Awww, now I'm all nostalgic. I used to own FIVE Citation IIs. Wonderful amp from the great Stu Hegeman.
Enjoy your amp but I'm wondering how hot it will run? Is it getting a cover or being left open?
Enjoy your amp but I'm wondering how hot it will run? Is it getting a cover or being left open?
Test equipment
Fluke 8060A
HP 3000A Function Generator
BK Precision Model 1474 30Mhz Scope
1st photo 10Hz square wave
2nd photo 100 Hz square wave
3rd photo 10k Hz square wave
4th photo 20k Hz signal
5th photo frequency response @ 20k down .67db. Frequency response from 20-20K is flat except for the drop at the high end.
6th photo meter reading 20k Hz.
Will post test results from a associate who does calibration testing as a living, when he gets free time available. Doing this for me as a fiend and curiosity,
Please remember this amp update uses the exact audio circuits as the original, but different transformers, no choke, and the RC network across the output transformer deleted.
Also, I'm just a retired 40 year technician with my only training was a 1st Class FCC license. I have been building amps and other things for fun since the mid 1970 as fun.
Fluke 8060A
HP 3000A Function Generator
BK Precision Model 1474 30Mhz Scope
1st photo 10Hz square wave
2nd photo 100 Hz square wave
3rd photo 10k Hz square wave
4th photo 20k Hz signal
5th photo frequency response @ 20k down .67db. Frequency response from 20-20K is flat except for the drop at the high end.
6th photo meter reading 20k Hz.
Will post test results from a associate who does calibration testing as a living, when he gets free time available. Doing this for me as a fiend and curiosity,
Please remember this amp update uses the exact audio circuits as the original, but different transformers, no choke, and the RC network across the output transformer deleted.
Also, I'm just a retired 40 year technician with my only training was a 1st Class FCC license. I have been building amps and other things for fun since the mid 1970 as fun.
Attachments
The 10 Hz square wave is certainly very good. The high frequency response could probably be adjusted for less ringing.
It has two covers, one the original steel one with vent holes , and a clear acrylic cover with vent holes. When ran with steel cover, for three holes it didn’t get that hot.
Will take any suggestion on fixing the high frequency response.
I’m using Antec output transformer MP-60W66
Main Antec AS-4T320.
Not using any taps.
Look at BOM & schematic supplied in an earlier post.
I’m using Antec output transformer MP-60W66
Main Antec AS-4T320.
Not using any taps.
Look at BOM & schematic supplied in an earlier post.
Where to find the schematic?
The OT has taps available:
https://www.antekinc.com/content/MP-60W66.pdf
The OT has taps available:
https://www.antekinc.com/content/MP-60W66.pdf
I'd first try removing (or decreasing to around 220pF) peaking capacitors C5 and C6, and see how the ringing is changed.
It should be less, and at a lower frequency.
It should be less, and at a lower frequency.
You can find some great deals on eBay if you search for incorrect spelling.
Nobody knows so they don't bid. The guy I got the Fluke 8060 from was
NOT happy. I bet he learned his lesson.
Happy New Year
G²
Thanks, I’ll look at this tomorrow. First shorting out the rec networks, then reducing it to 220 pf
The high frequency drop may cause by the digital meter. Direct input the signal to the meter to verify the frequency response of the meter.
I would restore C13/C29 and R34/R69 across the outputs. They're zobels or "tweeter savers" to tame spurious oscillations and protect your speakers. Might also help tame the HF ringing. Try increasing the value of C12 a bit at a time, maybe up to 240pF or a bit more. If the 10kHz wave looks smoother, dab a .1uF cap across the load and see if the square wave falls apart or goes into oscillation. HF stability into a partially capacitive load will be a key issue with the new output transformers.