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Author Topic: HH MA 150 problem  (Read 4129 times)

philly

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Re: HH MA 150 problem
« Reply #15 on: April 23, 2016, 02:49:13 PM »
Hi Enzo,
Scoped the sine wave on the o/p and it looked fine at the cross over point so I left well enough alone.
I played a guitar through it and it sounds good. I also left it on over night with no signal i/p. Today I played music through it for about an hour and it sounded good. The o/p tranny's feel cool to the touch which I presume is a good sign. The amp belongs to a guy who has been gigging for over 50 years. It hasn't seen a duster cloth since it left the factory but it is now ready to go back into action. Repair workshops are becoming a rarity these days so I was happy to help him out. At least the old stuff doesn't have any surface mounted components.
Thanks for all your help.

graham andersen

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Re: HH MA 150 problem
« Reply #16 on: May 14, 2016, 07:55:05 PM »
I just rebuilt the power amp stage of one of these on Friday and the correct schematic of the amp is the Laney KB80 .It uses 2N3773 as Output devices and Tip 31 /32 as drivers . Laney took over H/H .The power amp modules of the H/H MXA 100 ,MXA150 plus the Laney KB80 .The main difference is the output devices 2N3055 FOR the !00 and 2N3773 for the 150. The other difference is the Secondary voltages of the mains transfomer . Be sure to check the longtail pair TR3 and4.
« Last Edit: May 14, 2016, 08:08:39 PM by graham andersen »

philly

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Re: HH MA 150 problem
« Reply #17 on: May 16, 2016, 03:13:09 PM »
Thanks Graham,
My old 100w VS combo uses 2N3055 as O/P's. I must compare the specs of both the 3055 and the 3773. The latter might be a better replacement if I ever need to replace the 2n3055's in my 100w.
By the way, I got the MA150 running ok with help from Enzo and others on this site. Replaced all the electrolytic caps that had high esr readings while I had the unit on the bench. It's back gigging again.