Cathode Follower confusion

[Merlinb]

But you could make a horribly badly designed Cf and have the cathode at (say) only 2V above ground, and then of course it can't swing enough to follow a CD player signal. I have seen exactly this is a tube output Chinese CD player - HORRIBLE 2nd harmonic distortion - yet some people defended it's sound when I critiqued it!

Wasn't a Shanl!ng was it?

 

[Allen Wright]

Yes, it was a Shanling. How could you have guessed?

And I only got to check it after I had repaired the fire (!!) in one of the totally under rated edge connectors feeding the heater current to the PCB with tubes.

Don't know where these "designer's" learn their trade, but they needed bother trying for a job with us!

Regards, Allen (Vacuum State)

 

[Brit01]

1.6V across the bias resistor guys.

I changed the tube back to 6N6P with a current of 14mA.

Sounds very sweet no complaints.

I think the 6N1P may need more current. Didn't sound so good at 10ma IMHO.

I want to try the 5687. Got to look at the pin diagram and re-wire I believe.

 

[SY]

1.6V across the bias resistor guys.

Excellent!

Remember, for a cathode follower, there is no substitute for transconductance.

 

[Brit01]

Quick question regarding the wiring of the heaters for 5687's.

I've got a tranny with 12.6V (non CT).

How do I wire up 2 x 5687 tubes?

The 2 in series:

Tranny > pin4>pin5>pin4>pin5 > tranny

Or the 2 in parallel?

Thks

 

[Merlinb]

Quick question regarding the wiring of the heaters for 5687's.

Or the 2 in parallel?

Thks

Put them in parallel (pin 8 not used). i.e., Tranny > pin 4 + pin 4 > pin 5 + pin 5 > tranny.

If you want to create a centre tap you could use pin 8 of ONE valve as the centre tap.

 

[Brit01]

Thks Merlinb.

I've got a virtual CT running at the moment. Great to know I can use the pin 8 as a CT instead.

Was a bit concerned as the 5687 seems to glow much brighter than other tubes ( thought I had them wired up incorrectly). In fact as I experiment with various tubes they do all vary quite a lot.

I tried some 5963's last night (same config as 5687) and don't glow half as bright.

 

[Merlinb]

Was a bit concerned as the 5687 seems to glow much brighter than other tubes ( thought I had them wired up incorrectly).

As long as they have an orange glow they are probably wired up right. In my experience if you run valves at double their intended heater voltage the glow gets closer to white than orange.