Looking good and it is one hell of an amp. 

 

In other news we have an eruption here now. 

In other news we have an eruption here now. 

 

Keeping my eye on it.

Awesome.  Now sit back and enjoy.

 

Edit: This was directed at Headinclouds, not EruptionInProgress.

Edited August 23, 201411 yr by Kerry

Now they say we have no eruption... I has sad... 

Yes that's the one. (edit; of course that doesn't mean that everyone should be fitting that value, just note you might have to adjust this)

 

 

How would you know if you need to adjust to 1.1Kohm?

Edited August 23, 201411 yr by chiguy

http://nos.nl/artikel/690027-code-rood-voor-vulkaan-ijsland.html

This is a news item with a video from the Dutch television about the Vulcano eruption.

How would you know if you need to adjust to 1.1Kohm?

If you cannot get the tubes' offset adjusted with the 1k trimmer and the 1k5 resistor, try resizing the 1k5 resistor down to give more adjustment range.

From what Geoff was mentioning it sounds like a tube to tube variation problem, it may or may not be needed on an individual amp. First see if you can get the offset properly adjusted with the 1k5 resistor.

BTW Geoff, that photo looks nice. Quite inspiring! Working on my Mouser parts order as I type.

Thanks for the PCB group buy.

And thanks to Kevin and Birger for the design and prototyping.

What is a suitable pot for volume control? It has to be a 4 gang, 50k, log pot?

The issue with the trim pot is also present in the KGSSHV or any other amp like this.  Components have different specs even if they are working as they should

 

What is a suitable pot for volume control? It has to be a 4 gang, 50k, log pot?

 

Any pot will do.  We use 50K mostly to cater to any source that is out there but 10K is most often more than enough. 

A simple solution could be to choose a 2K trimmer and a 499R resistor, if there is not a minimum safe value for the cathode resistor higher than 499R?

No, that's not a good idea as you don't want the pot to dissipate all that heat. 

yes for a 1/2W trimmer but not for a 1W such as #652-3250W-1-202

Sure but spending 20$ to fix a non issue is a bit off isn't it? 

You are right. Considering the Kevin recommendation and the Headincloud experience the total resistance (R20+VR2) should be less than 1K5, so, a solution is to use the 1K trimmer and a 750R resistor. BTW, in case of using the 1K5 resistor, 1/2W is not enough ( the dissipation with 10+10 mA is 0,6W).

1W resistor wouldn't go amiss there but resistor ratings are a bit of a hit and miss at the best of times.  Take Mills for instance, they should never see even half their rated wattage but a Vishay CCF60 can be abused no end. 

Congratulated with your working amp, Headinclouds.

Can you send more pictures, so we can learn from you?

Which transformer(s) do you use?

It wasn't quite finished when I took this.  The little 0.1 caps are missing. 

 

Toroidy.

 

 

Hi Geoff,

Toroidy, the same as mentioned by Chiguy?

"Audio grade transformers with mounting pads:

TS 150VA PRI: 2x 117V SEC:

> 2x 280V @0.18A

> 15 - 0 - 15V @0.5A

> 2x [email protected]

cost: 75,80 EUR/pc"

That certainly would do it.  although it is a bit beefy, as Birgir said a few posts back you can cut the HT current to 140mA.

 

For Euro use you could have a single 230v primary.

I am not very sure about the transformer. The transformer from AnTek (AS-1T300 - 100VA 300V) seems okay, but in that case I need an other transformer for the 30V. What is better; 2x280V or 2x300V? Or doesn't matter at all?

Don't you have to pay for shipping and poss import duty on Antek?  In Europe I think Toroidy are an excellent choice.

 

If you are planning to run at the Birgir advised 350v,  280v ac will also be excellent.

It wasn't quite finished when I took this.  The little 0.1 caps are missing. 

 

Toroidy.

 

I put the trimpots as indicated on the silkscreening (both facing each other) but now that I think about it, I should have put them going the same way to make adjusting them easier.

 

Edit: To clarify, on the amp board silkscreen, the 1K trimpot has the adjusting screw on the right and the 2K trimpot has the adjusting screw on the left.  I wasn't thinking when I put them in and just followed the silkscreen.

Edited August 26, 201411 yr by chiguy

It really doesn't matter which way they face. 

You're right, it doesn't matter which way they face.  I'm just being OCD.