Yet another Heath W5M rebuild

[ab0ez]

My setup is still pretty much the same with the AVA T7 pre, Heathkits and Omega single driver bipoles as the core.

However..... I'm about to embark on a speaker build using SEOS 18 waveguides, BA750 compression drivers and Acoustic Elegance TD15M mid woofers to go along with my 3 subs. I'll probably add a Rythmic sub to the mix in the future.

Dang! We have got to get together and spin some tunes!

 

[ab0ez]

Heater wiring installed (except for the center-tap) and I bought some blue heatshrink and re-did the output transformer primary side leads. All of the heater wiring is silver-plated stranded Teflon. If you look at the 9-pin sockets, you'll see that the heater wires go to pins 4 & 5. That's so the amps can use 6CG7s instead of 12AU7s.

 

[audiodon]

Learning here.
So, I know you don't need the silkscreen ID'ing the tubes and stuff, but will you put something on if these'll get passed along? If so, how?

 

[ab0ez]

I'll include a copy of the modified schematic for the owner. If he wants to put dome dry transfer labels by the tube sockets, that would work.

 

[ab0ez]

Got the original old can caps polished up and installed. Hey! These are starting to look like real amplifiers!

The can caps will only be for original appearance, they will not be in the circuit.

Now the fun starts: Let's start wiring these babies up!

 

[Fran604g]

Nice! I can see why these amps are sought after. I'd love to hear a pair sometime. I MUST get out more! lol

 

[ab0ez]

Got the first filter and second cap filter sections and choke in. You can see the 4 capacitors in the 2nd filter section, which make up a 220uF 900V filter node. This is where the center tap of the output transformer will be wired for B+. Also shown is the 110 ohm dropping resistor which will feed another filter node. The filament wiring is also in.

 

[kward]

Jim, what is the purpose of those smaller film caps that straddle the pins on the electrolytics? What is their make make and size??

 

[ab0ez]

Bypass "snubber" caps. They are .01uF 1KV.

 

[ab0ez]

I thought I would get a little solder slung this morning before turkey and Master of Ceremony duties called me away.

Here you can see the new main solid copper ground bus, new 350 ohm 10 watt bias resistor, standoffs, and the B+ capacitor filter bank wired to the output transformer centertap. Drawing on a 1961 article written by Talbot Blake detailing the shortcomings and fixes for the typical Williamson amplifier, the 680uF 80V output tube cathode bypass capacitors will give a theoretical cutoff of around 3hz and excellent transient response (with the new stiffened power supply) down to around 30Hz.

 

[s-petersen]

If those 220 ohm 10w resistors get too hot, you can separate them for better dissipation.

 

[Gwedo]

Jim,

Is this the article you mentioned?

http://www.stiftsbogtrykkeriet.dk/~mcs/Williamson/

I noticed he mentions this. Will this need to be address in my PAS-3X?



Cheers

 

[ab0ez]

If those 220 ohm 10w resistors get too hot, you can separate them for better dissipation.

Good observation. The original resistor in this position was a 4 watt job, so if these get hot, there's problems!

 

[ab0ez]

Gwedo, That's the article. Your PAS should be ok.

 

[ab0ez]

It's just about BACON smothered bird eating time, so I will likely be in a carbohydrate induced coma in a short while.

Ground bus connections to the first and second filter caps made. All transformer center-taps grounded. Next up will likely be the front end and driver wiring. I'm waiting for some new 300 ohm rheostats...and hoping they will fit!

 

[s-petersen]

What are you gluing the caps in with?Clear silicone?

 

[ab0ez]

Industrial RTV. The stuff holds like crazy and works well since the owner did not want any holes drilled in the chassis.

 

[ab0ez]

More progress made on the input, driver and power supply sections.

Edit: I should have added make sure you check the original cathode resistor on the driver tube socket. Some early versions of the W5M had 560 ohm resistors here, which resulted in a poor bias point. You want a 2.2K 2 watt resistor here.

 

[Ken Boyd]

Looking good!:thmbsp:

You don't see that many amps that look that tidy under the cover.

 

[ab0ez]

Got half of the cathode bias network wired in and the output tube current monitoring/balancing test points. This is probably the hardest part of the entire rebuild. The two 30 ohm current sampling resistors are hand matched to about 1/10th of 1%.