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    need help with potential st-70 problem

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    wedg714

    Posts : 74
    Join date : 2011-11-23

    need help with potential st-70 problem

    Post by wedg714 on Sat Feb 25, 2012 7:58 am

    first off let me say that i didn't do this. i'm not that stupud!! i recently sold one of my st-70's on ebay. the buyer, i've unfortunately come to find out, didn't know a thing about electronics. the day he recieved it he messaged me that when he hooked up the amp and turned it on everything was alright for a few seconds and then suddenly there was a loud screeching sound that came from his speakers and the fuse blew. after a couple of messages back and forth, i realized that this guy knew nothing about electronics. it finally dawned on me to ask him what preamp he was using. he messaged me back saying that he had hooked it up to his harman kardon reciever. i thought i was going to have a heart attack right there. i told him to send it back. i recieved it yesterday afternoon. i checked the rectifier and it was ruined. replaced the rectifier, installed a new fuse and turned the amp on with absolutely nothing hooked up to it. the amp came on with no problems and i was able to bias the tubes with no problem. everything SEEMS to be o k. i don't really want to hook up a preamp and turntable until i get some feedback from someone as to what else this guy may have done to this amp. HELP!!

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: need help with potential st-70 problem

    Post by Bob Latino on Sat Feb 25, 2012 8:40 am

    If the fellow connected your ST-70 to the SPEAKER outputs of the receiver, then he would have overdriven the ST-70 resulting (probably) in what happened. He also may have used the TAPE OUTS on the receiver which have a FIXED output of maybe 2 volts. The TAPE OUTS are not controllable with the receiver's volume control and a stock ST-70 which needs about 1.3 volts IN for 35 watts OUT would have been overdriven by the 2 VOLTS.

    My feeling is that your amp is OK and just your rectifier and fuse blew. The only way to find out is to try playing the amp.

    To use an ST-70 with an older receiver then that receiver must have PRE-OUTS. PRE-OUTS are controllable with the receiver's volume control while the TAPE OUTS are not. Many of the older receivers DO have separate PRE-OUTS. On the back of the receiver the PRE-OUTS are usually connected to an "AMP IN" RCA with a removable "U-shaped" connector on each of the two channels. If you remove this connector from each channel, you can now use the preamp section of the receiver OR the amp section separately. Just run an RCA interconnect from the PRE-OUT of the receiver to the ST-70 and plug all your signal sources into the receiver. I know a few VTA ST-70/ST-120 users that do just this because their old receiver has a PHONO input which allows them to play vinyl records. Most new preamps don't have a phono input or have a phono board option that may be expensive.

    Bob

    wedg714

    Posts : 74
    Join date : 2011-11-23

    Re: need help with potential st-70 problem

    Post by wedg714 on Sat Feb 25, 2012 9:40 am

    he said that he hooked it up to the pre outs on the reciever but i bet he didn't know to disconnect the jumper. i'll hook it up this afternoon and see what happens. i'll never sell another piece of my equip. on ebay. thanks bob. will let you know what happens

    wedg714

    Posts : 74
    Join date : 2011-11-23

    Re: need help with potential st-70 problem

    Post by wedg714 on Sat Feb 25, 2012 11:55 am

    hooked the amp up to my system and everything seems to be fine. thanks for the help

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