new build 36lite with vvr

[chaliapin]

Went to bed and realised r24 and 25 probably can't go up on the board to feed the heater circuit. Are they a centre tap?

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R24 is a B+ dropping resistor and R25 is one of the artificial center tap resistors for the heater circuit.

Great thanks, and I'm right in thinking they can't be up on the board or can they?

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[chaliapin]

Not sure anyone can, understandably, face going through my hand drawn attempts at layout so im going to continue anyway...

Little tabs for grounding on the chassis...

Looking at my layout and the jmp lite 2bish I'm planning on drilling the chassis in the following places;

1. Close to the input jacks
2. Close to the output speaker jacks
3. directly under the mains plug input
4. Near the end of the board below the standby switch etc connecting to the big capacitor c14 and also taking the ground from the PT

The jmp layout appears to combine 3 and four?

Am I on the right lines?

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[JMPGuitars]

R24 is a B+ dropping resistor and R25 is one of the artificial center tap resistors for the heater circuit.

Great thanks, and I'm right in thinking they can't be up on the board or can they?

Do you need an artificial CT? Does your PT not have a real center tap?

[chaliapin]

Yes, it need am artificial centre tap

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[Bieworm]

Have you got the wiring diagram of that PT?

By the way, R24 can be connected berween both + lugs on the can capacitor.

[chaliapin]

Not planning a can cap either...

Attached what I have for the PT.

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[Bieworm]

Ok, you do need an artificial CT.. thats 2x 100R resistor to ground on the heater wires.

When you don't use a cap can, then you are going to put the individual electrolytic caps on the main board, or a separate board. Well, your R24 drops the voltage between those first 2 filter caps. So R24 is attached between the turrets of their positiv sides.

[chaliapin]

Argh, sorry ive caused confusion. R24 is in my board layout between the big caps. 25 and 26 are the CT resistors. The layout im referencing has them on a little tag strip on their own but I don't have a strip so wanted to put them on the end of the main turret board as long as that's not going to cause problems.

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[Bieworm]

That depends on which components are near. You don't want heater AC near any DC source.
A simple solution would be that you attach each R25 and 26 on the heater lugs of one of the power tubes and join them at the cathode lug of that tube. Then you have heater elevation too, which is a good thing.

[chaliapin]

Ok great thankyou, I'm getting somewhere. I assume r25 and 26 are .5w resistors?

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[Bieworm]

Ok great thankyou, I'm getting somewhere. I assume r25 and 26 are .5w resistors?

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That's a high current circuit. I use 2W resistors in that case... it's never bad to oversize when the cost is neglibile, and there is enough room/space

[chaliapin]

Brilliant thanks. Looking at the effects loop on one of the 18 watt layouts im unclear what needs to go on the turret board and what can come off the board to the Jack sockets?

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[JMPGuitars]

Brilliant thanks. Looking at the effects loop on one of the 18 watt layouts im unclear what needs to go on the turret board and what can come off the board to the Jack sockets?

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Which layout are you looking at?

Thanks,
Josh

PS. In general, I don't recommend less than 1W for resistors (and Bieworm's advice is correct).

[chaliapin]

Great thanks

Your 18w extra tmb layout with the loop in am optional box

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[JMPGuitars]

Great thanks

Your 18w extra tmb layout with the loop in am optional box

Check this out:



That's how I do it in all my builds. The 68K resistor is on the boards, and the other resistors and caps are PTP to the jacks. If you look in my Tremolo TMB thread, or my photos of other builds, you can see how I do it with turret boards also, same deal though.

Thanks,
Josh

[chaliapin]

Great thanks. That board is quite busy. I'll fit the 68k resistor on the board and worry about the rest later! So minimum 1w resistors everywhere except when specified higher?

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[JMPGuitars]

Great thanks. That board is quite busy. I'll fit the 68k resistor on the board and worry about the rest later! So minimum 1w resistors everywhere except when specified higher?

Exactly. And pay attention to the voltage requirements. I use CMF resistors, and their 1W resistors are rated for 500V. If you're using something else, make sure the voltage rating is well above their position in the circuit.

If I have to use a 1/2W resistor, it would be in the preamp, with very low voltage and current requirements.

[chaliapin]

Alright, I'm slowly getting somewhere, even though I haven't actually started yet... just missing a few components for the MV and fx loop and a couple of resistors I can't find for the main circuit. New iron tip arrived, looks good. Searched around and found two un used g50s-50 speakers plus all the mounting parts.

I was supplied a clone of an AC30 output transformer but I can't find any paperwork, ie, which wire is which. Can i work it out with a MM?

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[Bieworm]

Looks like the red wire is for the HT, and the yellow wires are for the power tube plates.
The black should be the - of the secondary winding. Green and blue are the + taps of the secondary winding. But what ohms they represent is measureable with a DMM.
On the hammond 1750T green is 8 Ohm and blue is 16 Ohm. Compare the resistances on the datasheet with your transformer.

https://www.tube-town.net/ttstore/hammo ... issue.html

[chaliapin]

You guys are great thankyou.

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