Tweeter Amp for OB or Horns

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IslandPink
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#121 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Closer ...
Tweeter_amp_progress.JPG
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IslandPink
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#122 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

On the home straight , should be running some time tomorrow afternoon. Pics to follow.
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IslandPink
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#123 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Spoke to soon ... ran in to some trouble with my simple-minded idea of how to feed 4 transformers from a single pair of tags fed from the mains switch. I soldered some thick wire of about 1" length in each tag and started trying to attach the first pair of transformer wires to them - they unsoldered and started flopping around in an unmanageable way. If anybody has ideas on this, post me a picture - otherwise I'll let the subconscious work on it overnight.
"Once you find out ... the Circumstances ; then you can go out"
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IslandPink
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#124 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

I think I can do it by making a complete rectangular loop of wire through the two tags, attaching all the transformer wires and the mains feed, then snipping-out the ends of the rectangle at the finish.
I'm sure that's what people were thinking - thanks for your telepathic input !
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IslandPink
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#125 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Just to illustrate my non-CE-approved madness :
Before
Mains_interim.JPG
Shortly before snipping -
Mains_snipped.JPG
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IslandPink
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#126 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

After a lot of swearing and sweating, amp now complete - every single thing that could be a little sh*t did its best to thwart me !!
ps. It's quite 'busy' -
Tweeter_amp_underside.JPG
A fairly poor shot due to lack of light - will improve...
Tweeter_amp_complete.JPG
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IslandPink
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#127 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

I did manage a first switch-on and voltage test on the kitchen table.
There were no bangs, and it all tested out OK :D
B+ is 289 ( a little low, somehow still failed to use PSUD properly - but have options on the first cap , to increase )
Anodes of 45's : 286V
Cathodes at 45V
Anodes of E83F drivers : 189V
G2 on E83F's : 145V
Filaments of E83F's : 6.1V
Filaments of 17AX4's : 16.6V
Filaments of 45's : 2.45V

No time to listen tonight , will get a first check rigged-up tomorrow with a 288/Yuichi and one of the G3 ribbons.
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Ali Tait
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#128 Re: Tweeter Amp for OB or Horns

Post by Ali Tait »

Top notch!
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Ray P
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#129 Re: Tweeter Amp for OB or Horns

Post by Ray P »

:thumbup:

Hope all goes well tomorrow...
Sorry, I couldn't resist!
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IslandPink
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#130 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Thanks !
Just realised I have a bit of additional work to do first, tomorrow.
The 4uf cap after the rectifiers is only 160Volts rating ( or 160 Bolts in Russian parlance ) . Funny I missed that :D
Even if it's an AC rms rating, that's good going for it not to blow ( I had heard they were somewhat over-specced ).
Luckily I have a 10uF/450v Ansar to hand. Just need to find the box of capacitor clips, which is now hiding.
That should give me an additional 25 or 30V, according to PSUD, which will be about right to get me near-enough 2W from the 45's.

ps. should say, I missed a couple of obvious things on the PSUD model ( probably forgot to update it ) , ie. the choke is around 139R not 40R , and I should have taken off 15V for the damper diodes at ~100ma. If I do this, I'm within 5V of the prediction.
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#131 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

10uF Ansar in there now, and B+ is now 302V. Hmmm... :scratch:
Was expecting another 10 or 15V based on PSUD. Would be surprised if the circuit's current-draw was much more ( hence more lost through 17AX4's ) so it's a bit mysterious.
Anyway, a pretty good level, mustn't grumble.
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izzy wizzy
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#132 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

IslandPink wrote: Mon Mar 11, 2019 7:52 pm 10uF Ansar in there now, and B+ is now 302V. Hmmm... :scratch:
Was expecting another 10 or 15V based on PSUD. Would be surprised if the circuit's current-draw was much more ( hence more lost through 17AX4's ) so it's a bit mysterious.
Anyway, a pretty good level, mustn't grumble.
Might be a stoopid question but did you measure the transformer parameters to bung into PSUD or take the manufacturers values? And the other things you have in there like chokes?

Cheers,
Stephen
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#133 Re: Tweeter Amp for OB or Horns

Post by IslandPink »

Yes, I believe so. I just quoted the choke DCR above, that's in. The mains, I think I got the off-load voltage from the Hammond datasheet, and scaled by 248/240 for my mains. The secondary resistance is in PSUD as 64 ohms, I probably measured that. It does more or less work for the 4uF case now if I allow about 15V drop for the valve diodes. So I'm surprised I don't get that close when I apply the change in cap size.
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izzy wizzy
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#134 Re: Tweeter Amp for OB or Horns

Post by izzy wizzy »

IslandPink wrote: Mon Mar 11, 2019 8:06 pm Yes, I believe so. I just quoted the choke DCR above, that's in. The mains, I think I got the off-load voltage from the Hammond datasheet, and scaled by 248/240 for my mains. The secondary resistance is in PSUD as 64 ohms, I probably measured that. It does more or less work for the 4uF case now if I allow about 15V drop for the valve diodes. So I'm surprised I don't get that close when I apply the change in cap size.
I wouldn't believe the manufacturer's data. Edit. That sounds real bad. I meant they might have a spec but things can change depending on where it's made.

Why are you "allowing" for the 17AX4 volt drops when it has 6AX4 available in the sim?

Cheers,
Stephen
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#135 Re: Tweeter Amp for OB or Horns

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izzy wizzy wrote: Mon Mar 11, 2019 8:09 pm 1. I wouldn't believe the manufacturer's data. Edit. That sounds real bad. I meant they might have a spec but things can change depending on where it's made.
2. Why are you "allowing" for the 17AX4 volt drops when it has 6AX4 available in the sim?
1. Which bit ? ie. which bit should I change that wouldn't upset the accuracy of the 4uF case ?
2. Who said I had some 6AX4's in the sim ? :D I just put a solid-state bridge in there and checked the 6AX4 dataheet yesterday.

Ooh, did you just change your comment - it changed in my reply to you - spooky !
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