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-   -   Noob Tube Preamp Finished Kit Transformer HOT! (http://www.diyaudio.com/forums/tubes-valves/195494-noob-tube-preamp-finished-kit-transformer-hot.html)

xetaprime 28th August 2011 12:02 PM

Noob Tube Preamp Finished Kit Transformer HOT!
 
Good Morning,

I have been an audio enthusiast for years but have never built my own or know the basics of tube amplification. I did however buy a finished tube kit from ebay that- although it sounds good and is working, the Transformer runs real hot. Maybe too hot? I have not been able to find the specs on this board and it is sold for 230v. The seller converted it to 110v.

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The one along1986090 sent is wired differently than the first with filament wires going directly to the tubes which I understand is correct? Remember 'noob'. Also the one pictured has 3 22uf capacitors and he installed 150uf.

http://img197.imageshack.us/img197/9011/p1050124p.jpg
http://img714.imageshack.us/img714/5526/p1050125f.jpg

What I'd like any info on is when you buy a kit that says 230v- what is the best way to go about powering it correctly? Use a 230V transformer with a step-up converter? etc. Just want to do it right.

Does anyone recognize this layout? I asked for a schematic and believe they sent the wrong one? Right now I consider this a test machine since I'd like to dig into it and if I blow it I blow it. I will be learning more about tube amplifiers but like I said this is ground zero jumping in-point for me.

Any insights welcome.

Xeta

kevinkr 28th August 2011 03:11 PM

The fact that the seller configured this unit for 120V operation makes the comments about 230V operation irrelevant - it is nothing more than a function of the transformer fitted or if it is a dual primary type whether the primary is wired in series for 230V operation or in parallel for 120V operation. You don't need to do anything.

How hot is the transformer running? If you can touch it without getting burned after several hours of operation it is operating in an acceptable temperature range. If you have a DVM with a thermocouple measure the temperature of the transformer after it has been running for a while.

xetaprime 28th August 2011 03:40 PM

Hi, after 15-20 minutes at no volume + with amps off I can't leave my finger on it for more than a few seconds.

xetaprime 28th August 2011 03:46 PM

Here is how it looked with 22uf caps. Isn't 150u a high substitute? Or do you think that's ok.

http://img853.imageshack.us/img853/2653/12ax702.jpg

dzseki 28th August 2011 04:32 PM

Check the current flow... a preamp such that should draw only a few miliamps + filament. a 10-15VA transformer should enough for thew whole circuit. What happens if you disconnect the board, and you let the transformer alone, maybe something wrong with the transformer itself...

tinitus 28th August 2011 04:35 PM

Quote:

Originally Posted by xetaprime (Post 2688967)
Hi, after 15-20 minutes at no volume + with amps off I can't leave my finger on it for more than a few seconds.

a trafo burning a bit hot :eek: and with just a preamp :confused:

my guess heater/bias is causing it, but I don't much about it

is there something about oscillation could cause this ?

hmm, a trafo changed from 115V to 230V could mean half ampere rating, running on its limit ?

just a few 'options'

xetaprime 28th August 2011 07:50 PM

dzseki,

When I asked about replacing the transformer perhaps with a smaller because it was not mounted to the chasis and nearly touching cover- only taped :0 I was told a 30VA. Perhaps a 10-15VA less heat then? Here is the schematic they sent me for reference...

http://img828.imageshack.us/img828/6981/12ax712au7.jpg

P.S. Forgive my noobness. But you gotta start somewhere. I'm pretty good at learning and I am excited about tubiness as it is new territory. It's funny after half a century on this rock and with SS I'm only tipping me toes into tubeland now. Feels good though.

kevinkr 28th August 2011 08:07 PM

Make note of how the transformer is connected to the PCB and then unsolder all of those wires and tape them off temporarily.

Next just plug in the transformer and wait a while and see if it gets hot.

A 30VA transformer should run fairly cool, if it does then there is probably an issue with a component on that PCB.. Should it run hot you will need to replace the transformer.. Measure the voltages on the secondary and buy a Hammond or Antek that is close.

If you are going to dabble with tubes you need a good DMM, decent temperature controlled solder iron, and appropriate hand tools. Also you should read the safety and high voltage threads associated with this forum.

xetaprime 28th August 2011 08:25 PM

Thank you. I will separate the transformer first. Great idea. I have a basic Radio Shack soldering iron and a decent multimeter but will look into getting a better Iron. Hand tools, I think I'm covered but have no issue with getting deeper involved, This is how it starts, yes?

Regards, Xeta

SY 28th August 2011 08:34 PM

Sadly, yes, this is how it starts.:D

Start saving for an oscilloscope- that's the one other useful tool you'll need when the tube disease hits you full-on.


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