[minus3Db]

Hi, first post. I joined this group having built valve amps in the last
millenium, that is the late '60s'. I got back into recently by
purchasing a used AMC 3030 valve/transistor stereo amp circa 1992, as a
stand-in until I build a high end tube set. The high tension winding of
the mains transformer is blown and I am fixing that. However, I would
like to hear opinions about this amp, How good is it, how high end. It
runs twin El34 pentodes in push pull by the look of it, but the output
transformers are about half the size of the ones I remember using. I
will be driving Jordan JX92's single drivers, in a back horn. My goal;
well the greatest stereo sound I can get at home, the new and expensive
stuff just doesn't do it for me like it used to- whats changed? Maybe
my ears? Any ideas what constitutes a great tube amp for home stereo?

[Sander deWaal]

"minus3Db" said:

Hi, first post. I joined this group having built valve amps in the last
millenium, that is the late '60s'. I got back into recently by
purchasing a used AMC 3030 valve/transistor stereo amp circa 1992, as a
stand-in until I build a high end tube set. The high tension winding of
the mains transformer is blown and I am fixing that. However, I would
like to hear opinions about this amp, How good is it, how high end. It
runs twin El34 pentodes in push pull by the look of it, but the output
transformers are about half the size of the ones I remember using. I
will be driving Jordan JX92's single drivers, in a back horn. My goal;
well the greatest stereo sound I can get at home, the new and expensive
stuff just doesn't do it for me like it used to- whats changed? Maybe
my ears? Any ideas what constitutes a great tube amp for home stereo?


I can't help you with that last question, as it is very much a
personal choice, and dependent on your speakers and room.

The AMC3030 is, IMHO, an abortion.
It uses tiny MOSFETs as drivers, the EL34 power tubes are soldered
*directly* to a flimsy PCB, without sockets, and the fans below it
start to make rattling noises after a year or so.
The part quality is cheap, electrolytics and bias pots will break by
just looking at it.

If you want to continue with this amp (despite my above comments, I
must admit it is able to sound reasonable well), be sure to replace
*all* small electrolytics on the tube boards, as well as the bias
potmeters (don't even attempt to turn the flimsy blue/white things,
they'll fall apart).

Check the entire amp for bad solder connections.
It's too bad you don't have the space to add tube sockets, if you want
to replace them, you'll have to use a solder sucking device and/or
solder wick, both of which may and will dfamage the PCB tracks as they
seem glued to the pertinax with wood glue or something.

Dear readers, do not fear that I'm really Bret Ludwig, sockpuppeting.
I'm usually not so outspoken about a certain product, but in my
opinion, the 3030 was and is a dog.
I repaired many of them.

But as I said, one in good condition, with some mods done, may sound
well enough to use for a while.

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[minus3Db]

Magic reply, yes, I soldered all of the dry joints, build qual is poor,
at one stage an arc started on the pins to the connector and I had to
pull the mains plug out faaaast, burned a hole in the PC board. Glad I
got it for a song though about $30 or so.
Dumb idea soldering the valves direct, good idea to have very quiet
fans, interesting idea to make a hybrid. If I can get a year out of it
I will be pleased, but I will install a fire extinguisher in the lounge
- and maybe a sprinkler system in case of fire.
Would you maybe have a circuit diagram? or details of the secondary
windings of the mains tranformer. seems the HT winding is burned out.
Great if you do. I will carry out your suggestons once the tranny is
fixed.

Do you know if single triodes are still available and maybe a build
spec for a decent amp? At least with tubes I can actually see what I
am soldering, unlike PCB's

-3Db

Sander DeWaal wrote:
"minus3Db" said:

Hi, first post. I joined this group having built valve amps in the last
millenium, that is the late '60s'. I got back into recently by
purchasing a used AMC 3030 valve/transistor stereo amp circa 1992, as a
stand-in until I build a high end tube set. The high tension winding of
the mains transformer is blown and I am fixing that. However, I would
like to hear opinions about this amp, How good is it, how high end. It
runs twin El34 pentodes in push pull by the look of it, but the output
transformers are about half the size of the ones I remember using. I
will be driving Jordan JX92's single drivers, in a back horn. My goal;
well the greatest stereo sound I can get at home, the new and expensive
stuff just doesn't do it for me like it used to- whats changed? Maybe
my ears? Any ideas what constitutes a great tube amp for home stereo?


I can't help you with that last question, as it is very much a
personal choice, and dependent on your speakers and room.

The AMC3030 is, IMHO, an abortion.
It uses tiny MOSFETs as drivers, the EL34 power tubes are soldered
*directly* to a flimsy PCB, without sockets, and the fans below it
start to make rattling noises after a year or so.
The part quality is cheap, electrolytics and bias pots will break by
just looking at it.

If you want to continue with this amp (despite my above comments, I
must admit it is able to sound reasonable well), be sure to replace
*all* small electrolytics on the tube boards, as well as the bias
potmeters (don't even attempt to turn the flimsy blue/white things,
they'll fall apart).

Check the entire amp for bad solder connections.
It's too bad you don't have the space to add tube sockets, if you want
to replace them, you'll have to use a solder sucking device and/or
solder wick, both of which may and will dfamage the PCB tracks as they
seem glued to the pertinax with wood glue or something.

