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The HK deuce I am working has a 39 ohm resistor + .04uf cap in series from the 16ohm speaker tap to ground. I don't have these parts on hand and I wonder if they are necessary for the proper operation of the amp. I have seen a similar circuit on the heathkit W5 that they called a tweeter saver. I left it off of that amp with no apparent harm to the amplifier or the sound. Should I get the replacement parts or can I leave them off? regards, dak
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My take is why design an amp to have such a huge frequency range that you need added compensation networks to keep everything tidy? I realize that with marketing wanting a leg up on the competition in the spec wars, you needed to have an amp that won't blow up customer's speakers, but why put yourself in that position anyway?
Replacing it is no big deal but personally I prefer a simpler design. cheers, Dak
Do you have a spare tire in your car? Or at least a tire inflator of some sort? A lug wrench and a jack? Do you consider that excessive complexity? After all, if you used solid rubber tires you wouldn't need all that stuff.
Since an amp designer has little control over what his amp gets hooked up to don't you think it's wise to consider the consequences of what happens outside the amp? Or that the amp has issues (the smoking .039 uf capacitors I've seen have all been in amps that weren't in the best shape). Have you ever had a speaker wire come loose? In the real world things like that can happen...
Stu took no chances in his amp!
I would say this is a safeguard that prevents a totally open output that might arc and damage OT and/or tubes.
It is RC network to suppress transformer ringing.
You can exclude it if you wish as long as you don't care about square wave performance. I don't think it will lead to amplifier instability.
Another interpretation of the function of that network is that it assures a partially resistive (non-reactive) load is present under all conditions at ultrasonic frequencies. This promotes amp stability when a highly reactive load is being driven, typically an ESL or possibly a long run of high capacitance speaker cable. Not all amp designs require this network (Mac unity coupled, QUAD II etc.) so if it's present, it's probably safe to assume the designer determined it to be necessary for unconditional stability.
I don't have direct experience with the Cit II so I can't speak from experience but I'd be inclined to leave the network in place unless you know the amp will never be used with capacitive loads. Maybe Jim McShane can provide a specific recommendation.
Yes. DO NOT remove it. I have seen those parts literally smoke under some conditions - would you rather have that energy pumping into your speakers? Some call those "tweeter savers" because they limit the amount of very high frequency energy among other things.That network was one of the reasons H-K could say the Deuce was stable under ANY load. Keep in mind the front end of the amp is flat to the MHz frequencies, and the OPTs have full power response to 40KHz and while it drops above 40 KHz there is still a lot going on above that.
Why would you want to risk your amp/tubes/speakers for $4.00 worth of parts?
Edits: 05/01/15
Yup, if Stu put it there, it needs to be there. And if you analyze deep enough, the reason becomes quite clear.
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