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Posted by firstname.lastname@example.org on March 13, 2009 at 15:41:23:
I just picked up a Futterman H-3 stereo block which has been modified to use 4 x 6LF6's per channel. It originally had either 4 or 6 x 6FW5's per channel. The reason I say 4 or 6 of the FW5's is because the chassis has 6 holes punched per channel for the FW5's but I know Futterman was a then an now kind of guy so he may only have installed 4 per channel as the attached schematic shows. Also he used many different tube types for the H-3 although mine has the 6FW5 printed on each hole the attached schematic shows the 6HB5 as the output tube of choice.
Now the H-3 I picked up pretty much has the front end shown on the attached schematic. Once you get to the output tubes it starts to become a NYAL OTL3 which uses the 6LU8 as well as the SS TIP 50 for regulation.
In the end the workmenship on the wiring is terrible inside the amp. I mean a mess!!!!! The sockets suck and are ready to give up the ghost as well as several key parts. I touched a metal oxide 1 watt resistor in one of the reg circuits last night with a hemostat and it crumbled.
So a rebuild is what is up and coming. Starting like as soon as I make some choices and there is where I am looking for help from a few of the members here who have experience with this amp.
1. Should I go back to the 6FW5's or 6HB5's?
2. Should I stay with the 6LF6's?
3. What about 6 JJ Tesla EL509's per channel? Current wise that will match the 6FW5's since they have a max of 550mA and the JJ's are 500mA. 6 replaced by 6 does not cause me a transformer issue. The 6FW5's are octal as are the JJ's. Heater current is higher but I could take care of that with a small additinal trans I tuck inside the box as it is large and once the birds nest of wiring is fixed all will be good under the sun
Thx in advance.