kgst

[sorenb]

I have made a spreadsheet here

I don't mind covering some excess ...

[UFN]

Good initiative, but it might be good if we could get a more realistic cost estimate first? Spritzers $10 ballpark is just the factory FOB-price, so some estimate on what would be the final price (including shipping/import costs and a small contingency) would make it more realistic.

If you commit to 50pcs the difference between $12 and $18 per unit suddenly matters

//UFN

[spritzer]

My price all in is around the 24$ mark if I'm lucky with customs.  If I'm unlucky then yeah.... it hurts. 

[UFN]

Yes, that's also one of the reasons I don't want to volunteer. The 25% VAT + additional duty and fees I would be asked to pay doesn't make a lot of sense to pay for the whole lot.

//UFN

[gepardcv]

Are these Alphas 50k pots?

[valve5425]

Hate to mention them here, but have you considered posting this on diyAudio site as well? A 1000's an awful lot of pots to shift and I guess you'd get quite a bit of interest there!

On a different note, some info here from Fairchild on heat sink mounting. (Apologies to those that have already seen it.) It includes optimum torque settings and differences between thermal grease/no thermal grease and washers/no washers. (Great if you're a bit OCD like me!) Recommended torque for the Aavid 7721-* washers is 0.565Nm to 0.678Nm (5.76 kgf.cm to 6.91 kgf.cm) which ties in nicely with the settings here for the TO-220(F).

Mounting packages-torques.pdf

[Pars]

What are these Alpha pots? Not one I'm familiar with...

 

I guess something like this?

http://www.alphapotentiometers.net/html/8mm_pot_4.html

 

Edited December 15, 2015 by Pars

[johnwmclean]

Pars,

Yes Alpha pots but not the one you referenced in the link.

The model is 3RP/2142G.

http://www.alpha-products.com/cd_catalog/new_catalogs/Pots/rotary/21mm/21mm%20rot%20pots_4.htm

[Pars]

Ahh, gotcha, thanks!

Why 50K? I might be interested in a 10K or 2. What is the general quality of these? TKD CP2500 realm? Better? Worse?

[valve5425]

Finished!!

Running at 375 volts, (I like to be different) and 10ma. 1K3 cathode resistors with the 1k0 trimmers.

42° C at the heat sinks (psu around 32° C) with the top barely getting warm, so no heat issues. PSU is actually putting out -377.37V and +376.16V when warmed up. There's less offset without the servo, around 200mv, so jumpers are out.

I've designed the chassis base to enable access to the boards from below. Also the brass valve platforms are removable, so balance and offset trimmers can be accessed without removing the full top cover.

Signal wiring is 4n silver foil, everything else 600V PTFE. Power lines twisted and heater wires run along the top of the chassis, so no hum. All grounds to star earth located near to the filtered mains in.

The volume control is an LDR kit (4 boards in the rear right hand corner) which I thought I'd try. I know the potential issues with these but it doesn't seem to be having any negative effects. I fancy playing around a bit more with LDR's to see if there's any mileage in them, but if I get bored with them I've got room for a conventional attenuator, so I'll see how it goes.

I know I said it was finished, well, almost. Just need to re-etch my relay/delay and 12V supply board for the LDR's which will slot in where the terminal blocks and small board sit next to the main psu board. Slight printing error, that I hadn't spotted, meant it had shrunk the image horizontally. Dooh!! TBH, it's not really needed, but it gives me something to do.

It's been 12 months from the design stage but well worth the effort. Oh, and did I mention that it sounds bloody fantastic? I guess that now I'll need to upgrade my SR-303's.

Thank you, Kevin Gilmore, Spritzer and anyone else responsible for the design of this amp. Now, did someone mention a T2?

 

[Blueman2]

Holy cow!!  That is a gorgeous build!!!  Freaking gorgeous!!!  Congratulations.  

I had not seen a build with quick disconnects for the tubes before.  Very cool.  Why did you go that route vs building the boards into the top directly?  Just curious as I embark on my very first build.  

Edited January 21, 2016 by Blueman2

[HemiSam]

Congratulations!  Serious artisanry involved and a whole lot to be proud of.

It's like a striking woman that just proves to be more beautiful the more you look....must stop.

HS

[valve5425]

Thanks Blueman2!

No reason really, just figured this would give best access to the boards without taking all the case apart. Also, I didn't like the idea of all those electrons upside down!

Good luck with your build.

3 minutes ago, HemiSam said:

Congratulations!  Serious artisanry involved and a whole lot to be proud of.

It's like a striking woman that just proves to be more beautiful the more you look....must stop.

HS

Cheers. Hmmm. I could send you some photos of it completely naked if you want?

Edited January 21, 2016 by valve5425

[kevin gilmore]

if people really want, I can probably flip the tubes to the other side to make stuff like this easier.

[valve5425]

I've slept on this and now recall that when I initially looked at designing the case, there was also the problem of heat sinking if I flipped the boards.

I did consider pushing the heat sinks through holes in the top cover but decided it would be messy. One solution of course would be to bolt the TO-220's directly to the top and fasten a fancy heat sink on top. (But then I guess if you wanted to use a 3mm copper lid, it would have sufficient mass to negate heat sinks!) Fastening directly also gives you the problem of having to re-seat the TO-220's every time you take the boards out for tweaking/repair.

Just a thought I had after I'd built this, was to place the 24V zeners on the bottom of the PSU board. (Wish I'd thought of it before I built!) As they are designed to blow if disaster strikes, then they would be easier to replace. If anyone's doing a re-design then it should be possible to position them on the outer edge of the board and not tucked between the heat sink and caps. However, with the current board, future builders may want to consider them underneath.

[wink]

Looks like the KGST MAY have some competition.......

http://knob.planet.ee/amps/staxneb1/staxneb1.htm

 

[HemiSam]

1 hour ago, wink said:

Looks like the KGST MAY have some competition.......

http://knob.planet.ee/amps/staxneb1/staxneb1.htm

 

Any internal shots, wink?

HS

[wink]

Nope, but you gotta love the engraved front and back panels.......... 

[valve5425]

Here are its innards!

http://knob.planet.ee/amps/stax/stax.htm

[HemiSam]

2 minutes ago, valve5425 said:

Here are its innards!

http://knob.planet.ee/amps/stax/stax.htm

Thanks, valve!  I'll stick to what I have...LOL

HS

[spritzer]

That one is a GES or some slight variation of that.  Those pencil tubes are kinda nice, they are what I used in my micro GES...

[charlo89]

Hi,

I can't find MPSW06G or 2SC2240 for my KGST can I replace it by a NTE128P ?

http://www.nteinc.com/specs/100to199/pdf/nte128p.pdf

Thank you

[JoaMat]

What is printed on the PCB - MPSW06 or 2SC2240?

[spritzer]

For the KGST, it should be both.  Try the MPSA..... 

[charlo89]

Thank you,

The MPSA will work fine ? it's the 625mw version of the MPSW, the  NTE128P has a fd of 850mw it's more closer to the 1W of the MPSW06.

I don't find many information and DIY use for the NTE128P. MPSA06 will be better ?