Added gain stage question

ivan H · Post by **ivan H** » Sat Apr 20, 2013 12:23 am

Hi, I'm just starting an added gain stage build, kind of switchable between Caswell/Levi type thing & am thinking, with the unused triode it would be best to not connect the heater (pin 5) & to ground the cathode, grid & anode to keep it from adding unwanted noise to the signal. Is this correct. Any input appreciated. Cheers

neikeel · Post by **neikeel** » Sat Apr 20, 2013 2:03 am

In my (limited) experience of this it seems to make no difference.

Slowly working on another one of these at the moment and when I get to the set up stage will retry.

ivan H · Post by **ivan H** » Sat Apr 20, 2013 4:10 pm

Ok, thanks Neil. I've just started this one, waiting on 1 more order from Valvestorm, panels, pots & electrolytics & I'll get right into it. I'll try & get some pics/clips posted when done. One more quick question, with V1a/b, supposedly the b triode is the quieter of the two, which is why the 2203/4's have the input going to that triode. Do u know if it makes that much of a difference, either way? If it does I was thinking maybe rotate V1 thru 180 degrees & also swap the heater wiring to keep the phasing the same on all heaters, or do u think not to bother. Thanks again. Cheers

neikeel · Post by **neikeel** » Sat Apr 20, 2013 11:56 pm

I would use V1b as the first stage, the phasing of the heaters should not be an issue simply because it is ac and there is no interatction between the heaters.

6burgh · Post by **6burgh** » Sun Apr 21, 2013 9:35 am

Neil's assertion is right from what I've been able to tell. I've tried every combo of heaters wired/not wired and I always come back to V1b as stage 1 and the added tube wired for only 1 half heated. I just built another version of the #39/#36 like amp and always come back to a modded superlead approach (ie V1b, then V1a, then "V0", then V2a for gain stage order).

ivan H · Post by **ivan H** » Sun Apr 21, 2013 5:07 pm

Thanks Neil & 6burgh, that is very helpful. Actually 6burgh, its ur layout that I have used mostly in the lead upto this build, altho I have the stages lined up in their respective order (so I will rotate V1 thru 180). Again, thanks for all the help guys. Cheers

ivan H · Post by **ivan H** » Sun Apr 21, 2013 5:33 pm

1 more question if I may 6burgh,,, the grounding scheme, do u recommend as in ur layout, or attempting Larry's scheme, altho I'm not 100% on how the added triode would tie in with this. Again, thanks for all the help guys. Cheers

6burgh · Post by **6burgh** » Sun Apr 21, 2013 6:26 pm

I definitely recommend the star/larry ground scheme. The added stage grounds to the same point as the volumes and V2. I wish I had Illustrator so I could build my layouts as well as others. I ride on the coattails of the better designers here though like SDM... I do love the 4 stage build though, so many ways to make it sound good! Good luck and keep us posted with where you end up in terms of layout and design!

ivan H · Post by **ivan H** » Sun Apr 21, 2013 9:02 pm

Ok, thanks heaps 6burgh, that is a big help. I will post pics/clips when done. Thanks again. Cheers

robert · Post by **robert** » Sun Apr 21, 2013 9:53 pm

Hello Ivan,

since the Vb systems always create a slightly less noise / hum (when using AC heating), it seems more efficient and easier to me to "rotate" all the ECCs.

Regards

Robert

ivan H · Post by **ivan H** » Mon Apr 22, 2013 3:07 pm

Hi Robert, thanks for the tip. Thinking about it now, it really does make sense to, so I will follow ur advice. When u say all ECC83's, do u mean the PI also, or just the stages up to (& including the cathode follower. Thanks again. Cheers

robert · Post by **robert** » Mon Apr 22, 2013 11:03 pm

It cannot hurt to "rotate" the PI socket too.
Makes things easier when you change the ECCs (less fiddeling, because all pins have the same "direction")

Regards
Robert

ivan H · Post by **ivan H** » Tue Apr 23, 2013 12:26 am

Ok, I rotated the 4 pre amp tubes as I figured it wouldnt make any difference with th e PI, & I managed to keep the heater wiring reasonably tidy without having to redo it. I will get pics posted when this is completed. I'll also properly thank everyone who has supplied all the nescessary components for this, & my last build. These will include Metro Amp, Marstran, Heyboer, Valvestorm & Brian Haberman. Thanks for the great products & the great service guys, & thank you to all the forum members who have helped by answering my questions & by posting all of the info that is available on this forum. Cheers, Ivan

robert · Post by **robert** » Tue Apr 23, 2013 12:45 am

Hi Ivan

if possible, purchase the two books from Valve Wizard (Merlin Blencowe):

http://www.valvewizard.co.uk/" onclick="window.open(this.href);return false;

They both are IMHO fantastic for us DIY ampbuilders and extremely helpfull!

BTW:
Sadly, we still have to wait for a book like this written by Randall Aiken and Larry Grohmann (hello guys, can you hear me?)

Regards

Robert

ivan H · Post by **ivan H** » Tue Apr 23, 2013 1:14 pm

Hi Robert, once again thanks for the tip. Cheers, Ivan

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