Hi RATs!

I listen to my CD collection, mostly. Lots of most everything At
this moment, some crunchy solo piano with lots of tasty dynamics and
mixes of voicings. My tripping thru the Ebay machineries has piled up
about half a hundred old tube amps in my little house. This LA-240 was
nearest when I recovered enough energy to give it a good touching up.

It got more PS filtering and new oil caps plus film caps in the signal
path, which was shortened a bit to bypass the tone controls. I did
keep the original caps between the phono preamp and the volume
control, just rerouted the output around the tone control network
This provides the DC decoupling from the CD input to the volume pot.
DC CD, get it ?

An external transformer was added for the 6.3Vac filaments. I use a
10A unit with enough R on the primary side to deliver ~5.9 volts at
the pins to all but the rectifier. This is on 24/7 and keeps the tubes
comfy and warm in the Air Conditioning. It was a vicious winter here
in Phx, rain and everything, but, it is back near 90 now and the sound
must go on

The oil cap cans are next to the open chassis, which stands on its
left end, with the power transformer and rectifier on the high end,
drawing heat up and away from the rest of the tubes.

I put 390R in series with each screen to its plate of the output tubes
and dropped the B+ voltage from 360 to about 305 by swapping out the
rectifier 5AR4 for 5R4. The NFB circuit was snipped out. I get about 3
watts, clean, according to John Broskie's new P-P tube calculator

I am driving the 80Hz ehorns with Lamba 15" drivers and a pair of
Cadence XT-7 bookshelves in series with ~10uF. The little guys are
rated 92dB ... the ehorns are a bit more ... sounds OK

None of the cats or dogs have shown any interest in my audio dungeon.
The open chassis is dangerous, but sounds OK and allows me to use
available energy for circuit mods, not casework deconstruction

I don't like tone control circuits. I like clear sound, which wanders
off in many circuits I know that these old amps were sold to people
who wanted all the latest whistles and bells, God love 'em. Here in
the vast wisdom of the Future, it is enough for me that the basic
circuits provide wonderful sound, even with the whistles and bells out
of the circuit. YMMV.

Happy Ears!
Al

PS I ain't the Tubegarden that built the amp on sale on Ebay. That is
some mother Tubegarden

"A superstar? Well, perhaps you are ... we all shine on ..."

in article , Al Marcy at
wrote on 3/11/05 6:25 PM:

Hi RATs!

I listen to my CD collection, mostly. Lots of most everything At
this moment, some crunchy solo piano with lots of tasty dynamics and
mixes of voicings. My tripping thru the Ebay machineries has piled up
about half a hundred old tube amps in my little house. This LA-240 was
nearest when I recovered enough energy to give it a good touching up.

It got more PS filtering and new oil caps plus film caps in the signal
path, which was shortened a bit to bypass the tone controls. I did
keep the original caps between the phono preamp and the volume
control, just rerouted the output around the tone control network
This provides the DC decoupling from the CD input to the volume pot.
DC CD, get it ?

An external transformer was added for the 6.3Vac filaments. I use a
10A unit with enough R on the primary side to deliver ~5.9 volts at
the pins to all but the rectifier. This is on 24/7 and keeps the tubes
comfy and warm in the Air Conditioning. It was a vicious winter here
in Phx, rain and everything, but, it is back near 90 now and the sound
must go on

The oil cap cans are next to the open chassis, which stands on its
left end, with the power transformer and rectifier on the high end,
drawing heat up and away from the rest of the tubes.

I put 390R in series with each screen to its plate of the output tubes
and dropped the B+ voltage from 360 to about 305 by swapping out the
rectifier 5AR4 for 5R4. The NFB circuit was snipped out. I get about 3
watts, clean, according to John Broskie's new P-P tube calculator

I am driving the 80Hz ehorns with Lamba 15" drivers and a pair of
Cadence XT-7 bookshelves in series with ~10uF. The little guys are
rated 92dB ... the ehorns are a bit more ... sounds OK

None of the cats or dogs have shown any interest in my audio dungeon.
The open chassis is dangerous, but sounds OK and allows me to use
available energy for circuit mods, not casework deconstruction

I don't like tone control circuits. I like clear sound, which wanders
off in many circuits I know that these old amps were sold to people
who wanted all the latest whistles and bells, God love 'em. Here in
the vast wisdom of the Future, it is enough for me that the basic
circuits provide wonderful sound, even with the whistles and bells out
of the circuit. YMMV.

Happy Ears!
Al

PS I ain't the Tubegarden that built the amp on sale on Ebay. That is
some mother Tubegarden

"A superstar? Well, perhaps you are ... we all shine on ..."


Al,

I've found that essentailly all of the gray Japanese coupling and bypass
caps must me changed in a restore, due to leakage. Some tests with a
variable HV DC power supply and an ohm meter and resistor to measure current
proved the wisdom of the practice.

Quite a nice collection there! Care to share . . . What are some of your
favorites, and which ones are dogs??

Cheers,

Jon