Sunn 200S

[bsco]

Hi. Received a Sunn 200S for repair from a buddy of mine...was worked on before and wires have been cut and taped together with dare I say...scotch tape and duct tape...it is in pretty hard shape and has a second bias pot connected in parallel to the original one....why...I do not know...The amp is equipped with 6550's but the owner gave me KT88's to install....are these drop in replacements.....there may have been some changes to the circuitry but i am not sure yet.. I just got the schematic today and it shows KT88's Whoever did this also taped some replacement caps down to the chassis using duct tape as well...and the power transformer was also replaced......I will have to go through the schematic and try to return the amp to it's original condition...the main thing I am concerned with now is if the circuitry was changed to accomodate the 6550 output tubes or if they were a drop in replacement for the KT88's.... There are extra resistors added to the output tube sockets as well.....and the stand-by switch has been completely disconnected...
Cheers,
Bernie

[drewl]

KT88's are about the same as 6550's so as long as there is enough bias voltage the original circuit should be fine.

[bsco]

Thanks drewl...The bias voltage on the schematic says -55volts....like I had said..I will have to go through this amp to see what was done to it...I just found out that the reason the stand by switch is disconnected is that the switch didn't work so the last tech used the polarity switch instead...thanks for that tube info...
Cheers,
Bernie

[bsco]

This was a thread that I had forgot to end.....I had redone the amp, replaced the sockets, took out the extra bias pot, shortened up the wiring, fixed up the chopped up wiring that was all taped together, removed the dozen resistors that were connected in parallel to get the right value and installed one resistor......repaired the grounds....were wrapped around transformer mounting screws and just tightened up the nuts to make a so called good connection and installed proper connectors and secured the grounds with lock washers as well...replaced some pots because the wrong ones were installed.....and then the amp worked fine....I was talking to the owner just the other day and it is working great...
Cheers....