Tweeter Amp for OB or Horns

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IslandPink
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#61 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Decisions, decisions ...
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izzy wizzy
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#62 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

That doesn't look like a piece of wood ;)

BTW, why is that coil thing at the front at an angle?

cheers,

Stephen
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#63 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

izzy wizzy wrote: Sun Jun 17, 2018 5:55 pm That doesn't look like a piece of wood ;)
BTW, why is that coil thing at the front at an angle?
It's actually not quite the first time I've built something that looks like an amp. However it could force me to improve the main power amp packaging a bit ... D'Oh !
The choke ( 10H ) fits nicely inside the box at a 45 degree angle, given that there are wooden reinforcing wedges in each corner of this wood surround. I've already drilled the holes now anyway :D ..but it does leave the maximum room for other stuff ( rectifiers caps snubbers etc ) . I was hoping to put the mains toroid on top ( perhaps with a cover ) but the wires come off it in several different places so it might be tough to feed them all down through one hole. That's not 100% decided yet.
Main two questions I'm trying to resolve at the moment are :
1. should I put the 45's or the output tranformers at the very front ?
2. Where are the speaker connectors going ? - current plan is on the side.

Did you notice the Black Gate in its original cardboard tube ?
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#64 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

IslandPink wrote: Sun Jun 17, 2018 6:17 pm It's actually not quite the first time I've built something that looks like an amp. However it could force me to improve the main power amp packaging a bit ... D'Oh !
The choke ( 10H ) fits nicely inside the box at a 45 degree angle, given that there are wooden reinforcing wedges in each corner of this wood surround. I've already drilled the holes now anyway :D ..but it does leave the maximum room for other stuff ( rectifiers caps snubbers etc ) . I was hoping to put the mains toroid on top ( perhaps with a cover ) but the wires come off it in several different places so it might be tough to feed them all down through one hole. That's not 100% decided yet.
Main two questions I'm trying to resolve at the moment are :
1. should I put the 45's or the output tranformers at the very front ?
2. Where are the speaker connectors going ? - current plan is on the side.

Did you notice the Black Gate in its original cardboard tube ?
It was more a comment about my "packaging" than anything else. One day I might make something that resembles an actual amplifier. I like the idea that things such as toroids and chokes are inside. Leaves only the valves and cool looking transformers on top.

Can you get the speaker conns on the top? Only because then the wood sleeve remains intact so any future changes of mind is only metal work. Where ever you can see the valves and wires aren't too long is the best place.

I spotted the BG and was wondering about the box. Never got one in a tube that I remember.
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#65 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

I got three from Chris Vryonides, they are a good few years old - I should really check the capacitance once it's had a few hours.
Dunno about speaker connectors on top - would save the wood, but not a lot of space and I wouldn't want the wires getting melted by the hot 45's.
The input phonos I will have on top and thanks for reminding me, I need to decide exactly where. Also I had the position of the volume pot wrong in my head ( near the back ) so I need to think that one through . Either at the side about half way down ( near the driver valve ) or get an extension and put the knob at the front. Hmmm, some engineering to be done there .... or maybe have the knob on the top plate ....
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#66 Re: Tweeter Amp for OB or Horns

Post by pre65 »

More knob problems. :lol:

EDIT. This reminds me I need to order some 6mm shaft knobs. Tons on Ebay. Got 10 for £3.60 delivered.
Last edited by pre65 on Sun Jun 17, 2018 7:19 pm, edited 1 time in total.
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#67 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

No no, my knob's brilliant now. I had the hole in my knob drilled out to 1/4" in the prototype shop last week. Now it's my shaft that's going to be getting in the way !
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#68 Re: Tweeter Amp for OB or Horns

Post by Ray P »

IslandPink wrote: Sun Jun 17, 2018 4:32 pm Decisions, decisions ...

Twamp_layout.JPG
That heatsink won't achieve its rated performance mounted like that.
Sorry, I couldn't resist!
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#69 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

What would your preference be Ray ?
I thought the best option in the circumstances would be to mount the PCB to the inside wall, leaving the heatsink sticking out horizontally - more in free air than if the board was underneath it, blocking convection .
I had an initial idea to have holes through the top-plate for the heatsinks to protrude, but not sure how to mount the PCB in that case.
Bear in mind the heatsinks are the 63mm high ones, bit bigger than the normal for 1.5A I believe. I need to check the C/W , let me get back to you on that. The power to be lost will be about 6.7W if I drop the toroid voltage on the primary side a bit.

edit : 4.5°C per W , so about 30 C above ambient if working ideally.
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#70 Re: Tweeter Amp for OB or Horns

Post by Ray P »

Mark, those heatsinks are designed to be mounted vertically with air 'flowing' along the fins. Ideally you would want some vent holes above it too if it's going to run hot. I don't know how much mounting it sideways will compromise performance but I think you're temperatures will be a bit higher than your calculation - might still be OK?

On PCBs I've designed that use that type of heatsink I always arrange for holes in the PCB under the fins to promote more airflow.
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#71 Re: Tweeter Amp for OB or Horns

Post by Ray P »

Just another thought. In the past I have mounted similar boards vertically by hanging them from the chassis top plate; I carefully tapped threads into the holes in top of the heatsinks, seemed secure and I used some heat transfer compound so some of the heat would be dissipated into the chassis plate, though I had vent holes too.
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#72 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Maybe I could do that - need to check if I can get the heat sink in the jaws of the workmate now I've got everything on the boards.
I can do vent holes, just use my smallest Q-max cutter.
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#73 Re: Tweeter Amp for OB or Horns

Post by little eddy »

IslandPink wrote: Sun Jun 17, 2018 6:52 pm Also I had the position of the volume pot wrong in my head ( near the back ) so I need to think that one through . Either at the side about half way down ( near the driver valve ) or get an extension...
I have a spare extension shaft/coupling/bush/bracket if you need one.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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#74 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Oooh ooh !... let me check your thread for pictures, sounds v.interesting !
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#75 Re: Tweeter Amp for OB or Horns

Post by Wolfgang »

IslandPink,
I was wondering what could have been the reasons for some of the choices you have made in this circuit. For example the ECC40 gets a CCS but the 45 doesn’t. I would have expected it to be equally important there (constant current sink).

How do you calculate the AC load line with a CCS, a choke , and a resistor? Do you use a Spice simulation? The linearity (and benefits) of the CCS depends after all on the impedance to which it is connected but if you want to adjust this as RC filter how do you make all these factors fit?

When you design a circuit like this do you start from a specific "sound" you want to achieve which would be the reason for setting the operating point of the tubes (considering the harmonic/distortions)and adjust the rest around this or do you simply define the output gain and work from there backwards?

Wolfgang
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