5F6A problem?

[vinceg]

It sounds like the TAD 12AY7 was ok for a day, then became noisy?
Now, all your 12AY7's are noisier than 12AX7's? Normally, I would expect the 12AX7's to be noisier as they will provide more gain in the V1 position.
It sounds like you have a bad bunch of 12AY7's, or you just can't get quiet ones any more.
But, it is possible something in the circuit is causing them problems.
What is the heater voltage (AC) at the V1 socket?
What are the DC voltages at pins 1,2,3,6,7,8 of V1 with 12AX7?
What are those same pins with 12AY7?

Yes, the TAD 12AY7 was low noise for a day, after became noisy.
Yes, I have two 12AY7 and both are noisy. Instead, two 12AX7 are quieter than the two 12AY7.It is strange but it is!!
The heater voltage in V1 is 6.15V
With 12AY7 the voltages are:
PIN1 +150V
PIN2 +0.9mV
PIN3 +2.21V
PIN4 3.20V
PIN5 3.20V
PIN6 +150V
PIN7 +2.4mV
PIN8 +2.36V
PIN9 3.20V

with 12AX7 the voltages are:
PIN1 +160V
PIN2 +0.9mV
PIN3 +2.21V
PIN4 3.20V
PIN5 3.20V
PIN6 +160V
PIN7 +2.4mV
PIN8 +2.36V
PIN9 3.20V

[vinceg]

I need to +1 on the commentary so far. It seems like anyone who gets into "whole amp" distortion troubles about noise early on. A whole amp at volume creating a lot of gain has a butt load of hiss!!! Not more than any other amp mind you, but the amp now in question is LOUDER! So the hiss is louder. I don' know why but this never got past me. I played most of my youth with Marshall's and RAT boxes! When I got to playing in a band I realized that noise control was part of the game. I recognized right away that hiss is directly proportional to gain at volume. And when put in perspective I noticed that the hiss of an overdriven amp at volume is generally LESS than the hiss of a distortion pedal through an amp at similar clipping and volume levels. You need to be really "apples to apples" to recognize it, but it's true. Obviously a master volume amp with a high gain preamp will have less hiss at similar gain AT A LOWER VOLUME!!! It's when all things are created equal that the picture comes into focus.

BTW, I haven't heard the clips yet. Maybe tomorrow?!?

What can I say? I am inclined to believe that I'm very unlucky with the 12ay7 tubes. I do not think that my amp has problem, because if I put a 12ax7 in V1 the amp is quieter. But it is just my thoughts. A friend of mine told me to change the plate resistors from 100K to 120k and the catode resistor from 820R to 1K. But nothing changes.
By mistake I put a 120R resistors instead 120K and the amp was very very silent like a church but the volume was significantly decreased, like a 2W amp
And if I put two 80K plate resistor instead 100K what would happen?

[Chuck H]

And if I put two 80K plate resistor instead 100K what would happen?

The hiss would be reduced proportionate to gain, just like with the 120R plate resistor.

Forgive me if this has already been covered and I missed it somehow, but what type/rating resistors are you using for the preamp and PI plate loads?

[vinceg]

The hiss would be reduced proportionate to gain, just like with the 120R plate resistor.

Forgive me if this has already been covered and I missed it somehow, but what type/rating resistors are you using for the preamp and PI plate loads?

I use a metal film resistor.

[Chuck H]

Ok. That's a good choice. I asked because carbon composition resistors are known to make a lot of white noise as plate loads. But that's not part of your problem then.

[vinceg]

Ok. That's a good choice. I asked because carbon composition resistors are known to make a lot of white noise as plate loads. But that's not part of your problem then.

I do not understand why with 12AX7 the amp is quieter than with 12AY7.

[g1]

Please redo your voltage readings. If the cathode voltages remain the same then the plate voltages must remain the same.

[vinceg]

Please redo your voltage readings. If the cathode voltages remain the same then the plate voltages must remain the same.

Ok, I will read the voltages with 12ax7 and with 12ay7 on more

[vinceg]

I read that lower the input grid resistor from 68k to 33k or 10k reduce considerably the hiss. What do you think? I do not want to spend a lot of money on research of perfect tube.

[Chuck H]

I wouldn't think so. Thermal noise in for that component in that circuit should be pretty small I'd think because there's very little voltage or current. I'm prepared to be corrected on this though.