Get the one with the biggest heat sinks or the one that weighs the most.
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The Forte you should try to find is the Model 4. It is a pure Class A version of the Model 5 and is generally recognized as a far better-sounding amplifier. As far as between the two you mentioned, both have reputations as good amps, you might go with the one that is in better shape (Forte used to be part of Threshold, don't know if it has much product support beyond a local tech who can work on it).
Actually Forte Model 4 is the Class A version of Model 6. (Not Model 5) I used to own a Model 6. I believe it's a Nelson Pass design. There was an article in Stereophile about the Model 4 and 6. Basically, he designed the Model 4 in pure class A, and the company wanted to put out a product with higher power rating, so he converted the Model 4 to Class AB to give it a 200WPC output.
Thanks for the response.
Actually, the Forte models 4,5,6 & 7 used IGBT's and
were all done after Nelson Pass left the company. I believe it was Michael Bladelius who deigned these (he did design work with Threshold & later with CODA).
I'm iterested in hearing from anyone who has compared this amp (model 5) to other amps.
I've never heard the model 5, but I did audition a model 4 which was an amp I was after. I liked it so much I went home with a Threshold T-100 (with IGBT's), designed by Michael Bladelius the same time the model 4's were. I later purchased a Parasound HCA (don't remember the #) for the bedroom, and it basically sounded like a Japanese receiver, so I got what I payed for. If you like Michael B's work, check out Primare. He was doing design work for them the last few years until recently, I believe.
The Forte Model#6 can easily be converted to the Class A version, (mine is) the 4+6 are pretty much the same amp. I have heard my amp in the 200 watt class A A/B version and in the lower watt Class A version.
The lower watt class A version is much, much better.
I believe the Model #5 is not as high current as the #4 or #6. I believe I also have the specs. for the model 5 in my manual at home, I will take a closer look when I get home.
I have used my Modded Class A #6 with maggies MG1 imp. and resently with Eminent Technology 8A which are 83 dB and the Forte worked great with them.
If you want I can post the specs for the Model 5 later.
It wasn't in my Manual, it was the model #4,#6 + #55 that I have.
But I do have a copy of Stereo Review Buyers Guide for 1992 which has the Forte Model#5 in it.
"Noninverting design, employs IGBT transistors at output stage. Fet/bipolar front end design: gain stage in pure Class A. High bias Class A/B output stage, 100 watts per ch, into 8 ohms. glass expoxy circut boards, custom toroidal power Transformers, 0.1% THD 20-20,000 Hz; slew rate 50v input imp;47,000 ohms, current capability 10 amps cont; 30 amps peak. 26 lbs retail $1,295.
Model #4+6 current 16 amps cont; 50 amps peak
I have a review with Nelson Pass in a 92(?) Stereophile. He said that the input stage on the Forte amplifiers had some of his circuits but Michael Bladelius was the primary designer.
The Model 5 is a 100w version of the 6, 7 was a monoblock version of the 4 that produced 75w. The other Forte amplifiers were MOSFET based I believe.