12az7a tube

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menger
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12az7a tube

Postby menger » Sat 03/05/11 5:14 pm

i found a couple 12az7a rca labeled, are these 12ax7? mark
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Postby CurtissRobin » Sat 03/05/11 6:50 pm

The RCA Receiving Tube Manual says it's an RF amp for VHF and UHF but it also says to refer to 12AT7 for characteristics as a Class A1 amplifier. The pinout's the same as a 12A_7.

KennyO
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Postby dotfret » Sat 03/05/11 8:59 pm

You can use 12AZ7 in place of a 12AX7 but the amplification factor is lower, nominal 60 as opposed to nominal 100 for a 12AX7.

They can be useful if your 18watt is too growly for your taste. There are a couple of hifi amps that used them - users generally insist on RCA for those hifi amps.
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Postby zaphod_phil » Sat 03/05/11 11:12 pm

12AT7s don't belong in 18W amps IMO, and therefore neither would these 12AZ7s. But it might still be fin to try as an experiment.
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Postby rsi » Mon 03/07/11 10:49 am

I have a couple of sylvania 12AZ7s that I tried out in different positions in my 18w TMB head. Didn't sound particularly bad. Didn't sound any better.
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Postby dotfret » Mon 03/07/11 4:34 pm

zaphod_phil wrote:12AT7s don't belong in 18W amps IMO, and therefore neither would these 12AZ7s. But it might still be fine to try as an experiment.
12AZ7 work a lot better in an 18W than 12AT7. I latched onto them from a comment MrDB made years ago, and they are a real "bang for buck" valve.

Also, sometimes it is useful to put a 12AT7 or a 12AZ7 in the trem channel, or a 5751, just to stabilise the thing. I know that Gabi has done this, and I know that Graydon always fits a 12AX7WA in that channel to avoid instability.

Apart from that, I'm inclined to agree about the 12AT7, but the 12AZ7 represents a useful alternative to me, and a lot of them look like RFT 12AX7 internally.

Things I could live with include
6n2p, 12BZ7, 6AQ4 and a lot of the obvious 12AX7 types with different numbers.
5751, 5755, or 12AZ7 as "growl tamers".

I've got a messy "18W" that has 7058 and PCL86 -there's a certain compatibility in the heater supply voltages that works well with a lighting transformer I got in a yard sale.

So you don't like 12AT7 - neither do I - but what do you actually like, Phil?
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Postby zaphod_phil » Mon 03/07/11 8:19 pm

Also, sometimes it is useful to put a 12AT7 or a 12AZ7 in the trem channel, or a 5751, just to stabilise the thing. I know that Gabi has done this...
Sure, it stops the oscillator working. You don't get much more stable than that. :lol:
So you don't like 12AT7 - neither do I - but what do you actually like, Phil?
Genuine Mullard ECC83s. Nothing comes close. :D BTW about the 12AT7s I once did some experiments with 12AT7s in place of 12AX7s in multi-stage preamps, and found that they introduced a muddiness into the tone when overdriven. Later I cane across an article which showed that overdriven 12AT7/ECC81s tend to produce a significant amount of high-odd-order harmonics, particularly 9th.
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