Sovtek 6C45pi-E bias

[siu sin man tho]

hi,

can the 6c45 use a very thin filter like stainess steel plate to make cover corn for it. is it enough to shielding it.


sorry my english is not good. I don;t know how to explain, I hope U will understand.

thanks

Thomas

 

[Sjef]

Yes, that will do as wel. As long as the tube is not totally in the open field it's okay. The main problem I have had without the shield was that there started a hum every time I came close with my hand (to turn the volume) This only stopped by touching the tube for and quickly move my hand away. Very strange effect. With the shielding this problem was solved. I did not need a complete shield, only a short circuit ring was enough.

 

[siu sin man tho]

hi sjef,

I also prepare use the mesh plate to make a cover for the 6c45.
Is it really a large dofferent???

thanks

Thomas

 

[siu sin man tho]

hi all gentleman,

I had a large problem, can anybody told me that the cathode resister for 6C45 use, whicg ohm in your test is better.

thanks

Thomas

 

[fdegrove]

6C45

Hi,

Thomas,

You could try 90R for the cathode R.

Cheers,

 

[siu sin man tho]

hi frank,

U so great. I was testing the 91ohm 1watt resister & feel very good. but i am think & hope to get more information that 91ohm is right or not,

Do U agree the cathode cap is 100uf.
I also testing.

thanks

thomas

 

[fdegrove]

6c45

Hi,

Do U agree the cathode cap is 100uf.

I use at least 470uF.

Cheers,

P.S. This tube tends to oscillate easily, so you better watch it on a oscilloscope.

 

[siu sin man tho]

hi frank,

I s 470uf will to large, I will test your advise tomorrow.


thanks

thomas

 

[EC8010]

The main problem I have had without the shield was that there started a hum every time I came close with my hand (to turn the volume) This only stopped by touching the tube for and quickly move my hand away. Very strange effect. With the shielding this problem was solved. I did not need a complete shield, only a short circuit ring was enough.

That is a sure-fire indication that the valve was oscillating. 6C45P oscillates very easily, and you really need a good oscilloscope handy.

 

[NG]

6c45p grid stopper and cathode stopper

Hi Sjef:


Thanks for the good advices on how to stop oscillation.

I am a just a diy beginner. Can you explain to me a bit more about :

- use as grid stopper 1 k or should I use lower values, because my grid bias resistor for 6c45p is only 1 k !
- you mentioned for the cathode stoppers :"connect 4 x 20ohm resistors to 4 pins of cathode and then OTHER END comes together". Do you mean, just soldering the other ends together and leave it there OR should the other ends be soldered together and then go to the ground ?

Thanks for your help !

DoeiDoei
NG

 

[Sjef]

Hi NG,

1K for gridstopper should be sufficient in most cases.
The 4 cathode resistors are just some extra resistors soldered as close as possible to the tube pins. The 6C45 has four pin connection for the cathode so in this way you will use all four of them.

Thet are in fact in parralell with each other, yes soldered to each other at the end wich isn't on the tube pins. They do not go to ground but to the cahthode bias resistor. Just see the point where the four resistors come together as your new cathode connection of the tube, that's it.

good luck

 

[ashok]

What is the need to use all four pins if they are all at the same potential by virtue of being directly connected together inside the tube ? If one is used the others automatically get tied to the same voltage. If not , why ?
Don't understand this at all.

 

[Sjef]

yes they are connected at the inside of the tube but only after a short lead wich is long enough to act like an antenna. Sovtek recomments using all four connection with eventually four stoppers for thei 6C45's because they are prone to oscillation at very high frequencies, yes in the hundreds of Mhz area. That's an area with very short wavelenghts and even a few mm is enoughto pick it up. This is also the reason why the tube has four cathode connections instead of one, this way you make the path a fourth of the inductance hence a fourth chance to pick up rfi.

 

[NG]

6c45p grid stopper cathode stopper

Hi Sjef:


Thanks for the explanation. I finally understand what the cathode stopper is all about .

For the grid stopper, do I need to put :
- 1 kOhm on pin 2 and another 1 kOhm on pin 8
- OR should I simply cut one of the grid pin short ?

Again, thanks for helping me out.

Best regards,
NG

 

[uberting]

After post #70 by Sjef, this discussion focuses on cathode and grid stoppers for the 6C45pi. Based on the points raised in posts 70, 73, 75, 76, 77, 91, and 93, does anyone have experience with the cathode follower line stage (figure 7.41 on page 576 of Valve Amplifiers 3rd Edition) described by Morgan Jones? In this figure he connects pins 1,3,6,and 9 of the 6C45pi together rather than using small resistors.

 

[Yuriy62]

If someone needs 6S45P-E still, I can send them.