Music Man 410-65 Service.

[Sea Chief]

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 modulates 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.

So the tremolois only ever expected to be useable with a clean sound then? I have a twin reverb, but of course cant get it to distort without giving myself a 'downstairs prolapse'.. nor ever dime my deluxe reverb I built, to see how the trem acted with distortion there either.

[pdf64]

It’s just the nature of overdrive, ie that it tends to maintain a more steady signal level, the quiet bits are brought up to the same level as the loud bits. Thereby counteracting what the trem did to the signal.

[Sea Chief]

It’s just the nature of overdrive, ie that it tends to maintain a more steady signal level, the quiet bits are brought up to the same level as the loud bits. Thereby counteracting what the trem did to the signal.

Hi pdf. So a super reverb/ dr/ pr etc have the same effect? Once volume dimed, the tremolo is swamped & effect pretty much unheard?

Anyway, back to the servicing of my lovely amp. The 'other two' caps in the doghouse, blue mallory 20/450. Now f&t nearest are 22uf 500v. Any issue?

Thx sc

[Sea Chief]

Chaps, i have 4 silver 'lytics in two " pairs ", close to the power stage/ transformer ( one pair in the bias area, next to a trimpot?).. but which don't show the usual uf value on. Voltage is seen (50v). They have made in mexico on, so Im wondering if they're sort of average/ generic lytics, & possibly 150uf, as this number '150' is seen on them.

I also have a single 150uf/ 50v, a different type a sprague orange, similar area of amp. Not quite so easy to find a replacement.

Any suggestions for the value of the 4x similar silver ones? And any recommendations for replacing these?

Schematic (2275-65) https://www.thetubestore.com/lib/the...-Schematic.pdf

Unfortunately I cant add a photo of my amp inside.. no idea why.. but I did add it on my other thread, here..

https://music-electronics-forum.com/...rem-prob/page2

Thanks for reading, SC

[pdf64]

Hi pdf. So a super reverb/ dr/ pr etc have the same effect? Once volume dimed, the tremolo is swamped & effect pretty much unheard?
…

Yes, trem is turning the vol level down and up, the overdrive brings everything up.
If you go to a music shop and tinker with trem and overdrive pedals, you’ll see that overdrive then trem produces the expected trem effect, trem then overdrive results in the significant diminution of the trem effect that you have noted.
You’ve found out why fx loops were seen to be beneficial for amps with overdrive preamps

[Sea Chief]

Yes, trem is turning the vol level down and up, the overdrive brings everything up.
If you go to a music shop and tinker with trem and overdrive pedals, you’ll see that overdrive then trem produces the expected trem effect, trem then overdrive results in the significant diminution of the trem effect that you have noted.
You’ve found out why fx loops were seen to be beneficial for amps with overdrive preamps

Hi pdf.. ok understood thanks. Good so that rules out a major problem with the tremolo then. The trimpot seems to 'shift' a bit, a minor thing I hope to iron out.

Ive just posted regarding mystery caps, could you shed any light?

Ive put links to the schematic & my pcb amp photo again.

Cheers, SC

[pdf64]

It seems reasonable to replace all vintage electrolytic caps.
150uF seems a likely value, unfortunately the schematic isn’t legible to that detail.
220uF 100V long life would be suitable replacements.

Also replace the beefy power supply dropper resistors with modern even beefier metal oxide flameproof types, mounted up away from the board, as noted on the other thread.

Those old CC types could ruin the board / amp if they fail.

[Sea Chief]

It seems reasonable to replace all vintage electrolytic caps.
150uF seems a likely value, unfortunately the schematic isn’t legible to that detail.
220uF 100V long life would be suitable replacements.

Also replace the beefy power supply dropper resistors with modern even beefier metal oxide flameproof types, mounted up away from the board, as noted on the other thread.

Those old CC types could ruin the board / amp if they fail.

I think i do i fact see four 150 uf capacitors just eligible in the schematic, buried so not so easy to spot. So I think I can assume these 4 mini silver " made in mexico" caps on the pcb are indeed 150uf, finding this & with your reply above.

But are these four just generic types needed here?

[pdf64]

5 caps would be much better, the bias supply is absolutely critical.
Dunno what is meant by generic in this context?
I suggest a long life type, eg >= 10k hours.
EDIT Not so easy to source, maybe consider https://www.mouser.co.uk/ProductDeta...P%2FRDfQ%3D%3D

[Sea Chief]

5 caps would be much better, the bias supply is absolutely critical.
Dunno what is meant by generic in this context?
I suggest a long life type, eg >= 10k hours.
EDIT Not so easy to source, maybe consider https://www.mouser.co.uk/ProductDeta...P%2FRDfQ%3D%3D

What I mean by generic is, I see 5x caps of 150 uf value. One is different, on its own board, made by a mfr I know, & see in high end tube amp builds Sprague usa ( the orange one in my pcb photo ). The other 4 are all identical, have no mfr name on just ' made in mexico'. I would assume then (this is just my hunch) that these 4 are not as good quality ( if they are unbeanded, primarily ) because, perhaps, they don't necessarily -need- to be, doing whatever duties they do. This is what i mean by a ' generic ' cap.

