Upgrading my 300B Fi Primer

[Pedro]

many thx Paul
- do you mean insert the C3M and its assoc components and just leave the 300B stage as is for now - ie. after the coupling cap leave as Fi Primier 300B , and before coupling cap make it a C3M audion circuit. ( I realise i wil have to mess with the PS of course for the C3m plate and screen )

Also I suppose that would be a good jumping off point for experimentation with the ouput stage operating conditions if OK to start with Fi Primer and modify from there. I like to be able to alter one thing at a time and see what the effect is.

also - any simple schems with el84 drivers for 300B - I have some mullards to try !

Rgds
Pete

[powertriode]

Hi Pete,
I posted this URL earlier in this thread.
http://www.fortunecity.com/rivendell...cy/Legacy.html

Follow this schematic and you can just drop one of Blackburn's finest straight in!

[Pedro]

thx PT, very useful.

Ive printed the article and will read & digest before I sleep tonight !

I have looked closely at my chassis space tonight and have minimal area for 2 additional 9-pin sockets between the existing octals and the 300B's , so may go with swapping the 6SN7's for the CM3 sockets first.
I have plenty of space under the chassis so could always mess with L-shaped brackets and hidden EL84s - but I dont like hiding valves - I like to see 'em

Funny enough the right hand channel died on me earlier tonight ( bad joint I think ) so I think the amp is telling me it needs a new life.......

Any more sugestions on pentode input for my simple stereo 300B are very welcome.

Rgds
Pete

[Paul Barker]

I wouldn't put el84's under the cover they get hot.

I would build 112a to 45 to 300b amp if I were you, but it would require a lot of changes. Oh what the heck if I were going that far I would swap out the 300b's for 2a3's.

[Pedro]

Paul,

maybe I should build that amp next - perhaps I'll breadboard it while I mess with the 300B/C3m.

cheers
Pete

[Paul Barker]

Your problem is three different voltage directly heated valves in a row. Indirectly heated Pentode and 300b is an easier way of going about it, a lot easier, but not necessarily better.

However from the triode camp the circuit Ian posted which has 76 into 6sn7 into 300b would be also excellent, and far better than one of the many Flesh and Blood clones.