Schematic help. (thread split)

[GeirW]

Gday.

Am back into this project again.

There have been some slight development in this case,
i recently got hold of a perfect condition 75-20
with mahogny cabinet (without speakers).

This would mean i got spare parts, and that`s temts
me to make that replica.
The consept wold be to make a "integrated amp"
new-style, keeping the original design/look.
The problem is that this schematic confuses me,
so if anyone can be a real helper, can redesign this schematic.
I need one mm/riaa stage and a line,
very simple circuits, a bit better quality.
(would be keeping the xformers though.

The existing amp. isn`t bigg, cosist of one shared ECC83,
and one EL84 pr. channel.
Haven`t measured anything, so i ain`t got any more
then what`s stated on the org. schematic.

Thread split:
Hello again, plus a couple of Q`s.

[GeirW]

Gday.

Just a question, is it duable to use 1x ECC83 pr. Ch.
with the same power supply.
(when i think about it, it is a unused 83 in the radio part)
btw. what is the basic difference between ECC83 and 82.

[audiousername]

Thanks for the message. I saw this thread before but was scared off by the complexity of the schematic. As long as you're asking about the audio stage, I'm ok

About using a single ECC83/12AX7 per channel... Of course it's possible. An extra 1mA or so shouldn't stress the power supply. Parallel the sections, and make the necessary adjustments (mu remains const, transconductance doubles and plate resistance halves). Unless you're making monoblocks I don't see why you'd want to though. The crosstalk between sections isn't significant at audio frequencies.

Of course, halving plate resistance and increasing current capability of the driver stage is generally seen as good for the amp (unless you're looking for an anaemic driver stage to produce an anaemic sound ) I don't like the ECC83/12AX7 as a driver stage, and I'm not alone. Others will of course disagree.

You could use the ECC83s in the phono stage you mention, and use the ECC85s from the tuner part of the amp (assuming you no longer need the tuner) as driver valves - though they still will almost certainly provide too much gain, the EL84 is not too difficult to drive. This may sound better. It may not. You'll never know for sure unless you try it.


Other suggestions, Anyone??


BTW: I don't see an ECC82 in your schematic.

[GeirW]

Gday.

About using a single ECC83/12AX7 per channel... Of course it's possible. An extra 1mA or so shouldn't stress the power supply.

That`s what i was thinking of, since am gonna rip out the radio,
removing the: ECC85. EF89. ECH81. EBF89. EABC80
should make enough "current" left.

Unless you're making monoblocks I don't see why you'd want to though. The crosstalk between sections isn't significant at audio frequencies.

The imidiate idea was to do dual mono/mono block construction,
for the ease of it, but if you think its a bad idea.--
(didn`t quite follow you here.
a bit early in the morning for me.)

I don't like the ECC83/12AX7 as a driver stage, and I'm not alone. Others will of course disagree.

Am not sure either, but i assume ECC83 is chosen
coz. of the other inputs. (etc.- phono/tape)
But i love the sound it produces now.
(all telefunken, but one 84. is filled with gass, so i have
taken a wild "guess", and ordered two EL84M.)
Q. What is the perfect driver for 84se.?
(If you can say that.?)

You could use the ECC83s in the phono stage you mention.

I was thinking along this lines, etc.- ECC83/12AX7
for phono. (2x.?) separate stage with batteries?)
There is a one tube ECC83 at bonavolta,
but am not sure about it`s quality, how about riaa correction.?

BTW: I don't see an ECC82 in your schematic.

There ain`t one, i was just curious.

[audiousername]

Originally posted by GeirW
The imidiate idea was to do dual mono/mono block construction,
for the ease of it, but if you think its a bad idea.--
(didn`t quite follow you here.
a bit early in the morning for me.)

Monoblocks/Dual Mono is fine. Just more expensive

Originally posted by GeirW
But i love the sound it produces now.

Then keep the 12AX7s in there, for now. Try using some alternate driver valves and see if you like it

Originally posted by GeirW
all telefunken

ooh, Telefunken 12AX7s are expensive! But I guess these aren't NOS

Originally posted by GeirW
What is the perfect driver for 84se.?

There isn't a perfect anything. Just different compromises. You could even try an EL84 as a driver!


On the issue of the RIAA section, read some articles out there on RIAA correction with valves, like those atTubeCad Journal, and try to make up your own mind whether the schematics you found are any good.

[audiousername]

I just thought of this.... Though it's not directly related to your question

You have a magic-eye indicator tube and an EABC80, right? Let's put them to good use!

Why not add something like this to your new amp. Looks great and will stand out from the crowd!



Some details here. Mark Schutte (the author of that webpage) wrote an article for Valve, but it's disappeared off the web.

[GeirW]

Gday.

Yup. looks cool.

I guess time will tell, am basicly into preserving
the original design.
Attached below are the orginal design,
and something i just made.
The front is in 3mm glass-plate, with black paper behind it.
(very simple, yet stylish. maybe a case in dark oak etc.-.)
The knobs are volume and source, am thinking of some
tone controls, incase they would be very anonymous and
black. There is that "magic eye" on the left, which have been
kinda cool to implement, but with that, it only would
serve the purpose of showing power on/off.
Btw. the "tangential" buttons on the midt, is:
on/off. bass-cut. tape/phono. M-F-K-FM radio. tweeter-cut. tweeter-boost.