Bridged KT88

[ArchieH]

Hi Does anyone know if it is possible to use two WD KT88 amps in bridged mode to drive a pair of stereo speakers?

[bikerhifinut]

Why?
If you want 60 watts then save the inevitable disappointment and ruined equipment and buy a pair of 60watt monos or a 2 x 60w stereo, like a quad II-80 for instance.
The basic and simple answer is no, technically its possible but inadvisable.
The WD 88 may be a "mere" 30W ( mine delivers a measured 35W into an 8 ohm resistive load at clip) but that's plenty to push a pair of quad 989 electrostatics hard in my set up.
If its raw power you are after then silicons cheaper and more reliable. If you must have valves then the practical solution at sensible HT voltages is to use paralleled output valves, Again this comes with its own issues of balancing the pairs of valves in push pull amps. Or use ginormous transmitter valves with HT measured in Kilovolts and invest in your own power station.

Sorry if that's not what you want to hear.

A.

[bob orbell]

Hi Archie, I agree completely with Andy, if it is more power you want then buy more powerful amps, but, if its better clarity and sound staging you are looking for, how about two WA88's in bi amp arrangement ? IE, one driving left speaker and the other driving right speaker, or one driving the bass the other the tweeter, assuming you have two way speakers. I did this with two KAT 6550 amps a long time ago, but then changed to the WA88 , again, I will ask, why, and do you have a problem. Bob

[bikerhifinut]

Hi Bob and Archie.
I think theres a clue in the coffee lounge thread and Archie will no doubt clarify it.
He's using Magnepan speakers. These things whilst having a reputation for excellent sound quality make an electrostatics load look benign!
They can drop to fractions of an ohm and are capable of destroying many otherwise perfectly capable silicon output stages, if they have poor protection circuits. They are also hugely insensitive, again making my ESls seem like a horn loaded single driver in relative effiency terms.
So using Valves makes a kind of sense as valve amps usually can survive the torture that a speaker like this can exert, but at the same time Archie probably does need industrial power outputs for when the Maggies look like a virtual short circuit.

Over to you Archie......…….

[bob orbell]

Before Archie responds, then maybe something like the Icon Audio 90 watt mono power amps are the answer, I had two, they are powerful, but I liked the WA88 better. Bob

[ArchieH]

Hi Andy And Bob
Thanks for the reply. To give you a bit more info regarding my inquiry, I dont absolutely need more power I was just thinking it might be an idea. My Maggies do have a link in the crossover so can be "bi - amped". I used to have two K5881's which i used one per channel and was very happy with that setup. I changed to the WAD 300b PSE with 4ohm output transformers and that is what I am using now. My wish for a change is I enjoyed building the Amps I have and would like to do that again and at a reasonable cost. Bob I'm afraid my funds won't stretch to a Quad II 80 and Andy even an Icon Audio MB 90 is out of my reach. What I would like is for a friend of mine who has a pair of Icon Audio MB845 to get fed up with them and sell them to me cheap !!
Thanks again guys for taking the time to reply
Archie

[ArchieH]

Hi
Just another thought do you know if the KT88's either have a 4ohm tap or can be fitted with 4ohm O/P TX's

[bob orbell]

No taps of choice Archie, just 6 ohm on the WD88 and the amp works very good. By the way, it was me that suggested the MB 90 and Andy that mentioned the Quad . Bob

[Richard]

Worth noting if still thinking about amps for bridging is that the output impedance doubles negating any advantage into a low imp load I think.

[snowman_al]

You could of course use them in 'parallel' rather than bridged. As long as they are very closely matched. That gets you half the output impedance and theoretically twice the power.

But then again, as you can bi-amp the maggies then go that way surely?