JE Labs 300b round 2! layout

[TubeHound]

Hello,

Well, the tranny's arrived in a timely fashion. Some shipping damage. Some of the laminations shifted, I called Jack at Electraprint and he said that I could loosen the bolts on the trannys and put them on a solid flat surface, gently put them back into shape. Seems ok to do this.

Ordered the copper plate (12.5"x 16" x .125") which leaves lots of room to manuver the various parts.

I have posted a pic of a temporary layout for this design. My question is, should the signal tubes be grouped away from the rectifier tube and the a/c mains input?

I know to orient the pwr and ot tranny's at 90 degs. to each other, the little one is one of two chokes for B+, the other one is small, so I will mount it underneath the top of the chassis. where can I buy a shield for the bigger choke? Hammond make some thing ?

Any way here is the pic, any suggestions? comments?

Thanks again

[fdegrove]

Hello,

Nice stuff you got there.

I have posted a pic of a temporary layout for this design. My question is, should the signal tubes be grouped away from the rectifier tube and the a/c mains input?

Yes,that is good practice.
Input close to front,work your way to the back where you can put on/off switch close to power inlet on one side and speaker connectors close to the OPT.
No need to shield the choke unless you're concerned with the look of things,you re doing fine.
You can also have a cage made out of sheetmetal to go over the grouped iron a la Audio Innovations.

Regards,

[Ciscokid]

Hi,

Good progress and cool looking parts. Tell me more about the meter? Where in the circuit will this go?

Best regards,
ck

btw, I finished up both my wood base's (five coats of tung oil). They look really cool. Picture soon (waiting on better camera).

[Brett]

The layout is probably fine. However when I used to build everything on one chassis (I use a seperate PSU chassis now), before I drilled holes for the power and OPT trans, I would power up the PS, and adjust the orientation between the two of them, and often the choke too, for minimum hum at the OPT. With the OPT not connected in circuit, check the primary and secondary on a DVM and/or a CRO for minimum 50/100Hz. Ninety degrees will probably be fine, esp with a PP amp, but a fine tuning of the position can kill a hum that you may not otherwise easily remedy.

Ideally I would complete the entire circuit, run it for a day, trim the hum with the cathode humpot, and then, tweak the positions of the tranny's for a null in the hum.

[TubeHound]

Hello,

ck,

Thanks for the compliment. Here is the email I recieved from Martin Bunjes, who lives in Amsterdam. Martin's JE 300B is featured in the last pages of Audio Illusion's website. Seems simple enough. Martin uses them as bias meters, I plan on doing the same. I do have two more brand new Simpson meters, but they say "micro amps 0-100 dc"
If you did not mine this and they can be used for milliamps, would you be interested in them? PM me if so, They were $73.00 US each.

Hello Paul,

Just hook them up after the 300B cathode resistor, between the resistor and ground. Yes, it shows the current through the tube and is a good tool to set the bias current. I'm in the process of re-biasing my amps right now because I want to use the TJ 300B meshplates wich have a lower maximum dissipation.
I'm curious how much hum you'll have left. I can't seem to get my amps below 5mV wich is too much for my liking. Please drop me a line when you have finished your amps.

regards
Martin

________________

Brett,

Jack at Electraprint had mentioned the same thing. Parting the PWR supply from the OPT supply is still an option. The connectors to achieve this are my main concern. Looking at amphenol type connectors. I have ordered the copper plate for the chassis and was told buy Jack that this was sort of a mistake. Copper is non-ferous metal and will allow RFI through. Steel would have been a better choice, he said. Aluminium is no better than copper, neither lends itself to a good grounding scheme. hmmm.



________________

fdegrove,

Thanks for the compliment and advice

[fdegrove]

Maybeim

If you did not mine this and they can be used for milliamps, would you be interested in them? PM me if so, They were $73.00 US each.

Putting a resistor in series with the input of the meter will make them usable for different scales.
You can than install a trimpot close to them so you have a visual oversight of what you're doing.
As a cautionary note: it is my experience that these meters are not always accurate unless some resistive recallibration is done,
so a comparative measurement with a decent DVM may be called for.

Thanks for the compliment and advice

My pleasure and enjoy your newborn,

[Brett]

Originally posted by maybeim
Jack at Electraprint had mentioned the same thing. Parting the PWR supply from the OPT supply is still an option. The connectors to achieve this are my main concern. Looking at amphenol type connectors.

I looked at the RS and Farnell catalogues (major parts suppliers here) and saw a number of different types and styles of locking connectors that would do the job and have the neccessary current and voltage ratings. Most were around $US10 - 15 each. Save some meoney, and make one end captive, ie no connectors, just a flying lead.

I have ordered the copper plate for the chassis and was told buy Jack that this was sort of a mistake. Copper is non-ferous metal and will allow RFI through. Steel would have been a better choice, he said. Aluminium is no better than copper, neither lends itself to a good grounding scheme. hmmm.

Here I disagree to an extent. The copper will allow a good grounding scheme, but will possibly let in RFI, esp if you're in an area that has a lot of it. Copper is also quite weak mechanically. If you decide not to use it, I'd be interested in buying it. Hard to get where I live, and no RFI.

Cheers
Brett

[fdegrove]

Brett,

You could get coppersheets from RS aswell last time I checked.

RFI shouldn't be a problem and I much prefer a copper groundplane over steel.

Here is what I do for chassis building:

Two oversized rectangularr aluminum sheets folded at the longer side to form a fitting double U.(one into the other)
The side I cover with wood boards cut to size.
Inside I fit a coppersheet the I mount on grommets,this plane serves as ground.
All kinds of finishing possible.
Nice and easy and good looking to boot,

Cheers,

[TubeHound]

Hello everyone,

Well, the copper plates are cut and all holes drilled,( did it myself). I need to finish the copper, polish. Any suggestion on how? I plan on putting a coat of clear laquer on them once there polished or whatever clear coat works best, any ideas here? Will post a pick if anyone is interested.

[fdegrove]

Hi Paul,

Give them a good polish with something like carpolish untill everything has a mirrorlike look.

Degrease everything afterwards with ether or other degreasing product such as isopropanol.

Then you can put a layer of transparent lacquer on it,polish when dry and repeat it till you have obtained a shiny finish.

You can than put it in a preheated oven at 180 degrees Celsius for about 10 minutes.

That should give you a good finish.

Cheers,