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jemshaw's picture

MM130hd 115 going over

Hi one of these turned up and I couldn't resist. Long drive and of course not quite as described. Well yes it is 240 volt (australia) - but thats because it has a step down trans in cabinet.Described as All Works well - but - no reverb and about half power on high, some tubes hot some not, biased at .245 volts at Y and hard to adjust.
Needs a sort out and renew . Still sounded good and clean which is a miracle as one el34 was dead and another was sus. The original evm 15inch speaker works well :)
Sans tubes - voltages all look good a,b,c,FGH
Some questions if someone is kind :)
1 ... solved (just do it) The flyback diodes have been removed, I imagine they should be replaced, someone on here said 3 kv ones should be ok what sort of current is spec?
2 ... solved found references :) This has both the 5kv caps on each anode set and the 1 kv caps on each screen set (which are not on schematic ) remove ? or leave... Im not totally sure about the 1kv caps purpose?
3 ... solved ... It has one of those big brown turd 0.047u caps Physically between the el34 pairs that goes from from ground to grounded 7 pins this puzzeles me but i see in pics online they have similar position but cant quite make out connections is this correct? in some pics of this area there are more of the same caps am I missing something here? (cant see it on the schematics correction, found it on output side of transformer. ) Still puzzeled

4 ....solved (just did it ) Would like to place 1% 1 ohm resistors to each cathode to see what each valve is doing. Is it considered gauche to just string those up or more correctly to leave the 10 ohm resistors and string up from there with some added lugs for the sake of those who come after and follow biasing instructions?

5 On low power the heater voltage drops to 4.something volts . I am used to later musicman amp. if one read the net people talk of cathode poisoning and such. How does operating experience go with these on low power setting?

If anyone could clear up some of my confusions that would be appreciated