Build Log: A Physician hooked on Crack (My very first DIY project)

[sanadsaad]

Cap removed from 21/22. Reading climbs from 0 to infinity. Cap still off. didnt resolder it. Without the cap, the resistance b/w ground and terminal 13 climbs from 0 to infinity as well.

[sanadsaad]

Aaaaaaaahahahaha(crazy laugh when one gets something right)!
It was the capacitor at 20/21.
New resistance readings:

Terminal 1,2,4,5 and 13: 0 climbing to infinity

Terminal 20 and 21: 0 climbing to infinity now when previously it was giving zero.

Turns out the cap terminals werent soldered properly. Actually they were soldered well but I desoldered, tested the cap as suggested by Grainger and then tightened the mechanical connection of cap, wire and terminal and then tested resistance. Then I soldered and rechecked. Onto the third fuse then?

[sanadsaad]

This is odd. I left for a coffee break, came back and re-did the resistance check and now im back to the same old readings I was getting before.

[sanadsaad]

Its definitely a soldering issue. I find that if I remove a little solder from the joint with a wick, I get proper resistance numbers. Finally fixed it and did the voltage checks. Theyre all perfect! As it's 240VAC here in Oman, my voltage numbers are more or less double what's in the chart. The only question is regarding A9. It should be 0 but im getting 5V. Other than that, the voltage numbers are perfect! I could smell something when I was voltage testing but it was probably the tubes heating up. There was absolutely no smoke and the fuse didnt blow. Thanks guys! You're awesome. Big thanks to you Grainger for pointing the 20/21 thing out. This is one hell of a forum! Ok, now should I solder the black wire to the headphone terminals and ground em to fix the headphone issue or should I leave it at that? Cant wait to connect it to source. Another question. I have a lot of HD tracks on my laptop. Can I burn em to ordinary discs? Never done that. Anyone who has, I'd appreciate the help.

[Grainger49]

I have a schematic marked with terminal numbers.  According to that schematic nothing should be connected to T14 except the cap and two resistors.  The power to the 12AU7 plate should come from T13 to T4.

T22 is a ground, T4 is connected to a plate load resistor.  They shouldn't be connected, ever.  I don't see a black wire from T4 to anything in the manual I have. 

The only thing I find in the manual using the search function for Terminal 4 is a red jumper to Terminal 2.

I will look further in the morning.

[sanadsaad]

The headphone terminal votage shoots to 31 for less than a second on startup then its all zero from there. Should I ground it as advised or start listening without that? I read Dave's thread where he damaged his headphones and wanted to avoid it.
Also, everywhere in the voltage checking, it's said not to touch the live amplifier with both hands. After fitting it in the wooden board and puttin it on my desktop connected to the CD player, can the top plate be touched or would it conduct current?

[Noskipallwd]

Hello again, this is a great forum isn't it, great to have guys like Grainger and Desmond sharing their knowledge and experience. As long as you don't plug your phones in until you turn the amp on you should be safe, I used mine that way for some time. The top plate does not carry current, so you are fine. If you use two hands when measuring voltage you make a nice circuit between your hands, if you happen to receive a shock it would travel right across your heart. Electrical current takes the path of least resistance. The amp is safe during operation, just don't reach under it when it is on, and when you take it from the base for any reason turn it off and let it sit a few minutes. Hope this helps.

Cheers,
Shawn

[Paul Joppa]

... As it's 240VAC here in Oman, my voltage numbers are more or less double what's in the chart....

If true, that's very bad. There is a version of the power transformer designed for 240v input; all the circuit voltages will then be the same. If you have the 120v transformer, don't put 240v on it. The circuit is designed for +/-10% variations, but can't handle 100% variation!

[sanadsaad]

Thanks Shawn! Yea I think i'll get the headphone grounding done while I have all the equipment out on the dining table(makeshift workplace).
Paul, it's a 240V transformer! I mentioned it to Doc when I placed the order. And if the readings are for 119VAC as mentioned in the manual, shouldnt the ones for 240 be more or less double?

[Noskipallwd]

As it's 240VAC here in Oman, my voltage numbers are more or less double what's in the chart.

I completely missed the double part in your post, the circuit voltage readings should be the same, as Paul said. The 240v and the 120v transformer will produce nearly identical voltage and current readings on their respective output taps. I would verify what transformer you received before putting power to it again. I am not sure how to do that. I think you use resistance readings, I am sure Paul, Grainger, or Desmond will let you know what you need to do.

Cheers,
Shawn

[Laudanum]

Not tech savvy enough to help with the transformer and voltage, sorry.

To Grainger ... The reference was to the connection between terminal 4 of the transformer, not a terminal strip.   It was originally instructed to take the wire from transformer terminal 4 to 22 but a revision suggested that taking it to 14 may result in more quiet operation.  It's a ground.

Per manual:

"Cut a 2" (50mm) piece of black wire, strip both ends back 1/4" (6mm). Attach and solder one end to power transformer terminal 4. Attach and solder the other end to terminal 22L."

"REVISION 5/6/10:
Making this wire 3" long and connecting it to Terminal 14U instead of terminal 22L may yield more quiet operation."

[Grainger49]

Desmond,

Thanks, that makes sense this morning.  Somehow I had missed his two posts above my last one. 

I'm with everyone else, double voltages are bad.  That will make the capacitors blow up, literally.  This worries me.

Does your transformer label say 240V or 120V?  Transformer terminal 1 is 0 Volts, what does your transformer terminal 2 say? 

[sanadsaad]

Ok now im concerned. When I read "The following voltages have been made with an AC mains voltage of 119VAC" in the manual, I thought that implied that 240VAC would be different.
Grainger, Terminal 1 is 0, 2 is 1. The transformer is for 240V. Says so on the sticker.

[Grainger49]

I'm wondering if the transformer was somehow mislabeled.

Dan or Paul might have some insight on whether there is a physical difference in the two transformers.  Maybe a resistance measurement of the primary winding will tell if it is indeed 240V or a mislabeled 120V.

[Laudanum]

Not for the OP but for those who may be able to help ...  If the secondary is 6.3 volts for both 120V and 240 volt versions of the transformer,  then wouldnt the turns ratio be different for each?   Double for the 240 volt transformer compared to the 120 volt?  (or is it half?).    But I suppose you would have to know the number of turns anyway, to be able to work out the math ... 

If it does turn out to be a mislabeled transformer,  couldnt an inexpensive step down could be used while waiting on a 240 volt transformer?    Im jumping the gun here, I know, but maybe some preemptive food for thought.