Single ended EL34 amplifier. - UK Vintage Radio Repair and Restoration Discussion Forum

yestertech · 14th Jun 2008, 6:19 pm

Probably about 3-4 watts - It's nothing special ( no feedback ! ) Andy

Aub · 15th Jun 2008, 8:36 pm

Hi,

If it's an EL84, not a EL34, then two of them would require about 100mA from the HT supply and then a couple of amps from the 6.3v heater supply.

Cheers

Aub

love kt3 · 16th Jun 2008, 11:57 am

Hi,100k for ef 86 cathode-isnt that much to high?

quantum · 16th Jun 2008, 4:00 pm

Yes, if it is 100k - it is difficult to tell from the image. I'd reckon 2.2k or 3.3k would be adequate for a triode connected EF86, but I don't think this circuit is particularly special anyway. By using the EF86 is pentode mode you'd get more gain to enable some negative feedback to improve response.

Herald1360 · 16th Jun 2008, 5:29 pm

Or you could use the same valves in the amplifier circuit of the Mullard 3-3 which would probably give better results and is interesting too!

'LIVEWIRE?' · 16th Jun 2008, 7:09 pm

Looking at the schematic carefully, I'd say that the EF86 Cathode resistor is 100R, not 100K, though the former value may be too low.

ppppenguin · 16th Jun 2008, 7:33 pm

I'm not convinced about the design of this amp. Apart from the 100K cathode resistor the volume control is used as the grid bias resistor. This is poor practice and tends to give scatchy control with anything less than an absolutely perfect pot.

Dickie · 16th Jun 2008, 9:04 pm

Are there any advantages in running an EF86 in "triode" mode , as opposed to a proper triode (ECC83)?
I might be a traditionalist, but any circuit drawn with valves on their side ( apart from those in push-pull, of course) can't possibly work very well

julie_m · 17th Jun 2008, 10:18 am

Am I missing something?

Instead of using a pentode in triode mode, why not use something like an ECL82 which contains both a triode and a power pentode in one package?

Herald1360 · 17th Jun 2008, 12:49 pm

Quote:

Originally Posted by Dickie

Are there any advantages in running an EF86 in "triode" mode , as opposed to a proper triode (ECC83)?
I might be a traditionalist, but any circuit drawn with valves on their side ( apart from those in push-pull, of course) can't possibly work very well

Ultimately, a triode is a lower noise device than a pentode, but it's unlikely to be relevant here. Presumably the increased gain of the pentode connection wasn't required either. Maybe the valves just happened to be the cheapest combination (if the design was for commercial manufacture) or just what the designer had available.

Chris

14th Jun 2008, 6:19 pm	#1
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,130	Re: se el34 amp Probably about 3-4 watts - It's nothing special ( no feedback ! ) Andy

15th Jun 2008, 8:36 pm	#2
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: se el34 amp Hi, If it's an EL84, not a EL34, then two of them would require about 100mA from the HT supply and then a couple of amps from the 6.3v heater supply. Cheers Aub

16th Jun 2008, 11:57 am	#3
love kt3 Retired Dormant Member Join Date: Nov 2007 Location: Hifa Israel Posts: 146	Re: se el34 amp Hi,100k for ef 86 cathode-isnt that much to high?

16th Jun 2008, 4:00 pm	#4
quantum Retired Dormant Member Join Date: Mar 2003 Location: Birmingham, West Midlands, UK. Posts: 785	Re: se el34 amp Yes, if it is 100k - it is difficult to tell from the image. I'd reckon 2.2k or 3.3k would be adequate for a triode connected EF86, but I don't think this circuit is particularly special anyway. By using the EF86 is pentode mode you'd get more gain to enable some negative feedback to improve response.

16th Jun 2008, 5:29 pm	#5
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: se el34 amp Or you could use the same valves in the amplifier circuit of the Mullard 3-3 which would probably give better results and is interesting too!

16th Jun 2008, 7:09 pm	#6
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: se el34 amp Looking at the schematic carefully, I'd say that the EF86 Cathode resistor is 100R, not 100K, though the former value may be too low.

16th Jun 2008, 7:33 pm	#7
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: se el34 amp I'm not convinced about the design of this amp. Apart from the 100K cathode resistor the volume control is used as the grid bias resistor. This is poor practice and tends to give scatchy control with anything less than an absolutely perfect pot.

16th Jun 2008, 9:04 pm	#8
Dickie Octode Join Date: Sep 2004 Location: St. Albans, Hertfordshire, UK. Posts: 1,478	Re: se el34 amp Are there any advantages in running an EF86 in "triode" mode , as opposed to a proper triode (ECC83)? I might be a traditionalist, but any circuit drawn with valves on their side ( apart from those in push-pull, of course) can't possibly work very well __________________ Regards, Richard, BVWS member

17th Jun 2008, 10:18 am	#9
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Single ended EL34 amplifier. Am I missing something? Instead of using a pentode in triode mode, why not use something like an ECL82 which contains both a triode and a power pentode in one package? __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.