[tubegarden]

Hi RATs!

OK, old DIY kits are interesting puzzles to attempt to decipher what
the previous listeners/victims did to make it shake their treehouses. I
have several 1956 Heathkit A7 units to draw from. No two are alike.
Some common themes: the 12V filaments are wired in series parallel, two
wires from transformer to first tube, two wires to second tube, etc.
Some used fibre (cloth) covered wire, some plastic. All used the same
physical layout. Twisting the pairs is universal, but, varies from two
or three turns to twenty or so. Soldering is all "large lump", although
the style of physical connection underneath varies from tight pinched
u-hook to loose straight needle through the hole.

Considerable variation appears in implementation of the circuit
diagram. All attempted the feedback loop, but, even though all used the
supplied 6.8K resistor, most went to the 16 ohm tap, one to 0 ohms,
that one reversed the 12SN7 (to 12A6) signal splitter connections to
resolve the phasing issues

Several had substituted the 12A6 pair with 12V6 pair. One changed the
bias resistor (adding 300 ohms), two did not.

The one I am still trying to modify showed three (3!) routes to ground
from the cathodes of the tied together 12A6 pair. While I attempt to
pick one, I took the amp out of service and substituted my old
Consonnance 9.9C, a 300B SE I got as a shipping damaged tubeless wonder
from eBay for less than $70. some years back. Plus shipping ...

The A7-C (no phono stage) with dual output cathode bias R-C mod and the
9.9C, with added 100K pot on the input, make a pleasant pair.

My anxiety about not completing the mods to the second A7 has
dissipated.

The A7-C was about $15. as a new kit, with tubes, The 9.9C was about
$3K, with tubes. The 200X price differential says much about retail
marketing over the intervening forty odd years, the technology is
similar: less than ten watts and perhaps a bit better than your average
Home Theater installation

I will continue to attempt Alan "Flower-Power' Blumlein's garter
circuit .. no hint as to test start date 8^P

I am not sure when I fell in love with the sound of tubes. It wasn't
today, but, it continues

Happy Ears!
Al

[tubegarden]

Bret Ludwig wrote:

SOP among true pros, when required to make Heathkits work, is to
slather all soldered connections with RMA flux and suck everything off
with a Pace tool. Save of course for those connections too far gone,
which are summarily diked out.



Hi RATs!

Us phoney-baloney post-pros just do what we find needed to get the unit
to function. Any larger engineering changes are just for grins

I like to get something working with as little 'improvement' as
possible to hear what it sounds like. I don't pretend to remember what
things sounded like, but, it gives me something to consider when I go
go into Mad Scientist mode and start changing the circuits. I even
build DIY stuff as drawn. OK, I try, OK? - before I get creative and or
crazy.

An example is filament wiring. It works OK to string them together. I
prefer to run a simple pair from transformer, or filter, to each tube.
It may not make the Music sound much better, but, it keeps a lid on my
imagination

Being old and crazy is not recommended for Audio, but, it is considered
wise to just be whatever you are at the moment and just let others
argue about Heaven and Hell

Listening to junk I got to work is great. It does make me wish I could
do more, but, apparently The Force wants me to actually listen, too.

I take it as it comes

Happy Ears!
Al