HoSo56 & 5879 OD and Dual Pentode amp ideas

[tubenit]

I don't currently have a good photo of the top of the chassis with the PT and OT and choke mounted

I've used a cheapo Harbor Freight knock out punch kit for over 10 yrs on all my chassis blanks.  I paid about $20 for it brand new

http://www.harborfreight.com/catalogsearch/result?q=metal+punch+

Paul, if you are using a tube rectifier,  I don't think you need a standby switch.

[Paul1453]

Thank you!   

Working on my cardboard layout design tool.  LOL

I'm also trying to see if I can use one of my cap cans on this.

So I tried to make a PSU simulation with my parts.
What do you think?  Am I straying to far off the path?
I will likely eliminate the Standby switch.  ;^)

Best regards,

[tubenit]

Paul,

I have no idea how to read the PSU sim?  You're talking well above my knowledge level. Maybe Pete or Sluckey can weigh in on this?

I've always just made a guess on stuff like that, then built it, then measured voltages and then adjusted if needed.

With respect, Tubenit

[Paul1453]

So I made a cardboard cutout of the 20"x8" chassis you used.

I needed something like that so I could put my actual parts on it and trace around them to see how they fit.
My PT and OT both need a big hole cut and will intrude on the space available inside the chassis.
I had to make sure that there would still be space available for my PS and Component boards.
They appear to fit, but there is not much room to spare.

My choke will mount topside, and directly below it is where I plan to mount the PS components.
I also have a number of cap cans I could potentially use.
Unfortunately, none of them are the exact values specified.
I have one nice big can with values of 120uF 40uF @ 450V.
If I could use that, it would free up some space under the choke for the rest of the PS parts.
I modified the PS design on PSU implementing the part values I have in stock to use.
I was concerned about the big increase to 120uF on the 1st cap.
With those values, I get a warning about exceeding rectifier current levels when the current ramps up to max values after 5 sec.
I have penciled in 2 potential locations for a cap can.
Getting these major components placed properly will be critical to my chances of completing a successful build. IMO

I appreciate any feedback or guidance y'all care to offer.   
Thank you and Best Regards,
Paul

[tubenit]

Paul,

Look up the max capacitance for 5V4 and GZ34 tubes.  IF you are saying three caps of 40uf each with a combined 120uf total, then I think you're OK.  IF you are saying the first cap alone will be 120uf, then I think you have a problem.

You could use 120uf for a solid state rectifier, I think?

I would center the PT and OT in the middle of the 8" as much as reasonably possible rather then have the OT be somewhat off center from
the PT.  I say this because I tested the noise level on an OT positioning once.  And because if you look at the chassis PT & OT locations on
most Marshall amps and Marshall clones, they are fairly centered next to each other.

With respect, Tubenit

[Paul1453]

I guess that the Data Sheet is telling me 60uF is max, I wasn't sure of that.

Probably why you have put a 50uF as the 1st cap in your design.
Thank you. 

Back to my box of new cap cans to see if I can find a better choice.   

[Paul1453]

Centered, spaced 1" apart.
New proposed 50/50uF 450V cap can location.
The rest of the PS components go underneath in that general area.
Choke in proposed orientation, or should it be rotated 90' CW?
There seems to be adequate space for the turret board and internal wiring like this

[tubenit]

I think you're fine with the layout and trannie positions.

With respect, Tubenit

[sluckey]

If you put four 1/2" x 3/4" x 3/4" L-brackets (from Lowes) on that OT, you can stand it up for more versatile layout options. Like this...

     http://el34world.com/Forum/index.php?topic=19557.msg203903#msg203903

[Paul1453]

Thanks guys!

Trying to visualize the insides from my model now.

This is my initial take on proper placements.

Wondering about my PS parts and 26-28 parts placements.
It seems the PS parts might also be able to rotate 90' and move more above the PT.
Then the 26-28 board section?
It feeds through the PPIMV to the 6L6s, so I'm not convinced about my proposed placement.
The main component board could be placed at an angle, creating a little more space between it and the can for 26-28 to go.

I'm really trying to get a grasp of these layout issues on a high gain amp like this.
I'm also trying to comprehend the differences in layout between rectangle guitar amps and square PA/Organ amps.

[Willabe]

If you place the eyelet/turret board there the grid wires going to the preamp tubes will be kinda long.

[PRR]

> how to read the PSU sim?

It plots the expected voltages (over time) with the values given (which are guesses or defaults).

It pops-up to almost 360V no-load, then settles near 343V.

