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Old 11th May 2009, 03:01 AM   #11
kevinkr is offline kevinkr  United States
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Again as I indicated increasing C7 by 5X is not going to do much if the limitation lies elsewhere.

I would start by shunting C4 with some additional capacitance, but I would also just consider the possibility that this amplifier is not right for the speakers you are using it with.

Before running off and making a lot of changes can you fill in the details; music preferences, room size, speaker type, etc?
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Old 11th May 2009, 03:32 AM   #12
Sheldon is offline Sheldon  United States
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Old 11th May 2009, 08:09 AM   #13
tmhajw is offline tmhajw  United Kingdom
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Hi again
Firstly, as only my second every amp build I'm delighted with it; however I'm wondering if the mids/bass could be a little 'richer' -perhaps more how I imagined a valve amp to be!

I've tried it with Spendors (lots of bass) Lowthers (no bass!!) and its now in my kitchen, 5mx5m playing low thru' wilson benesch, of all things...

Overall I'd say the sound was quite well extended bass/treble, actually, especially compared to my Loftin-White (all midrange but grabs the music by the scruff of the neck..!) and with quite good 'grip'. If anything its just a tad 'bright'....

I shall drop in those 100uf's across C4 in a minute just to see...
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Old 13th May 2009, 12:25 PM   #14
tmhajw is offline tmhajw  United Kingdom
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Hi took me slightly longer to drop in those caps- bad hangover & deaf after a Jesus Lizard gig..!
Anyway, firstly I put a 100uf across the 47uf fo the 300b cathode (C4), bit of an overkill but these were the only ones I had lying around. I noticed a subtle but useful increase in actual depth of bass response...
I then went ahead and dropped in those 1uf pio across the 0.22uf teflon coupling caps 6SL7 to 300b (C7) and was immediately struck by the much better 'richness', and a bass response verging on 'wayward'. Presumably other design limitations are kicking in, perhaps those big Hammond Tx.
I guess the moral for me is to ditch the teflons here as they are too lean. Might keep the 1uf in for now as the sound is kind of fun...Any downsides to this, please?

I'm sorry I still don't understand the significance of lowering the value of the grid leak resistor (R5) and I admit my useless 'newbie' abilities, here... Morgan Jones I find painfully frustrating at times as scant regard is given to the basics! Please elaborate on this...? A few schematics I've seen of the WE 91 suggest 220k; my Loftin white uses 100k; Morgan Jones seems to like 1M!
Thanks Thomas
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