Rebuilding my M125s - can I use this cap in the SCM module?

I've started rebuilding my M125s as one has had some troubles.

I'm rebuilding the SCM module and the existing caps look fine except one has a very short lead I think from trying to stuff both on that 3 leg terminal strip the kit comes with.

So I've ordered two replacements that I thought would be pretty exact - along with a 5 leg terminal strip.





Both 330/400v/380LQ /85

But the old ones are 400WV and the new ones are 400V/450SV.

Will these work?

Thanks for the help.

Just about ready to start rebuilding.  

should work fine

tubes4hifi wrote:should work fine

Awesome - thanks very much!

The M-125 has about a 550VDC max supply, so you could have used 300V or 315V CDE caps and gotten more C and lower ESR in the same package.

Making some progress....

Seamus wrote:The M-125 has about a 550VDC max supply, so you could have used 300V or 315V CDE caps and gotten more C and lower ESR in the same package.

Thanks - I know nothing about that stuff - I just wanted to use exactly what it had in it - as the amps were always dead silent.

I might in fact use the old caps as I can get it to connect with the 5 lug terminal strip - I thought the lead on one might be too short - but seems ok as it does manage to touch the lug.

Caps have a finite life. Production quality keeps rising.

If you have the new caps, use them.

It's better to have a soldered mechanical connection than just a soldered connection alone.

Seamus wrote:Caps have a finite life. Production quality keeps rising.

If you have the new caps, use them.

It's better to have a soldered mechanical connection than just a soldered connection alone.

Thanks - that makes good sense. I'll use the new ones.

It is coming along nicely. I'm going to run the switch in the rear on the input up front.

That spaghetti stuff sure makes the exposed leads nice - I'm glad I ordered it.

Why not run the v2/v4 heater directly up from the PT?
Why the big heater loop between v2 & v4?
Why route v1/v3 heater out to the chassis thus creating a longer radiation length?

IMO, you are better off to run directly.

Twisted pairs crossing at right angles contamination will be next to zero.
Field generation is proportional to length, so the shorter the better.

Also remove the tie wraps around the yellow bypass caps.
You don't want to distort the cap shape.

Why the piggyback of the three caps?

Seamus wrote:Why not run the v2/v4 heater directly up from the PT?
Why the big heater loop between v2 & v4?
Why route v1/v3 heater out to the chassis thus creating a longer radiation length?

IMO, you are better off to run directly.

Twisted pairs crossing at right angles contamination will be next to zero.
Field generation is proportional to length, so the shorter the better.

Also remove the tie wraps around the yellow bypass caps.
You don't want to distort the cap shape.

Why the piggyback of the three caps?

Thanks Seamus - the heater lines were recommended - and made sense to me - to route along the chassis away from crossing any wires/components in the middle - and tightly twisted up to and on the bottom of the tube sockets. I'll find it if it makes any difference - but does seem very reasonable.

https://www.diyaudio.com/community/threads/heater-wiring-the-good-the-bad-and-the-ugly.211731/

And the 3 caps came with the kit - 11 years ago - and in the instructions says to tie them together. That's been like that for a while.

Thanks,

SCM module installed:

And here is my thread on this build at AK where I'm getting some great advice.

Thanks all!

https://audiokarma.org/forums/index.php?threads/yellow-paper-mod-vta-m125s-did-it-help-my-situation.985784/

We'll I've guess we've come to the end of our journey

.  The amp is now finished:



I'd say that is a huge difference from what I started with:



I definitely feel much better about the build and it works(3 hours of listening):



A little disappointment as there is some low level hum.  I'm not using the HumX devices - and they used to hum and that is why I bought the HumX devices many years ago.  I was hoping some of the changes would have avoided hum.  Anyhow - it isn't that bad and goes away with music playing.  

But I'm super happy with the results - so much better - I took my time and made sure all the wiring was free of burns etc - and super strong fittings - and spaghetti to make sure no open leads anywhere.  I'm much more confident of this build vs the old rats nest I had where I always felt that a push on the wires would result in an explosion.   This is going to be much more reliable.