I don't know why he is simulating "all" the nodes. We kinda know that if the main B+ node is good, a few K of dropping filters will be OK for the small stuff; because the small stuff (13mA) isn't a heavy load on the big nodes (147mA).

Vacuum diode to a 120uFd cap.... if the primary resistance is really like 26 Ohms, I am sure this exceeds the peak current of the rectifier. In fact it appears to hit 6.4 Amps!

120uFd 4H and 40uFd, or 40uFd, 4H, 120uFd --- they filter about the same, but the 40uFd first cap is much less rectifier start-up strain. With a C-L-C filter it is not uncommon to make the first cap quite small, even 16uFd on a big amp. See the early Sunn amps. While the first node is ripply, the L-C cleans it up well.

Use "reporting delay" of several seconds, zoom in, and see what the operating ripple is. Anything under 5% is good enough for plates. Under 2% may be better for screens (why we usually tap them one node down from plate). I think you are sending a super-sanitary supply to do a dirty job (rock-n-roll).

[Paul1453]

Thanks for the feedback.

I chose to use that choke because it is my best looking one.
I want to try to make this build look as good as it sounds.
This choke has a high mA rating and was suggested to use it pre-plate supply.

I do have some other junky looking in comparison chokes.
They would have to go post plate supply, so a dirty R-R plate voltage results if I used one of them.

I'm still working on finding good sheet metal for my chassis'.
HD and Lowes did not have a good selection or prices.
I'm going to check the local builder's supply and collision repair shops.

[Paul1453]

I found a steel shop not too far away.   

They have 4'x10' sheets of 20 Gauge untreated steel for $35,
which they said they would cut in half for me for no extra charge.

That's about what HD/Lowes wanted for a 2'x2' piece.

He said he could order the same size and gauge aluminum sheet for $40.
I'm thinking of going with the aluminum, no rust and easier to bend. 
I read that aluminum can be better for the chassis because of it's non-magnetic properties?   

Any preference you experienced guys have for metal and gauge thickness for your chassis'?

[John]

Alum is easy to work with.


You want 14 ga. alum though, not 20. At least, IMO.

[Paul1453]

Thanks for your input, John.

Really that thick 14 gauge?

I'm just learning this metal fabrication stuff.

They had some 16 and 26 gauge stuff at Lowes, with nothing in between.
26 is far too flimsy, and 16 looked really thick to me.
So I guessed 20 gauge might be about right.
They had 18 gauge steel on display at the steel shop.
That looked like it was still a little stronger than necessary, to me.   

OK, so I looked up a standard gauge thickness chart.
https://www.tedpella.com/company_html/gauge.htm
It is the same for aluminum, No?

Then I measured some of the chassis' I have on hand.
Many seem to be 16 gauge, but others appear to be possibly 22 gauge.

I want it sturdy enough for the transformers weight,
but not really any thicker than it needs to be.
The smaller amps I intend to build with the rest of this sheet,
will have much lighter transformers.

20 gauge aluminum is too thin in your guys opinion? 

[Willabe]

It is the same for aluminum, No?

No, it's a little different.

It's the weight of the transformers that you need the strength for.

Guitar/instrument amps are moved from gig to gig. They get bounced around in the back/trunk of cars or trucks if the band is on the road and they get dropped by (drunk/high) players/roadies. The weight of the iron is what shocks the chassis.

Most/all of the gear you've been buying is not moved around much. So they can get away with a thinner gauge chassis.

The aluminum chassis I've been using are ~.090".     

[Willabe]

Here's a link for a sheet metal gauge chart that has a few different metals on it;

http://www.engineeringtoolbox.com/gauge-sheet-d_915.html

[Paul1453]

Thanks Willabe,

So it looks like aluminum is like 2 gauges thinner than steel.

I see why 14 Ga. was recommended now.

Now economic reality kicks in.  Aluminum is almost 4x the cost of steel.

A 20 Ga. 4'x10' steel sheet is $35.
Same thing in aluminum is almost $150.

And that is not even the thicker stuff y'all recommend.

Is the strength of 20 Ga. steel good enough for this purpose?
Or go to 18 Ga. for steel?
I'd plan to paint the steel to keep it from rusting.

[Paul1453]

Checked out the scrap metal place today.

I might have found the metal I needed to start on the HoSo.

Well you have to go dig through their pile of aluminum, just to see if they have anything one might use.

Then it's dangerous and dirty, but there is a good side.

Paid $13 cash for these pieces.

All are at least as thick as my on hand chassis.

Those serving trays just might be able to serve as chassis's for 2 HoSo builds.

I need to complete my 6V6 Plexi I started in the mean time.

I hope you as enjoying your weekend.