[E=Fb]

Hi guys.

I bought a JJ 12at7 and JJ el84 for my epi valve jr combo. They sure sound
sweet but I wondered if the 12at7 was rather weak when I use it at lower
volume. When I put my sovtek 12ax7 back in it sounded pretty damn good but
kinda harsh even at lower volume. What will a 5751 be like or should I just
get a JJ 12ax7 and replace the 12at7?

Was it a good idea to keep them the same brands or do y'all have a favorite
combinations of tube brands and types? I'd like to hear about them.

By the way I have an ecc83 high gain that I found at my local shop but it's
unmarked and inside a plastic tube. The shop's a fender dealer so it might
be fender branded. It's only good if I play with distortions and it's real
good at that. Louder too.

Thanks

[Bob H.]

On Jan 25, 9:41 am, "E=Fb" wrote:
Hi guys.

I bought a JJ 12at7 and JJ el84 for my epi valve jr combo. They sure sound
sweet but I wondered if the 12at7 was rather weak when I use it at lower
volume. When I put my sovtek 12ax7 back in it sounded pretty damn good but
kinda harsh even at lower volume. What will a 5751 be like or should I just
get a JJ 12ax7 and replace the 12at7?

Was it a good idea to keep them the same brands or do y'all have a favorite
combinations of tube brands and types? I'd like to hear about them.

By the way I have an ecc83 high gain that I found at my local shop but it's
unmarked and inside a plastic tube. The shop's a fender dealer so it might
be fender branded. It's only good if I play with distortions and it's real
good at that. Louder too.

Thanks

The 12at7 has about 1/4 less gain than the 12ax7, and a lower plate
resistance.
The 12ax7 will give more gain, but also will sound harsh due to
distortion, if the circuit is optimized for the 12at7. The higher
plate resistance of the 12ax7 (about 8 times) requires a larger value
plate resistor to keep the ratio about at least 4 times, and many times
more. Also, the higher plate resistance of the 12ax7 reduces plate
current, changing the biasing of the tube.

A 5751 has close to the gain of a 12at7, but still about 4 times the
plate resistance.

What is the amp built for: 12at7 or 12ax7?

regards,

[Bob H.]

On Jan 25, 9:41 am, "E=Fb" wrote:
Hi guys.

I bought a JJ 12at7 and JJ el84 for my epi valve jr combo. They sure sound
sweet but I wondered if the 12at7 was rather weak when I use it at lower
volume. When I put my sovtek 12ax7 back in it sounded pretty damn good but
kinda harsh even at lower volume. What will a 5751 be like or should I just
get a JJ 12ax7 and replace the 12at7?

Was it a good idea to keep them the same brands or do y'all have a favorite
combinations of tube brands and types? I'd like to hear about them.

By the way I have an ecc83 high gain that I found at my local shop but it's
unmarked and inside a plastic tube. The shop's a fender dealer so it might
be fender branded. It's only good if I play with distortions and it's real
good at that. Louder too.

Thanks

The 12at7 has about 1/4 less gain than the 12ax7, and a lower plate
resistance.
The 12ax7 will give more gain, but also will sound harsh due to
distortion, if the circuit is optimized for the 12at7. The higher
plate resistance of the 12ax7 (about 8 times) requires a larger value
plate resistor to keep the ratio about at least 4 times, and many times
more. Also, the higher plate resistance of the 12ax7 reduces plate
current, changing the biasing of the tube.

A 5751 has close to the gain of a 12at7, but still about 4 times the
plate resistance.

What is the amp built for: 12at7 or 12ax7?

regards,
Bob H.

[E=Fb]

"Bob H." wrote in message
oups.com...


On Jan 25, 9:41 am, "E=Fb" wrote:
Hi guys.

I bought a JJ 12at7 and JJ el84 for my epi valve jr combo. They sure
sound
sweet but I wondered if the 12at7 was rather weak when I use it at lower
volume. When I put my sovtek 12ax7 back in it sounded pretty damn good
but
kinda harsh even at lower volume. What will a 5751 be like or should I
just
get a JJ 12ax7 and replace the 12at7?

Was it a good idea to keep them the same brands or do y'all have a
favorite
combinations of tube brands and types? I'd like to hear about them.

By the way I have an ecc83 high gain that I found at my local shop but
it's
unmarked and inside a plastic tube. The shop's a fender dealer so it
might
be fender branded. It's only good if I play with distortions and it's
real
good at that. Louder too.

Thanks

The 12at7 has about 1/4 less gain than the 12ax7, and a lower plate
resistance.
The 12ax7 will give more gain, but also will sound harsh due to
distortion, if the circuit is optimized for the 12at7. The higher
plate resistance of the 12ax7 (about 8 times) requires a larger value
plate resistor to keep the ratio about at least 4 times, and many times
more. Also, the higher plate resistance of the 12ax7 reduces plate
current, changing the biasing of the tube.

A 5751 has close to the gain of a 12at7, but still about 4 times the
plate resistance.

What is the amp built for: 12at7 or 12ax7?

regards,
Bob H.


I think it's built for 12ax7 since it came with it. The amp's a single ended
class a, one preamp and one power.

[Bob H.]

I think it's built for 12ax7 since it came with it. The amp's a single
ended
class a, one preamp and one power.


Then a 5751 may work for you, though with somewhat lower gain. The
slightly lower plate resistance may tame that harshness, but only
trying one will detirmine that. The circuit should be close to
optimum for a 5751, while it's probably not for a 12at7 due to the
significant difference in plate resistance. This means that the 5751
should sound more robust than the 12at7 in that circuit, but not quite
as loud as the 12ax7.

Some here swear by 5751's, and for good reason: they're usually well
built, and offer very consistant operation. I personally don't prefer
them for audio, but they were all I had, it would be ok.

Also, try searching for 12ax7 "taste tests", as they can shed some
insite into the various attributes of modern built 12ax7's. Of
course, any subjective reporting must be taken with a very large grain
of salt.

Bob H.

[E=Fb]

"Bob H." wrote in message
oups.com...
I think it's built for 12ax7 since it came with it. The amp's a single
ended
class a, one preamp and one power.


Then a 5751 may work for you, though with somewhat lower gain. The
slightly lower plate resistance may tame that harshness, but only
trying one will detirmine that. The circuit should be close to
optimum for a 5751, while it's probably not for a 12at7 due to the
significant difference in plate resistance. This means that the 5751
should sound more robust than the 12at7 in that circuit, but not quite
as loud as the 12ax7.

Some here swear by 5751's, and for good reason: they're usually well
built, and offer very consistant operation. I personally don't prefer
them for audio, but they were all I had, it would be ok.

Also, try searching for 12ax7 "taste tests", as they can shed some
insite into the various attributes of modern built 12ax7's. Of
course, any subjective reporting must be taken with a very large grain
of salt.

Bob H.


It sounds it really can sound sweet so I'll get one. I felt I needed
something that's between the 12at7 and the 12ax7. This may be it. Thanks.

I sure like this amp.

[E=Fb]

ok I ordered a 5751 (other) from tubedepot. Will let you know how it goes.