yamaha t50c hum

[chopstuck]

Roberto,
Thanks for the T50 mod info and I have started them.

I just have a few questions on the terms in the mods,
just to be clear.



- 1st and 2nd OD channel's coupling caps from 22n to 4n7
Is this V2 a+b or V1a + V2a

-
- sostituire la resistenza da 5M6 con la coppia 1M//270pF
My Italian not so good but I figure that's the 5M6 dropping resistor off the plate of V1b right ?

- 470pF snubber caps on 2nd and 3rd lead gain stages-

So would you add snubbers from the plates of V2 a+b through the cathode to ground ?
I mounted them on the V2 socket pins from pin 3 to both 1 and 6 so they have an easy path to ground through the cathode cap.

- 470k 470k voltage divider before the 3rd lead gain stage
- Is that V2b or V3a ? They both seem to have dividers already.


- substitute the 39k NFB with 47k plus 100k//4n7
Is the 47k in series with the (100k/4n7) in parallel ?

The majority of the mods are done and It has really transformed the amp so far.

Thanks again for sharing your info. This is much easier than a total rebuild and it has been teaching me a bit about the effect of the individual changes.

[Marioverkill]

Hey Chopstuck,

Glad you are trying these mods.We will be able to compare.I haven't forgot about doing a clip.I purchased a new computer,interface,recording software and am trying to get all of this setup.I also purchased an oscilloscope.I have the amp sounding pretty good.It still has a small amount of that ringing after it warms up.I was hoping to solve this before sending you a clip.

How do you like the effect of the mods on your amp?

Mario

[chopstuck]

I like the smoothness of the snubbers and the decreased flab with the smaller coupling caps.
I can turn up the lead gain now. Couldn't before, it would just turn to one note of bubbling bass.

Marc

[Marioverkill]

Did you install choke and bigger filter caps as per Soldano? These really tightened up the low end.

Mario

[chopstuck]

Yes, the PS mods reverb mod and choke were done by Soldano. Although the PS caps were upped to only 100 mfd each.

Since the first gain stage is shared by both channels I'm not clear on which stage is "third lead" etc.
I also wold like to see how to change the nfb resistor with the paired cap/resistor.

[Marioverkill]

I installed a Dept mod(resonance mod).This give you control for nice low end.It is easy to install and reversible.I used the 2nd speaker jack for the pot.Let me know,I can send a pic if you want.

Mario

[chopstuck]

Yes please, post a shot of your depth mod.

[Marioverkill]

Resonance mod pic.

[Marioverkill]

Chopstuck,

I also changed the speaker.Mike Soldano told on a phone conversation that the amp was designed with V30's in mind.I put in an Eminence Governor(similar with less shrill).This make a HUGE difference in sound with this amp.Good or Bad is up to you.

Mario

[stephenl]

I picked one of these up a while back in a pawn shop for cheaps, it had a similar hum issue.
I'd have to take look at the schematic again, but I think the OT secondary was grounded through a non-insulated speaker jack - in this case the jack was loose. I re-did the grounding including moving the OT ground to the screen Supply filter cap ground.
I also re-capped it, put in higher wattage screen resistors, and a new bias pot. There are a few mods floating around as well.
It was a pretty good sounding amp after clean up. I ended up selling it on ebay for a decent profit.
I think I have schemos and mods I can dig up if your interested.

Edit: I should have read the whole thread before posting - looks like many of the mods have already been posted.

[chopstuck]

Roberto, I have tried a few speakers with it and have to say thay make a huge difference.

Seems most of the midrage comlexity is lost with a flat speaker like a EV12l or an Eminence Delta Pro 12. The V30s seems to make everything sound the same and shrill too.
My pair of Celestion G12 65 have a midrange hole with this amp.
My current fave for this amp is the Celestion G12-85K. Nice midrange, smooth top and dirt cheap too. I think they come from old Peavey 4x12 cabs.
I got a set a while back for $25 each .......and bulletproof too.

Topologywise, I had some time to look over the Soldano X-88 Preamp.(I hope that's the right model,) and the hi gain and clean channels are really similar to this Yamaha amp.
Of course this combo amp has the tube driven effects loop and reverb but otherwishe it's almost the same with just some substituted values.

Some of these are similar to the mods posted, others are not.

