I have a BHK 250 (beta unit) which has worked pretty much flawlessly from day one. Aside from a couple of minor hiccups, a blown fuse and a noisy transformer (probably from poor power), no issues, until today. I had swapped out the speaker cables just to check if there was an issue with my Goertz cables (see below for more). When I went to put the Goertz's back in I found that one of the binding posts seemed to be stripped, it would tighten then loosen. I also discovered on another post the nut was locked in position and would rotate the whole assembly. I recalled this issue from other beta testers and found that both Alekz and woot had similar problems. I never saw a specific solution, but I believe there is one. Anyone know what it is?
As mentioned above I was checking a possible issue with my Goertz MI-2 speaker cables. The Goertz cables use flat conductors which offer very low inductance for good impedance matching between the amp and speakers, but have the side effect of high capacitance (compared to other cables). The factory specs show capacitance of 0.95 nF/ft and I am using a six foot pair with separate runs (true bi-wire) so the total capacitance is 11.4 nF. Doesn’t seem like much to me, but this supposedly can cause some amps to isolate. My question, probably to BHK himself, is this a problem? I’m assuming the only way to tell if this is an issue (other than the amp shutting down) is with an oscilloscope to check for the oscillation. Is that correct? I have an oscilloscope, but I haven’t used it in years and don’t know if it works and if I can remember how to use it!
Oh Boy, those output terminals. I have the first produced beta BHK 250 and several of my terminals had stripped early on. My first solution was to use something like Monster Cable Exterminators to accept spade lugs and insert the Exterminator into the output terminals banana plug holes. In my case, since I am not b-wiring, I was lucky to have two good terminals for hot and ground in each channel. Although the Exterminator type of device works, it is still one more interface between the speaker cable and the actual output terminal. In your amp, the one terminal that all of it turns, you might get pliers around the part closest to the chassis and with a wrench on the part that is supposed to turn, break it loose.
On the subject of capacitance, typically capacitance values in the neighborhood of 0.1 - 1 uf can cause instability in some power amps. Early on, we re compensated the BHK amps to be stable with typical capacitive loads of up to low tens of uF. So, I think your 0.0114 uF should be OK!
If you wanted to test with your scope, you could get a generator program for your phone or tablet that would output, say, a 10-20 kHz square wave and look at the waveform with a scope across the output. Keep the output amplitude to a few volts p-p. But, major caution, since the amp is a bridged output, the scope chassis MUST be floated from third wire AC ground. If the scope has good differential inputs, then the scope can be AC grounded with each phase of the output going into the diff inputs of the scope. I have used Audio Tools, Audio Tool, SimplyNoise, and RTA, IOS apps on my Apple devices with great success as signal sources for not in the lab but in the house testing.