driver voltage tests - changing values after a while on one side

[fritzthecat]

Hello

I'm chris from Switzerland - my first post in here...

just got two Kaiju kits for my active 3 way horn system - the Kaijus are for midrange and high channels. For bass (Klipschorn, self built like almost everything in my actual system) I'm using two Silvercore 833c monos.

If I measure IA on both sides I get 421 V @ 235 V AC input - much to low - before all measurements went fine. Nevertheless I get the needed 300 (298) V on OA.

Adjusting the voltages @ 32U and 46U with the trim pots - I get 175 Volts on the A Side board. On the B side as well in the beginning - then I thought let it sit for a while and measure again and after maybe 20 minutes I get 186 V on the B Side board at the end of the trim pots way and the voltage seems to even climb higher - that's where I pulled the plug - what may this be?

And why are the voltages @ IA to low - before all values in the high voltage tests were within tolerance (521 V @ 14U), all others well within tolerance as well.

critical? What to do / check / resolder / replace?

Thanks for advice.

chris

[Paul Joppa]

The 421v measurement might be because the 300B tubes were installed.

The drifting driver plate voltage (175v target) could be a tube issue - swap the 5670 between sides and see if the issue follows the tube.

[fritzthecat]

Hi Paul

thank you for replying so fast - amazing! You just made my weekend...

I had no 300B tubes in place - what else might it be? I will swap the 5670 - and see what happens.

I checked everything about 10 times - no wrong placed parts on cs4 boards or misplaced connections in the rest of the circuit visible so far and the magic smoke remains inside the circuit...:-)

Maybe soldering issue?

I'm soldering for about 5 years now and am using 4% silver solder wire for this kit - for me it works great and as it is so easy to use that I did not want to change habits (even against your recommendations) - normally I even take 6% Audio Note or 10% Silver 1% Gold Mundorf solder wire which works great as well for me (80 Watt Weller solder station - regular use of tip cleaning and tip regenerator recommended) - hope I did not screw up there as it has a higher melting temp of about 227 degrees Celsius.

Looking forward and let you know about results.

Thanx a lot for further advice...

Chris

[fritzthecat]

Weird things happening here - I only changed the 5670 tubes (using the same ones just changes sides) and reattached my testclips and now I have 505 V @ 230V input on both sides @ IA, 298,6 on both OA and stable 175 V on 23u and 46u after letting it sit for more than two hours - wonder how it looks when I measure again tonite...:-)

Maybe some issues with my probes or soldering or the 5670 not pluged properly or all of it or just magic? Actually I don't get the point - any idea or someone who expierienced the same?

Just one question bothers me right now: should I go ahead or resolder everything?

thanx a lot for advice, regards from lake constance,

Chris

[Paul Joppa]

My best guess about the 5670 is that its cathode was not fully "formed", probably from sitting idle for decades since it was made. I have no guess about the high voltage issue.

If it is working correctly now, there is no way to get evidence about what  is wrong. So I would just use the amp but watch carefully, possibly re-checking the voltages once or twice during the initial 100 hours of operation. I would not leave it on and unattended during that time. If there are no further issues then you can have some confidence in the build and components.

[fritzthecat]

I will do so - thank you very much.

I only had one issue when I measured high voltage supply some weeks ago - my probe touched 12u/13u - little flash but no smoke - first I thougt I blew it but not even the fuse blew - I'm still using the same 1.5 A fuse and afterwards all measurments went very fine and stable - after that I decided to wear my glasses and not contact lenses anymore as one really has to be very carefull during measurement procedures...:-/

Then no tubes were inserted - just thougt that might have had some impact on the caps - maybe I should change them? But actually after more than two hours being stable again this evening they should be fine.

Will see...

Thank you and have a nice Sunday,

Chris

[fritzthecat]

I checked the voltages again yesterday evening and this morning - letting the amp sit for more than 2 hours respective 1 hour - everything fine and stable now - I guess I didn't blow or damage the 220uF /350v Caps when by shorten 12u/13u by touching both with my testclips during HV tests - just realized how important it is to be very very careful when performing measurements - puah, lucky me.

The voltages @ 32u/46u shift around a little bit but stay between 174 and 176 all the time.

@ IA I have stable 505 V on both sides - great!

I realised (i am using a variac) that when turning input voltage up, the voltages @ 32/46 stay @ zero until input reaches about 85 Volts, then climb up as high as 335V @ about 180 V input and then fall to the expected values of 175 V @ 230 V input - I guess this has to do with the regulators? Does anyone know if this is okay or within specs - so far I never just turned the amp on - always used the variac to slowly raise input voltage. Any answers to this would be very much appreciated as I really have to and want to learn as much as possible.

Gonna continue now with output transformer wiring.

Great kit, super manual, great fun building it so far - the only thing I would wish for is a check list with all connections that have to be made for each chapter for easier rechecking the work one has just done - if I can find the time I'll do an excel containing this - lets see.

Thanx so much for advising and helping to gain security and improve knowledge.

Best regards from Switzerland,

Chris

[Paul Birkeland]

I realised (i am using a variac) that when turning input voltage up, the voltages @ 32/46 stay @ zero until input reaches about 85 Volts, then climb up as high as 335V @ about 180 V input and then fall to the expected values of 175 V @ 230 V input - I guess this has to do with the regulators? Does anyone know if this is okay or within specs - so far I never just turned the amp on - always used the variac to slowly raise input voltage. Any answers to this would be very much appreciated as I really have to and want to learn as much as possible.

This has to do with the tubes' inability to conduct if they aren't adequately heated, and there isn't anything here to cause concern.

[fritzthecat]

Thanx - great - gonna continue building the rest...:-)

Cheers,

Chris