2. amps-preamps
  3. 169899-137306

MC 240 ReTube or Replace

About a year and a half ago I acquired an old McIntosh MC 240.

I replaced the capacitors and retubed it using:

Genalex Gold Lion 12AU7 gol

Genalex Gold Lion 12AX7 gold

Tube Amp Doctor TAD 12BH7

TUNG-SOL 7581A

 

Now after some 1,000 hours of operation, driving a pair of Salk SS 6m speakers, one channel will intermittently give out a blast of static within minutes of power up and blows the fuse. This leads me to believe I have a tube which may be intermittently shorting.

 

With the MC 240 being almost 60 years old I’m wondering if modern technology has surpassed it.

Thus, the question retube or replace it.

 

Currently my choices are:

Quick Silver 60 watt mono amps

Mc Gary Audio SA 1

Van Alstine Vision SET 400

 

I would appreciate any comments.

TNX



pelletfan

Showing 4 responses by oldhvymec

oldhvymec
5,101 posts
 
Mcintosh MC240 is one of the best sounding amps around.

You rebuilt the power supply? Did you replace the filter caps and resistors to bias the unit correctly. Loosing a valve is easy to check. Swap left to right on the power tubes after giving them a GOOD visual. Same with the small valves, swap left to right.

3-5000 hours on power valves, 7-10,000 for the small valves. BUT valves do fail.. No matter who makes the gear.. No matter who makes the valves.

Regards
oldhvymec
5,101 posts
 
https://www.amazon.com/Extreme-Max-5001-5083-Hydraulic-Motorcycle/dp/B06XNZ5GV6/ref=asc_df_B06XNZ5GV...

:-)
oldhvymec
5,101 posts
 
It sure sounds like a valve or a bad connection at a valve. Clean and tighten the pin pockets. Then take the valves and plunge them into a cotton ball with WD40 a dozen times. Wipe everything off and insert the valves back in the sockets.. 101 valve maintenance..

On that PS rebuild, did you re-bias the the PS, did it come with a little pot? or did it have a fixed resistor?

7581 vs 6L6GC 23watts vs 30watts, your better off with 6L6WGC (military aircraft) or just GC 30 watt valve, tough too.

Regards
oldhvymec
5,101 posts
 
They get dirty, they get loose. They are 55+ years old. I've fixed at least a dozen amps and preamp with cleaning pin pockets and tightening them..

Sold for JUNK and fixed for pennies.. :-)

Regards
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