5670 SRPP DC coupled to 6S4A

[alexg]

I attempted to draw a DC coupled 5670 SRPP into a 6S4a, any comments will be highly appreciated.

 

[sam8888ysl]

5670 SRPP verry good I like the sound
your OPT are 6K
while the Ra of 6S4A here is about 3K
I suggest 9K -12K may have better THD and less Pout
and the Mu of 5670 is enough to drive 6S4A
so the coupplling Cap with 270R is not necessary
thats my experence

 

[alexg]

Thanks.

But I don't have a coupling capacitor, is taking out the cathode bypass capacitor what you meant? 🙂

Is my B+ voltage and cathode resistor computation for the 6S4A reasonable?

 

[Geek]

I suggest 9K -12K...

I'll back that up. A 6S4 isn't the finest sounding tube and could use the extra load, IMO.

Cheers!

 

[alexg]

I'll back that up. A 6S4 isn't the finest sounding tube and could use the extra load, IMO.

Cheers!

How bad is the sound of a 6s4? I have not yet heard any equipment with this tube.

I have a few PL84 and 12b4 tubes too which I can use.

Am I better off using PL84 or 12b4 instead of the 6s4?

 

[Geek]

Hi,

Try them all and see what you like.

PL84... that's a 15CW5 (not a 15V EL84 as the # suggests) and a different animal in the mix. Low voltage, current hungry little guy capable of 22W in a PP amp. Very clean. Trioded, even cleaner, but needs HUGE current at low voltage (for a tube). 1/4 amp for peaks 😱

12B4 is a really, really sweet tube and given the choice, the one I'd grab unless I had substantial power iron for the PL84's.

I remember that day very clearly... I tested the 6S4A after testing 6AH4GT's and shuddered. The difference was night and day. Made the 6S4 into a power supply pass tube instead 😉

Cheers!

 

[sam8888ysl]

Thanks.

But I don't have a coupling capacitor, is taking out the cathode bypass capacitor what you meant? 🙂

Is my B+ voltage and cathode resistor computation for the 6S4A reasonable?

1. taking out the cathode bypass capacitor of 5670
2. higher B+ to got better THD

12B4 is very good and easy to built
7233 seems good too
even 5687 could work as power tube well
i have some 6s4 but i'll use them to drive some bigger power tubes not use them for power tube

 

[alexg]

Thanks for all the advise guys.

I have a few pairs of EL84, I might as well stick with them and use the 6s4 somewhere else. 😀

I am having some custom power transformers wound for the PL84. 😉