Summary of changes:

Heater wires - tightly twisted and routed to the sides of the chassis (note there is a unavoidable heater wire set that goes to the driver board for the driver tubes) - I've twisted the crap out of it - but it is over the section with the components trying to avoid crossing - so no real way to avoid it with this amp.  Probably the original wire-routing would have been fine.

Input moved to the front (super short lead from the driver board) (ieLogical recommendation)

Chokes facing each other (ieLogical recommendation)

Used better wiring.   Ex 600V 16AWG to ground SCM caps vs 20AWG which comes with kit.  I used very little of the 20AWG solid wire as the Tefzel 18AWG/HTFE so much tougher and nicer to work with and higher rated for heat and 600v vs 300v.

Moved switch to rear (ieLogical recommendation)

Changed the power switch to switch on hot lead vs neutral.   Hot to tip of fuse.  Fuse to switch.  Switch to Transformer.   Neutral to Transformer.

New caps for SCM module (just replacement no improvement expected) - and SCM module grounded to Star.  Note the ground on the IEC is not grounded to the star - but to the corner by the power transformer bolt.

The top mount sockets are nice (Fender drop in) the KT88s now sit right on the black part of the socket - nice and flat vs on the screws.  I ordered these by mistake - glad I did (same brand as that of the kit - just top mount.)

Open to ideas to eliminate the low level hum.

Thanks!

16 awg wire is total overkill. It may also be adding small amounts of capacitance to the circuits. I might be wrong but bigger isn’t always better.

corndog71 wrote:16 awg wire is total overkill.  It may also be adding small amounts of capacitance to the circuits.  I might be wrong but bigger isn’t always better.

I only used the 16 awg - for the SCM ground wire to star - since the caps are rated at 450V and I figured 300v wire was undersize. The original terminal strip I had - grounded on the lug - this one doesn't - so I needed to wire the ground. The only other place is the IEC Hot lead to fuse.

So no 16AWG in the circuits.

rebellovw wrote:
A little disappointment as there is some low level hum.

What are the speakers?
What is the source?

How is system powered as far as AC connections?

Start with both amps with shorting plugs.
Power on each amp individually and note hum level. You can measure the voltage across the speaker terminals.

Any difference on either amp with both amps on?

Seamus wrote:

rebellovw wrote:
A little disappointment as there is some low level hum.

What are the speakers?
What is the source?

How is system powered as far as AC connections?

Start with both amps with shorting plugs.
Power on each amp individually and note hum level. You can measure the voltage across the speaker terminals.

Any difference on either amp with both amps on?

Thanks @seamus

Klipsch Cornwalls

Source Turntable through McIntosh C220 pre.  Source doesn't matter - hum remains when I change the source.

Usually each amp is plugged into the wall directly with the rack gear (TT,pre,CD) on a strip (I've also tried all plugged into the strip - no difference.)

As far as the amps being on - the old amp - after I took it off the HumX - I found it quiet.   I plugged in the rebuilt amp - and very low faint 60hz hum - and can now be heard through the other speaker on the other amp.   HumX helps but I don't want to use them.

These amps though have always had hum wether or not one introduces it - so nothing from the build - in fact I think it was worse - but just can't recall as I've done the ground lift 10 or so years ago to fix it - and bought the HumX devices to use permanently.   At this point I want safety vs silence - I've since ordered two GFCI Woods units to plug each amp into.

Thanks!

Klipsch Cornwalls

Source Turntable through McIntosh C220 pre.  Source doesn't matter - hum remains when I change the source.

Usually each amp is plugged into the wall directly with the rack gear (TT,pre,CD) on a strip.

As far as the amps being on - the old amp - after I took it off the HumX - I found it quiet.   I plugged in the rebuilt amp - and very low faint 60hz hum - and can now be heard through the other speaker on the other amp.   HumX helps but I don't want to use them.

These amps though have always had hum wether or not one introduces it - so nothing from the build - in fact I think it was worse - but just can't recall as I've done the ground lift 10 or so years ago to fix it - and bought the HumX devices to use permanently.   At this point I want safety vs silence - I've since ordered two GFCI Woods units to plug each amp into.

