DIY Audio Projects Forum

eBay 6SN7 / 300B Amplifier PCB Kit
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Author:  Woodo [ 11 Apr 2018, 18:01 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

Woodo wrote:
quite possibly the dropping R value should be worked based on 2A as there are two windings. not sure how the transformer ratings work. if so that would mean a 4 watt 1R.

edit: Reading further about this it looks i should be using 1.2 A. Also the V drop of the bridge rectifier is 0.9v per diode giving 1.8v drop. So dropping resistor needs to drop 8.4 - 1.8 - 5 = 1.6v at 1.2 A. if correct that is about 1.9 w 1.3 R. Alternatively the approach used in the 300b set in Gio’s link above is to use a further adjustable regulator.

Author:  Woodo [ 14 Apr 2018, 07:28 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit updated schematic

edit: updated schematic from another look at the pcb

Author:  Gio [ 16 Apr 2018, 21:47 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

You can use resistors to drop the voltage. However, you will likely end up doing trial and error to get the right value. The issue with using resistors is the heat generated. In that regard, you will want to use resistors with power ratings much larger than the power to be dissipated. Give consideration to spacing and airflow around the resistors. Most heat issues won't arise until after several hours of continuous operation, so keep that in mind when testing.

Also note that with 6V transformers you may be cutting it close even with a low dropout regulator like the LT1085.

Author:  Woodo [ 18 Apr 2018, 22:12 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

Thanks Gio. I expect it will be a lot of trial and error mixed with the experiences of those who have had success on the site.

Author:  Woodo [ 19 May 2018, 04:30 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

After arrival of a package of Edcor transformers I hope to successfully put together this ebay kit amp. Reading the forum and Youtube there seems to be a number of possibilities to layout the major components. I would appreciate members’s views on the examples below or any others I haven’t thought of.

Author:  Woodo [ 19 May 2018, 04:58 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

I also had another crack at the schematic using DIY Layout Creator. still learning to use it. Sorry about the component values. there in the system not sure why they haven’t labelled the values. I’ll repost them when i work that out. There’s also an LED in one of the 300b filament circuits to add.

Author:  Pete D [ 19 May 2018, 06:11 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

Hi Woodo, yes this is a problem - getting a pleasing layout whilst satisfying the electronics!

Firstly I wanted my build to be symetrical for aesthetic reasons, secondly it had perform well as well as possible with short lead lengths etc etc. Very simplistic I know, but that led me to only one possible layout.

So my mains tx and choke were central, the choke being 20mm or so from the glass of the rectifier. The output transfomers were centrally right behind the 300B's (note the mains tx is rotated 90 deg). The resultant amp has no discernable noise/hum etc.

When I did my trial layouts I found that no commercially available chassis would quite give me the layout I wanted, so had to bite the bullet and make my own.


Author:  Woodo [ 20 May 2018, 04:49 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

Thanks Pete. I enjoyed watching the build on youtube of your amp and along with a number of diyers on this site were my inspiration to try this. it appears I should have got a slightly bigger box to achieve a better layout so i will have to consider pressing ahead with the current one or look for a different size. i recall the options from hammond were a bit limited. also the one i have is a bit thin and bends with the weight of the transformers when moving it. buying the base for it might brace it better. i have been known to do a bit of slap together woodwork for a set of kef concertos an chris rogers pro9 TLs kits but that was over 40 years ago and would take some effort and tools to get back into it. maybe for my next amp i would like to do one of Matt Renaud’s designs on this site if i can learn more about doing point to point wiring up. i would like to use the Lacewood timber Matt has used as one of the tree species grows right in my region and can still be bought.

Author:  Woodo [ 02 Jun 2018, 19:14 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

decided to push ahead with chassis I have on hand. Started drilling holes after considering many possibilities and pics on the site. can lead to procrastination. still waiting on some washers, grommets and other parts.

not sure if i need to drill other holes for heat dissipation but on the pcb there will be a few 2 and 5 watt resistors - any ideas would be appreciated.

Author:  Woodo [ 02 Jun 2018, 22:51 ]
Post subject:  Re: eBay 6SN7 / 300B Amplifier PCB Kit

New photos attached

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