A
Arfa Daily
Guest
Phil
While you've got your head into amps that eat EL84s, what is your opinion of
running these valves at wildly excessive anode voltages? All of the data
books that I've got show them specced to 300 v max, but there seems to be
several manufacturers that run them way beyond this. It is a Peavey Classic
50 that has prompted me to look into this. It's one that I have looked at a
couple of times for a local shop. It's used out on the road for gigging, and
eats output valves. It's had three sets that I know of in the last 18
months, so this time, I decided to look a bit closer, and discovered that in
subdued lighting, the anodes had a significant glow at idle. I looked at the
anode voltage, and was amazed to find it at around 425 v. Looking at the
bias, the raw bias supply is only -29v to start with, and is then potted
down by a fixed potential divider to around -20 volts or so. By the time
this is 'distributed' to the four grids, it's about -18v. The output valves
seem very 'uncomfortable' as they sit there. They are radiating a LOT of
heat and tend to 'ping' a bit. When they have been on for a while, they get
quite microphonic.
Just for sport, I lifted the bottom resistor of the bias divider, and hung a
pot in series with it. Adjusting for around -24 v at the grids eliminates
the hot anodes, and makes the valves seem altogether happier. Although they
will still burn your fingers if you touch them, they do not feel like an
electric fire element in front of your hand at that level of bias, and are
no longer microphonic when hot. I only measured a drop of a few watts, which
initially was well over the 50 watts that this amp is supposed to do anyway,
and didn't detect any difference in distortion levels or the 'sound' of it,
although I would be the first to admit that I am no 'muso'. On that note,
from what I can gather, these Peaveys tend to be used by blues-y players
rather than rock players anyway, so I would have expected them to be softly
biased for a 'fat' sound, rather than run to the limit for a hard edgy rock
sound.
I've let the shop take it back for the moment with the bias at this new
level, and let the shop owner have a go with it, as he is a muso. I spoke to
him a few minutes ago, and he reckons that it sounds fine, so I am tempted
to declare this as a reliability mod.
Just interested in your opinion on this, and your experience of these
Classic 50s if you have much or even any experience of them.
Arfa
While you've got your head into amps that eat EL84s, what is your opinion of
running these valves at wildly excessive anode voltages? All of the data
books that I've got show them specced to 300 v max, but there seems to be
several manufacturers that run them way beyond this. It is a Peavey Classic
50 that has prompted me to look into this. It's one that I have looked at a
couple of times for a local shop. It's used out on the road for gigging, and
eats output valves. It's had three sets that I know of in the last 18
months, so this time, I decided to look a bit closer, and discovered that in
subdued lighting, the anodes had a significant glow at idle. I looked at the
anode voltage, and was amazed to find it at around 425 v. Looking at the
bias, the raw bias supply is only -29v to start with, and is then potted
down by a fixed potential divider to around -20 volts or so. By the time
this is 'distributed' to the four grids, it's about -18v. The output valves
seem very 'uncomfortable' as they sit there. They are radiating a LOT of
heat and tend to 'ping' a bit. When they have been on for a while, they get
quite microphonic.
Just for sport, I lifted the bottom resistor of the bias divider, and hung a
pot in series with it. Adjusting for around -24 v at the grids eliminates
the hot anodes, and makes the valves seem altogether happier. Although they
will still burn your fingers if you touch them, they do not feel like an
electric fire element in front of your hand at that level of bias, and are
no longer microphonic when hot. I only measured a drop of a few watts, which
initially was well over the 50 watts that this amp is supposed to do anyway,
and didn't detect any difference in distortion levels or the 'sound' of it,
although I would be the first to admit that I am no 'muso'. On that note,
from what I can gather, these Peaveys tend to be used by blues-y players
rather than rock players anyway, so I would have expected them to be softly
biased for a 'fat' sound, rather than run to the limit for a hard edgy rock
sound.
I've let the shop take it back for the moment with the bias at this new
level, and let the shop owner have a go with it, as he is a muso. I spoke to
him a few minutes ago, and he reckons that it sounds fine, so I am tempted
to declare this as a reliability mod.
Just interested in your opinion on this, and your experience of these
Classic 50s if you have much or even any experience of them.
Arfa