Using 12AZ7's

[[email protected]]

The tube books show the 12AZ7 as a direct sub for the 12AX7. Out of
curiosity, I put 4 RCA 12AZ7's in my Dynaco PAS-2.

Could not tell any difference in sound compared to the the Telefunkens
that were in there.

Any comments on this tube or has anyone used them ?

Thanks,

Dave

[KeithR]

wrote:
> The tube books show the 12AZ7 as a direct sub for the 12AX7. Out of
> curiosity, I put 4 RCA 12AZ7's in my Dynaco PAS-2.
>
> Could not tell any difference in sound compared to the the Telefunkens
> that were in there.
>
> Any comments on this tube or has anyone used them ?
>
> Thanks,
>
> Dave

You can't post that here, this is Il Jute's personal anti global warming
news group. Stay on topic please.

[Fu Knee]

On Dec 6, 8:03�pm, keithr > wrote:
> You can't post that here, this is Il Jute's personal anti global warming
> news group. Stay on topic please.

Hi RATs,

The only consistent topic is how dumb other posters are ;)

Ha!

Al

[Peter Wieck]

On Dec 6, 3:21*pm, wrote:
> The tube books show the 12AZ7 as a direct sub for the 12AX7. Out of
> curiosity, I put 4 RCA 12AZ7's in my Dynaco PAS-2.
>
> Could not tell any difference in sound compared to the the Telefunkens
> that were in there.
>
> Any comments on this tube or has anyone used them ?
>
> Thanks,
>
> Dave

At Lasts!! Something on tubes!

OK, a few things. Others have noted the lower gain and higher filament
current. However, in my limited experience the 12AZ7 is slightly less
prone to microphonics which can be a good thing given how sensitive
12AX7s can be and those Telefunkens in particular (again in my
experience).

In the PAS from modern sources you will not notice the lower gain.

As far is you are concerned, you probably did not notice that you had
to put the volume control slightly higher than with the Teles, and you
will probably have no problem with the extra current.

But, if you are into swapping tubes, hunt down some Sylvania Mil.Spec.
5751s and see how you like them. I think you will notice that
difference, particularly in that pre-amp. Also, do the X mod if you
have not already.

Peter Wieck
Melrose Park, PA

[Edward Morris]

Hi Peter,
You mentioned to the OP to do the "x mod". What is that? I'm curious
because I have an PAS 3.

Thanks,
Eddie

"Peter Wieck" > wrote in message
...
On Dec 6, 3:21 pm, wrote:
> The tube books show the 12AZ7 as a direct sub for the 12AX7. Out of
> curiosity, I put 4 RCA 12AZ7's in my Dynaco PAS-2.
>
> Could not tell any difference in sound compared to the the Telefunkens
> that were in there.
>
> Any comments on this tube or has anyone used them ?
>
> Thanks,
>
> Dave

At Lasts!! Something on tubes!

OK, a few things. Others have noted the lower gain and higher filament
current. However, in my limited experience the 12AZ7 is slightly less
prone to microphonics which can be a good thing given how sensitive
12AX7s can be and those Telefunkens in particular (again in my
experience).

In the PAS from modern sources you will not notice the lower gain.

As far is you are concerned, you probably did not notice that you had
to put the volume control slightly higher than with the Teles, and you
will probably have no problem with the extra current.

But, if you are into swapping tubes, hunt down some Sylvania Mil.Spec.
5751s and see how you like them. I think you will notice that
difference, particularly in that pre-amp. Also, do the X mod if you
have not already.

Peter Wieck
Melrose Park, PA

[Peter Wieck]

On Dec 7, 1:55*pm, "Edward Morris" > wrote:
> Hi Peter,
> * * You mentioned to the OP to do the "x mod". *What is that? *I'm curious
> because I have an PAS 3.

You will find the modification described in later amp manuals such as
the ST-80/120 and so forth. It is to match the output impedance to
'modern' solid-state amps (and doesn't hurt with tube amps). It
consists of changing one resistor and cutting another on each channel
- not a big deal. It will make the pre-amp a bit less noisy and tubby-
sounding with SS equipment.

Also, the true X tone-controls were out-of-circuit when flat - a thing
that modern 'enthusiasts' attempt to duplicate by taking them out of
the circuit altogether. Those controls were specially made for Dynaco
and are almost unobtanium these days. But the output matching mod is
simple and worthwhile.

I will try to remember to look it up some evening and post the "how"
here.

Peter Wieck
Melrose Park, PA

[Edward Morris]

Hi Peter,
Thanks for replying. How would I know if my PAS has the X tone
controls?

Thanks again,
Eddie

"Peter Wieck" > wrote in message
...
On Dec 7, 1:55 pm, "Edward Morris" > wrote:
> Hi Peter,
> You mentioned to the OP to do the "x mod". What is that? I'm curious
> because I have an PAS 3.

You will find the modification described in later amp manuals such as
the ST-80/120 and so forth. It is to match the output impedance to
'modern' solid-state amps (and doesn't hurt with tube amps). It
consists of changing one resistor and cutting another on each channel
- not a big deal. It will make the pre-amp a bit less noisy and tubby-
sounding with SS equipment.

