BHK 250 Binding Posts


#1

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!


#2

Based on what you’re writing I think you’re fine with the amp and speaker cable though it does sound like we should get that rascal back and replace the binding posts for you.


#3

Thanks Paul! Ship it back eh? I’ll have to figure out when the best time is … never! Hah, I’ll at least wait until January, no need to give your employees something to do when they would rather be with family.


#4
pmotz said 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.


#5

Yes indeed I did have that problem and sent my beta unit in for new binding post. They also replaced some relays and REALLY kicked the BHK up some notches. Send it back at a convenient time as Paul suggested and you’ll be very very happy. I sure am.


#6

So does that mean the production units sound better than the early beta units? Hope not.


#7

It did in my case. I’d ask Paul if yours needs an update.


#8
woot said It did in my case. I'd ask Paul if yours needs an update.
Uh oh. I've got S/N 5B0009. Not a beta unit, but early production. Are those posts/relays the new version or the beta?

#9

Only a very few got out with the other binding posts. Yours is perfect.


#10

Mine is Serial #PWA-A1-5D0013. Should I be worried? Mine is a pretty early beta unit (early enough to require the pin expander).


#11

Yes, I have the same problem with my beta unit. I think I couldn’t use a half of the posts after trying to connect the cable for the first time… I do not think they are stripped, but rather loose from the inside. Mine is PWA-A1-5D0005. Do I need to send it back? surprised-011_gif


#12
stevem2 said Mine is Serial #PWA-A1-5D0013. Should I be worried? Mine is a pretty early beta unit (early enough to require the pin expander).
What is a pin expander?

#13

The pin expander is a tool, with a white handle, PSA sent in the BHK Beta Tester care package. The instructions said our tube sockets were too tight for the tube pins. Sliding the pin expander in each tube socket, hole, resolved the problem. Not sure how many BHK Stereo 250s required this. PWA-A1-5D0010


#14

Good description of the pin expander. I haven’t had any problems with my binding posts but that may be because I have been extremely cautious with them because of the early problem reports. I’m equally interested Paul’s take on woot’s report about improved sonics with the relay fixes.


#15

Interesting… I do not think I received the pin expander… I’ll recheck the box, just in case, but also my box was packed differently than the others’ (no straps).


#16

The pin expander came in a separate care package box a week or two after the amp. Other items included in the box were; instructions, a Beta Tester test CD, an extra set of Gold Lion vaccum tubes and a pair of white gloves.


#17

Interesting comments on the care package. My BHK did not come with those items (not sure if anyone did), but I did get the CD in a separate package shortly after getting the amp. No gloves, pin expander, and no spare tubes. No problem, I didn’t have any issues with the tube pins and I should have a pair of gloves somewhere from the PWD upgrade years ago. Would be nice to have a spare set of tubes, but I did get the Tungsrams that Bascom recommended, so no issue with spares. I will be sending my amp back in January (my back can’t wait!) so we’ll see what happens. With respect to the discussion on pin expander and binding posts I think something got garbled in the discussion. My take on it was the problem was solved by the use of expanding pin banana plugs. Good answer if you have speaker cables with bananas, but doesn’t help me unless I get a new set of cables which isn’t happening just yet.


#18

The expander has nothing to do with the binding post. It’s for stretching out the tube pin holes in the tube sockets making it easier to install your tubes.

The early beta amps binding post were not build to spec (no fault of PSA). Paul ordered new post, from a different source I believe. The later post are much hardier. @Paul please correct me if I’m incorrect.


#19

Some of the beta units had binding posts that did not meet spec, you’re right. We don’t know how many, though we suspect only a small few of the betas. If yours are working fine then yours did meet spec. You’d know it if they didn’t. They became obvious quickly.


#20
nortonkp said The pin expander came in a separate care package box a week or two after the amp. Other items included in the box were; instructions, a Beta Tester test CD, an extra set of Gold Lion vaccum tubes and a pair of white gloves.
I did receive the tester CD, but no tubes, white gloves or expanders cry