Received: by 10.224.220.12 with SMTP id hw12mr9753027qab.8.1349548576443;
        Sat, 06 Oct 2012 11:36:16 -0700 (PDT)
Received: by 10.236.91.99 with SMTP id g63mr1526570yhf.4.1349548576415; Sat,
 06 Oct 2012 11:36:16 -0700 (PDT)
Path: e10ni211270746qan.0!nntp.google.com!l8no28524647qao.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: rec.audio.tubes
Date: Sat, 6 Oct 2012 11:36:16 -0700 (PDT)
In-Reply-To: <John.L.Stewart.ab19299@audiobanter.com>
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com; posting-host=99.238.136.126;
 posting-account=7eatwQoAAAA7jEgZiH-tBO0RJMP2eeGB
NNTP-Posting-Host: 99.238.136.126
References: <6429e0f3-aab6-4a81-a425-edda5a371915@googlegroups.com>
 <e1995a15-1024-4ec3-be3d-07cd3646c35d@googlegroups.com> <John.L.Stewart.ab19299@audiobanter.com>
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <e3eb64a3-f86b-4f57-8c09-9517b7132860@googlegroups.com>
Subject: Re: Tales of a Heathkit W7-M amplifier
From: Analogdino <analogd...@rogers.com>
Injection-Date: Sat, 06 Oct 2012 18:36:16 +0000
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

On Tuesday, 2 October 2012 21:41:59 UTC-4, John L Stewart  wrote:
> Analogdino;963098 Wrote:=20
>=20
> > Quick update:
>=20
> > Tried a pair of good 5881's, bias optimized, even balanced the cathode
>=20
> > currents to around 1.5 mA.
>=20
> > No good!
>=20
> > Max p-p volts across 8 ohms =3D 40 VAC, 200 Hz.
>=20
> > Thus, power =3D 25 watts.
>=20
> > Pretty much same as 6L6's, not really surprised.
>=20
> > We soldier on...
>=20
> > Cheers,
>=20
> > Roger
>=20
>=20
>=20
> An intriguing solution to the drive problem can be found in the 6U10
>=20
> triple triode. Triodes 1 & 3 look like a 12AU7 while triode 2 is similar
>=20
> to 1/2 of 12AX7. All that makes possible a drive cct as used in the
>=20
> Mullard 5-10 & 5-20.
>=20
>=20
>=20
> Input gain stage uses triode 2 while the LTP consists of triodes 1 & 3.
>=20
> No need for another hole in the chassis, just enlarge the existing hole
>=20
> to accomadate the duodecar socket.
>=20
>=20
>=20
> A much better drive for the 6L6's or whatever.
>=20
>=20
>=20
> Cheers, John
filename: Avater.gif                                               |
>=20
> |Download: http://www.audiobanter.com/attachment.php?attachmentid=3D303|
>=20
> +-------------------------------------------------------------------+
=20
>=20
> John L Stewart

Interesting idea, John, but there's a lot of chassis space for an extra hol=
e. Also, that would give a bit more wiring space (the 6AN8 is already "tigh=
t".} Anyway, now it's all back together with "borrowed" EL34's (from my Lea=
k TL/25) I now get over 40 watts RMS, max, so I'll not be redoing the front=
 end as planned, will just leave it "as-is" (but with a 470K screen dropper=
 replacing the original 1.5 Mohm) - this slightly increases the 6AN8 plate =
current to, IIRC, just over 1 mA - better, IMHO.
BTW, I've got a line on a couple of new Russian EL34's (that I can afford!)=
, so the Leak TL/25 will likely get them and the W7-M will have to live wit=
h the present weak ones! Loud enough for me, for now...
Cheers,
Roger