gatchaman wrote:Hi all,
I just scored a pair of Dynaco A-10's. I have been searching for a good pair for a long time, and now I finally scored a mint pair. I want to recap the crossovers, but I can't read the values on the capacitors anymore. Can someone help me? (I have no equipment to measure the values myself.)
Kindest regards, Marlon.
I found this post on AudioKarma and it appears to come from a reputable poster. Cheers.
"A brief visit from a very vintage Dynaco A 25 and an A 10
I've recently had the privilege of restoring a pair of each of these. The A 25 proved to be a particularly pleasant surprise. It proved to be a very early version with Scanspeak Drivers and the FG stuffed vent located ABOVE the tweeter (see pics). The A 25 had a conventional crossover with 6 resistors and one 8 uF Jensen NPE cap. I replaced the cap with a Sonicap 8 uF, cleaned the rotary switch and left the original resistors intact.
The rotary switch forms a conventional 2 resistor L-pad combining a varying series resistor (depending on switch position) with a 10 ohm parallelresistor. The resistors are 2.2, 4.4, 6.6, 8.8 and 11 ohms. The middle "normal" switch position utilizes the 6.6 and 10 ohm parallel resistor resulting in a 4 ohm resistance upstream of the tweeter. The other positions result in 1.8 ohm, 3.06 ohms, 4.7 ohms and 5.22 ohms. Each click of the rotary switch changes the SPL response about 2 dB.
The cabinet was lined with thick rock wool-like batting and two extra layers loose under the woofer the length of the cabinet. The woofers were hard to remove due to assembly with a black, tar-like substance that remains to this day extremely sticky.
When the work was completed, I took some measurements. The A 25's tweeter rolled off at about 10 kHz as shown here
http://www.audiokarma.org/forums/sho...=425850&page=2.The A 10 also had Dynaco drivers. The cabinets had two batts of yellow FG. The crossover was more complex, consisting of an 8 uF cap, 5 ohm series and 8 ohm parallel resistor in the tweeter circuit. The woofer had a 4 mH series wired air core inductor and 24 uF parallel cap. The woofer cap was replaced with Dayton caps and the tweeter cap was another Sonicap cap. i have the speakers for a few more weeks. Let me know if you have any questions or need any further info. The A 10 HF roll off started at about 10 kHz also (see below), but at a steeper rate than the A 25. Its bass response was also not as good as the A 25.
Attached Images
File Type: jpg vintage Dynaco A 25 portrait.jpg (124.9 KB, 75 views)
File Type: jpg Dynaco A 25 scanspeak woofer.jpg (99.7 KB, 72 views)
File Type: jpg Dynaco A 10 with upgraded xover.jpg (134.5 KB, 59 views)
File Type: jpg Dynaco A 10 schematic.jpg (112.0 KB, 49 views)
File Type: png dynacoa10freqresp.png (52.4 KB, 50 views)"
