Music Man 410-65 Service.

[Sea Chief]

Hi again chaps,

Im doing a general service on my fab new used buy (Reverb) Music Man 410-65 & need some general advice if I may.

Having 700V flying around, & it's fantastic condition ( it looks never to have been opened since new, only 1 previous owner ) I want to do the best I can, as carefully as possible. Its my amp for life.

Ive got 2x f&t 100/450 main filter caps on their way (the old huge mallory pair showing obvious leakage). Ive done a servisol pot clean, retweaked the tremolo ( a bit more to do, it doesnt work well with the amp vol distortion for some reason.. but works well clean).

So could I get any tips? Do the new caps need ' forming' 1st, or is it ok to just plunge them right in, just recapping & turning amp on? Such high voltage, albeit split between the pair in series I think to approx 350v each, i want to treat them as best I can.

Any other ideas welcome. Very kind if so.. SC

[pdf64]

Newly manufactured ecaps don’t benefit from being formed, the manufacturer already did that recently.
Maybe consider it if there’s a data code and it’s getting towards 5 years ago.

After doing any work on an amp, it’s a wise precaution to do the initial power up via a light bulb limiter.

[Sea Chief]

Newly manufactured ecaps don’t benefit from being formed, the manufacturer already did that recently.
Maybe consider it if there’s a data code and it’s getting towards 5 years ago.

After doing any work on an amp, it’s a wise precaution to do the initial power up via a light bulb limiter.

Hi pdf. That's a good point.. id forgotten i have a limiter. Will dig it out. Thanks SC

[Bill Moore]

I refurbed a MM RD-115 One Hundred a few years ago, and ended up rebuilding both power supplies. The low voltage side was starting to cook the PCB, so I raised the new resistors higher off the board. Another problem I had was one of the "protection" diodes was shorted, and I ended up subbing a lower voltage rated part, as no originals could be found.
Great sounding amps!

[Helmholtz]

Hi pdf. That's a good point.. id forgotten i have a limiter. Will dig it out. Thanks SC

Major electrolytic cap manufacturers recommend a re-forming treatment when a cap has been stored (or not used) for more than 2 years.
This means connecting to rated voltage via a 1k series/current limiting resistor for at least 1 hour.

A bulb limiter will take care of the necessary current limiting and the amp provides the voltage.
So it makes sense to leave the amp running on the limiter for at least one hour with replaced caps.

[Leo_Gnardo]

it doesnt work well with the amp vol distortion for some reason.. but works well clean

Distortion that way doesn't work for everyone. Same for the master volume Fenders. Some people do manage to sound good with it. No sweat, use your fave fuzz overdrive or boost box(es) and enjoy the big clean sound when they're in bypass.

[Steve Blackdog]

Distortion that way doesn't work for everyone. Same for the master volume Fenders. Some people do manage to sound good with it. No sweat, use your fave fuzz overdrive or boost box(es) and enjoy the big clean sound when they're in bypass.

I read that as the tremolo not working on the distortion channel, not that the distortion channel doesn’t work. Perhaps Sea Chief can clarify.

[Sea Chief]

I read that as the tremolo not working on the distortion channel, not that the distortion channel doesn’t work. Perhaps Sea Chief can clarify.

Yup exactly thanks mr.dawg.. so the trem effect clean is great, turn up the vol/ turn down the mv ( distortion sounds great) & the tremolo effect is muddied to almost inaudible.

[Leo_Gnardo]

I read that as the tremolo not working on the distortion channel, not that the distortion channel doesn’t work. Perhaps Sea Chief can clarify.

Gotcha. I misunderstood the complaint. Works OK clean, but trem not apparent with gain/master vol dialed for distortion. I'm at a loss for an explanation.

[Sea Chief]

Gotcha. I misunderstood the complaint. Works OK clean, but trem not apparent with gain/master vol dialed for distortion. I'm at a loss for an explanation.

Maybe I tweaked the trimpot a mite too far.. will get at it all again this ev & recap it: been away from amp for 2 days.

thx

[Sea Chief]

Hi chaps, ( been trying to get on MEF for days..)

recapped my two huge leaky 100/450 mallorys with my f&t type A's fine. The tremolo timpot is set as best it can be, with the mv low & vol max ( distortion ) the tremolo effect still becomes muddied & lost almost totally.. but Im sticking there: tweaking a mite either way & the clean sound tremolo is weakened. So be it.

In my photo above, there re two blue mallorys: these don't show any signs of leaking like the two huge silver mo-fos.. so is it essential to replace these too?

thanks for reading, SC

[Sea Chief]

Hi chaps. If I could pick up on a few minor things still to iron-out on this amp. It lookslike Im doing 1st service ever done since '76.

Ive recapped the two big 100/450 filter caps. Would the advice be to recap the 2x blue smaller caps on this board too, even with no signs of oozing leakage?

I also get a big drop in volume with the tremolo switched on, & the vol decreacing turning down "intensity" to nil around 2.. then back up to full volume dialing it the last bit to 0. Any ideas?

I also get a bit of distortion sort of occasionally 'leaking/ creeping' into the clean sound ( say mv 5, vol 1).. suggesting a minor issue.

Would be great to get this in tip top shape, close at the mo, but not quite there I think.

Thanks for reading, SC

[pdf64]

It the absence of suitable cap tester (ie that measures leakage and ESR), it seems reasonable to just shotgun replace all old electrolytic caps.
As the clipping stage is shared by both channels, it doesn’t seem feasible for distortion to leak inyo the clean sound.
Therefore the source of the distortion may be elsewhere, eg one or more of the speakers may have dome voice coil rub.
Check whether plugging into a different speaker cab eliminates the issue.

[Sea Chief]

It the absence of suitable cap tester (ie that measures leakage and ESR), it seems reasonable to just shotgun replace all old electrolytic caps.
As the clipping stage is shared by both channels, it doesn’t seem feasible for distortion to leak inyo the clean sound.
Therefore the source of the distortion may be elsewhere, eg one or more of the speakers may have dome voice coil rub.
Check whether plugging into a different speaker cab eliminates the issue.

Hi pdf.. yup that makes sense to me/ will do the other two blue ones in my photo, in the 'doghouse'.

Just two more lytics.. on the bias ( i think ) area. I wonder if the 12ax7 has any bearing on the tremolo? IE if so, & it has bearing on the vol distortion too, then might it signify the tube needs replacing?

Re. the " leaking" distortion occasionally dipping into the clean low ' vol' setting: as Im using the amp at low volume so far ( MV no more than 5, with vol say 2 ) it doesn't seem or sound like a speaker cone rubbing thing, to me.

The " leaking" distortion sound, is identical to the vol knob being at 8, rather than a rubbing or different distort. And its 'behind' the clean sound too, like the two sounds mixed, not a prominent sudden LOUD distortion happening at all. Its reasonably quiet in fact, but just sort of leaching in.

Thanks, SC

[pdf64]

Yup exactly thanks mr.dawg.. so the trem effect clean is great, turn up the vol/ turn down the mv ( distortion sounds great) & the tremolo effect is muddied to almost inaudible.

I think that’s normal, to be expected, due to the clipping stage being later in the signal chain than the point where the trem modulation is applied.
That characteristic might be used to be player’s advantage, in that at higher gain settings, the strength of the instrument signal seems to modulate the modulation
Somewhat akin to the ducking control of more complex fx units.
The trem depth of cranked non master vol amps such as 60s type Fenders does the same thing.