Threshold Cas-2

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6JohnS

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Joined 2014
#1
I just got back the exact Threshold Cas-2 amplifier I owned back in the early 80's. Unfortunately if has some blown output transistors. I don't have a schematic and it seems impossible to find one. I would be very grateful if someone could get one to me or post one somehow. I am interested in finding the proper transistors to put back in it. My amp currently has 4 different numbers and I don't know which ones are correct, if any? I would very much like to get this amp operational again and any help I can get would be greatly appreciated. Thank You.
 
#4
Hello Sound Happy, There is nothing conclusive on those sites to tell me what transistor numbers I should install. Some of the Cas-2 stuff is actually Cas-1 stuff and I need more clarity before I make any move. I have looked extensively through this forum and nothing I can find is clear enough. In fact what I do find just adds more discord. Is there anyone in this forum that has a real schematic that lists part numbers? Thank You

Here's a list of the transistors I currently have installed. There are 2 boards that hold 10 transistors each. 1 board for each channel. The forward board which is the right channel has (5) 2N6339 on the left side of the board and the Left channel board (rear board) is exactly the same. The right channel board on the right side has (4) 2N6437 and (1) 2N6438. The left channel board has (4) 2N6437 and (1) unmarked. I don't want to buy or install the incorrect transistors and could use a professionals touch on what goes where. Thanks
 
#5
maybe this will partially help - sch made by Tiefbassuebertr

hope Papa will chime in , with hellpful info
 

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#7
Soundhappy, Thank you for your efforts and perhaps contacting him would yield more results but when you hit his link to the Threshold Cas-2 you get routed back to where you sent me.

Zen Mod, Thanks for sending those .pdf's. I had already seen them all though. The first one is labeled cas-2 but is actually cas-1. It is a very nicely done schematic. A few people have said they are the same but I am unwilling to assume that. The Cas-1 stuff shows yet another Transistor number making things less clear.

Perhaps I should be asking for someone with a STOCK Threshold CAS-2 to remove the top off the unit and look on the boards. What is the part number on the transistors on the left side of both boards (2N????) and then what is the number of the transistors on the right side of both boards (2N????)
A am very grateful for every ones help. There must not be very many of these amps around if this info is so hard to find. Thanks again for all the help.
 
#11
Original transistors were most likely CAS5, CAS6, CAS8.
Look at CAS1 schematics - CAS5 and CAS6 (could be marked as A5 and A6)
Look at 400A / 4000 schematics - CAS8 and CAS6 (could be marked as A8 and A6)

There have been several threads on recommended replacements for these amplifiers.
 
#12
Thanks for the help and I grateful for everyone steering me in a direction. I am a very analytical guy but I have very little electronics education. I follow instructions well and I have built more than a few amps (mostly tube) in my day. What I am not understanding is why someone doesn't tell me what I asked for, the part numbers for the original transistors or a suitable replacement. I will follow your suggestion in hopes that I can figure it out. Thanks again.
 
#14
James, Thank you. That is exactly what I needed. I have already ordered new ones. Would you advise me to replace the power capacitors as well? They have been discharged for at least 15 years. Thank you again for the direct help. John
 
#15
I always have replaced the filter caps with as large a value in capacitance with the same voltage rating that will fit in the space available.

But, using a variac, you could slowly bring up the voltage. Maybe they will not fail, at which point, listening test may confirm need or not need to replace capacitors.
 
#16
I am in this amp for the long haul but I will bring it up slowly and see what happens. The Caps are marked well and shouldn't be too hard to find replacements. I will look into how much they are and if they aren't prohibitively expensive I will replace them all now. I will do a full tear down and a thorough cleaning and perhaps I will get many more good years out of this amp. Thanks again for your and everyone's help and advice. John
 
#17
Hi all,

Sorry to bring this thread back from its graveyard. I have one and i know it old and dont know how many owners has it been through but it is still one good amp. In the future i am planning to power planner speakers. Do you guys know if this amp can handle the low impedance from the planners or maybe martin logan electrostatic speakers.
 
#20
well , he and boyz claimed some things long ago , most of them working in your favor

see here : Treshold Treasure …….. ads,brochures,tech papers | Zen Mod Blog


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