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#91 Re: Tweeter Amp for OB or Horns

Posted: Tue Jun 26, 2018 8:38 pm
by simon
How about this monster?

https://www.cromwell.co.uk/shop/hand-to ... MX0451129G

Not sure what I'd use it for, but someone obviously does.

Anyway, I've just realised that Owston is THIS weekend (my life is too busy!) - if you're coming on Saturday you can borrow mine?

#92 Re: Tweeter Amp for OB or Horns

Posted: Tue Jun 26, 2018 10:13 pm
by IslandPink
Well I must say this is a jolly fine idea. I will be there and welcome it with open arms.
Life just gets better and better ( see 'what are you listening to ...' thread ) .

#93 Re: Tweeter Amp for OB or Horns

Posted: Tue Jun 26, 2018 10:30 pm
by simon
Just need to remember to bring it now :-)

#94 Re: Tweeter Amp for OB or Horns

Posted: Tue Jun 26, 2018 10:41 pm
by IslandPink
simon wrote: Tue Jun 26, 2018 8:38 pm How about this monster?
https://www.cromwell.co.uk/shop/hand-to ... MX0451129G
Not sure what I'd use it for, but someone obviously does.
Only weightlifters need apply.

#95 Re: Tweeter Amp for OB or Horns

Posted: Thu Jun 28, 2018 9:51 pm
by IslandPink
I powered up the filament toroid from a Variac today , with the DHT supplies on there. The voltages checked-out well. With 10R and 5.1k on the board, I got 2.45 and 2.47V out to the 45's.
I had the oscilloscope down ( thanks, Neal ! ) and did some playing around to check limits.
The supply 'out' becomes clean at 5.62V AC into the boards. Obviously some margin is required then.
Even at that input voltage and the 63mm heatsinks they are getting slightly too hot to touch for more than a couple of seconds, after 15mins.
This only takes 198V AC into the toroid primary.
So , I will have to burn off a few volts/watts going into the primary, and probably will attach the heatsink to the top plate.

#96 Re: Tweeter Amp for OB or Horns

Posted: Sat Jul 21, 2018 3:07 pm
by IslandPink
Slow going at the moment, but not stalled entirely !
Top plate has progressed a bit.
When I went to Owston, Simon very kindly got out his tool...kit in the pub beer garden and we went to work cutting two 37mm holes for the UX4 sockets. Since then I've drilled a few holes for those and the output transformers.
In the meantime I've realised I lost another thing on the Farnell order - didn't get the SiC rectifiers , something happened with that 'shopping basket' never got to the bottom of that. Anyway...
Tweeter_top_plate.JPG

#97 Re: Tweeter Amp for OB or Horns

Posted: Sat Jul 21, 2018 4:50 pm
by simon
For you Mark, it was a pleasure :D

#98 Re: Tweeter Amp for OB or Horns

Posted: Mon Sep 24, 2018 11:46 am
by IslandPink
Just about to re-start after electrics review and re-fitting of kitchen, which seemed to take most of the summer :!:
Decided pentode driver has least risk, easy to get going and is proven in the HF . I have a pair of nice E83F gold-pins saved for future phono, but plan has changed on that circuit so these are free. I will try & do a diagram later, but here is the gist of the driver –
  • E83F running at around 6ma
    Anode 210V , G2 150V, cathode about 3.4V
    Anode load ~15k , cathode R ~430R if no additional current from G2-setting.
    No cathode by-pass required as gain is around 90 with it decoupled, estimate ~60x with no cap.
    Now G2 setting is an area worth discussion. My starting position would be a resistor from B+(310? ) of about 66k , and a 100uF cap from there to cathode. I don’t think the extra stability afforded by a VR tube from k to G2 is necessary from midrange upwards. Comments welcome.
In terms of holes on the top-plate, starting with just the noval drivers does provide flexibility for future ideas that need more/bigger holes - eg. with Loctals or VR tubes.

#99 Re: Tweeter Amp for OB or Horns

Posted: Sun Oct 28, 2018 4:53 pm
by IslandPink
What's that coming over the hill, is it some progress ?
Tweeter_moreholes.JPG

#100 Re: Tweeter Amp for OB or Horns

Posted: Sun Nov 04, 2018 6:24 pm
by IslandPink
More holes done this week, but the more I look at the 'stuff' that needs to go into this, the more it's going to be a bit of a shoehorn job - I need to sit down carefully and think carefully about where things are going !

#101 Re: Tweeter Amp for OB or Horns

Posted: Mon Nov 12, 2018 10:28 pm
by IslandPink
What kind of dunce would design something with a mains transformer and three filament transformers ! :roll:

#102 Re: Tweeter Amp for OB or Horns

Posted: Mon Nov 12, 2018 10:53 pm
by izzy wizzy
IslandPink wrote: Mon Nov 12, 2018 10:28 pm What kind of dunce would design something with a mains transformer and three filament transformers ! :roll:
Hey I resemble that remark. My amp has a mains tx and 3 fil transformers :P

Cheers,
Stephen

#103 Re: Tweeter Amp for OB or Horns

Posted: Mon Nov 12, 2018 11:07 pm
by pre65
IslandPink wrote: Mon Nov 12, 2018 10:28 pm What kind of dunce would design something with a mains transformer and three filament transformers ! :roll:
I could be that person when I finally get round to the 833a rebuild. :lol:

#104 Re: Tweeter Amp for OB or Horns

Posted: Sun Jan 13, 2019 10:36 pm
by IslandPink
Some progress. Still pondering the placement of two filament transformers, the volume control and the input sockets !
Tweeter_internal2.JPG

#105 Re: Tweeter Amp for OB or Horns

Posted: Sun Jan 13, 2019 10:41 pm
by RhythMick
izzy wizzy wrote: Mon Nov 12, 2018 10:53 pm
IslandPink wrote: Mon Nov 12, 2018 10:28 pm What kind of dunce would design something with a mains transformer and three filament transformers ! :roll:
Hey I resemble that remark. My amp has a mains tx and 3 fil transformers :P

Cheers,
Stephen
If we're counting mains transformers, I'm up to 4 HV mains (6 secondary windings in use) plus 6 toroidal (12 X 7v secondary).