I have recently acquired a Threshold CAS-1. I have replaced the power supply capacitors, so it plays music again, but I had a couple of questions. It was suggested that I replace the existing tantalum capacitors (green blobs) on the board to a more modern electrolytic type. I also noticed that the output devices are not the same on both channels, one channel has 2n5876 devices and all of the others just say class ab and have a date code. Any thoughts?
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The CAS 1 was/is a great amplifier. The 2N5876 and "CLASS A6" marked transistors are the same part. I would definitely swap out the tantalums for aluminum electrolytic's like the Elna silks.
Graeme
Graeme
This brings back some good memories.......
The ceramics need to go too. You could also replace the bridge rectifier with a high speed or soft recovery type and how about some 1% metal film resistors for good measure.
Jam
The ceramics need to go too. You could also replace the bridge rectifier with a high speed or soft recovery type and how about some 1% metal film resistors for good measure.
Jam
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I owned one of those baack in the 80s. It was a pretty decent amp and was my first taste of the Mastrer's work...
I borrowed one from a friend for a couple of days just to see if it would drive the Dayton Wright XG8's. I was told it would and it did.
I consider the CAS 1 and 2 to be noteworthy designs from that period.
I think it would be very cool if FirstWatt were to re-release the CAS 1. The obsolete parts would need to be subbed and perhaps other parts improved but generally the basic circuit could and should be left intact. The FW amp chassis would be perfect.
IMHO.
Graeme
I consider the CAS 1 and 2 to be noteworthy designs from that period.
I think it would be very cool if FirstWatt were to re-release the CAS 1. The obsolete parts would need to be subbed and perhaps other parts improved but generally the basic circuit could and should be left intact. The FW amp chassis would be perfect.
IMHO.
Graeme
No, no, please, I couldn't possibly accept a gift like that.
I'm just trying to help promote the success of FW in whatever small ways I can. Friends helping friends. Really.
Graeme
I'm just trying to help promote the success of FW in whatever small ways I can. Friends helping friends. Really.
Graeme
Now that's a wonderful gift I would be very pleased to accept. Thank you.
If you need help loading the truck, let me know. I would be happy to come over and lend a hand. I figure you have Colin and Sean totally booked keeping the pipe full and flowing.
Graeme
Decided to use one of my CAS1's again, but one channel gives a -0.6v thump when turned off - when +49v and -49v supplies discharge (after 1 second) to ~ 20v. Just replaced tantalums with Elna silk electrolytics and also the three 0.1uF caps. All my measurements with VOM show all 4 8000uF 50V capacitors to be the same - discharge rates, actual dc voltages and initial and final ohm readings with 1.5v VOM - 500 ohms initially slowly reaching >200Kohms after 1 minute. Have ordered new power supply caps. Any thoughts?
Update to my CAS1 turn-off thump. I replaced filter caps with 14,500uF units. No effect on thump. While magnitude won't damage speaker, hearing noise after powering-off is disconcerting. My next step is to confirm that output bias current is 100mA. 
I have one of these Old Threshold amps in very bad shape that I would like to do something with. Pretty much all of the output devices are blown but the boards are rebuild-able. I love the metal work of these amps! Nice big fat heatsinks! a nice N.P. approved mod/update/upgrade/rebuild would be very very cool!
I thought about building something with TO-3 metal can mosfets but dang those seem hard to find. It looks like I could replace one metal plate per channel of the heatsink assembly easily and then be able to use the more common TO-247 type plastic devices.
Zc
I thought about building something with TO-3 metal can mosfets but dang those seem hard to find. It looks like I could replace one metal plate per channel of the heatsink assembly easily and then be able to use the more common TO-247 type plastic devices.
Zc
Hi!
I have one of these. I'll replace the 4 power supply caps, and the tantalums. What do you think, should I use other than electrolytics for the tantalums? Polyprop or something?
And do I really need to change Silver Micas? They are known to be good, are they too old?
I have one of these. I'll replace the 4 power supply caps, and the tantalums. What do you think, should I use other than electrolytics for the tantalums? Polyprop or something?
And do I really need to change Silver Micas? They are known to be good, are they too old?
