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Lance Cochrane tube amp - never got it working correctly

BmWr75

BmWr75

Top octave? pfffffftttttt
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Edit February 18, 2024: Am done trying to fix this amp. Returning it to the seller.


Was lucky enough to pick this amp up today. Is a one off build by Lance Cochrane running 6L6GC tubes in push pull.
 

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Nice!

I have had a few email conversations with Lance (Cochrane) and always enjoy them. Wanted to buy one of his amplifiers but never did and then picked up a Jim Nicholls amplifier for parts or repair and got it working with minimal effort. Lance was very helpful in answering some questions about it and giving me some suggestions about tubes.
 
Well he does build them from bits and pieces and then tunes them until they sound good to him. Some look better than others, I have done searches and most of them look pretty good IMO. FWIW I think a previous owner put the tube labels on as I have never seen that on his builds before.
 
All his amplifiers are one offs.
Do a search of ways (glue, silicone, liquid nails, etc) to attach caps in an amp, the results and controversy will make your head spin.
Lance has been at it a long time and probably has experienced some thing that work or not along the way.
 
Some hot glues are pretty tuff. I used some made for gluing wood.
I had to use a pretty hot glue gun to get it to flow good. The wood broke before the flue let go. I started using it on wither stuff. I haven't used it in while though.
 
Hooked it up today. Put four new power tubes, new rectifier and new inverter/driver tubes. Lots of midrange and bass distortion. Not unlistenable, but no where near enjoyable either. Tweeters are dead quiet to my old ears when no music is playing, so appears no heater noise leaking in.
 
It would be interesting to know the part number on the output transformers. Could be an impedance mismatch, or maybe something else is amiss. What speakers are you trying to drive with it?
 
zackthedog said:
It would be interesting to know the part number on the output transformers. Could be an impedance mismatch, or maybe something else is amiss. What speakers are you trying to drive with it?
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Had it hooked up to a pair of Tyler Acoustics Reference Monitors, they are 8 ohms nominally. Was unable to see any transformer markings when I had it open.
 
I see partial numbers on the upper in your pic, but its hidden by wiring. Maybe that will be the answer.
 
Thought I had discovered the potential problem earlier today while looking more closely at the internals. Center left in the picture below is a 50K blue resistor and one end was unsoldered. Whoever installed it didn't make a mechanical connection with the loose end lead and the solder joint failed. It is suppose to be in parallel with the tan resistor beside it (evidently?). I fixed that, but it made no difference in the midrange and bass distortion.
 

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I got in touch with Lance Cochrane (sorry for the previous misspelling of his last name) and he calls this the San Francisco Giants amplifier. He sent me a schematic too. He only built one for a guy that owned a record store, in CA I assume. If it could talk would ask it how it made it to MS.
 
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