Author Topic: EL86 Valve Designs  (Read 301 times)

Offline Nidri

« Last Edit: May 12, 2018, 05:58:29 AM by Nidri »

Offline Ampdog

Re: EL86 Valve Designs
« Reply #1 on: May 13, 2018, 02:03:14 AM »
Nidri,

In practice I found EL86s mostly in use as a voltage regulators. But the difference with EL84 is mainly (if not only!) that the latter requires almost half the input voltage for the same output. Maximum for both is around 14 - 15W; about 13W after the output transformer. (One often overlooked detail: Max. output given in tube data sheets is for the valve itself, one has to subtract the OPT efficiency, which might be about 88% for small ones.)

There is some variation in claims for practical amplifiers; American models can claim 16W or more. This is usually under conditions exceeding the maximum ratings. As said, the triode for EL86 is mainly 8-9 whereas for the EL84 it is 19. This is an indication that lower input grid signal is required for the same output, for an EL84. The distortion for p.p. EL86 seems to be very slightly higher, but will depend on the circuit values.

There is no reason why one cannot use an EL86 for an output stage, but with different grid bias.  Complete schematics for EL86 amplifiers are not plentiful.
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Nidri

Re: EL86 Valve Designs
« Reply #2 on: May 13, 2018, 07:06:06 AM »
^^^ Thank you for the explanation.

Offline Steerpike

Re: EL86 Valve Designs
« Reply #3 on: May 14, 2018, 02:11:56 AM »
I have two such amplifiers.
Philips created the EL86 specifically for their transformerless amplifiers. They can deliver a high anode current with a lowish anode voltage, and most importantly have a very high heater-cathode breakdown voltage. The last feature allowed the EL86 to be used in what they called the series balanced output", essentially a direct-coupled push-pull output stage, much like is done in transistor amps using two NPN transistors.

With the Phillips 800Ω loudspeakers, they make excellent amplifiers - with a 7 Hz to 50 kHz, +/-0,5 dB frequency response. That is quite spectacular linearity from a valve power amp.

Offline Ampdog

Re: EL86 Valve Designs
« Reply #4 on: May 14, 2018, 04:07:01 AM »
Stereo,

Ah! Juggled the grey matter somewhat. That then was the original application - long time ago!
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)