[JP]

I need this...

[Jon Yaeger]

I need a new car.

Can you afford $16.95? If so:

http://www.audioxpress.com/bksprods/BKSTUBDES.htm

If not, oh well . . .


On 8/21/08 1:23 PM, in article ,
"JP" wrote:

I need this...

[Iain Churches[_2_]]

"JP" wrote in message
...
I need this...

*Buy* the book.
It is exceptionally good value
Iain

[Patrick Turner]

Iain Churches wrote:

"JP" wrote in message
...
I need this...

*Buy* the book.
It is exceptionally good value
Iain

Fancy someone **needing** Mullard schematics.
Sometimes i've wanted one, but never needed one.
Some mass manufactured amps I have had to repair will have circuits
with nearly full Mullard detail, but be slightly different,
so I have to get the schematic of that amp model somewhere or simply
trace it out on my exercize book and draw what's there.

Most Mulard power and preamps are all in the public domain and can be
found around the web
if you google enough, but a book at 17 bucks is very cheap.

Things like the Mullard 520 with a pair of EL34, 12AX7 LTP phase
splitter, EF86 input pentode
don't much interst me much these days because there are better designs
to be had.

Patrick Turner.

[Phil Allison]

"JP"

I need this...


** Here's one for ya:

http://www.ampslab.com/vintage_dynaco_mullard.htm

30 watts, ultra-linear and damn near class A.



....... Phil

[Patrick Turner]

Phil Allison wrote:

"JP"

I need this...

** Here's one for ya:

http://www.ampslab.com/vintage_dynaco_mullard.htm

30 watts, ultra-linear and damn near class A.

...... Phil

Yes, that's extraordinarily Mullardish for a schematic,
and with 6CG7 phase inverter LTP which would give
better performance than a 12AX7.

Notice the 12pF between a screen tap on the OPT taken to the cathode
of EF86 for FB at HF. There is also a 33pF across the 18k RFB,
so that was their answer to keep the amp stable at HF with the Dynaco
OPT.

DIYER people might find that with any other OPT, the HF feedback through
the
12pF and 33pF won't work, and othger C values would have to be used.

There are other things I'd change, like having one x 470 ohm Rk and
470uF Ck from *each*
EL34 cathode to 0V, and to have much larger C on rails for B+.

The other thing that is plain wrong is that they have a note saying
some R have to be within 1% matching.
This is to get accurate ac balance to drive the two EL34 grids.

But anode loads to the 6CG7 ( or a 6SN7 which is electrronically equal )
should be slightly different values unless you have a constant current
sink
from 6CG7 cathodes to 0V instead of the 22k.

The Mullard specs originally mentioned that the anode RL for the
original
12AX7 should be nearly equal, but swapped around for best balance,
and in fact the difference of RL at the anodes becomes quite a lot
with low µ triodes used for LTP with a common Rk.

The signal current change in Rk summed with current change in the right
hand side RL
is equal to the current change in the RL on the left hand side nearest
the EF86.

To get equal signal voltages at each anode, the anode RL must be
different, and ideally
adjusted until RL value give the balance.

With slightly different RL to the LTP, and with balance,
the 2H does not balance exactly, so expect some 2H in the output
in addition to mainly 3H.

Patrick Turner.

[JP]

On Fri, 22 Aug 2008 16:06:48 +1000, "Phil Allison"
wrote:


"JP"

I need this...


** Here's one for ya:

http://www.ampslab.com/vintage_dynaco_mullard.htm

30 watts, ultra-linear and damn near class A.



...... Phil

Ther's a couple of Dynaco trannys on Ebay for $50 each BTW .. or were
yesterday...

[Peter Wieck]

On Aug 22, 8:57*am, JP wrote:


Ther's a couple of Dynaco trannys on Ebay for $50 each BTW .. or were
yesterday...- Hide quoted text -

That's pretty much because they *ARE* on eBay. If one gets out more
into the real world, reputable vintage iron gets pretty cheap. I
picked up a complete set of Fisher Iron (500C) in excellent condition
for $15 at Kutztown some time ago. A complete set of Scott 340-series
Iron went for less in May, and the seller had quite a bit of similar
material at similar prices from Dynaco, Fisher, Scott, Sherwood, Eico
and the like, as well as quite a few NOS/NIB Hammond pieces.

Peter Wieck
Melrose Park, PA

[JP]

On Fri, 22 Aug 2008 07:48:48 -0700 (PDT), Peter Wieck
wrote:

On Aug 22, 8:57*am, JP wrote:


Ther's a couple of Dynaco trannys on Ebay for $50 each BTW .. or were
yesterday...- Hide quoted text -

That's pretty much because they *ARE* on eBay. If one gets out more
into the real world, reputable vintage iron gets pretty cheap. I
picked up a complete set of Fisher Iron (500C) in excellent condition
for $15 at Kutztown some time ago. A complete set of Scott 340-series
Iron went for less in May, and the seller had quite a bit of similar
material at similar prices from Dynaco, Fisher, Scott, Sherwood, Eico
and the like, as well as quite a few NOS/NIB Hammond pieces.

Peter Wieck
Melrose Park, PA
I gotta get out of this place! Small town Texas has almost nothing to
offer.... Dallas Ham Day here I come! lol

[[email protected]]

You need an AC drive balance control since the tubes are never
identical anyway.

[John Byrns]

In article ,
wrote:

You need an AC drive balance control since the tubes are never
identical anyway.

Or you can just learn to love a little imbalance, do away with the complexity of
a balance control and its potential reliability issues, stop obsessing, and
enjoy the music. If people can enjoy SE amplifiers they ought to be able to
enjoy PP amplifiers with a slight imbalance.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/