LarMar wiring check

GlideOn

GlideOn

Member
Finally ready to move to a Type 3 to a LarMar Master Volune in my Traynor YBA1. Don't hate the type 3 it does the job admirably without drama, but still somewhat fizzy at low volume, can't help but wonder if I could do better.

I think others have used LarMar on their YBA1 to great effect and I see no reason why I can't accomplish the same.

Using Rob's diagram, I made my own doodle. I may need an extra pair of eyes to verify my work is correct.



Notable differences in my YBA1 from stock:

Master Volume pot is where previous Volume II pot was. I'd like to leave it there.

Installed an adjustable bias curcuit with 25kl pot installed (to help run KT77s), stock 15k bias resistor kept after pot to filtering section.

Have not forgotten about the 1.8M safety resistors, simply ommited yo keep the drawing somewhat readable.
 

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I highly recommend a dual 250K PEC pot instead of an Alpha or CTS brand. Yes the PEC is more money but it seems to make a difference. I used Alpha and PEC and the PEC had better characteristics at lower settings. It's not that the Alpha sound bad it's just the PEC even at $60.00 might be worth the investment for you.
 
harddriver said:
I highly recommend a dual 250K PEC pot instead of an Alpha or CTS brand. Yes the PEC is more money but it seems to make a difference. I used Alpha and PEC and the PEC had better characteristics at lower settings. It's not that the Alpha sound bad it's just the PEC even at $60.00 might be worth the investment for you.
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I would love to use an appropriate DC rated pot, but the PEC or similar mil-spec can't be found anywhere these days. None of the pots are rated, really so just have to rely on good bias caps and resistors that haven't burned up or drited. They've all been replaced and are working fine.

That being said I did manage to get a very good Alpha Dual 250k; they are within 7k of each other throughout the sweep which is less than 3% spec, better than I could possibly hope for on any dual pot.
 
Most 250K pots will read lower than 250K more like 220-230K that why you can use them in place of the bias splitters/grid leak resisistors.

Valvestorm carries the PEC dual audio pots, yep your right ne's out of stock I just looked. The Alphas work fine.
 
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The 250k pots should read in spec, not always low. Add 2M2 safety resistors so that the parallel resistance is 220k. Done.
 
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