Tweeter Amp for OB or Horns

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IslandPink
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#46 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

I was thinking the same. Black Gates have a pretty low Zout in any case.
I can get an OD3 in there to drop B+ from 300 to 150V for the choke-loaded ECC40's ( both ) for some 'bling' .
Found a few more bits this evening ( eg. UX4 sockets ), so layout can progress.
Will get an LT Spice model going soon, useful for showing the circuit if nothing else :)
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#47 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

No, need more smoothing to drivers, so CCS from B+ to OA2 ( that should be enough shunt current ) to supply ECC40 sections at 150V minus drop through each choke ( 235R ) ie. 148V .
Maybe, looking at ECC40 curves, 200V or 210V is more linear, so that would be CCS to 2x OB2 ( is it ? ) at 210V, or 208.5V after chokes - valves at 5ma or 6ma.
Sorted !
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#48 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Think I'll use a couple of damper diodes in PS anyway - slow start is good.
More or less finalised now, see pic below :
Tweeter_circuit1.jpg
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#49 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

Looks fine. The only thing I'd do different for starters is a resistor feeding the glow tubes and then sub in the CCS after. Just to see what happens rather than assuming the CCS is the go. I'm going to try similar on my line stage/headphone thingy.

cheers,

Stephen
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#50 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Could do , yes , worth checking. I put DN2540 one in there, also have one of Gary Pimm's self-bias ones upstairs too.
I didn't draw the zobel around the OB2's , but that will be done, though I'd like to look into the values a bit more this time, after that article you linked.
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#51 Re: Tweeter Amp for OB or Horns

Post by simon »

How about using all SS bridge with the 6AX4 in the earth rail between the negative side of the bridge and the negative of the first filter C? I have this built nearly (about 5 months ago!) but haven't finished it off yet.

Benefit of only one 6AX4 and half the heater current. But I've seen jc morrison do this - supposedly has the benefit of the stiffer SS supply but still has the soft start.
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#52 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

IslandPink wrote: Wed May 30, 2018 7:07 pm Could do , yes , worth checking. I put DN2540 one in there, also have one of Gary Pimm's self-bias ones upstairs too.
I didn't draw the zobel around the OB2's , but that will be done, though I'd like to look into the values a bit more this time, after that article you linked.
All glow tubes have different impedance so you might have to measure them as Bjorn did to get the right values.
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#53 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

simon wrote: Wed May 30, 2018 7:45 pm How about using all SS bridge with the 6AX4 in the earth rail between the negative side of the bridge and the negative of the first filter C? I have this built nearly (about 5 months ago!) but haven't finished it off yet.
Benefit of only one 6AX4 and half the heater current. But I've seen jc morrison do this - supposedly has the benefit of the stiffer SS supply but still has the soft start.
Interesting idea - but whether I'd notice the difference given this is working typically only in the kHz, I doubt it. I'm likely to have a few volts to 'waste' with this transformer and full bridge, so it's not an issue to lose 15 or 20V through the damper diodes.
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#54 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Bit of buying today. Spoke to Gerry at Crowthorne and managed to get some 7-pin sockets and a couple more ECC40's.
Ordered some MIlls resistors and Nichinon ES caps and some other sockets from HiFi Collective.
Checked upstairs and found an unused 15VA 2x15V toroid and so I bought 4-off 17AX7 damper diodes from the states.
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#55 Re: Tweeter Amp for OB or Horns

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RS order in, for Crees and IEC panel socket.
Ordered HV toroid and a 10H/125ma choke from Bluebell.
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#56 Re: Tweeter Amp for OB or Horns

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Ladies and Gentlemen... the starting gun has been fired . I soldered 3 components into one of the filament supply boards this evening :bounce:
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#57 Re: Tweeter Amp for OB or Horns

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Just bought some of these. Looked quite fancy for an OD3. Better than the taped-up ones I have to hand at the moment.
Ok, they are probably not going in the tweeter amp...
Zaerix.jpg
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#58 Re: Tweeter Amp for OB or Horns

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Three of those were from Langrex ; 'See seller's other items' ....
No, please, don't tempt me :
https://www.ebay.co.uk/itm/DA100-CV1219 ... 48a73d5ee3
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#59 Re: Tweeter Amp for OB or Horns

Post by pre65 »

Can I tempt you with 833c ? :lol:

Carbon anode version.
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#60 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Thankfully no !

It amazes me how much 'stuff' goes into a simple amp. This doesn't even show everything.
( Two DHT supply boards done, a start has been made )
Tweeter_bits.JPG
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