tube rectifiers, HexFreds, and Hammond Organs

[Bill Layer]

Hi Mark,

>I have a Hammond S-6 Organ which uses a 5U4 rectifier. I know of a solid
>state replacement that fits in the same socket. Is this anything like
>the HexFred thing?
>
>I was told by Groove Tubes about the power sagging on lower notes and
>that the s.s.rectifier (or was that the "U.S.S. Rectifier" :-) might
>improve bass response. I'm thinking getting it just to try it. only $20.
>A 5U4 is $30.

I wouldn't do it. The 5U4 has one of the largest voltage drops of all the
large vacuum rectifiers, on the order of 40 volts or more. If you replace
it with the SS rectifiers, supply voltages will rise accordingly. This will
more than likely lead to damage to the aged filter and coupling
capacitiors, and may also over-bias or otherwise damage the output power
tubes. What type are they? 6V6GT? The 6V6 is famous for being intolerant of
excessive plate voltage.

If you want to improve bass response, I can make some suggestions.

>Has anyone done anything (mods?) to this organ? According to a friendly
>organ salesman it's not a true "Hammond" because it doesn't have tone
>wheels or drawbars and therefore is useless. I say it sounds cool and
>therefore is useful!

The S-6 is a chord organ, with a an abbreviated monophonic solo keyboard.
It's interesting point (or so I've heard) is the bass feature. Have you got
that strange 2-pedal setup? Does it work?

I think that this organ has a lot of useful parts in it. Firstly, it's got
about 28 6SN7GTs in it, which is a giant among audio tubes. Also, it
produces it's tones with a long series of fixed L-C oscillators. I think
that these tone generators would make a very cool base for a polyphonic
all-tube synth.

It's not valuable as hammonds go, but then again, what would it cost to
replace it? The thing was *not* cheap when it was new. If it were mine to
do, I'd think about modifying the heck out of it. 

Let me know if you need parts, I've a bunch in the attic. 
 
 >
Bill Layer
Sales Technician
<b.layer at vikingelectronics.com>

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