Has anyone tried doing an exact coppy of one of these channels in this amp? The clean side is easy enough to mess with. But of course people mod stock Soldanos too. I'm not sure if its a lateral move. Mabe your mods are a mod of the proper purple Soldano circuit ?

[Marioverkill]

Hi everybody !

Been busy all summer.I did a quick clip of the noise the amp makes when playing single notes.The "ringing",extra note is also there on the clean channel.I apologize for the racket,when I played chords on the drive channel,the volume was too high for the camera mic.Turn down your speakers or headphones before playing the clip.You can hear the sound on the single notes of the clean in the beginning and the single notes on the drive.I was trying to show the drive channel but failed !!!I will make another clip later of the drive channel....
Any suggestions welcome as to what is causing this annoying lower note.Again,this is only after the amp is on for about 20-30 minutes.

Thanks
http://www.youtube.com/watch?v=955XZR1Dkfk

Mario

[roberto]

Sorry for my late reply, I've not seen your posts.

Roberto,
Thanks for the T50 mod info and I have started them.

That's good, I'm sure you'll enjoy them, maybe with some small variation to fit them to your tastes, but you'll notice a more dynamic amp, that sounds really good in the mix of the band.

- 1st and 2nd OD channel's coupling caps from 22n to 4n7
Is this V2 a+b or V1a + V2a

It's V1a + V2a. I call V1a both 1st lead stage and 1st clean stage, because it's both.

- sostituire la resistenza da 5M6 con la coppia 1M//270pF
My Italian not so good but I figure that's the 5M6 dropping resistor off the plate of V1b right ?

Sorry, I made a Ctrl+V from an italian forum n which I suggested the same mods to a guy with the same amp and same problems you noticed. Yes, change the 5M6 after V1b to 1M//270pF.

- 470pF snubber caps on 2nd and 3rd lead gain stages
So would you add snubbers from the plates of V2 a+b through the cathode to ground ?

Across the plate resistors of those gain stages (V2a and V2b). It's just a starting point, I prefer something less on 2nd stage.

I mounted them on the V2 socket pins from pin 3 to both 1 and 6 so they have an easy path to ground through the cathode cap.

You can try also this way, of course!

- 470k 470k voltage divider before the 3rd lead gain stage
- Is that V2b or V3a ? They both seem to have dividers already.

It's between V2a and V2b.

- substitute the 39k NFB with 47k plus 100k//4n7
Is the 47k in series with the (100k/4n7) in parallel ?

Yes, then you can raise the 47k to something more if you like. I prefer a more free power amp. Instead of the 100k//4n7 you can install a 1M log pot as depth mod, of course.

The majority of the mods are done and It has really transformed the amp so far. Thanks again for sharing your info. This is much easier than a total rebuild and it has been teaching me a bit about the effect of the individual changes.

That's good. This is basically what I've done in my first yahama, then evolved in what is now my "classic" amp.

[roberto]

Roberto, I have tried a few speakers with it and have to say thay make a huge difference.

Absolutely, and that combo is not very well built, so a 2x12" or 4x12" cab is even better.

Seems most of the midrage comlexity is lost with a flat speaker like a EV12l or an Eminence Delta Pro 12.

Yes, I've not modded this amp with those speakers in mind.

My current fave for this amp is the Celestion G12-85K. Nice midrange, smooth top and dirt cheap too. I think they come from old Peavey 4x12 cabs. I got a set a while back for $25 each .......and bulletproof too.

Exactly. I've a 4x12" Peavey XXX cab, a 1972 London city cab and a 2x12" cab with tonetubby. I test my amps with those cabs (a cheap standard one, an old fat one, and a sparkly one).

Topologywise, I had some time to look over the Soldano X-88 Preamp.(I hope that's the right model,) and the hi gain and clean channels are really similar to this Yamaha amp.

Yes, but layout, components and circuit differences make the two very different.

The clean side is easy enough to mess with. But of course people mod stock Soldanos too. I'm not sure if its a lateral move. Mabe your mods are a mod of the proper purple Soldano circuit ?

Well, I'm a mod(erator) on sloclone forum, so of course I've "studied" some mods to that preamp too, but the mods I've told you comes from my first yamaha T100 some years ago.

[roberto]

http://www.youtube.com/watch?v=955XZR1Dkfk

It's a private video, I can't see it.