Dear readers, do not fear that I'm really Bret Ludwig, sockpuppeting.
I'm usually not so outspoken about a certain product, but in my
opinion, the 3030 was and is a dog.
I repaired many of them.

But as I said, one in good condition, with some mods done, may sound
well enough to use for a while.

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[Ruud Broens]

"minus3Db" wrote in message
ups.com...
: Magic reply, yes, I soldered all of the dry joints, build qual is poor,
: at one stage an arc started on the pins to the connector and I had to
: pull the mains plug out faaaast, burned a hole in the PC board. Glad I
: got it for a song though about $30 or so.
: Dumb idea soldering the valves direct, good idea to have very quiet
: fans, interesting idea to make a hybrid. If I can get a year out of it
: I will be pleased, but I will install a fire extinguisher in the lounge
: - and maybe a sprinkler system in case of fire.
: Would you maybe have a circuit diagram? or details of the secondary
: windings of the mains tranformer. seems the HT winding is burned out.
: Great if you do. I will carry out your suggestons once the tranny is
: fixed.
:
: Do you know if single triodes are still available and maybe a build
: spec for a decent amp? At least with tubes I can actually see what I
: am soldering, unlike PCB's
:
: -3Db
:
: Sander DeWaal wrote:

: The AMC3030 is, IMHO, an abortion.
: It uses tiny MOSFETs as drivers, the EL34 power tubes are soldered
: *directly* to a flimsy PCB, without sockets, and the fans below it
: start to make rattling noises after a year or so.
: The part quality is cheap, electrolytics and bias pots will break by
: just looking at it.
:
: If you want to continue with this amp (despite my above comments, I
: must admit it is able to sound reasonable well), be sure to replace
: *all* small electrolytics on the tube boards, as well as the bias
: potmeters (don't even attempt to turn the flimsy blue/white things,
: they'll fall apart).
:
: Check the entire amp for bad solder connections.
: It's too bad you don't have the space to add tube sockets, if you want
: to replace them, you'll have to use a solder sucking device and/or
: solder wick, both of which may and will dfamage the PCB tracks as they
: seem glued to the pertinax with wood glue or something.

You could change it to a new -3Db1212 or so,
use the EL34's in triode mode PP, in sockets, use the AMC's OT's,
ECC99 as driver, working out the right supply voltage backwards from the
OT reflected load, as you are rewinding B+ anyway. Just a wild thought :-)
Probably a new cabinet required, too.

Single triodes:
~half an SN7~
6J5, suitable as driver, found it here USeD 3.36:
http://w3.mit.edu/cheever/www/tubes_all.htm
and http://zs6pta.iwarp.com/tubes.htm had 20 of 'm, 5 years ago ;-)
http://www.organservice.com/tubes/tubes.htm for USD 7,95
http://www.radiodaze.com/tubes-04.htm 6J5GT USD 9,-

9002 - ccs load preferred, nice line input tube
http://www.radiodaze.com/tubes-10.htm USD 5,-
http://www.ultraelectronicactive.com...uum-Tubes.html
has 1 for 3,50, and 3 6J5's at USD 5,-

European EC90
http://home.planet.nl/~rotte322/Voorraad/buizene.htm has a few
(lot's of bike stuff links when googl_ooking for ec90

but generally, singles are _as_ expensive, or more so, as their
dual equivalents !

Rudy

[izozaya]

Sander was so right!

I bought mine for 80€ because the tube boards had burnt out the G2
resistors, but before that the connectors in the PCB went arcing too,
pots made scratching noises and all sort of strange things too.

Sooo, I gave up trying to bring it back to life, and will probably use
the case and the transformers for something else.

Even bought for a bargain, this amp can be extremely difficult to
amortize given the large number of design pitfalls inside that have to
be fixed, and little space where you really need it (i.e. around the
tubes).

Ruud Broens ha escrito:

"minus3Db" wrote in message
ups.com...
: Magic reply, yes, I soldered all of the dry joints, build qual is poor,
: at one stage an arc started on the pins to the connector and I had to
: pull the mains plug out faaaast, burned a hole in the PC board. Glad I
: got it for a song though about $30 or so.
: Dumb idea soldering the valves direct, good idea to have very quiet
: fans, interesting idea to make a hybrid. If I can get a year out of it
: I will be pleased, but I will install a fire extinguisher in the lounge
: - and maybe a sprinkler system in case of fire.
: Would you maybe have a circuit diagram? or details of the secondary
: windings of the mains tranformer. seems the HT winding is burned out.
: Great if you do. I will carry out your suggestons once the tranny is
: fixed.
:
: Do you know if single triodes are still available and maybe a build
: spec for a decent amp? At least with tubes I can actually see what I
: am soldering, unlike PCB's
:
: -3Db
:
: Sander DeWaal wrote:

: The AMC3030 is, IMHO, an abortion.
: It uses tiny MOSFETs as drivers, the EL34 power tubes are soldered
: *directly* to a flimsy PCB, without sockets, and the fans below it
: start to make rattling noises after a year or so.
: The part quality is cheap, electrolytics and bias pots will break by
: just looking at it.
:
: If you want to continue with this amp (despite my above comments, I
: must admit it is able to sound reasonable well), be sure to replace
: *all* small electrolytics on the tube boards, as well as the bias
: potmeters (don't even attempt to turn the flimsy blue/white things,
: they'll fall apart).
:
: Check the entire amp for bad solder connections.
: It's too bad you don't have the space to add tube sockets, if you want
: to replace them, you'll have to use a solder sucking device and/or
: solder wick, both of which may and will dfamage the PCB tracks as they
: seem glued to the pertinax with wood glue or something.

