Here's the correct link. I'll see if I can edit the original post later:
Vacuum Tube - 6HB5, Beam Power Amplifier | Antique Electronic Supply
Vacuum Tube - 6HB5, Beam Power Amplifier | Antique Electronic Supply
The Acoustat Model Six uses two interfaces per speaker, each driving three panels. However, it is a special version of the interface, with a LF transformer with less boost to compensate for the increased panel area. You could drive six panels with a standard interface, but the additional capacitive load would have dire effects on the overall frequency response. These systems were intended to be driven by two amplifier channels per speaker.
Even the Spectra 44/66/4400/6600 uses a different transformer than the 22/33/2200/3300 to compensate for the increased panel area. Unlike the MK-series of speakers, the four and six panel Spectras are set up to be driven by one amplifier channel per speaker.
Even the Spectra 44/66/4400/6600 uses a different transformer than the 22/33/2200/3300 to compensate for the increased panel area. Unlike the MK-series of speakers, the four and six panel Spectras are set up to be driven by one amplifier channel per speaker.
Sorry, there's no free lunch on this one. For proper operation with 6 panels, you'd need to change the LF transformers and...forgot to mention this before...you'd also need to adjust the value of the two HV coupling caps. And even if you were able to do that, I'm still not sure about the advisability of driving six panels with one amp channel. There's a good reason Model 6s and 8s were supplied with two different interfaces per channel.
Does anyone happen to have a photo or diagram showing the internals of a MK-2123 interface? I am trying to determine whether accessing the PCB that contains the bias supply requires uninstalling the LF/HF transformers. FYI: My MK-2123 have the 15VAC wall wart supplies, it seems that some MK-2123 were supplied by 120V, 60HZ.
I don't have any photos handy right now, but you most certainly do NOT have to (or want to) remove the audio transformers to access the bias circuitry, which is located at the opposite end of the oblong interface enclosure. Only the original Spectra 2 and 3 hybrid speakers used a mains-powered bias supply. All Spectra models after that used the wall-wart powered Ultrasonic Bias Power Supply.
There are 2 small Allen head bolts (vertically aligned in the first photo, one down by the label) that need to be removed, that should allow the board to be jiggled out, but the wires may need to be de-soldered to remove the board. This may require lifting the main circuit board. Transformers should not need removal.
Cheers
Gn
Cheers
Gn
Thanks for the reply. I am not having any electrical trouble with either of my MK-2123... I need to replace a broken 3.5mm jack bias supply on the PCB and I am trying to figure out how much trouble I am in for! The broken jack still functions.
Thanks for the photos. I agree that tilting the main HV PCB out of the way will help with removal of the bias supply. These photos also serve to jog my memory. In this version of the chassis, provisions were made for BOTH mains power and Ultrasonic power. Had forgotten about that. Note the large hole-plug in the corner, which is where the mains cord strain-relief would have gone, and the extra small holes to mount the bias transformer. So I will amend my statement to say that some very early non-hybrid Spectras were mains powered. My personal Spectras are a later revision and lack the extra holes for mains power.
Thanks for the photos! Much appreciated. I will try to figure out the location and orientation of the 15VAC bias supply jack from your interior pictures.
...j
It's great to see so many replies and the thread is still active! Happy New Year everyone,
Best,
Luther
Hi Andy,
I was hoping you could provide some advice. I own a pair of Martin Logan CLS II that have MK-121-2A interfaces. I've owned a lot of wonderful speakers and have to say, they are quite extraordinary. I have an issue where the one channel plays at a vastly lower level than the other. I'm being told this is probably an interface issue but plan on swapping them to make sure.
My question is, would the interfaces have to have been modified to work with the CLS? I have access to a pair of MK-121-B and am wondering if I can just then swap them out without any type of modification.
Thank you!!
Being unfamiliar with the CLS, I cannot say if an Acoustat MK121 interface would be suitable. Let's just say I would be very surprised if at least some modification wasn't necessary. For one thing, I seem to recall the ML uses a lower bias voltage. Perhaps some other folks can chime in here. TYU - haven't you done this?
I was hoping you could provide some advice. I own a pair of Martin Logan CLS II that have MK-121-2A interfaces. I've owned a lot of wonderful speakers and have to say, they are quite extraordinary. I have an issue where the one channel plays at a vastly lower level than the other. I'm being told this is probably an interface issue but plan on swapping them to make sure.
My question is, would the interfaces have to have been modified to work with the CLS? I have access to a pair of MK-121-B and am wondering if I can just then swap them out without any type of modification.
Thank you!!
Being unfamiliar with the CLS, I cannot say if an Acoustat MK121 interface would be suitable. Let's just say I would be very surprised if at least some modification wasn't necessary. For one thing, I seem to recall the ML uses a lower bias voltage. Perhaps some other folks can chime in here. TYU - haven't you done this?