Here are some interesting posts from the old Yahoo group about the Westlabs Matchless transformers:
Matchless Trannies from West Labs?
They are awesome, IMO. They are very hefty and they say that the OT has a great interleave. The impedance matching on the primary of the OT is off by 100% (on the 15W set), but that is the way Matchless spec'd them. I installed them on a rather stock Lightning Circuit. I love that amp. I tried Hammonds first and it didn't sound at all the same. It is that OT. I suppose it is harder on the tubes with the wrong Z but so far I haven't lost a tube yet and what a tone. icon_biggrin.gif And I guess you could always wire it up so it wasn't using the wrong primary Z.
Now I ask...is this for an 18watt? What are you experimenting with? If you are trying to remain true to the Marshall tone get the Heyboer. I have both the Lightning and the 18watt and they are definitely different birds...even though much of the circuit is the same. But they are both so cool...and have a distinctly different gain quality.
~Ross
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Chris
Dirty's right on this one. All the (Vox type) Matchless versions tht I've seen are 4K primary. Can't speak for the others. Measured the "Westlabs" sets myself by putting AC through the primary & doing the math.
Both "Westlabs" sets have 4,8 & 16 ohm taps. Chris probably meant wire up the 4 & 8 ohm only on the spitfire & label them 8 & 16 respectively, to double the reflected impedance to correct the impedance " mismatch".
One other thing, there has been much discussion about screen protection with these amps. The real ones I've been in had screen voltages at or near plate voltages. Probably why they eat tubes.
My latest "fix" is sort of a compromise. I added an extra filter stage (4K7-3 watt metal oxide with a 22 uf cap.) for the screens & left the 100r individual screen resistors (1 watt also metal oxide ) in place. This dropped the screen voltage to about 290 volts at idle. Increased shared cathode resistor to 75ohms(up from 62) on the "30" watt. ( 120 up to 150 o the "15" watt). Plate disspation dropped from around 16W per tube to 12 on both amps.
The amps retain most, but not all, the chime, however, they overdrive a little earlier than the real thing. Hopefully though they are protected from the screen current problems inherent in these designs.
If you end up building the lightning (two knob tone stack) you may also want to experiment with the cathode resistor on V1 (say reduce to 10 or 5 uf) to take some of the low end out of the circuit & make the bass control a little more useable.
Good Fortune
Philip Morrison
famp69wv@yahoo.com
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I did wire the OT with a switch and some jacks to make all ratios possible and my favorite was the 8k primary .
Sorry for the confusion !
Chris (CMW Amps)
c.m.winsemius@hetnet.nl
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Matchless trannies
Deadbeat2
Well, I have built a Spitifre using Westlabs trannies and I have an 18 watt using Heyboer's with Jason's PI/AC30 mod. The amps do NOT sound near the same. The Spitfire has a much more "complex" tone I guess the best way to describe it. The 18 watt with the PI mod is very cool, though. The 18 watt is a bit more clean and punchy until it is cranked, then more Marshall. The Spitfire is a bit gritty at all volumes, will do a nice clean or dirty but there is this complexity in there that I like. I have to say I like both amps VERY much! They are just very different. I hope this helps, it is hard to describe a sound in words.
Bruce