peavey transformer for new build. Relay board?

[norburybrook]

OK, so I'm going to do my final Dumble build. I'm replacing my Bluesmaster.

I have a set of Peavey Iron, which sounded great in the wonderland.

I'm going to put the FET on a relay like my series 2 build as that sounds great and I have an old 3 way footswitch I was given sat doing nothing.


So my question is about the relay rectifier board. Looking at the standard board it would seem it is in fact a voltage doubler, something I've never noticed before. I've being using 5v relays from my 6 v seconday taps and it would appear I've been doubling the voltage to ~12v but the regulator has taken it back to 5v so they've always worked fine.

So, the peavey has a set of secondary's that are 20-0-20. My plan is to use half of that so just 20-0 and rectify that and use 12v relays with a 7812 regulator. if I use the standard board I'll end up doubling that so it would be too much. I presume I only need one Cap and diode to rectify this and still be under the 35v maximum for the regulator.

Does this make sense, and will it work using the 20-0 of the 20-0-20 taps?


Marcus

[erwin_ve]

Hi Marcus,

You can use the 20-0 tap with a fwbr and a 7812 regulator. I used this tap in my first HRM build and is still going strong( since 2009).
Have you built the Tweedle Dee yet?

[norburybrook]

Hi Marcus,

You can use the 20-0 tap with a fwbr and a 7812 regulator. I used this tap in my first HRM build and is still going strong( since 2009).
Have you built the Tweedle Dee yet?

Don't...…

So a full wave bridge rectifier? do I need to do the bridge though or would a half wave work? is the BIAS supply a half wave? that's what I was thinking.

Would I require less filtering then using a FWBR, what would you suggest?



M

[erwin_ve]

So a full wave bridge rectifier? do I need to do the bridge though or would a half wave work? is the BIAS supply a half wave? that's what I was thinking.

Would I require less filtering then using a FWBR, what would you suggest?



M

1000uF for filtering is used with mine.
I used the FWBR for having more current capacity.
Being lazy I didn't calculate if the half wave is sufficient.

[norburybrook]

So a full wave bridge rectifier? do I need to do the bridge though or would a half wave work? is the BIAS supply a half wave? that's what I was thinking.

Would I require less filtering then using a FWBR, what would you suggest?



M

1000uF for filtering is used with mine.
I used the FWBR for having more current capacity.
Being lazy I didn't calculate if the half wave is sufficient.

Ah, I always forget about current I've got 3 relays to power as well so I'll go with your FWBR then. Thanks Erwin.

M

[martin manning]

Hold on there hombre, You have a 20-0-20 secondary, with a CT? I’d go with a FW rectifier, which will have the same output voltage and more current capability than a FWB using half of it.

[norburybrook]

Ooohh..I think I'm going to have to do some googling.... Wouldn't 20-0-20 give me ~40v?

M

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[sluckey]

Ooohh..I think I'm going to have to do some googling.... Wouldn't 20-0-20 give me ~40v?

No. It would give you 20 x 1.414 = 28vdc

[norburybrook]

Would I be better using 24v relays then, and would the LED's on the foot switch still be ok with a 1k CLR?

M

Ooohh..I think I'm going to have to do some googling.... Wouldn't 20-0-20 give me ~40v?

No. It would give you 20 x 1.414 = 28vdc

Sent from my Nexus 6 using Tapatalk

[martin manning]

I'd just stay with 12V relays. An LM7812 shouldn't have any problem with the 28V input as long as it's bolted to an aluminum chassis. Referring to the eyelet board I drew up, just leave out the two diodes going to ground, and connect the CT of the 20-0-20 winding to the negative end of the first 1000uF cap. Done.

[norburybrook]

I'd just stay with 12V relays. An LM7812 shouldn't have any problem with the 28V input as long as it's bolted to an aluminum chassis. Referring to the eyelet board I drew up, just leave out the two diodes going to ground, and connect the CT of the 20-0-20 winding to the negative end of the first 1000uF cap. Done.

Martin I drew this up in my head last night after the discussion. I'm making my own boards.
12v it is then as I've already got them.




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[martin manning]

Looks good to me. You only need about 130 mA with all three relays and LED's on, and the regulator will only be dissipating around 2W.

[norburybrook]

thanks, Just drawing out my bias and main rectifier board now. I remember the last transformer bias tap didn't have enough negative voltage so had a to do a doubler. need to check this transformer to see what the bias tap is putting out on this one.

edit; so this transformer has a 56-0 secondary which 'should' I think work without a doubler as it's roughly the same as a fender bias tap IIRC ~50v

what value resistors would you use, there seems to be a lot of variation here. Your board layouts show a 3.9k - 24k -10k pot, but I've seen:

1R-10k-10k
3.3k-27k-10k
1.2k-15k-10k
470r-10k-10k

looking at the peavey schematic they have 15k 68k 10k fixed giving -60Vdc







M

[martin manning]

Follow the Dumble circuit to start and tweak as needed. You're right it's very close to the typical Fender bias tap.