You could change it to a new -3Db1212 or so,
use the EL34's in triode mode PP, in sockets, use the AMC's OT's,
ECC99 as driver, working out the right supply voltage backwards from the
OT reflected load, as you are rewinding B+ anyway. Just a wild thought :-)
Probably a new cabinet required, too.

Single triodes:
~half an SN7~
6J5, suitable as driver, found it here USeD 3.36:
http://w3.mit.edu/cheever/www/tubes_all.htm
and http://zs6pta.iwarp.com/tubes.htm had 20 of 'm, 5 years ago ;-)
http://www.organservice.com/tubes/tubes.htm for USD 7,95
http://www.radiodaze.com/tubes-04.htm 6J5GT USD 9,-

9002 - ccs load preferred, nice line input tube
http://www.radiodaze.com/tubes-10.htm USD 5,-
http://www.ultraelectronicactive.com...uum-Tubes.html
has 1 for 3,50, and 3 6J5's at USD 5,-

European EC90
http://home.planet.nl/~rotte322/Voorraad/buizene.htm has a few
(lot's of bike stuff links when googl_ooking for ec90

but generally, singles are _as_ expensive, or more so, as their
dual equivalents !

Rudy

[Sander deWaal]

Sorry for the late reply, real life sometimes gets in the way of the
fun tube stuff.


"minus3Db" said:


Magic reply, yes, I soldered all of the dry joints, build qual is poor,
at one stage an arc started on the pins to the connector and I had to
pull the mains plug out faaaast, burned a hole in the PC board. Glad I
got it for a song though about $30 or so.


OK, that's a fair enough price for it.
If only for the output transformers, whicg are rather smallish for
EL34 in penthode/UL operation, but can be used with say 2A3 or 6B4G
triodes to make a nice amplifier.


Dumb idea soldering the valves direct, good idea to have very quiet
fans, interesting idea to make a hybrid. If I can get a year out of it
I will be pleased, but I will install a fire extinguisher in the lounge
- and maybe a sprinkler system in case of fire.


Actually, I may have exaggerated a bit, but as other posters already
said, the build quality isn't really that good.


Would you maybe have a circuit diagram? or details of the secondary
windings of the mains tranformer. seems the HT winding is burned out.
Great if you do. I will carry out your suggestons once the tranny is
fixed.



I am sorry, I don't have a schematic, but judging from the setup, I'd
expect something like 280V/400 mA AC for the HV, 6.3V/8A AC for the
heaters of the EL34a, and some auxiliary voltages like 2 x 15V AC at
some half amp or so to supply the solid state parts of the amp.
IIRC, the MOSFET drivers were supplied from the HV of the EL34s via a
RC filter and/or stabilizer.
It has been too long sonce I've seen one...........

I just did a Google search, but it's not available on the net as far
as I've seen.


Do you know if single triodes are still available and maybe a build
spec for a decent amp? At least with tubes I can actually see what I
am soldering, unlike PCB's


I'd use the output trannies for some DIY project, as I suggested
above.
Single triodes like 2A3, 6B4G, 6A3 etc. are available, some are even
made new by companies like Sovtek.

The advantage in using these trannies will be a higher anode load,
which will lower the available power, but also the amount of
distortion with the use of triodes.
In penthode, beam-tetrode or ultra linear use, the anode load must be
close to the recommended or calculated value, with the use of triodes
you have some more freedom in choosing the operating point.

It is also possible to use beam tetrodes or penthodes like 6L6GC, 807,
6550, KT66, KT88, KT99, EL34 etc. etc. as triodes, by tying the screen
grid (g2) to the anode, usually with a screen stopper of about 100
ohms to prevent oscillations.

Remember, however, that some tubes only allow for a lower voltage on
the screen grid, while the anode voltage may be much higher.
In case of a EL36, for example, the static screen grid voltage may not
exceed 150V, while the anode voltage may be 350 V or even more.
So, using such tubes in triode presents some problems.

If you're only starting with all this, or merely trying to improve
your 3030, try putting the EL34s in triode as suggested above, and
build a tube driver for it.

That way, you can use a standard HV transformer, available from one of
the many tube vendors .
Throw out all the solid state crap, also the tube cooling "towers",
that way, you'll have room for tube sockets.

I have seen pictures of converted 3030s, where there was room for a
suitable power transformer, both existing output transformers, 4 x
EL34s with sockets, and a tube driver circuit.
I can't remember if they left the tone controls intact.

--
"Due knot trussed yore spell chequer two fined awl miss steaks."