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    Assembled kits and 4 ohm speakers?

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    LEVLHED

    Posts : 21
    Join date : 2009-10-26

    Assembled kits and 4 ohm speakers?

    Post by LEVLHED on Mon Oct 26, 2009 12:09 pm

    Looking at Bob's assembled kits, I was wondering if they are built to drive 4 ohm speakers as well as 8 ohm?
    Since they appear to only have one set of posts per side I am wondering how that works.
    I have a pair of Polk in-wall LCi-RTS105's that are 4 ohm, supplemented by a pair of powered 10" subs.

    Thank you,

    levlhed

    Bob Latino
    Admin

    Posts : 2415
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Assembled kits and 4 ohm speakers?

    Post by Bob Latino on Mon Oct 26, 2009 12:56 pm

    LEVLHED wrote:Looking at Bob's assembled kits, I was wondering if they are built to drive 4 ohm speakers as well as 8 ohm?
    Since they appear to only have one set of posts per side I am wondering how that works.
    I have a pair of Polk in-wall LCi-RTS105's that are 4 ohm, supplemented by a pair of powered 10" subs.

    Thank you,

    levlhed

    Hi,

    All kits come with output transformers which have 4, 8 or 16 ohm secondaries. The kits may be set for either 4, 8 or 16 ohms. It is also easy to change from one impedance to another at a later date should you change to a new set of speakers which have a different impedance. All you do is move one wire on each channel.

    You could also put in a DPDT slide switch in place of the dummy SPST stereo/mono switch on the front of the amp. It would then be easy to switch back and forth between two different impedances if you run the amp on two different systems at times and want to quickly switch between say 4 an 8 ohms. The Radio Shack DPDT switch listed below would fit the opening perfectly and work just fine for this job.

    Radio Shack DPDT slide switch

    Bob

    LEVLHED

    Posts : 21
    Join date : 2009-10-26

    Re: Assembled kits and 4 ohm speakers?

    Post by LEVLHED on Wed Oct 28, 2009 9:12 am

    I am only going to use my 4ohm. Is there a print out/schematic/instructions for changing it?
    I haven't looked around the site yet, I'm sure it's around somewhere.

    I just bought the completed ST-70 kit from the guy in Puerto Rico off agon. Bob you may remember that one as it doesn't sound like he's even had it very long.
    I literally have had a "stock" ST-70 for less than a week, also bought off agon. I'd bought the stock one specifically with the intention of doing all the upgrades over time, but my obsession kicked in and I ended up getting what I think was a pretty good deal on this one already upgraded. When the cost of it was less than if I'd bought all the parts and done it myself it was kind of a no-brainer. Also, I'm not exactly a maestro w/a soldering iron and a schematic.
    This has been my first foray into tube audio. I'm even selling off some of my other hobby-stuff now to go a little further. I have really been enjoying the stock ST-70. Even with the Chinese EL84's I think it's pretty nice. Looking forward to hearing the difference between this and the mod/kit one!

    So now I'm trying to learn all the ins/outs of your kit, Bob.
    And I'll need to switch it to 4ohm before I can use it. Hoping I can get one of the engineers here @ work to do it for me before I even bring it home.

    I am also going to look up what the preferred tubes are so I can get them onto various Christmas lists. I understand the Gold Lion KT88's are generally well regarded? Also interested in options for the other tubes. Again I'm sure the info is already around here...

    Thanks
    Dan in Plymouth, WI
    aka LEVLHED

    Bob Latino
    Admin

    Posts : 2415
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Assembled kits and 4 ohm speakers?

    Post by Bob Latino on Wed Oct 28, 2009 9:26 am

    Hi Dan,

    Inside the amp, if the amp has been set up for 8 ohms, the ORANGE (8 ohm) wire on each channel will be soldered to the red speaker binding post. You will also see a BROWN wire coiled up inside the amp. The BROWN wire is the 4 ohm wire. Simply unsolder the ORANGE wire from each binding post and solder on the BROWN wire. The amp is now set up for 4 ohms. One other thing is to make sure that the bare metal end of each ORANGE wire is insulated with a piece of electrical tape so that it won't short out against the chassis.

    In an ST-70 (IMHO) the best output tube you can use in there is the Genalex Gold Lion KT66's NOT their KT88's. You CAN use the Gold Lion KT88's in there but you won't get any more power out of the amp by their use AND the KT88's cost about $50 a quad more than the KT66's.

    Bob

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