6SL7 pre-amp (driver)

[hschaser]

Easy if you have a multi-meter.
Select either the 200 or 2K Ohms range. Make sure the transformer is not connected to anything of course and clip one meter lead to any lead/tag on the transformer, then touch each of the other leads/tags in turn.
- If it is an Auto Transformer, every lead will give a resistance reading.
- If it is an Isolating Transformer, only one or two of the leads give a resistance reading, but all the others will read 'Open Circuit'.

Go and test the low voltage one you have and see.

This might help.

Thank you Alan.. indeed

The connections shown to the 'copper ground bus' appear to be in random order, so once you resolve the safety issue you may get hum. The PSU ground should be at the output of the PSU, not halfway along.

The situation you describe is impossible (mains breaker tripping when an internal ground is connected), therefore you have not built what you think you have built and told us you have built.

Is the transformer a proper power transformer, providing isolation (as shown in the diagram), or is it some sort of autotransformer? The high current rating is a hint towards the latter.

I now understand that this is not a preamp (and not a driver either) but actually the voltage amplifer stage of a power amp. Maybe you could ask the Mods to change the thread title?

HI DF96,

You are indeed sharp... about the auto transformer i am using.. Thanks alot. I did not realised it myself..

Hi all
thanks for all inputs and comments. They are priceless. Will get an isolating Transformer and work from there. Will keep this post updated. Between tube rectification and solid state rectification which is better sonically?

Thanks

 

[DF96]

Is there a proper way / order of grounding? Pls enlighten me if yes.

Yes. A search will find lots of information.

Pls forgive me for an ignorant question, are there differences in a preamp, Driver and voltage amplifier?

A preamp comes before an amplifier; it is not part of an amplifier. A voltage amplifier is the usual first stage in a power amplifier. A driver comes between the voltage amplifier and the output stage, but on most cases is not needed.

Between tube rectification and solid state rectification which is better sonically?

Done properly there should be no difference. In any case, I would not worry about that on your first build as there are more important things to learn about and get right.

You are fortunate that your house has a good electrical system so the trip has saved your life.

 

[TonyTecson]

i lived in singapore for 4 years, and i have seen first hand how good their house wiring is, with proper grounding, and with elcb and mcb's used....

 

[hschaser]

HI DF96,

Am I right to say 6SL7 in my case is a voltage amplifier?

 

[kodabmx]

Yes, the 6SL7 in your case is used as a voltage amplifier. As for a proper power transformer, you could use the Triad VPT230 series, available at Digikey and Mouser, or you could get a proper tube power transformer from Hammond or the likes.

 

[PRR]

The couple-hundred volt load is 4 milli-Amps (AC), not 4 AMPS!!!

You want a much smaller transformer. You probably can not find one as small as 4mA; 50mA is fine.

 

[kodabmx]

He's building a KT88 SE amp with the same transformer. The 6SL7 is just the input for it. The 4A was an autoformer.

 

[LJT]

Hammond transformers as mentioned by kodabmx has viable options. Another make that does not mean having to transport a lump of iron across the world is SAC transformers from Thailand. SACThailand
Transformers are not cheap so make sure that you identify one with the right voltage and mA rating for the amp you envisage to be your final product. This include current draw of the voltage amplification stage discussed above, your driver, phase splitter (if PP amp), current in output tube(s). then multiply by 2 if stereo and then add som for margins - you dont want your transformer running 100% load at all times.
Do some searches on similar designs to yours and/or ask questions on this forum if in doubt.

 

[hschaser]

The couple-hundred volt load is 4 milli-Amps (AC), not 4 AMPS!!!

You want a much smaller transformer. You probably can not find one as small as 4mA; 50mA is fine.

Hi,

Thank you for your advice.

He's building a KT88 SE amp with the same transformer. The 6SL7 is just the input for it. The 4A was an autoformer.

Hi Kodabmx,
I have mistaken the autoformer for an isolation one.
Currently am sourcing a suitable one.

Thank you..

Hammond transformers as mentioned by kodabmx has viable options. Another make that does not mean having to transport a lump of iron across the world is SAC transformers from Thailand. SACThailand
Transformers are not cheap so make sure that you identify one with the right voltage and mA rating for the amp you envisage to be your final product. This include current draw of the voltage amplification stage discussed above, your driver, phase splitter (if PP amp), current in output tube(s). then multiply by 2 if stereo and then add som for margins - you dont want your transformer running 100% load at all times.
Do some searches on similar designs to yours and/or ask questions on this forum if in doubt.

Hi LJT,

Thank you for your precious insight and experiences. Will definitely look at thailand for the right transformer.

Cheers

 

[Burnedfingers]

Done properly there should be no difference. In any case, I would not worry about that on your first build as there are more important things to learn about and get right.

Power supplies done properly there should be no difference...

There are probably countless pages devoted to SS power supplies vers tube power supplies. Both if done properly will of course work. Sonics? Some will claim to hear differences and I'm probably of that group just the same as some claim to hear differences in capacitors and resistors. Not trying to start WWIII but I beg to differ. Some SS power supplies I've heard sound harsh to my ear and some tube supplies sound much better and maybe things weren't designed correctly. In my case with my Aikido I've used 5AR4's, 5Y3's, #80 with adapter, and #83 with adapter. The very best sounding was a number 80.

If it were me I would experiment and see what sounds the best and that is part of diy.

 

[kodabmx]

For me, the only place to use tube rectification is in a guitar amp where you want the voltage sag etc. To me, DC is DC. The tubes vs SS argument is as silly as "Duracell sounds better than Energizer" IMHO.

 

[DF96]

Not trying to start WWIII but I beg to differ.

I said two things about audio PSUs:

Done properly there should be no difference. In any case, I would not worry about that on your first build as there are more important things to learn about and get right.

In the context of this thread the second is by far the most important. This is not a place to debate the pros and cons of rectification methods, when the thread starter did not realise that he had used an autotransformer even though it said "autotransfomer" on the label.