Tripped over an interesting possible modification for this preamp while browsing yesterday. I noticed there are adaptor plugs available to change from a 5687 9 pin tube to an octal ECC32
Steven and I had a bit of a discussion on the possibility of adding another gain stage to the killeramp while I was visiting in
Sydney and I guess this was still in the back of my mind. I guess that it would be possible to get this but from the preamp out instead of an extra stage in the killeramp?
Questions for the technically advanced (your there Zen? Rawl?)
1. How close are the 5687 and the ECC32 electrically in there characteristics, power supply requirements? heater voltage, current draw etc.
2. Hoping that they are similar, what needs to be done/changed to give this a try
I love the sound of the ECC32 and would dearly love to try one in my pre.....
Cheers
Graham
Hi guys
Adding a gain stage is not a bad idea because it can give a lot of advantages in one swoop
The trouble with 1 stage (tube) to drive OP tube is you need a lot of voltage gain, or a high u, so tube choice get
thin, hence ECC32 and equivalents. Also generally tubes with high u, don't have a lot of current drive.
Once you go to a 2 stage IP, you only need a gain of 20 per stage to get total of 400.
This opens up many more possibilities, especially some nice high current high drive tubes.
5687 and ECC32 are very different tubes. 5687 is like a 6DJ8 on steroids but with a bit lower gain.
Used in a lot of Audio Note stuff.
If you sub 5687 for ECC32 with same configuration it wont work. Less voltage gain, but will want to
run at much higher current. 5687 should work well in a 2 stage cascaded circuit. IOW 1 stage following
the next.
Another option is to try a cascode. This means one half of the tube on top of the other but different to
SRPP. This will give high voltage gain and still only 1 coupling cap. I don't know of any cascode
1 driver stage amps but 5687 should be suitable for cascode. Something like an ECC32 wouldn't work
very well as a cascode.
How much voltage have you got available at the HT? From memory it was 350 or so?
I'll do a bit of poking around the net and see what I can find but as you can see it's a can of worms.
PS cascade and cascode are 2 different things, cascade = 1 after the other, cascode = one on top of the other.
PSS I think I'm going to cascode the missus
cheers
T