transformer ambiguity

OK, Thanks for all the advice, progress has been a bit slow, but I'm well on my way on the first amp, the w4. As has been noted, the wiring is actually a lot different than the w4-am, so I've made a few slight modifications to make it work. One problem I'm having is the power transformer (54-29) has no markings on its wires. I numbered them before tearing it apart, but I have no clue as to where they go on the new w4-am wiring. Any help would be appreciated.
I'm considering just buying a new transformer.