Thanks!



rebellovw,

If properly built, the VTA M-125's are basically silent with any average type speaker of 88 to 92 dB efficiency. Your Cornwalls are 102 dB efficient and will MAGNIFY even the smallest amp noise by about 10 dB over a 92 dB efficient speaker. My own VTA M-125's were tested by a friend of mine and they were found to have a noise level of about -95 dB. Here at my home with 89 dB speakers, I hear nothing at my listening position about 10 feet away from the speakers and the tiniest hiss if I place my ears literally on the grille cloth. Below is a link to a test done by VTA M-125 builder Ken Galer in which he measured a signal to noise ratio for one of his M-125's at -99 dB. This is exceptionally low noise for a tube amp.

M-125 residual noise level

If your amps were driving speakers of normal efficiency, you probably would notice any residual noise from the amp.

Bob

Bob Latino wrote:Klipsch Cornwalls

Source Turntable through McIntosh C220 pre.  Source doesn't matter - hum remains when I change the source.

Usually each amp is plugged into the wall directly with the rack gear (TT,pre,CD) on a strip.

As far as the amps being on - the old amp - after I took it off the HumX - I found it quiet.   I plugged in the rebuilt amp - and very low faint 60hz hum - and can now be heard through the other speaker on the other amp.   HumX helps but I don't want to use them.

These amps though have always had hum wether or not one introduces it - so nothing from the build - in fact I think it was worse - but just can't recall as I've done the ground lift 10 or so years ago to fix it - and bought the HumX devices to use permanently.   At this point I want safety vs silence - I've since ordered two GFCI Woods units to plug each amp into.

Thanks!




rebellovw,

If properly built, the VTA M-125's are basically silent with any average type speaker of 88 to 92 dB efficiency. Your Cornwalls are 102 dB efficient and will MAGNIFY even the smallest amp noise by about 10 dB over a 92 dB efficient speaker. My own VTA M-125's were tested by a friend of mine and they were found to have a noise level of about -95 dB. Here at my home with 89 dB speakers, I hear nothing at my listening position about 10 feet away from the speakers and the tiniest hiss if I place my ears literally on the grille cloth. Below is a link to a test done by VTA M-125 builder Ken Galer in which he measured a signal to noise ratio for one of his M-125's at -99 dB. This is an exceptionally low noise level for a tube amp.

M-125 residual noise level

If your amps were driving speakers of normal efficiency, you probably would notice any residual noise from the amp.

Bob

Thanks Bob!  Hope you are enjoying your retirement.  Yes - it isn't too bad at all and when music plays I don't even notice it.  And it was very quiet when I tested it on a small bookshelf speaker.

Thanks again!

I had residual hum that went away when I replaced my metal PCB stand-offs with nylon.  The nuts securing PCB had scraped away solder mask exposing and creating continuity to chassis with what I’m pretty sure is copper ground plane trace on the driver board.

See post #11 on this thread for photo:
https://dynacotubeaudio.forumotion.com/t4721-coupling-cap-substitutions

vtshopdog wrote:I had residual hum that went away when I replaced my metal PCB stand-offs with nylon.  The nuts securing PCB had scraped away solder mask exposing and creating continuity to chassis with what I’m pretty sure is copper ground plane trace on the driver board.

See post #11 on this thread for photo:
https://dynacotubeaudio.forumotion.com/t4721-coupling-cap-substitutions

Awesome - thanks very much I'll look into that.  So the idea here might be to replace the stainless steel screws, 2 keep nuts - and the final nut with all nylon counterparts. That would be an easy swap out.

I'll give it some thought.

Thanks again.

one of these days in the future those metal caps on the driver board are going to short something out.
They should be covered with shrink wrap or electrical tape.

tubes4hifi wrote:one of these days in the future those metal caps on the driver board are going to short something out.
They should be covered with shrink wrap or electrical tape.

Thanks - that is a really good idea. The leads are covered in shrink tube - but the big metal bodies are exposed - I'll wrap them in electrical tape.

Thanks again!

tubes4hifi wrote:one of these days in the future those metal caps on the driver board are going to short something out.
They should be covered with shrink wrap or electrical tape.

What metal caps?
c14&16 exposed metal is 0 volts.

There are many HiPot points on the resistors r 12, 14, 16, 20, 22

Can you be more explicit?