[denverartist]

Started assembling my Cornet 2 on the workbench. Not all the parts have arrived but I decided to get going on it!  Taking it slow and double checking my work. Man, this is fun!

Mostly stock parts, with a few 'special' bits.

- Pete
Denver

[mingles]

Are those K40's in C203? Nice! Where did you get them?

[denverartist]

Here's where I am today. The hole cutting was hard.  The K40s came from a guy in Ukraine (eBay). I bought 10 for my Scott 299D, used 8, so I had these 2 .1uf caps coincidentally.

Man, it's a false economy to try to make one of these Cornet 2's without the Lansing enclosure (unless the builder was a die-hard woodworker).  It fits so nice.  But I am not using the IEC plug.

Pete

[taskerc]

Hey Pete - taskerc here - looks good!

I agree on the metalwork, but it looks like you did a good job - I struggled with the hammond chassis and broek down and got the Lansing - I also invested in some chassis punches which made hole cutting ridiculously easy - especially for the impatient like me

Hopefully you get the grommets soon unless homeland security reclasses them into something sinister .....

Enjoy the project!

taskerc

[Big Jim]

I don't see what's so hard about using the Hammond chassis. I did for mine and heck, I put it in, pulled it out because I didn't like the green LED glowing like that all the time. I wanted red because all the other lights in my system are red LEDs. No problem with the Hammond at all. Maybe mine was a bit bigger than the typical Hammond. Whatevs, as long as you get the PCB in and running right.

Listening right now and can't stop smiling at the sound.   

[taskerc]

Hi Big Jim - my hammond was the 2" tall case and the PCB would not fit in unless I removed most of the end panel tab/ledge material - which would mean no end panel retaining surface unless I then (after installing PCB) added a small L clip or something to provide end support to the panel.

The Lansing case specified in the Cornet parts list is a good bit taller and since the lansing had removeable sides, all PCB mounting pain was history.

I think a 3" hammond would do it since it then provides more wiggle room.

taskerc

[denverartist]

Here's my finished Cornet 2. This was (is) a fun project.  It is working great. Voltages are very near spec.  I can't claim to have had success because I am great DIYer (I'm not) but because I double- and triple-checked everything as I worked. I have a vintage British 5AR4 rectifier, a lousy 12AU7 until my (hopefully) good 5814 arrives, and using Telefunkens in the 12AX7 positions.

I do have a bit of hum, not that noticeable, certainly not when music's on. I wonder if my hard-wired cord had anything to do with it.  I notice on this forum, when people have trouble with their Cornets, it's because they deviated from the original design.  The only different component I have is a 1.5 ohm Mills resistor for the heater filaments circuit, bringing that up 6V.  I have Kiwame in the 220ohm signal path Rs.

Top is painted with a metallic black, to match my Rek-o-kut N33H turntable top (a restoration).
I think the sound is improving by the hour.

Pete

[taskerc]

Well done Pete!

I stuck to standard and still have a small hum - it was far more noticeable when I was using my Low Output DL 103, but as you say, during music it is not an issue.

taskerc

[mgalusha]

Very nice Pete! I think the hum also depends a bit on the cartridge. With a Grado Reference Platinum mine hummed pretty bad and no amount of tinkering with the grounding cured it. However with the current Scheu/Benz cartridge it's dead quiet unless I peg the volume and then it's a very low tube rush.

Note mine is an original Cornet. It's possible the cartridge loading could affect the hum as well. Not sure if the Cornet 2 has any facility for changing this short of swapping resistors but it may be worth trying.

Again, very nice job. Congrats.

Mike

[mingles]

Pete, where did you pick up the vintage British 5AR4 tube?

[denverartist]

The 5AR4 is a Mullard, labelled GE, that I got from an eBay seller - very cheap for a Mullard, now I know why (it buzzes), but it does work okay.  Voltages are way low when using a good-testing vintage 1959 GE 5Y3 recifier tube.  With the 5AR4 I am within 1-4% of spec voltages, and it warms up slow. Not bad - attributable to the excellent design.