A good eg of a genetic cap might be the ubiquitous blue 'alcap' electrolytic found in speaker crossovers. Half decent. Do the job.

So do I concentrate on replacing the single orange sprague, with as decent as I can get... & just put in anything half decent for the other 4x 150/50 ?

If these values are not easily found ( rarely do i find any at the mo ) my choices then are very limited.

thanks SC

[Sea Chief]

It seems reasonable to replace all vintage electrolytic caps.
150uF seems a likely value, unfortunately the schematic isn’t legible to that detail.
220uF 100V long life would be suitable replacements.

Also replace the beefy power supply dropper resistors with modern even beefier metal oxide flameproof types, mounted up away from the board, as noted on the other thread.

Those old CC types could ruin the board / amp if they fail.

Could you identify the 'power supply dropper resistors'? Sorry my amp knowledge isnt sufficient even googling these words & trying to figure out which they could be would take me hours, without being fully sure.

Thanks if so, SC

[Sea Chief]

Chaps, could anyone help me identify the power supply dropper resistors ? If mentioned by pdf they're 'beefy' I think this means a higher wattage than the regular 1/4 or 1/2 w types, & ( i think is usual if higher power than 1/2w) actually labelled on the schematic. Eg 10k 10w.

Thing is Ive scored the schematic & find:

one 1.5k on its own @ 10w (r63). Between filter caps & pins 4 of power tubes.
two 620 r @ 2w (r44, r46). I think this might be the rectifier area.
two 3.9r @ 1w (r56, r61). Seem to be between pins 8 of the power tubes.

Pdf's info being plural suggests at least two.. so maybe i can narrow it down & discount the single 1.5k 10w? Unless I have missed a second one making a pair, though 10w is indeed ' beefy '.. so maybe it is just this one-?

Thanks, SC

[Sea Chief]

Schematic again here. https://www.thetubestore.com/lib/the...-Schematic.pdf

The 1st one seems to have the 7025 PI tube, like mine.. but difficult to dicipher the print.

The 2nd one replaces this 7025 with a LM transistor.. readable print.

I hope it would be likely all is the same, for the caps & R values I need to identify & replace specifically, between theses two schematic versions.. apart from the tube subbed for a transistor.

Thanks SC

[pdf64]

What I mean by generic is, I see 5x caps of 150 uf value. One is different, on its own board, made by a mfr I know, & see in high end tube amp builds Sprague usa ( the orange one in my pcb photo ). The other 4 are all identical, have no mfr name on just ' made in mexico'. I would assume then (this is just my hunch) that these 4 are not as good quality ( if they are unbeanded, primarily ) because, perhaps, they don't necessarily -need- to be, doing whatever duties they do. This is what i mean by a ' generic ' cap.

I think you may be assuming / inferring too much. My guess is that the boards were made at different times and a different batch of caps was being used to populate the boards.
My previous suggestion to replace all ecaps still stands, depending on the failure mode, any might cause big problems / damage when they fail.
Its just the the bias supply is most critical and is often overlooked.
And actually, 2 of the ecaps on the main board deal with the negative voltage supply, which the bias supply takes a feed from. So when they fail, the bias supply would, or at least might, be affected.
If maintaining an amp you wish to keep for the long term, how could it possibly be in your interest to penny pinch?

Chaps, could anyone help me identify the power supply dropper resistors ? If mentioned by pdf they're 'beefy' I think this means a higher wattage than the regular 1/4 or 1/2 w types, & ( i think is usual if higher power than 1/2w) actually labelled on the schematic. Eg 10k 10w.

Thing is Ive scored the schematic & find:

one 1.5k on its own @ 10w (r63). Between filter caps & pins 4 of power tubes.
two 620 r @ 2w (r44, r46). I think this might be the rectifier area.
two 3.9r @ 1w (r56, r61). Seem to be between pins 8 of the power tubes.

As far as I can make out, yes to all the above. Though I can’t read component references on the schematic.

[Sea Chief]

I think you may be assuming / inferring too much. My guess is that the boards were made at different times and a different batch of caps was being used to populate the boards.
My previous suggestion to replace all ecaps still stands, depending on the failure mode, any might cause big problems / damage when they fail.
Its just the the bias supply is most critical and is often overlooked.
And actually, 2 of the ecaps on the main board deal with the negative voltage supply, which the bias supply takes a feed from. So when they fail, the bias supply would, or at least might, be affected.
If maintaining an amp you wish to keep for the long term, how could it possibly be in your interest to penny pinch?


As far as I can make out, yes to all the above. Though I can’t read component references on the schematic.

Hi pdf. Thanks, points taken. Its not a q of penny pinching, more a q of putting in as close I can to what was there before ( just seems most sensible ).

The single orange sprague ( i have a hunch this might be the bias supply board?) is clear to see, to replace like for like. But the others.. well if two are next to a trimpot, & I know the other one is trem trimpot, then this suggests its a bias adjustment trimpot.. so.. the caps bang next to it, are bias caps?

When you say replace these two, &/ or the other two, with different values, it doesn't compute/ I don't quite understand.

What about the idea of just buying 5x sprague 150/50 (dims Ive checked similar to the pcb ones) & replace all these the same-? Costly. But if that's my closest choice ( of the same value that is ) does that seem a sensible idea maybe?


thx SC