Hard financial times and a lack of funds has forced me into building a GM70 amp

Well, I got side tracked on my Obla-wave project but I am back now. I am laying out the top plate this weekend and finishing the chassis (sans clear). Then next week I will be working (for money) at the shop one day for a couple house and after I am done with a little job I have going, I will Punch the top plate.

The only thing I need to assemble the amp (without wiring it) is holders for the big ass caps. Hopefully I can source them locally. Pix to come.
 
It should look good. I went to the Grainger website today to look for Cap holders and, man, are expensive....for what they are. I'll keep looking. It won't deter me from punching the holes though. I have access to an 80 ton punch press that should make short work of it.
 
Hi All, with the cool weather settling in, I have more energy to put into my projects. While my RatRod amp is being pin stripped I am laying out my GM70 amp. I can use the shop all day tomorrow so trying to make a late minute decision. What do you like better? The power supply in the middle and the signal path on both sides of the PS or the PS on one side and the signal path on the other? I am smack dab on the fence on this one.

I am also tired of moving all these parts. For a point of reference, the top plate is 21" w x 23" deep.....it a huge amp.


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I like symmetry, so the first one does it for me. ONLY if you can keep power and signal from crossing over each other, needlessly.
 
Yep, power can go right up the middle and signal will go on the outside with seperate volume pots....if I go this way. I just got a vote for the first one from my wife
 
How about putting the pt & opt on the rear just like you have them turn the choke or whatever that is at 45 place caps at a 45 next to that and tubes biggest to smallest it will look like a V front to back.

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Jason
 
WOW, and I thought my amp was big, 21x23? Yikes. This is a tough call, I guess visually I like 1, but, I wonder if option 2 may be better noise wise? I'm no expert though...I went through the same dilemma when I designed mine.
 
How about putting the pt & opt on the rear just like you have them turn the choke or whatever that is at 45 place caps at a 45 next to that and tubes biggest to smallest it will look like a V front to back.

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Jason

I did lay it out that way and it seems to mix the power and signal a bit too much. The B+ is 850v and at that level there might be too much leakage....if there is such a thing.

WOW, and I thought my amp was big, 21x23? Yikes. This is a tough call, I guess visually I like 1, but, I wonder if option 2 may be better noise wise? I'm no expert though...I went through the same dilemma when I designed mine.

That is what I was thinking as well, but late last night I got off the idea of one volume pot and I think I can get just as good of seperation with version 1.


Thanks for all your input guys. I am off to the shop and will post pix tonight.
 
Well, the side to side simetrickal (SP) won out. I got it all laid out and all the holes center punched and then the power in the entire industral complex went out. So we did the next best thing....went sailing. I will be back there bright and early and finish it off.
 
no fishing, just sailing. It was a great day on the lake. Strong winds and sunny skys. I am sun burnt.
 
I got the top plate all punched and drilled out and the transformers painted. Tonight I will polish the oil caps. Pix later tonight or tomorrow.
 
This is how far I got yesterday. I punched the top plate for most of the holes but had to use a hole saw for the caps and GM70 holes. They came out very ragged so I need to clean them up. I put a pack of smokes in the pic to give a reference of the size of this amp. Man is it huge. It will weight about 80lbs when done. The OPTs will be painted the same modeled bronze I painted the PTX and Choke. It was nice to have a sand blaster yesterday for cleaning up the PTX and Choke.

Also in the pix you can see I rounded over the chassis edges. I hope to have the chassis all done and cleared by next week.

One concern I have after looking at my handy work, is the caps next to the PTX are rate for a max operating temp of 40c. That is 104f. If that PTX gets hot, it may be an issue.
 

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This is how far I got yesterday. I punched the top plate for most of the holes but had to use a hole saw for the caps and GM70 holes. They came out very ragged so I need to clean them up. I put a pack of smokes in the pic to give a reference of the size of this amp. Man is it huge. It will weight about 80lbs when done. The OPTs will be painted the same modeled bronze I painted the PTX and Choke. It was nice to have a sand blaster yesterday for cleaning up the PTX and Choke.

Also in the pix you can see I rounded over the chassis edges. I hope to have the chassis all done and cleared by next week.

One concern I have after looking at my handy work, is the caps next to the PTX are rate for a max operating temp of 40c. That is 104f. If that PTX gets hot, it may be an issue.

The caps will be fine. The PT doesn't radiate that much heat. You can help keep them cool by thermally insulating them (nylon washers) from the chassis so there's no conducted heat to them.
How about a couple of lifting lugs so you can get a chain hoist on it to move it around?
 
Hah! I actually have them to put on. They will be installed next week.....really!

Cool about the heat thing. I am mounting from the underside with a squash fit of the lip of the cap against the bottom of the top plate.

Sorry about the early morning call yesterday. Forgot you work so late.
 
Hah! I actually have them to put on. They will be installed next week.....really!

Cool about the heat thing. I am mounting from the underside with a squash fit of the lip of the cap against the bottom of the top plate.

Sorry about the early morning call yesterday. Forgot you work so late.

You can heat insulate with the pressure fit. Just find large neoprene O-rings (or similar) and fit them between the lip of the cap can and the bottom of the chassis plate. You could cut a spacer out of some insulating material. It'll cut down the heat transfer a lot.

9:00 am isn't early morning by far for most people, but most people aren't rolling in at midnight. My fault for leaving the phone on. No harm done.
 
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