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TGM8 - an amplifier based on Rod Elliot P3a
TGM8 - an amplifier based on Rod Elliot P3a
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Old 15th April 2019, 01:04 PM   #1001
Ian Finch is offline Ian Finch  Australia
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Quote:
Originally Posted by danielwritesbac View Post
To collar the mosfet gate pin, these miniature ferrite beads seem similar to fb43-110:.....
Those are VHF range ferrite with a 100MHz rating. You may need to come down a bit in the nominal frequency range to get a grade that is effective down to say, 5MHz. Perhaps grade 73? though I haven't knowingly used it on mosfet gate leads. EMI Suppression Beads Archives - Fair Rite
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Old 15th April 2019, 10:57 PM   #1002
Bigun is offline Bigun  Canada
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TGM8 - an amplifier based on Rod Elliot P3a
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Originally Posted by bsd04 View Post
The measured rail voltages of my old amp are +-55V at idle.
Any special considerations? It is not much higher than "as designed" +-50V, but better safe than sorry.

I've specced smoothing caps and C8, C9 as 63V...
I think it should be OK if the caps are properly sized. It'll run warmer. As I haven't tested it as such at these voltages you'll be treading new territory.
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Old 15th April 2019, 11:27 PM   #1003
apnneto is offline apnneto  Brazil
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Originally Posted by Bigun View Post
Ran out of boards so I've ordered another batch (it was 35% more expensive this time, I think they messed up last time, oh well):


1/ 'Scotty123' - paid for 1 pair
2/ available
3/ available
4/ available
5/ available
6/ available
7/ available
8/ available
9/ available
10/ available
Any board left?
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Old 16th April 2019, 12:38 AM   #1004
Bigun is offline Bigun  Canada
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TGM8 - an amplifier based on Rod Elliot P3a
Hi apnneto,

I am currently out of stock. I have ordered 10 more pairs of boards and when they arrive in a couple of weeks I can start sending them out. Scotty123 has the first pair reserved and somebody else already asked me for another 4 pairs, but there will still be plenty if you would like boards too. Just send me a PM to confirm what you want (how many).
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Old 16th April 2019, 01:48 AM   #1005
apnneto is offline apnneto  Brazil
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Originally Posted by Bigun View Post
Hi apnneto,

I am currently out of stock. I have ordered 10 more pairs of boards and when they arrive in a couple of weeks I can start sending them out. Scotty123 has the first pair reserved and somebody else already asked me for another 4 pairs, but there will still be plenty if you would like boards too. Just send me a PM to confirm what you want (how many).
Thanks ... Iíll PM you.
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Old 16th April 2019, 04:36 AM   #1006
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by Ian Finch View Post
Those are VHF range ferrite with a 100MHz rating. You may need to come down a bit in the nominal frequency range to get a grade that is effective down to say, 5MHz. Perhaps grade 73? though I haven't knowingly used it on mosfet gate leads. EMI Suppression Beads Archives - Fair Rite
https://classicvalve.ca/docs/MooseFET_docs_v1.pdf
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Old 16th April 2019, 03:54 PM   #1007
bsd04 is offline bsd04  Estonia
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Boards arrived, thanks Gareth
I would still like confirmation that last BOM is suitable for +-55V PSU.
Click the image to open in full size.
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Old 16th April 2019, 04:44 PM   #1008
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by bsd04 View Post
I would still like confirmation that last BOM is suitable for +-55V PSU.
All the semiconductors are rated for minimum 160V and your maximum rail to rail voltage is 110V so that's fine. Most of the semiconductors are rated for higher voltage. The solid state relay FETs should never see rail to rail but you can choose the IXFP110N15T2-ND which is rated for 150V.

Unless there's a fault, the only capacitors we need to worry about are the electrolytic rail capacitors which must all be 63V minimum, the 50V options won't suffice. The BOM for C8 & C9 are OK at 63V. However, the BOM for C15 & C18 are only rated 50V and a little oversized. Instead, you need 63V rated caps and I will recommend 493-15498-ND which are a better size too so everyone else might like these. I've uploaded a revised BOM for you.

Edit: I will check the simulation for VAS power dissipation.

I probably don't need to remind you - it's a tightly laid out PCB and not an easy one to assemble. There are some tips earlier in the thread worth following but I'll repeat a few here:

Install the small bits first. Clean off the flux before you add larger components - it gets harder to clean as the board gets busy.

The higher power resistors (through hole) should be mounted so they are slightly off the surface of the board to allow for better cooling

The 'spacer' TO126 parts are essentially non-functional washers, you might find something else you can use but they can be fiddly to install, I could probably come up with a better option but heck, it's DIY. Only solder these in place with mounting bolts in place to hold them to the underside of the PCB so that they are both flat and aligned.

Only solder the power devices once the pcb and power devices are bolted to the heatsink. This is to ensure they are all properly aligned and flat and parallel to the heatsink etc. If you don't and instead try to align them by hand they will not lie properly against the heatsink and it's almost impossible to move them once soldered so you end up cutting them off and removing their legs from the board one at a time and then installing new ones properly - don't ask me how I know this !

In general, removing parts is difficult so check your work carefully as you progress. Watch for little items, like getting the fuse holder clips the right way around etc.

The big power caps might not 'snap-in' but rather appear as a loose fit - at least on my boards they were.
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Last edited by Bigun; 16th April 2019 at 04:58 PM.
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Old 16th April 2019, 05:07 PM   #1009
Bigun is offline Bigun  Canada
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Originally Posted by Bigun View Post
Edit: I will check the simulation for VAS power dissipation.
These TO-126 devices are generally rated at 600mW in room temperature ambient (without a heatsink) and we'd like to be at around half that power level. In my simulation the VAS device, Q4, will experience the higher rail voltage and also higher current which is set by R14 and R15.

The VAS and the driver devices will all be running at around 300mW. This should be fine. But they will get pretty darn warm. You can reduce the VAS current slightly by increasing the value of R15 to say, 4k7. That's up to you, it's a simple adjustment that I don't feel with have any negative consequences.
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Old 17th April 2019, 10:36 PM   #1010
Bigun is offline Bigun  Canada
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TGM8 - an amplifier based on Rod Elliot P3a
update:


1/ 'Scotty123' - paid for 1 pair
2/ 'apnneto' - 1 pair reserved
3/ 'Dave S' - paid for 1 pair
4/ available
5/ available
6/ available
7/ available
8/ available
9/ available
10/ available

additional batch ordered:

1/ to 5/ 'arthur' - paid for 5 pair
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