v.h.f rx using ef91s - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

G8HQP Dave · 24th Jan 2010, 5:24 pm

Sorry, I misunderstood what you were asking. A cascode and pentode have similar gain, but a cascode has lower noise so has better sensitivity. Either would stop RF going back to the aerial and would improve things. Use whatever you have handy. If you are near a transmitter you might benefit from having some gain control to avoid overloading V1, so use a variable-mu valve - cascode ECC84,89 or 189, pentode EF93,85 or 183. If out in the sticks then cascode ECC84 or 88, pentode EF91,80 or 184. You might get away with using an ECC81 or ECC85, but these were not intended for cascode use.

Trevor · 24th Jan 2010, 11:31 pm

thanks dave
i thing i will try a cascode basicaly because i have not used 1 before for rf and i will see what i learn
regards trev

Trevor · 25th Feb 2010, 8:43 pm

THe Tuner project is still on the go but as I have been ill latley I had to go to hospital for a heart operation "had a stent fitted" I have been unable to work on my beloved fm tuner
I will try to post my last valve amplifier build Lola
She is a gorgeous little thing 4 x 6V6 2 X ecc81 fixed bias ,ultralinear of about 12 watts output per channel with minimal feedback 6db
That sound really good with my Pm6 Lowther Acousta,s
regards For now Trev

24th Jan 2010, 5:24 pm	#21
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: v.h.f rx using ef91s Sorry, I misunderstood what you were asking. A cascode and pentode have similar gain, but a cascode has lower noise so has better sensitivity. Either would stop RF going back to the aerial and would improve things. Use whatever you have handy. If you are near a transmitter you might benefit from having some gain control to avoid overloading V1, so use a variable-mu valve - cascode ECC84,89 or 189, pentode EF93,85 or 183. If out in the sticks then cascode ECC84 or 88, pentode EF91,80 or 184. You might get away with using an ECC81 or ECC85, but these were not intended for cascode use.

24th Jan 2010, 11:31 pm	#22
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: v.h.f rx using ef91s thanks dave i thing i will try a cascode basicaly because i have not used 1 before for rf and i will see what i learn regards trev

25th Feb 2010, 8:43 pm	#23
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: v.h.f rx using ef91s THe Tuner project is still on the go but as I have been ill latley I had to go to hospital for a heart operation "had a stent fitted" I have been unable to work on my beloved fm tuner I will try to post my last valve amplifier build Lola She is a gorgeous little thing 4 x 6V6 2 X ecc81 fixed bias ,ultralinear of about 12 watts output per channel with minimal feedback 6db That sound really good with my Pm6 Lowther Acousta,s regards For now Trev Last edited by Trevor; 25th Feb 2010 at 8:48 pm.