Also, the true X tone-controls were out-of-circuit when flat - a thing
that modern 'enthusiasts' attempt to duplicate by taking them out of
the circuit altogether. Those controls were specially made for Dynaco
and are almost unobtanium these days. But the output matching mod is
simple and worthwhile.

I will try to remember to look it up some evening and post the "how"
here.

Peter Wieck
Melrose Park, PA

[Peter Wieck]

On Dec 8, 1:54*am, "Edward Morris" > wrote:
> Hi Peter,
> * * Thanks for replying. *How would I know if my PAS has the X tone
> controls?
>
> Thanks again,
> Eddie
>
> "Peter Wieck" > wrote in message
>
> ...
> On Dec 7, 1:55 pm, "Edward Morris" > wrote:
>
> > Hi Peter,
> > You mentioned to the OP to do the "x mod". What is that? I'm curious
> > because I have an PAS 3.
>
> You will find the modification described in later amp manuals such as
> the ST-80/120 and so forth. It is to match the output impedance to
> 'modern' solid-state amps (and doesn't hurt with tube amps). It
> consists *of changing one resistor and cutting another on each channel
> - not a big deal. It will make the pre-amp a bit less noisy and tubby-
> sounding with SS equipment.
>
> Also, the true X tone-controls were out-of-circuit when flat - a thing
> that modern 'enthusiasts' attempt to duplicate by taking them out of
> the circuit altogether. Those controls were specially made for Dynaco
> and are almost unobtanium these days. But the output matching mod is
> simple and worthwhile.
>
> I will try to remember to look it up some evening and post the "how"
> here.
>
> Peter Wieck
> Melrose Park, PA

Eddie:

To do the impedance mod - per the Dynaco literature:

1. Obtain two 100,000 ohm, 1/2-watt 10% tolerance resistors.
2. Unsolder and discard the two 510,000 ohm (green-brown-yellow)
resistors connected to the audio-output sockets on the back panel of
the preamplifier and replace them with the 100,000 ohm resistors.
Solder all connections.
3. Snip out and discard the two 62,000 ohm (blue-red-orange) resistors
on the PC-5 circuit board adjacent to eyelets 8 & 18. This completes
the modification.

Given the relative difference in cost, I would use 5% resistors and
screen them as well.

As to how you can tell if you have the X tone-controls:
1. with your VOM go to either element terminal and the wiper.
2. Operate the control through its range. At/near the center-point
there should be a signficant drop or a significant increase in
resistance. If that happens, you have the X controls. If the
resistance change is approximately linear to the control and with no
change at the center-point you have the pre-X controls.

Hope this helps.

Peter Wieck
Melrose Park, PA

[Edward Morris]

Hi Peter,
Thanks so much for the mod instructions and the explanation of the X
controls.

Regards,
Eddie

"Peter Wieck" > wrote in message
...
On Dec 8, 1:54 am, "Edward Morris" > wrote:
> Hi Peter,
> Thanks for replying. How would I know if my PAS has the X tone
> controls?
>
> Thanks again,
> Eddie
>
> "Peter Wieck" > wrote in message
>
> ...
> On Dec 7, 1:55 pm, "Edward Morris" > wrote:
>
> > Hi Peter,
> > You mentioned to the OP to do the "x mod". What is that? I'm curious
> > because I have an PAS 3.
>
> You will find the modification described in later amp manuals such as
> the ST-80/120 and so forth. It is to match the output impedance to
> 'modern' solid-state amps (and doesn't hurt with tube amps). It
> consists of changing one resistor and cutting another on each channel
> - not a big deal. It will make the pre-amp a bit less noisy and tubby-
> sounding with SS equipment.
>
> Also, the true X tone-controls were out-of-circuit when flat - a thing
> that modern 'enthusiasts' attempt to duplicate by taking them out of
> the circuit altogether. Those controls were specially made for Dynaco
> and are almost unobtanium these days. But the output matching mod is
> simple and worthwhile.
>
> I will try to remember to look it up some evening and post the "how"
> here.
>
> Peter Wieck
> Melrose Park, PA

Eddie:

To do the impedance mod - per the Dynaco literature:

1. Obtain two 100,000 ohm, 1/2-watt 10% tolerance resistors.
2. Unsolder and discard the two 510,000 ohm (green-brown-yellow)
resistors connected to the audio-output sockets on the back panel of
the preamplifier and replace them with the 100,000 ohm resistors.
Solder all connections.
3. Snip out and discard the two 62,000 ohm (blue-red-orange) resistors
on the PC-5 circuit board adjacent to eyelets 8 & 18. This completes
the modification.

Given the relative difference in cost, I would use 5% resistors and
screen them as well.

As to how you can tell if you have the X tone-controls:
1. with your VOM go to either element terminal and the wiper.
2. Operate the control through its range. At/near the center-point
there should be a signficant drop or a significant increase in
resistance. If that happens, you have the X controls. If the
resistance change is approximately linear to the control and with no
change at the center-point you have the pre-X controls.

Hope this helps.

Peter Wieck
Melrose Park, PA