Thanks very much, Mike G. I will try other turntables and cartridges. I am about to trade for a Grado wood body cartridge - hope it works okay in my system.

Besides the ROK, I also have Rega Planar 3 (generally not good w/ Grado, but I've never tried it myself), and an Ariston RD40 TT.

I have Amperex I can try in 12AX7 positions.

Thanks to all,
Pete
 


(I hope someone can help Sr. leitmo with his voltage issue - that was what I feared most. Now I feel lucky!)

[tubesforever]

I suspect that your RCA's, either the grounding post of the rca or the cable you plug into it might be grounding to the chassis. 

This is the most common source of hum.  Carefully inspect this area of your Cornet2.  It is easy to forget you are creating a big ground loop unless the rca is floating on the chassis. 

Also make certain the ground of the rca cable does not touch the chassis in any way.  I helped find a similar hum on a friends Cornet2. 

Also, I am using shielded braid over my AC lines going to a front mounted lighted switch.  I connect the shield to the earth ground. 

No hums from my Coronet2.  It is dead silent.  .

[tubesforever]

Important note.

If you check continuity on any of your RCA grounds to the phono earth ground post you should have a dead short.

Any continuity and the hum is because of the RCA's.  I had one of mine touching.  I just had to loosen the nut recenter it and tighten it back down.

I noticed you are floating your Transformer and I am doing the same on mine....  Did you remove the ground wire behind the back cover and run this to your earth ground?

Finally on my power cord, I run the earth ground directly to the phono ground and then run all grounds out from this single point.  This will establish star grounding and might help eliminate ground loops.

Both my Clarinet and my Cornet2 are dead silent.  I do get a trace amount of hum from my SUT which is more effected by its physical placement than anything else.  When I hear a hum I just move it or angle it to reduce the effects from stray fields.

Cheers!

[denverartist]

Here's a picture of my Cornet 2 underneath. Nothing that fancy. It works great - not too concerned with the slight hum, which only manifests itself past 12 on the volume control.  The hum diminished somewhat after tightening the RCA jacks. Though installed very tight, the nylon washers compress and they get a tad loose from plugging ICs in and out.

Thanks for suggestions.
All grounds are as they should be. Continuity where there should be continuity, no shorts between inputs and grounds.  Transformer isn't really 'floating', it's attached firmly underneath chassis, grounded to alloy top.  It was probably pointless of me to use rubber washers there. No worries.

Pete

Scott 299D amplifier - restored
JM Lab Cobalt 810

[tubesforever]

I meant that from a grounding standpoint the trannie is floating.  Even if you ground it to the casework it is still a mess.

The wire that Hammond describes as gray has been black on both my units.  It is terminated in a o-terminal and grounds the Trannie to trannies case.

I am using rubber footings as you are and I simply cut off the O-terminal and soldered on a longer ground wire.  I take this straight to the ground post near the RCA input jacks. 

Again, my incoming earth ground (center lug) goes first to that ground post.  Then everything is star grounded from that point. 

If you do this your hum might disappear.

If you have the trannie grounded to the top cover or straight to the board, you can create a ground loop.  It is best to run everything from a single ground point.  This eliminates a bunch of headaches.

You mentioned that the hum went down when you tightened the RCA jacks.

There is a definite possibility that the jack is touching the casework.  There should be a 1/16 inch clearance all the way around the jack.  The nylon washer sets have one with a relief that positions the RCA in the center of the hole.  If you do not have these positional reliefs then you can wrap the jack with teflon plumbers tape until the tape is thick enough to center the RCA.  Use a knife to cut back the teflon where you need to catch the threads.  This will insure you are floating the RCA's.

My friend drilled his case with too small a drill.  He was not able to properly engage his relief. He had to increase the size of the hole to allow the clearance for the step to postion the nylon washer.  Now his Cornet2 is as dead silent as mine.

Hope this helps!  It is hard to think about all this stuff without seeing it up close and personal.